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Volcanic stratigraphy, chemical stratigraphy, and hydrothermal alteration of the Petiknäs South volcanic-hosted massive sulﬁde deposit, Sweden 0Z

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Denis Martin Schlatter

Luleå University of Technology Department of Chemical Engineering and Geosciences Division of Ore Geology and Applied Geophysics :|: -|: - -- ⁄ -- 

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Volcanic stratigraphy, chemical stratigraphy, and hydrothermal alteration of the Petiknäs South Volcanic-hosted massive sulfide deposit, Sweden

Denis Martin Schlatter

Division of Ore Geology and Applied Geophysics Luleå University of Technology SE-971 87 Luleå Sweden

Luleå, September 2005

ABSTRACT

Keywords: Volcanic-hosted massive sulfide deposit, volcanic chemostratigraphy, immobile elements, hydrothermal alteration, mass changes, Petiknäs South, Sweden The main exploration methods which have been used in the Skellefte district are prospecting for ore boulders in young glacial deposits and electrical geophysical methods. The discovery of new ores which likely are located at deep levels (>200 m), requires improved exploration methods, which in turn require a better understanding of the geology and alteration patterns of the known VMS deposits. This thesis seeks to improve the understanding of the geology and alteration patterns of VMS deposits in the Skellefte district by providing new data and new interpretation of the geology and alteration system of the Petiknäs South VMS deposit.

The Skellefte district is an important ore province, containing more than 80 pyritic Zn-Cu-Au-Ag massive sulfide deposits within volcanic rocks of the Paleoproterozoic Skellefte Group. The Petiknäs South volcanic-hosted massive sulfide deposit is a producing underground mine in the eastern part of the Paleoproterozoic Skellefte district. The deposit consists of several ore lenses (A, B, C and D) and prior to mining contained 6 Mt of ore grading 5 % Zn, 1 % Cu, 1 % Pb, 2.5 g/t Au and 105 g/t Ag. The deposit occurs on the southern limb of a tight, steeply plunging, upright, anticline. The mine stratigraphy dips subvertically and youngs consistently southwards. A major thrust fault truncates the downdip portion of the deposit at the 700 m level of the mine. The volcanic rocks of the mine sequence generally have one penetrative tectonic foliation and have been metamorphosed to greenschist facies, although garnet-biotite bearing rocks are present locally.

Application of immobile-element lithogeochemical methods to 469 samples has allowed classification of the mine sequence into a series of chemostratigraphic units, while the degree of hydrothermal alteration of these units has been quantified using mass change methods. From oldest to youngest, the main units are: The footwall complex (Unit 1) consists of rhyolite B and minor rhyolite C, B/C, and dacite feldsparporphyritic rhyolitic cryptodomes, sills and volcaniclastic rocks, and is overlain by rhyolitic sandstone-siltstone beds, an up to 20 m thick unit hosting the B/C ore lens (Unit 2). The B/C ore lenses formed a single lens prior to intrusion of the late andesite sills. Unit 2 is overlain by unmineralized basaltic andesite volcaniclastic rocks (Unit 3). Above this, Unit 4 is host to the D and A ore lenses. This unit comprises mainly rhyolitic volcaniclastics with several thin andesitic intercalations. A WNW-ESE trending fault separates Unit 4 from Unit 5, which comprises feldspar-quartz porphyritic rhyolite sills and sandstone-siltstone volcaniclastic rocks. The lower part of Unit 5 is a mass flow deposit of distinctive low-Ti mafic composition that can be traced for 700 m eastwards from the proximal part of the mine. Unit 6 comprises the post-ore andesite sills and mafic dykes. A portion of the chemostratigraphic sequence (Units 1 and 2) has also been recognized on the northern limb of the Petiknäs South anticline. In summary, 6 chemostratigraphic units can be identified at the Petiknäs South mine and these can be correlated throughout and beyond the mine, even where they are strongly altered. Two good chemostratigraphic marker horizons were identified: one is of basaltic andesite and andesite composition (unit 3) and one is of low-Ti mafic composition (unit 5a) and both markers can be correlated on the mine-scale and semi-regional scale. The chemostratigraphic

results show that ore lenses (B/C, D and A) occur at different stratigraphic positions within clastic stratigraphic intervals of dominantly rhyolitic composition. The most favorable exploration horizon (the B/C ore horizon) is located at the contact between a felsic clastic and a basaltic-andesitic clastic unit. Based on identification of magmatic affinity, chemostratigraphy revealed that the volcanic succession at Petiknäs South comprises calc-alkaline to transitional footwall rocks representing a proximal facies association and this succession is overlain by tholeiitc juvenile volcaniclastic rocks which were derived from a different and relatively distal volcanic center. In terms of ore location chemostratigraphy revealed that the main ore body at Petiknäs South is located at the contact between rhyolitic calc-alkaline to transitional and basaltic-andesitic tholeiitic rocks. This ore horizon can be traced along strike for several hundred meters and its position has also been located on the northern limb of the regional anticline, 700 m north of Petiknäs South. These extensions of the Petiknäs South ore horizon are potential drill targets for new VMS ore lenses.

The main alteration minerals are sericite, quartz, chlorite, garnet, and locally carbonate. Intense chlorite-garnet alteration occurs immediately below the A and D ore lenses, and in the distal footwall of the B and C ore lenses. These zones are interpreted as hydrothermal upflow or feeder zones. Haloes of serizitization occur around the ore lenses and are wider than the zones of chlorite-garnet alteration. Carbonatization occurs in narrow zones throughout the mine sequence.

In moderately to strongly altered rocks of the mine sequence, there has been no demonstrable mobility of typically immobile elements such as Ti, Al, Zr and REE.

Although the composition of the precursor rocks has had an influence on the mineral assemblage that formed during alteration, the chemical changes in the rocks were due mainly to factors such as the composition of the hydrothermal fluids, the degree of mixing with seawater, and the overall water/rock ratio. Sericitic alteration in felsic footwall rocks that show only small mass changes in K and Si is explained by hydration at low water/rock ratios. By contrast sericitic altered felsic rocks immediately below the B/C ore lens show large gains in K and Si and are attributed to alteration by hot fluids.

Restoration of the Petiknäs South stratigraphy and alteration system prior to deformation indicates that the Petiknäs South deposit originally contained three stacked ore lenses: from oldest to youngest, the B/C, D and A lenses. The B/C and the A ore lens were formed at the seafloor above a zone of hydrothermal upflow and the D ore lens is interpreted to have formed in the footwall of the A ore lens via replacement. Alteration zones below the B/C and the A ore lens and around the D ore lens are characterized by large mass gains of FeO, MnO, MgO and K2O together with large mass gains or losses in silica. The latter alteration zones are around three times larger than the actual ore lenses, and consequently could provide a good exploration guide to ore. Other alteration zones with Na2O and CaO depletions occur on a semi-regional scale, but are most intense close to the ores. The proximal part of the footwall complex, which is dominated by synvolcanic felsic intrusions, is only weakly altered, which suggests that the intrusions were emplaced slightly after formation of the massive sulfide lenses. The results of this study can be used to help identify ore horizon and favorable alteration zones in other parts of the Skellefte district and elsewhere.

PREFACE This licentiate thesis “Volcanic stratigraphy, chemical stratigraphy, and hydrothermal alteration of the Petiknäs South Volcanic-hosted massive sulfide deposit, Sweden” comprises an “Introduction and Geology” part and the two following manuscripts: I. Schlatter DM, Barrett TJ, Allen RL (2005) Chemostratigraphy of the Petiknäs South volcanic-hosted massive sulfide deposit, Skellefte district, Sweden. (To be submitted). II. Schlatter DM, Barrett TJ, Allen RL (2005) Mass changes in alteration zones of the Petiknäs South volcanic-hosted massive sulfide deposit, Skellefte district, Sweden. (To be submitted). The following abstracts have been published, but are not included in the licentiate thesis: Schlatter DM, Barrett TJ, and Abrahamsson S (2003) Chemostratigraphy of metamorphosed and altered Paleoproterozoic volcanic rocks associated with massive sulfide deposits at Rävliden and Kristineberg West, Skellefte district, Sweden. In: Eliopoulos DM, et al. (eds.) Mineral exploration and sustainable development. Proceedings of the Seventh Biennial SGA Meeting, Athens, Greece, 24-28 August 2003, Millpress, Rotterdam, Netherlands, pp. 1103-1106. (Extended abstract). Schlatter DM, Allen RL, Jonsson R, and Barrett TJ (2004a) Volcanic and chemical stratigraphy of the Petiknäs South Zn-Cu-Au-Ag-Pb VMS deposit, Skellefte district, Sweden. 26th Nordic Winter Meeting, Uppsala, Sweden, January 6-9 2004, Abstracts volume, Geologiska Föreningens i Stockholm Förhandlingar, v. 126: 151. (Abstract). Schlatter DM, Allen RL, Jonsson R, and Barrett TJ (2004b) Stratigraphy of the Petiknäs South volcanic-hosted massive sulphide deposit, Skellefte district, Sweden. IAVCEI International Volcanological Congress 2004, Pucon-Chile, November 14-19 2004. Abstracts volume 67. (Abstract).

The Petiknäs South volcanic-hosted massive sulfide deposit, Skellefte district, Sweden: Introduction and Geology INTRODUCTION Volcanic-hosted massive sulfide (VMS) ores are the main source of non-ferrous metals (zinc, copper, lead, silver and gold) mined in Sweden and the Skellefte district is the main mining region for these ores in Sweden. The Skellefte district covers an area of 120 by 30 km in Northern Sweden and comprises a 1.9 Ga old volcanic succession with over 85 pyritic Zn-Cu-Au-Ag VMS deposits. Mining commenced in 1924 and since then, 22 deposits have been mined and five are currently in production: Storliden, Kristineberg, Maurliden, Renström and Petiknäs South (Fig. 1). The median deposit size based on 52 known deposits that contain 100,000 tonnes or more is 1.1 Mt (Allen et al. 1996). Several recent geological studies have described VMS deposits and their relations to host rocks in the Skellefte district (Richard and Zweifel 1975; Grip 1978; Trepka-Bloch 1985; Vivallo and Claesson 1987; Weihed et al. 1992; Allen et al. 1996; Billström and Weihed 1996; Allen and Svensson 2004; Montelius et al. 2004). Allen et al. (1996) attributed the formation of the massive sulfide deposits to a stage of intense volcanism and crustal extension in a marine volcanic arc situated on continental margin or mature arc crust. The main exploration methods which have been used in the Skellefte district are prospecting for ore boulders in young glacial deposits and electrical geophysical methods. The discovery of new ores which likely are located at deep levels (>200 m), requires improved exploration methods, which in turn require a better understanding of the geology and alteration patterns of the known VMS deposits. This thesis seeks to improve the understanding of the geology and alteration patterns of VMS deposits in the Skellefte district by providing new data and new interpretation of the geology and alteration system of the Petiknäs South VMS deposit. In particular, this study has combined the disciplines of physical volcanology and volcanic facies mapping (cf. Cas 1992; McPhie et al. 1993; Gibson et al. 1999) with chemostratigraphy and advanced lithogeochemical techniques (MacLean 1990; MacLean and Barrett 1993). Petiknäs South is located in the Renström area in the eastern part of the Skellefte district about 17 km west of Boliden. The Renström area hosts five VMS deposits within an area of 4 km2: Renström, Kyrkvägen, Renström East, Petiknäs North and Petiknäs South (Fig. 2). The Petiknäs South orebody was discovered in 1988 by Boliden Mineral AB using a combination of deep drilling, downhole electromagnetic surveys (EM3) and geological modeling based on volcanic facies analysis and lithogeochemistry; the case history of the discovery of the Petiknäs deposits is summarized by Jonsson et al. (1995) and Allen and Svenson (2004). The Petiknäs South deposit has been a producing underground mine since 1992. It consists of four stacked ore lenses that are hosted by a complex sequence of felsic to mafic volcanic rocks and intrusions (Fig. 3). The ore is mainly pyritic massive sulfide and prior to mining the deposit contained 6 Mt grading 5% Zn, 1% Cu, 1% Pb, 2.5 g/t Au and 105 g/t Ag. The Petiknäs North deposit is located about 700 m north of Petiknäs South (Fig. 3) and contains 1.3 Mt grading 5.6% Zn, 1.3% Cu, 0.9% Pb, 5.6 g/t Au and 103 g/t Ag (Allen and Svenson 2004). The Petiknäs North deposit replaces the lower part of a thick succession of felsic mass flow breccias (Jonsson et al. 1995; Allen et al. 1996). The potential for mining of Petiknäs North is currently being evaluated. A summary of the geology of the Petiknäs South area is provided below. This summary provides background and context for the two manuscripts, which form the main part of this thesis. Manuscript I 1

2

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Synvolcanic granitoids of I-type (Jörn III granit, Gallejaur monzonite) c. 1.87- 1.85 Ga Synvolcanic granitoids of I-type (Jörn II granodiorite), c. 1.87 Ga Synvolcanic granitoids of I-type (Jörn I tonalite and undivided) c. 1.89 Ga

Ultramafic intrusions

Gabbro and diorite

Post-volcanic granitoids of A- and I-type (Revsund type), c. 1.82-1.78 Ga Post-volcanic granitoids of S-type (Skellefte type), c. 1.82-1.80 Ga

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Conglomerates and sandstones, polymict (Vargfors and Ledfat Groups) c. 1.87-1.85 Ga Basalt-andesite and minor dacite lavas and sills (Vargfors Group), c. 1.88 - 1.86 Ga Mudstone, black shales, sandstones and turbidites (Bothnian Group, Vargfors Group, Skellefte Group) c. >1.95 - 1.85 Ga Subaerial to shallow water basalt-andesite (Arvidsjaur Group) c. 1.88 -1.87 Ga Subaerial to shallow water rhyolite, dacite and minor andesite (Arvidsjaur Group), c. 1.88 - 1.87 Ga Basalt-andesite and minor dacite lavas and sills, mainly submarine (Skellefte Group), c. 1.89 - 1.87 Ga Rhyolite, dacite and minor andesite, mainly submarine (Skellefte Group), c. 1.90 - 1.87 Ga

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Fig. 1 Simplified geological map of the Skellefte district, showing structure, geology and location of the major ore deposits. Five VMS-mines and one orogenic gold mine are in production (marked by slightly larger fonts). Björkdal is a producing gold mine in the eastern part of the Skellefte field. Modified from Allen et al. (1996, Fig. 1). Coordinates are given in the Swedish national grid coordinate system.

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Feldspar-phyric dacitic (±low silica rhyolite, PMFZ Petiknäs Main Fault silicic andesite) syn-eruptive pumiceous zone mass flows ± reworked volcaniclastics Fine grained rhyolite lavas, intrusions, and Antiform hyaloclastites

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one 7209000

Fig. 2 Geological map of the Renström area. Two major faults (PMFZ and Renström fault zone) divide the Rentström area into three blocks: Petiknäs North, Petiknäs South and Renstöm. Petiknäs South and Renström are producing mines. The location of the proximal and distal cross-sections of this study is indicated. Modified after Allen et al. (1996, Fig. 6). Coordinates are given in the Swedish national grid coordinate system.

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Ore horizon of the C+B ore lens

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Silty matrix Pumice-rich Angular clasts

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Primary volcanic textures

Quartz-feldspar phyric rhyolitic mass flow unit

Rhyolitic mass flow unit

Strongly porphyritic dacite

Petiknäs North Stratigraphy

Andesite to dacite v’clastic sandand siltstone (U1a)

Mudstone-turbidite unit Low Ti mafic mass flow unit minor felsic intercalations (U5a) Rhyolitic volcaniclastic (U4 and U5b) sandy and silty matrix Basaltic andesite v’clastic sandstone and siltstone (U3) Rhyolitic volcaniclastic (U2 of southern limb) Rhyolitic volcaniclastic (U2 of northern limb) Strongly feldspar porphyritic rhyolite (U1d and U5b) Weakly to moderately porphyritic dacite (U1c) Dacitic volcaniclastic sandstone (U1b)

Strongly porphyritic dacite (Storåliden intrusion) Rengård granodioritic synvolcanic intrusion Weakly to moderately feldspar and qz porphyritic rhyolite Strongly feldspar and quartz porphyritic rhyolite Andesitic post-ore sill (U6)

Petiknäs South Stratigraphy

Fig. 3 Simplified geology around the Petiknäs South mine modified after Allen et al. (1996, Fig. 6). The geology of the mine area has been projected from the 300 m level of the mine to surface, as the bedrock is covered by glacial till and the Skellefte River. The Petiknäs South deposit is located in the southern limb of the F2 anticline and the Petiknäs North deposit is located north of PMFZ. X and Y coordinates are given in the local “Petiknäs coordinate system” which is used by Boliden AB; for coordinates of the Swedish national grid see appendix 1.

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describes the advanced lithogeochemical techniques which were applied to chemically define the mine sequence and to establish the chemostratigraphy at Petiknäs South. Manuscript II describes the alteration system at Petiknäs South and provides results and interpretation of quantitative lithogeochemical alteration studies using mass change calculations. The study of the Petiknäs South VMS deposit is part of Georange project 9: “Chracterization of the ore horizons and alteration systems of volcanic-associated massive sulphide deposits in the Skellefte district, Sweden” (Allen et al. 2005). The Georange project was funded by the EU, the Swedish national government and Swedish county governments. This study is a contribution to IGCP project 502: “Global comparison of volcanic-hosted massive sulphide districts: the controls on distribution and timing of VMS deposits.” REGIONAL GEOLOGY AND STRUCTURAL SETTING F2 Anticline and hanging-wall fault The Petiknäs South block is located between the Petiknäs Main Fault Zone (PMFZ) to the west and the Renström fault zone to the east (Fig. 2). The block contains a set of tight upright largescale folds that trend west-northwest and plunge steeply to the east (Fig. 3). These regional F2 folds are the dominant structure and are associated with the penetrative cleavage (S2) at Petiknäs South. Two additional minor fold generations and associated foliations, one earlier and one later than F2, are evident from outcrops in the Petiknäs block (Allen and Svenson 2004). Moderate to strong lineation plunging steeply east-southeast occurs in most rocks. The Petiknäs South deposit occurs on the southern limb of a major F2 anticline and dips subvertically. The stratigraphy on the southern limb at Petiknäs South youngs consistently southwards and in this study a mine sequence comprising six main stratigraphic units has been defined. An abbreviated equivalent of this mine sequence is repeated on the northern limb of the anticline. The mine sequence on the southern limb is a continuous conformable succession except that units 4 and 5 are separated and truncated by a west-northwest trending fault (the “hanging-wall fault”). On the northern limb the mine sequence is intruded by a large intrusion known as the Storåliden-dacite. Petiknäs Main Fault Zone The Petiknäs Main Fault Zone is a major reverse fault that dips moderately to the south and separates rocks of the Petiknäs South block from those of the Petiknäs North block (Fig. 3). The fault postdates F2 folding. Although the amount of displacement of the PMFZ is not known, it is probably significant because the stratigraphy below and above the fault can not be correlated and additional future research is required to try to make such correlation. The Petiknäs South ore lenses are located in the hanging-wall of the PMFZ and are truncated by the fault between the 600 and 700 m levels of the mine. The Petiknäs North deposit lies underneath the fault zone in the Petiknäs North block. Hydrothermal alteration and subsequent metamorphism The volcanic and subvolcanic rocks of the Petiknäs area have been subjected to regional deformation and greenschist facies metamorphism. However most of the rocks display at least some volcanic or sedimentary structures and only a few of the rocks have been entirely altered and metamorphosed to schistose assemblages without relict primary textures. The main alteration minerals at Petiknäs South are sericite, quartz, chlorite, garnet, and locally carbonate. Strong chlorite-garnet alteration occurs close to the ore lenses and in the most altered portions of the footwall. Haloes of serizitization occur as wide zones in the footwall complex, around the ore lenses and in the hanging-wall. At Petiknäs South carbonatization occurs locally in thin horizons. The post-ore andesite and rhyolite sills and mafic dykes are relatively weakly altered. As all rocks described in this thesis are metamorphosed the prefix meta has been omitted and primary volcanic and sedimentary terminology is used for brevity. 5

METHODOLOGY The Petiknäs South mine sequence has been investigated by geological logging of 10,000 m of core from 40 bore holes, underground and surface mapping, and lithogeochemical analysis of 469 rock samples (445 samples from drill core and 24 samples from surface and underground exposures). These data were combined with selected existing data of the Boliden Mineral company. The drill cores were logged in detail using graphic logging techniques emphasizing rock textures and facies characteristics. Each major rock type and alteration facies was sampled along the core; samples generally comprised 25 cm of whole core and were taken at intervals of about 15 to 20 meters. Where rock types could not be identified due to strong alteration samples were taken routinely every 15 to 20 m. Lithogeochemical analyses including major elements and certain trace elements of 562 rocks (469 from Petiknäs South and 93 from Petiknäs North) were performed by the Canadian ACME laboratory (see appendix 3 for details). Thin sections and polished thin sections from selected rocks were prepared. From this data a surface geological map, a proximal geological cross section centered on the ore body, one distal cross section 270 m to the east and two geological plans at the 300 and 550 m levels of the mine have been constructed. STRATIGRAPHY OF THE MINE SEQUENCE Stratigraphy located above the Petiknäs Main Fault Zone Mine sequence exposed from bore holes and underground exposures At Petiknäs South the stratigraphic succession has been defined by Allen et al. (1996, Fig. 8F) and the detailed geology and chemostratigraphy of the mine sequence is summarized by Schlatter et al. (2004a, 2004b). The mine sequence has been divided into 6 units (Figs. 3, 4); from north to south (oldest to youngest) these comprise: Unit 1 (footwall complex) essentially consists of feldspar-porphyritic rhyolitic sills and domes with 2-3 mm feldspar phenocrysts that comprise about 20 % of the rock (Fig. 5a). Feldspar-quartz rhyolites occur as thin sills within the feldspar-porphyritic rhyolite. Contacts between the strongly feldspar-porphyritic rhyolitic sills and domes show evidence of quenching in the form of in situ hyaloclastite breccias (Fig. 5b) or sediment-matrix hyaloclastite breccias (peperite; Fig. 5c). The peperitic margins typically contain a grey silty sediment matrix or clastic pumiceous matrix. Beds of rhyolitic to dacitic crystal and lithic rich pumiceous sandstones up to 10 m thick occur locally. Generally Unit 1 is moderately sericite altered, however some parts remain unaltered. A narrow zone in the distal footwall is strongly chlorite-garnet altered. Unit 2 (felsic clastic unit hosting the B and C ore lenses), is relatively thin (20-50 m) and comprises interbedded rhyolitic tuffaceous sandstone and siltstone, locally with larger pumice and lithic clasts, and minor andesitic mudstone beds. Some minor basaltic andesite beds also occur. The rhyolitic tuffaceous sandstone and siltstone contain 0.5-1 mm feldspar and quartz crystals with variable abundance. This unit is sulfide impregnated and sericite, quartz and partly chlorite altered with strongest alteration occurring close to the B/C ore lens (a core photograph of the C ore is given in figure 5d). Feldspar-porphyritic rhyolite of Unit 1 has a peperitic contact with Unit 2. Unit 3 (basaltic andesite clastic hanging-wall unit) is an 80 m thick normally graded and weakly polymict mass flow breccia succession of basaltic-andesitic and andesitic composition. Feldsparphyric scoria and pumice clasts, large rounded quartz crystals and andesitic lithics are abundant in Unit 3 (Fig. 5f). The presence of both free quartz crystals and andesite lithic clasts without quartz crystals, suggests that Unit 3 contains a mixture of andesite and some rhyolitic (quartz crystals) detritus. Thin mudstone beds are minor and occur only in the distal section (2300 East). Unit 3 is 6

Proximal Stratigraphy 2030 East BH 207

Distal Stratigraphy 2300 East BH 292 Mine scale units:

U6 A lens

UNIT 4

(h) (younging direction)

(g) (f) (e) U6

UNIT 3

B lens U6 U6 B/C ore horizon

UNIT 2

F

C' lens

(d)

C lens

U6

(c) UNIT 1 (FW)

(b)

M

(a)

Fig. 4 . The mine sequence seen from a proximal (BH 207) and a distal bore hole (BH 292). Letters (a) to (h) refer to the core photographs shown in figure 5; legend of the geological log is given in figure 13.

only weakly sericite altered or silicified and sulfide impregnation occurs only locally. Some horizons within Unit 3 are carbonate altered. Unit 4 (unit hosting the A and D lens) is a complex unit which is mainly comprised of rhyolitic tuffaceous sandstones and siltstones. The most distinct characteristic of Unit 4 is the presence of large rhyolitic pumice clasts in siltstone (Fig. 5g). These juvenile pumice clasts in siltstone suggest that Unit 4 is syneruptive. Unit 4 also contains intercalated beds of normal graded basaltic andesitic pumiceous massflow breccia. Minor andesitic and rhyolitic mudstone beds and a thin rhyolitic sill occur in the middle part of Unit 4. Unit 4 is sericite altered and strong chlorite-garnet alteration together with patchy sulfide impregnation occurs below the A ore lens in zone several tens of meters wide (Fig. 5h). 7

Unit 5a is faulted against unit 4 and consists of a poorly sorted mass flow breccia of low-Ti mafic composition. The mass flow deposit of Unit 5a is 10 to 20 m thick and consists of abundant (5%) large pale grey and pinkish feldspar phyric andesite lithics. The unit is texturally and chemically uniform and is albite altered. Unit 5b, the youngest stratigraphic interval of the mine sequence, consists mainly of strongly feldspar porphyritic rhyolitc sills and volcaniclastic rocks at the proximal section and of andesitc mass flow breccias at the distal parts (2600 East; Fig. 3). The margins of the feldspar porphyritic rhyolitc sills are frequently quenched, except at the contact of one strongly quartz feldspar porphyritic sill. Unit 5b is locally sericite-quartz altered and some narrow zones are chlorite-garnet altered or carbonatized. Andesitic, basaltic-andesitic and andesitic-dacitic rocks occur as minor and small sills or dykes. The andesitc mass flow breccias of Unit 5b are exposed in surface outcrops and are described in a later section. Unit 6 comprises andesite sills and mafic dykes. These sills and dykes cut the massive sulfide ore lenses and are unaltered and consequently are interpreted to have been intruded after hydrothermal alteration and ore formation. These post-alteration andesite sills and mafic dykes are described in a later section.

UNIT 1

(a)

UNIT 1

(b)

2.5 cm

2.5 cm

C‘ ore lens (c)

UNIT 1

UNIT 3 UNIT 6

(d)

UNIT 3

(f)

(e)

2.5 cm

UNIT 4

(g)

UNIT 4

2.5 cm

(h)

2.5 cm

Fig. 5. Drill core photographs from proximal BH 207. (a) Feldsspar-porphyritc rhyolite, @18.25m. (b) In situ hyaloclastite breccia, @49.25m. (c) Feldsspar-porphyritic peperite with silt matrix, @65.8m. (d) Massive pyritesphalerite-chalcopyrite ore, C’ lens, @ 147.1m (e) Contact of massive andesite sill and breccia, @ 215.1m. (f) Basaltic andesite pumice breccia, @220.75m. (g) Rhyolitic ash with water settled pumiceous debris, @ 250.9m. (h) Strongly chlorite-garnet altered schist, @278.35m.

8

The mine sequence is summarized in Table 1. Generally the stratigraphic succession is best preserved in the distal section (2300 East) where the post-ore andesite sills are absent.

Table 1 Simplified geological description of the 6 mine scale units. Based on geological mapping and facies the mine sequence was divided into 6 stratigraphic intervals; the units 1 to 6. The table also summarizes relations between sills and dykes and their hosts. Mine sequence

Unit 6 (x) Unit 6 (+)

description post-ore sills: andesitic post-ore sills/dykes: mainly Hi-Mg-Cr-Ni-basalt

principal lithology dark-green, even fine to medium grained granular andesitic sill with fgr margins green-yellowish soft, chlorite-talc altered, calcareous mafic volcanic

Unit 5b Unit 5a Unit 4

faulted HW-complex lowest sub-unit of faulted HW-complex A+D ore lens package

Unit 3 Unit 2 Unit 1d Unit 1c Unit 1b Unit 1a

Basaltic andesite clastic HW Felsic clastic hosting B/C ore lens

various lithologies, rhyolitic coherent and volcaniclastic mass flow breccia of low Ti-mafic composition with fgr pale-pink lithics rhyolitic pumice breccia, siltstone-sandstone with thin basaltic-andesitic and rhyolitic mudstone intercalations basaltic andesite pumice-lithic mass flow breccia with sandy and silty matrix rhyolitc volcaniclasitc sandstone and siltstone, presence of pumice-lithics strong 20 %, 2-3 mm, feldspar porphyritic coherent rhyolite with peperitic contacts dacitic coherent sill mainly dacitic volcaniclastic, minor basatic andesites and andesites andestic, basaltic-andesitic and dacitic volcaniclastic

shallow footwall complex (thins out towards east) deep footwall complex (east of Petiknäs S mine) deep footwall complex (east of Petiknäs S mine) deep footwall complex

post-ore sills

x x x x x

+ + +

Surface exposure of the mine sequence Outcrop exposure in the Petiknäs area is relatively good compared with most areas in the Skellefte district. Generally the mine sequence was best defined from drill core logging however the deep footwall is better exposed in outcrops than in drill core. Outcrops between 2400 and 3000 East (Fig. 3) expose three subunits of the footwall sequence that are either not exposed or are poorly defined in the mine: Unit 1a, the deep footwall, consists of green-grey diffusely stratified andesitic breccia containing abundant scoria lapilli (Fig. 6d). Unit 1a is intruded by fine grained rhyolitic sills which are unaltered (Fig. 6g). Unit 1a is overlain by Unit 1b which is a normal graded, pumice breccia mass flow unit of unusual high-Ti dacitic composition. Large, green, chlorite or sericite altered and compacted pumice fiamme occur in a pale grey finer grained pumiceous matrix (Fig. 6a). Outcrops of basaltic andesitic fire-fountain breccias also occur 30 m east of BH 9 within Unit 1b (Fig. 6e). Unit 1a is intruded by Unit 1c which consists of a green fine grained massive, coherent dacitic sill containing less than 3 % feldspar phenocrysts and irregular chlorite and carbonate patches (Fig. 6b). This sill has the same high-Ti dacitic composition as the pumice breccia of unit 1b, which suggests that the sill and volcaniclastic rocks are comagmatic. On the northern limb Unit 1b is exposed at 2500 East and the dacitic volcaniclastic rocks are sericite-quartz altered and sulfide stringers crosscut these rocks (Fig. 6c). Units 2, 3 and 4, including the ore host stratigraphic intervals are not exposed in surface outcrops. Unit 5a is exposed in several outcrops at 2700 East (Fig. 3) and comprises a sequence of normalgraded andesitic breccia beds. These beds contain abundant, lineated, globular andesitic bombs within a fine grained breccia matrix (Fig. 6f).

9

Stratigraphy located below the PMFZ fault A few bore holes penetrate below the PMFZ at the Petiknäs South deposit. These bore holes intersect feldspar porphyritic dacite intercalated with felsic volcaniclastic and sedimentary rocks. The dacites have distinct chilled margins and are interpreted to be sills. These sills intruded subparallel to bedding in the volcaniclastic and sedimentary rocks and are unmineralized (Jonsson et al. 1995). Below the Storåliden-dacite the succession comprises rhyolitic and dacitic massflow deposits with abundant large lithic clasts, siltstones, sandstones, coherent rhyolites, and rhyolitic in situ hyaloclastite breccia. This stratigraphy is significantly different to that above the PMFZ, has younging directions to the north, and to-date no stratigraphic correlation across the fault has been possible. Late synvolcanic intrusions An I-type granitoid intrusion known as the Rengård tonalite is present less than 500 m south of Petiknäs South (Figs. 2, 3). The Rengård tonalite shows similarity with the first phase (GI) of the Jörn batholith which is located about 7 km to the north, along the northern margin of the Skellefte district (Fig. 1). The GI Jörn intrusions are regarded as comagmatic with Skellefte volcanism (Allen et al. 1996). Although most of the Jörn-type granitoids appear to have intruded stratigraphically below the massive sulfide deposits, the Rengård tonalite has intruded into the Petiknäs South hanging wall. Synvolcanic intrusions are commonly associated with VMS deposits elsewhere and might have played a role in providing heat, magmatic fluids and metals to the formation of massive sulfides (Galley 2003; Scott and Yang 2005). Post-ore andesitic sills and high-Mg-Cr-Ni mafic dykes The andesitic sills are green, fine-grained, homogenous and are typically crosscut by tiny calcite veinlets. They are only weakly altered but contain abundant chlorite and carbonates in patches and locally also contain magnetite and feldspar crystals. The sills are up to 50 m thick, and have intruded various levels of the mine stratigraphy and the main massive sulfide body in the proximal part of the deposit. The andesite sills commonly have sharp and chilled contacts with their hosts (Fig. 5e). The high-Mg-Cr-Ni mafics dykes are soft, have a greenish-yellowish color with a “soapy” appearance and are rich in chlorite-talc intergrowths and carbonates. They contain opaque accessory minerals. The mafics dykes are only a few meters thick and crosscut the andesite sills. On the discrimination diagram by Shervais (1982) the andesite sills and the high-Mg-Cr-Ni mafic rocks plot in the field of island arc tholeiites (Fig. 7a). On the diagram by Mullen (1983) the andesite sills plot in the field of island arc tholeiites and the high-Mg-Cr-Ni mafic rocks in the field of calcalkaline basalts (Fig. 7b). These mafic dykes possibly represent feeders to Vargfors group volcanics which are stratigraphically higher then the Skellefte group volcanics. Allen et al. (1996) describes high-Mg basaltic rocks in the upper part of the Skellfte group and interprets them as sills and dykes related to the Gallejaur volcanics (belonging to the Vargfors group). Bergström (1997, 2001) describes rocks with high content of Mg-Cr-Ni from Vargfors sills, dykes and lavas which are chemically very similar to the high-Mg-Cr-Ni mafic rocks from Petiknäs South.

10

(a)

(b)

5 cm

UNIT 1c (d)

5 cm

UNIT 1b (c)

UNIT 1a (e)

2.5 cm

(f)

10 cm

UNIT 1b

UNIT 1b post-ore rhyolitic sill

UNIT 5a

(g)

5 cm

Fig. 6. Photographs from outcrops at Petiknäs South, in parenthesis: XYZ locations. (a) smpl 2232 from Unit 1b at S-limb: clastic dacite with elongated pumice clasts, (2834;2350;45). (b) smpl Re 76 from Unit 1c at S-limb; coherent dacitic sill, (2914;3150;30). (c) smpl 220604-02-A from Unit 1b at N-limb: chlorite altered massive dacite, pyrite stringers, (3115;2447;25) (d) smpl Re 78 from Unit 1a at N-limb: andesitic pumice breccia with silty rip up clast (3020;3214;30). (e) smpl Re 70 from Unit 1b at S-limb: volcaniclastic basaltic andesite fire fountain breccia (2720;2850;45). (f) smpl 2406 from Unit 5a at S-limb: andesitic massflow deposit with large clasts, fire fountain breccia, (2462;2704;35). (g) smpl Re 80, post alteration at S-limb: intrusive, fine grained massive rhyolite, (2980;3070;30).

11

600

10 Low-Ti IAT BON

V ppm vf

500

Post-ore andesitic sills and high Mg-Cr-Ni mafic dykes

ARCOFB

IAT

MORB BABMORB

400

Greenish, “soapy”, mafic dyke (post-ore), n=6 Fine grained, massive, andesite sill (post-ore), n=31

50

300 Alkaline

100

200 100 (a)

0

0

5

10

15

20

25

Ti ppm vf/1000 TiO2 % vf

Post-ore andesitic sills and high Mg-Cr-Ni mafic dykes

OIT MORB

IAT

OIA

Greenish, “soapy”, mafic dyke (post-ore), n=6 Fine grained, massive, andesite sill (post-ore), n=31

CAB MnO % vf * 10

P2O5 % vf * 10

(b)

Fig. 7. Andesite sills and mafic sills in discrimination diagrams. (a) by Shervais (1982) and (b) by Mullen (1983). Samples from sills and dykes plot in different and relatively tight clusters.

GEOCHEMISTRY OF LEAST ALTERED VOLCANIC ROCKS A set of 22 least altered samples has been selected on the basis of having 2% Na2O, and lacking abundant sericite, chlorite, carbonate and secondary quartz in hand specimen. These samples have been classified according to facies and stratigraphic position. In standard discrimination diagrams (Winchester and Floyd 1977; Le Bas et al. 1986), the least altered samples are andesites, rhyodacite/dacites and rhyolites. One rock from the stratigraphy located below the PMFZ fault (feldspar porphyritic dacitic sill) and one rock from the synvolcanic I-type granitoid (Rengård tonalite) are dacites in these diagrams (Figs. 8a, 8b). Whole rock analyses of selected least altered rocks from Petiknäs are shown in table 2.

12

least altered volcanic rocks from the Petiknäs area (n=22)

80 Rhyolite

75

Rhyolitic tuffac. silt to fgr sandstone (Unit 4) Rhyolitic fsp and qz HW porphyry (Unit 5b)

70

Fsp porphyritc HW rhyolite (Unit 5b)

Rhyodacite/Dacite

Fsp>qz porphyritc FW rhyolite (Unit 1) Fsp porphyritc FW rhyolite (Unit 1)

SiO2 % vf

65 60

Aphyric HW Rhyolite (Unit 5b) Fsp >> qz porphyritc HW rhyolite (Unit 5b) Fine grained green and massive dacitic sill

Andesite

Fsp porphyritic dacitic sill (below PMFZ)

55 50

Andesitic massflow deposit (Unit 3) Andesitic massflow deposit (Unit 5b) Sub-AB

45

Basaltic Andesite v'clastic breccia (Unit 3) Alk-Bas

40 .001

.01

Bas/Trach/Neph

(a)

.1

Zr/TiO2

1

Andesitic fine grained massive post-ore sill (Unit 6) Granodioritc synvolcanic intrusive of GI type(Rengård tonalite; sample is taken 1.7 km South of Petiknäs South)

16 Phonolite

14

Tephriphonolite

12 Na2O + K2O % vf

10

PhonoTephrite

8 6 4

Trachybasalt

Trachyandesite

Trachydacite

Rhyolite

Basaltic trachyandesite Dacite Basaltic andesite

Basalt

Trachyte

Andesite

2 0 45

(b)

50

55

60

65

70

75

80

SiO2 % vf

Fig. 8. Discrimination plots for 22 least altered samples from Petiknäs South. (a) SiO2 versus Zr/TiO2 (Winchester and Floyd 1977); (b) Na2O+K2O versus SiO2 (Le Bas et al. 1986). The sample from the synvolcanic Rengård granitoid plots in the field of rhyodacite/dacite and is chemically similar to dacites from the Petiknäs South mine sequence. vf=Volatile free

13

Table 2. Chemical composition of least altered Petiknäs samples. 1. BH9-529.2m, grey, fgr, fsp and qz pxtals, coherent volcanic, rhyolite A. 2. BH206-14.1m, beige, massive, fsp pxtals, coherent volcanic, Rhyolite B. 3. BH206483.9m, grey-green, massive, fsp pxtals, coherent volcanic, Rhyolite C. 4. 2232, grey, massive, presence of fiamme, volcaniclastic, Dacite II. 5. BH72-10.3m, grey-green, fgr-mgr, m-flow, volcaniclastic, Andesite. 6. BH206-188.85m, dark-grey, layered, volcaniclastic, Basaltic andesite. 7. Gq-124, unaltered granodiorite, igneous synvolcanic, Rengard Tonalite of G-Ia type. 8. BH207-121.5m, dark-green, fgr, coherent volcanic, Andesite sill. 9. BH209-226.05m, greenyellow, calcareous, soapy volcanic dyke, High-Mg-Cr-Ni basalt dyke. Abbreviations: fsp = feldspar, qz = quartz, pxtals = phenocrysts, fgr = fine grained, mgr = medium grained, m-flow = mass flow deposit. Sample ID Chemical Classification Stratigraphic interval Drill hole Depth (m) X (Northing. Petiknäs grid Y (Easting. Petiknäs grid Z (0 Z = 210m asl) all data on LOI free basis SiO 2 % TiO2 % Al2 O3 % FeO % MnO % MgO % CaO % Na 2 O % K2 O % P 2 O5 % Cr2 O3 % Ba ppm Cu ppm Pb ppm Zn ppm Au ppb Ag ppm As ppm Sb ppm Bi ppm Cd ppm Hg ppm Tl ppm V ppm Ni ppm Co ppm Sc ppm Mo ppm Sn ppm W ppm Ga ppm Rb ppm Sr ppm Cs ppm U ppm Ta ppm Th ppm Hf ppm Nb ppm Y ppm Zr ppm Al2 O3 /TiO2 Zr/ Al2 O3 Zr/TiO2 Zr/Y Lan/Ybn La ppm Ce ppm Pr ppm Nd ppm Sm ppm Eu ppm Gd ppm Tb ppm Dy ppm Ho ppm Er ppm Tm ppm Yb ppm Lu ppm LOI %

1 Rhy A unit 5 9 529.2 2460 2577 431

2 Rhy B unit 1 206 14.1 2805 2039 179

3 Rhy C unit 5 206 483.9 2370 2004 342

4 Dacite II unit 1b outcrop

6 Bas. And. unit 3 206 188.9 2648 2046 255

7 Ton. G-Ia outcrop

2834 2350 45

5 And. unit 3 72 10.3 2579 2319 51

1013 2379 0

8 And. sill unit 6 207 121.5 2738 2036 264

78.72 0.164 12.36 0.94 0.02 0.26 1.41 4.34 1.64 0.023 0.000 543 7 1 8 2 0.0 24 0.4 0.0 0.1 0.0 0.0 3 2 2 9 0.5 2 1 16 24 85 0.1 3 0.5 5 5 9 31 182 75 15 1109 5.9 5.4 26.8 54.6 6.4 26.3 5.5 0.9 4.7 0.6 5.1 1.0 2.9 0.5 3.3 0.5 1.5

76.46 0.243 13.43 0.99 0.02 0.46 1.44 5.54 1.28 0.033 0.001 402 7 7 16 3 0.1 11 0.4 0.0 0.0 0.0 0.1 16 4 3 6 0.1 1 1 13 25 139 0.3 3 0.5 5 4 8 24 144 55 11 593 6.1 9.2 26.6 51.0 6.1 22.3 3.5 0.7 4.0 0.7 4.2 0.7 2.1 0.3 1.9 0.3 1.4

73.08 0.362 13.86 2.17 0.04 0.61 3.04 4.48 2.08 0.072 0.000 549 7 2 21 1 0.0 8 0.7 0.1 0.1 0.0 0.0 35 1 6 12 0.7 2 1 18 37 123 0.3 3 0.7 6 6 8 34 176 38 13 487 5.2 5.0 28.4 52.5 6.7 29.6 5.4 1.0 5.2 0.9 5.1 1.1 3.2 0.5 3.8 0.5 3.2

67.27 0.545 14.73 9.39 0.19 2.20 1.30 2.08 2.01 0.106 0.000 469 2 3 147 0 0 1 0 0 0 0 0 3 0 4 19 0 2 1 22 33 72 0 2 0 4 5 9 39 172 27.0 11.7 315.6 4.4 4.4 25.2 51.8 7.0 29.6 5.9 1.6 6.1 1.0 5.8 1.3 4.0 0.5 3.9 0.6 0.1

62.45 0.636 16.66 7.75 0.13 2.89 2.45 6.42 0.41 0.096 0.000 173 10 2 87 2 0.0 10 0.8 0.0 0.0 0.0 0.0 193 3 22 27 0.3 2 1 18 6 81 0.4 1 0.3 2 3 5 24 95 26 6 149 4.0 4.5 13.5 26.9 3.5 15.7 3.6 1.0 3.7 0.6 3.8 0.8 2.4 0.3 2.0 0.4 3.5

58.46 1.004 15.62 9.77 0.15 5.15 5.07 3.65 0.85 0.141 0.000 326 32 19 190 11 0.2 21 1.7 0.2 0.2 0.1 0.2 256 1 25 41 1.0 0 0 19 19 115 0.3 1 0.3 3 3 4 29 80 16 5 80 2.8 2.3 10.3 24.1 3.1 14.0 3.6 1.2 3.9 0.7 4.8 0.9 3.0 0.4 3.0 0.4 5.4

71.16 0.267 15.09 4.15 0.05 0.79 3.48 3.72 1.04 0.092 0.001 454 398 1 56 1 0.3 1 0.2 0.2 0.1 0.0 0.2 22 2 6 7 2.0 0 0 18 23 307 1.1 1 0.4 1 3 5 24 115 57 8 432 4.9 4.9 17.1 34.9 4.1 17.1 3.5 1.0 3.5 0.6 3.5 0.8 2.2 0.4 2.4 0.4 1.0

58.64 0.952 15.06 11.69 0.18 3.08 4.78 5.34 0.02 0.134 0.000 47 100 1 108 8 0.3 1 0.5 0.0 0.0 0.0 0.0 298 2 26 37 0.2 0 1 18 0 204 0.0 2 0.5 1 2 3 19 66 16 4 69 3.4 3.0 10.7 22.9 3.1 14.2 3.3 1.1 3.8 0.6 3.2 0.7 2.1 0.3 2.4 0.3 5.3

14

9 mafic dyke unit 6 209 226.05 2678 2034 349 48.23 0.633 11.66 10.88 0.23 18.52 9.40 0.01 0.03 0.142 0.155 8 1 14 139 0 0 69 1 0 0 0 1 180 326 57 33 0 0 1 11 1 124 0 1 0 1 1 3 13 38 18.4 3.3 60.6 2.9 4.1 7.4 16.8 2.4 11.8 2.5 0.6 2.4 0.4 2.4 0.5 1.5 0.2 1.2 0.2 11.8

Magmatic affinity Magmatic affinity of rock types can be assessed using Zr/Y and (La/Yb)n ratios (Barrett and MacLean 1999). On the basis of Zr/Y ratios, all least altered samples except three plot in the transitional field, whereas (La/Yb)n ratios suggest that the samples are transitional to calc-alkaline and only one is tholeiitic (Fig. 9a). Rhyolites tend to have somewhat higher Zr/Y ratios than the dacites and andesites. Typical chondrite-normalized REE patterns are shown for the main rock types in figures 9b and 9c. The REE curves have a moderate slope for felsic rocks of calc-alkaline and transitional magmatic affinity (Fig. 9b), but they are somewhat flatter for intermediate rocks of tholeiitic and transitional magmatic affinity (Fig. 9c). In summary, at Petiknäs the felsic rocks are generally transitional or mildly calc-alkaline whereas the basaltic-andesitic and the andesitic volcaniclastic rocks are transitional to tholeiitic. The andesite sills and the mafic dykes are tholeiitic. least altered volcanic rocks from the Petiknäs area

10 Transitional

8

Rhyolitic tuffac. silt to fgr sandstone (Unit 4)

Calcalkaline

Calc-alkaline

Tholeiitic

Rhyolitic fsp and qz HW porphyry (Unit 5b) Fsp porphyritc HW rhyolite (Unit 5b) Fsp>qz porphyritc FW rhyolite (Unit 1) Fsp porphyritc FW rhyolite (Unit 1) Aphyric HW Rhyolite (Unit 5b) Fsp >> qz porphyritc HW rhyolite (Unit 5b) Fine grained green and massive dacitic sill

Transitional

(La/Yb)n

5.5 4

Andesitic massflow deposit (Unit 3) Andesitic massflow deposit (Unit 5b)

Tholeiitic

2.5

Fsp porphyritic dacitic sill (below PMFZ)

0

2

Basaltic Andesite v'clastic breccia (Unit 3)

(a) 3

4

Zr/Y

5

6

7

8

1000

least altered coherent felsic volcanic rocks from Petiknäs South Fsp >> qz porphyritc HW rhyolite (Unit 5b) (BH206-498m) Rhyolitic fsp and qz HW porphyry (Unit 5b) (BH9-511.55m) Fsp porphyritc FW rhyolite (Unit 1) (BH206-14.1m) Granodioritc synvolcanic intrusive of GI type(Rengård tonalite; sample is taken 1.7 km South of Petiknäs South)

100

Rock/Chondrites

Andesitic fine grained massive post-ore sill (Unit 6) Granodioritc synvolcanic intrusive of GI type(Rengård tonalite; sample is taken 1.7 km South of Petiknäs South)

10

(b) 1

La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb Lu

least altered intermediate volcanic rocks from Petiknäs South

1000

Basaltic Andesite v'clastic breccia (Unit 3) (BH206-188.85m) Andesitic fine grained massive post-ore sill (Unit 6, BH207-121.5m)

Rock/Chondrites

100

Andesitic massflow deposit (Unit 3) (BH72-28.35m) Andesitic massflow deposit (Unit 5b) (outcrop 2406)

10

(c) 1


Fig. 9 Magmatic affinity of Petiknäs South samples based on Zr/Y and (La/Yb)n ratios (Barrett and MacLean 1999). (a) Least altered samples are mainly of transitional magmatic affinity; only a few are slightly tholeiitic. Least altered felsic volcanics (b) and least altered intermediate rocks (c) have moderate slope for REE curves for felsic rocks and somewhat flatter REE patterns for intermediate rocks. REE data were normalized to the chondrite values of Evensen et al. (1978).

15

CORRELATION AND INTERPRETATION OF THE MINE SEQUENCE Units of the mine sequence were identified in each of the 40 drill holes logged in this study by using volcanic facies characteristics such as grain size, nature of components and abundances and sizes of phenocrysts. Contacts between intrusions and clastic rocks were also described in detail. The identified units were then correlated between the drill holes allowing construction of two main cross-sections and two main level plans (Figs. 10, 11, 12, 13).

0Z

3000 X

2900 X

2800 X

2700 X

2600 X

2500 X

2400 X

2300 X

66

NE 54

Petikån river

SW

Skellefte river = 162 m asl

Overburden

Overburden ?

100 Z

? ? ? ?

51

?

200 Z

?

233

71

? ?

300 Z

? ?

70

FW 314

206 A

400 Z

373

209

D

HW

511

B/C

500 Z

588

267

207

593

49

458 66

600 Z

54


51

233

Unit 1: FW-complex

71

Unit 4: A+D lens package

314

A

70

206 207

373

209

511

PM

700 Z

FZ

267

588


593

49

458

100 m


inset showing mine-scale packages (post-ore sills are not shown)

231

800 Z

231

Fig. 10. Detailed Geology of the proximal cross-section (2030 East). Stratigraphic younging is north-south. Boundaries of the mine scale units (Units 1 to 5) and the location of the B/C ore horizon are given. Primary textures generally are preserved however strong alteration transformed the rocks below the A and D ore lenses into chloritegarnet schist. Andesite sills have intruded into the B and C ore lens and into most of the stratigraphic intervals. For legend see figure 13.

16

0Z

2800 X

2700 X

2600 X

2500 X

2400 X

NE

SW 68

72 Overburden


100 Z

200 Z

FW

300 Z

291+292

356 69

315 400 Z

291

HW 500 Z

677 676 600 Z 68

69

72


291+292 356 315


700 Z

677

673 B/C 291


Unit 1: FW-complex

Unit 5: faulted HW-complex 676

673

800 Z

441

441


662

662

100 m 900 Z

Fig. 11. Detailed Geology of the distal cross-section (2300 East). Stratigraphic younging is north-south. Only few andesite sills intrude the mine sequence. Boundaries of the mine scale units (Units 1 to 5) and the location of the B/C ore horizon and the intrusive contact of the footwall rhyolites are given. For legend see figure 13.

17

1900 Y

2000 Y

2900 X

2100 Y

2200 Y

2300 Y

2400 Y

54

314

31.9o

315

Petiknäs N


50 m

291

267 207/209

2800 X

(292 is just below 291 and both BH have the same drill direction)

FW

266

262 B/C

Drift 356 330 m 273 49

2700 X

72 68 2600 X

A

54

314 315 267 304 207/209

2500 X

266

262


238

70 71

291

Unit 1: FW-complex Drift 356 330 m 273

Unit 3: 72 Bas. Andesite clastic HW

49


679

HW

68

207 233

69

238

70 71

Unit 5: faulted HW-complex 679 69

2400 X

206

proximal section (2030Y)


distal section (2300Y)

206

100 m 2300 X

Fig. 12. Detailed Geology of the 300 m level of the mine. Stratigraphic younging is north-south and at the 300 m level of the mine the ore lenses B/C and A occur. Boundaries of the mine scale units (Units 1 to 5) and the location of the B/C ore horizon and the intrusive contact of the footwall rhyolites are given. X and Y coordinates are given in the local “Petiknäs coordinate system” which is used by Boliden AB; for coordinates of the Swedish national grid see appendix 1. For legend see figure 13.

18

1900 Y

2000 Y

2900 X

2100 Y


100 m

2200 Y

inset showing mine-scale packages 315 (post-ore sills are not shown) 267 Unit 1: FW-complex 511

Unit 2: Felsic clastic hosting B/C lens 366 588

593

2800 X

2300 Y

distal section (2300Y) 677

315




441

2400 Y

292

676

267 677

FW 511 49 2700 X B/C

366 588

292

2600 X

441

31.9

593

HW

2500 X

Weakly to moderately feldspar porphyritic rhyolite Strongly feldspar porphyritic rhyolite Strongly feldspar and quartz porphyritic rhyolite Peperite

273

676

50 m

Andesite sill Pumice rich Fiamme rich Angular clasts

Autobreccia Felsic mass flow unit, poorly sorted with angular clasts (occurs in BH70&71) Felsic mass flow unit with angular clasts Rhyolitic volcaniclastic sandstone


Rhyolitic volcaniclastic siltstone

Strongly dissiminated sulfides

Mudstone Basaltic andesite and andesite mass flow unit (faulted HW) Basaltic andesite volcaniclastic sandstone Basaltic andesite volcaniclastic siltstone Weakly to moderately porphyritic dacite Strongly porphyritic dacite

Fault

Bore hole (BH)

o

Petiknäs N


Chlorite-talc rock Massive sulfide Semi-massive sulfide

PMFZ Petiknäs Main Fault zone Ore horizon of the C/B ore lens FW-Rhyolite intrusive contact Stratigraphic younging FW HW

Footwall complex Hanging wall complex

Fig. 13. Detailed Geology of the 550 m level of the mine. Stratigraphic younging is north-south and at the 550 m level of the mine the B/C ore lens occurs. Boundaries of the mine scale units (Units 1 to 5) and the location of the B/C ore horizon and the intrusive contact of the footwall rhyolites are given. X and Y coordinates are given in the local “Petiknäs coordinate system” which is used by Boliden AB; for coordinates of the Swedish national grid see appendix 1.

19

The distribution of the units of the mine-sequence, the geological relations and the volcanic and sedimentary environment of each unit are discussed below, from footwall to hanging-wall (north to south). Unit 1 (footwall complex) can be correlated between sections, plans and surface and comprises coherent strongly feldspar-porphyritic proximal rhyolite to the ores and andesitic and dacitic volcaniclastic rocks towards the east. The porphyritic rhyolites intrude into high-Ti dacitic volcaniclastics in the deeper footwall and into the altered rhyolitic volcaniclastics of the overlaying Unit 2 at the top of the footwall. Peperitic contacts between these intrusions and the volcaniclastic rocks imply that the intrusions were shallow and intruded into non consolidated wet clastic deposits (Kokelaar 1982; Busby-Spera and White 1987; Allen et al. 1996). The high-Ti dacitic volcaniclastic rocks are likely remnants of a clastic footwall sequence that was subsequently intruded by the rhyolite sills. Interestingly such unusual high-Ti dacitic rocks also occur in the footwall of the Renström ores. Allen et al. (2004) suggest that the footwall of Petiknäs South and Renström can be directly correlated based on the very similar high Ti-P-Fe chemistry and physical characteristics of the dacitic rocks. Surprisingly, except for a narrow zone, the footwall at Petiknäs South is little altered (feldspar phenocrysts remain). This suggests that the rhyolitic sills intruded into parts of the footwall and parts of the overlying rhyolitic clastic unit (Unit 2) after the strongest hydrothermal alteration and after formation of the ore lenses. Sodium-rich, weakly altered felsic intrusions occurring below VMS deposits and intruding the ore horizon have been documented elsewhere e.g. at the Fukazawa mine in the Kuroko district (Date et al. 1983; Hashiguchi et al. 1983). The Petiknäs South footwall was interpreted by Allen et al. (1996) to consist of multiple generations of subaqeous cryptodomes, sills and dykes with abundant peperite and in situ hyaloclastite breccia. This is a characteristic proximal facies association (Allen et al. 1996; Gibson et al. 1999). Association of this particular facies association with VMS deposits has been documented from many VMS districts (Allen et al. 2002). The remnant dacitic footwall observed in bore holes at the proximal section crops out more extensively towards the east. Emplacement of the diffusely stratified breccia seen in Unit 1a is interpreted to have been subaqueous and the unit is attributed to rapid resedimentation of pyroclastic andesite lapilli on the flanks of an andesite shield (Allen et al. 2004, p. 89). Bed forms observed by Allen et al. (2004) elsewhere in the area indicate that depositional environments ranged from deep water to shallow water and were locally emergent. The thick normal graded dacitic pumice breccia of Unit 1b indicates subaqueous, syneruptive emplacement (Allen et al. 1996). Interbedded in Unit 1b are basaltic andesitic fire-fountain breccias. These breccia form from water-settled fall and avalanching deposits (Allen et al. 1996; Simpson and McPhie 2001). The narrow zone of chlorite-garnet schists seen in the distal footwall likely corresponds to a discordant hydrothermal discharge zone. Unit 2 (felsic clastic unit hosting the B/C lens) comprises reworked tuffaceous sandstones and siltstones and hemipelagic black mudstone. Single beds of mudstone can be correlated between bore holes. Unit 2 has best exposure from bore holes of the distal section (2300 East) as the unit is intruded by post-ore andesite sills in the proximal part of the deposit and only thin screens of rhyolitic siltstone and sandstone remain. The Unit 2 facies are interpreted to be post-eruptive and to have formed below wave base (Lowe 1982; Allen et al. 1996). Unit 3 (basaltic andesite clastic hanging-wall unit) can be correlated between sections and plans. However there are no surface exposures because this part of the mine sequence is covered by glacial till and the Skellefte River. The juvenile, weakly polymict, normal graded massflow deposits of Unit 3 were rapidly emplaced and may have eroded parts of the underlying felsic unit 2. Emplacement is interpreted to have been syneruptive and subaqueous (Allen et al. 1996). Some of the mass flow deposits of Unit 3 show lateral variations, ranging from siltstone to sandstone over distances of

20

a few hundred meters. As Unit 3 consists almost entirely of basaltic andesite mass flow deposits and these facies and unique composition are not observed in other units, Unit 3 is an excellent stratigraphic marker. Unit 3 is also the only stratigraphic level at the Petiknäs South deposit that contains only andesitic rocks and no rhyolitic rocks. The ore horizon of the B/C ore lens is located at the contact between Unit 2 and Unit 3. Unit 4 (unit hosting the A and D lens) is best preserved at the distal section and can be correlated between sections and plans. The unit does not crop out. Unit 4 comprises mudstone and normal graded tuffaceous sandstone to siltstone turbidites, which were likely emplaced in a subaqeous environment below wave base. The siltstone-sandstone beds contain large rhyolitic pumice clasts and this facies could be similar to the ones described by Allen and Svenson (2004) and Allen et al. (2004) at the Renström mine and by Steward and McPhie (2004) from Pliocene volcaniclastics at Milos, Greece. At Milos the course pumice clasts were settled from suspension of the waterlogged large pumice clasts which in turn originated from submarine explosive eruption. Several beds of Unit 4 were strongly altered into an assemblage of chlorite garnet-schists and might have been volcaniclastic rocks prior to alteration and metamorphism. Unit 4 at Petiknäs South could correspond to the Renstöm ore horizon (Allen and Svenson 2004; Allen et al. 2004). Unit 5a is located immediately south of the hanging-wall fault and has a unique low-Ti basaltic composition which was not found elsewhere in the Petiknäs South stratigraphy making Unit 5a an excellent stratigraphic marker. Unit 5a can be correlated from the proximal section to BH 9, 600 m to the east (Fig. 3). The Unit 5a mass flow deposit is juvenile, monomict and poorly sorted and likely represents rapid subaqueous emplacement of volcaniclastic debris following and andesitic eruption. The facies characteristics of the deposits (globular bombs, quench fragmented breccia matrix) suggest they were fed from Hawaiian style fire fountain eruptions and were deposited below wave base on the sea-floor from subaqueous mass flows (Simpson and McPhie 2001; Allen et al. 2004). Unit 5b, comprises felsic coherent sills and volcaniclastic rocks at the proximal and distal crosssections. This succession thins out laterally and distal to the Petiknäs South deposit mainly comprises andesitic mass flow breccias (Fig. 3). Post-ore rhyolitic sills occur in the middle and upper parts of unit 5b. The pumiceous and lithic-rich rocks are interpreted to be turbidites which were emplaced below wave base. The coherent sills have peperitic contacts or show hyaloclastite margins, which imply that these sills were intruded at shallow levels into wet unconsolidated sediments. Unit 6. The sharp regular contacts of the sills with their host rocks (Fig. 5e) and presence of distinct chilled margins imply that the mafic magma was intruded after lithification of the host rocks (Best 1982). Lack of alteration of the sills indicates that they were intruded after hydrothermal alteration. One andesite sill split an initially single massive sulfide body into two parts, forming the B and C ore lenses (Allen et al. 2004). Other andesite sills intruded various levels of the mine stratigraphy in the proximal part of the deposit. The mafic dykes are mainly high Mg-Cr-Ni basalts. They crosscut the andesite sills and are the youngest rocks in the mine area. Table 1 gives the relations between sills and dykes and their host rocks. STAGES OF HOST ROCK FORMATION AND SULFIDE DEPOSITION Prior to injection of the post-ore andesite sills (Unit 6), the B and C ores formed a single massive sulfide lens within a thin interval of rhyolitic volcaniclastic rocks (Unit 2). Rapidly emplaced basaltic andesitic graded mass flow deposits directly overlay Unit 2. The D and A ores formed at 21

a stratigraphically higher level, in an interval of mainly alternating rhyolitic tuffaceous siltstone to fine grained sandstone with pumice clasts (Unit 4). Weakly altered feldspar-porphyritic rhyolite sills with peperitic margins were then intruded into the footwall complex and into felsic volcaniclastic rocks directly below the B/C ore lens. (Unit 1 and Unit 2). As Unit 4 is truncated by a fault which places it in contact with unit 5 it is uncertain if the A ore lens represents the last stage of massive sulfide deposition. The original position of the block containing unit 5 is unknown. CONCLUSIONS (1) The mine sequence at Petiknäs South has been defined on the southern limb of the regional anticline which hosts the Petiknäs South ores. Each of the six units of the mine sequence have been correlated between cross-sections, level plans and the surface. Primary sedimentary structures (normal grading in clastic rocks) allow determination of younging direction which is constantly towards the south. The volcanic and sedimentary environment is interpreted to be dominantly below wave base; except for the volcaniclastic rocks in the deepest part of the footwall, which could have been emplaced in shallow water. In proximity to the ores the footwall comprises multiple generations of cryptodomes and sills and likely corresponds to a felsic volcanic center or vent area (Allen et al. 1996). (2) Most coherent volcanic rocks in the Petiknäs South area are felsic. However the post-ore sills are andesitic. The non-coherent volcaniclastic rocks range from felsic to andesitic; one unit of the mine sequence consists exclusively of basaltic andesite and andesite mass flow breccia. The stacked ore lenses at Petiknäs South all occur in dominantly felsic clastic stratigraphic intervals. (3) The ore horizon of the B/C ore lens is located at the contact of felsic and basaltic andesitic volcaniclastic rocks and can be identified even in unmineralized parts of the area. (4) The magmatic affinity of volcanic rocks in the Petiknäs South area is transitional to mildly calcalkaline for most of the felsic rocks and tholeiitic for the sills and dykes. (5) Rocks at Petiknäs South were altered and subsequently deformed and metamorphosed to the greenschist facies resulting in assemblages of sericite, quartz, chlorite, garnet, and locally carbonate. Alteration is strongest close to the ore lenses and in the portions of the footwall where chloritegarnet schist occur. (6) We suggest that the Petiknäs ores were deposited at and/or slightly below the sea-floor for the following reasons: VMS deposits are interpreted to form over tens of thousands of years to over a million years (Rona et al. 1993; Hannington et al. 1999). All ores at Petiknäs South are hosted within reworked silty to sandy volcaniclastic rocks which are interpreted to have formed at very slow accumulation rate. As the ore lenses at Petiknäs South likely formed at a faster rate than the host facies it is possible that the Petiknäs South ores formed at sea floor. By contrast ores hosted within rapidly emplaced facies such as a mass flow deposit must have formed by replacement, because the time span to form the host facies is much shorter than the time required to form a seafloor deposit (Doyle and Allen 2003). At Petiknäs South the rapidly emplaced basaltic andesite mass flow breccia which overlays the B/C ores is unmineralized. Some typical characteristics of well documented sea-floor VMS-deposits (Franklin et al. 1981; Date et al. 1983; Hashiguchi et al. 1983; Gibson et al. 1999) were recognized at Petiknäs South, such as upflow alteration zones in the footwall, lack of hanging-wall alteration and the occurrence of of post-alteration felsic and intermediate sills in the footwall and ore horizon.

22

ACKNOWLEDGEMENTS Adjunct Prof. Rodney Allen is thanked for having introduced me into the world of subaqueous volcanoes and associate Prof. Tim Barrett is thanked for having shown me how fascinating geochemistry can become. Rodney Allen and Tim Barrett are thanked for their encouragement and patience. They have been excellent supervisors and are thanked for assistance in the field and in the drill core library. Rodney is acknowledged for his careful review of the manuscripts I and II and the introduction; Tim is thanked to have reviewed the manuscripts I and II. The constructive, thoroughly and throughout review has improved this thesis substantially. We thank company geologists Rolf Jonsson and Sven-Åke Svenson for providing helpful discussions and sharing their wide knowledge of the Petiknäs-Renström area Boliden Mineral AB is gratefully acknowledged for providing geological information on the Petiknäs area, and access to their lithogeochemical data base, and Agnetha Steinwall and Martin Lindfors for their help with data retrieval and handling of drill cores At Luleå University, Prof. Pär Weihed provided encouragement and useful discussions, Milan Vnuk kindly digitized the geological sections and maps and Maj-Len Knutsson, is thanked for her assistance to solve administrative problems. All my colleagues at the division of Ore Geology and Applied Geophysics are thanked for support and encouragement. This study has been funded by Georange Project 9 (Contract 89124): “Characterization of the Ore Horizons and Alteration Systems of Volcanic-associated Massive Sulphide Deposits in the Skellefte District, Sweden” and is part of the IGCP Project 502 “Global comparison of volcanic-hosted massive sulphide districts: the controls on distribution and timing of VMS deposits.” I also would like to thank my family for all the patience and support.

23

REFERENCES Allen RL, Weihed P, Svenson SÅ (1996) Setting of Zn-Cu-Au-Ag massive sulfide deposits in the evolution and facies architecture of a 1.9 Ga marine volcanic arc, Skellefte District, Sweden. Economic Geology, v. 91: 1099-1053 Allen RL, Weihed P, Blundell DJ, Crawford T, Davidson G, Galley A, Gibson H, Hannington, M, Herrington R, Herzig P, Large RR, Lentz D, Maslennikov V, McCutcheon S, Peter J, Tornos F (2002) Global comparisons of volcanic-associated massive sulphide districts. In: Blundell DJ, Neubauer F, von Quadt A (eds.) The timing and location of major ore deposits in an evolving orogen. Geological Society Special Publications, v. 204: 13-37 Allen RL, Svenson SÅ (2004) 1.9 Ga volcanic stratigraphy, structure, and Zn-Pb-Cu-Au-Ag massive sulfide deposit of the Renström area, Skellefte district, Sweden. Society of Economic Geologists Guidebook Series, v. 33: 65-88 Allen RL, Svenson SÅ, Jonsson R (2004) Day two field guide: Volcanic stratigraphy and structure of the Renström area and mine tour of the Petiknäs South Zn-Pb-Cu-Au-Ag massive sulfide deposit. Society of Economic Geologists Guidebook Series, v. 33: 89-93 Allen R, Barrett T, Billström K, Lickorish H, Freeman S, Schlatter D, Imaña Osorio M, Montelius C, González Roldán M, Pascual E, Liedberg S, Jonsson R, Svenson SÅ, Årebäck H, Abrahamsson S, Leijd M (2005) Characterization of the ore horizons and alteration systems of volcanic-associated massive sulphide deposits in the Skellefte District, Sweden. Final Report, Georange Project 89124, pp 26 Barrett TJ, MacLean WH (1999) Volcanic sequences, lithogeochemistry, and hydrothermal alteration in some bimodal volcanic-associated massive sulfide systems. In: Barrie CT, Hannington MD (eds.) Volcanic-associated massive sulfide deposits: processes and examples in modern and ancient settings. Reviews in economic geology, v. 8: pp 101-131 Best MG (1982) Igneous and metamorphic petrology. Brigham Young University, Publisher; Freeman WH and Co, 630 pp Bergström U (1997) Marginal basin magmatism in an ancient volcanic arc; petrology of the Palaeoproterozoic Mala-Group basalts, Skellefte District, northern Sweden. Geologiska Föreningens i Stockholm Förhandlingar, v. 119: 151-157 Bergström U (2001) Geochemistry and tectonic setting of volcanic units in the northern Västerbotten county, northern Sweden. In: Weihed P (ed.) Economic geology research, v. 1, 1999-2000Sveriges Geologiska Undersökning, Research Paper C 833: 69-92 Billström K, Weihed P (1996) Age and provenance of host rocks and ores in the Paleoproterozoic Skellefte District, northern Sweden. Economic Geology, v. 91: 1054-1072 Busby-Spera CJ, White JDL (1987) Variation in peperite textures associated with differing host-sediment properties. Bulletin of Volcanology, v. 49: 765-776 Cas (1992) Submarine volcanism: eruption styles, products, and relevance to understanding the host-rock successions to volcanic-hosted massive sulfide deposits. Economic Geology, v. 87: 511-541 Date J, Watanabe Y, Saeki Y (1983) Zonal alteration around the Fukazawa Kuroko deposits, Akita Prefecture, northern Japan. In: Ohmoto H, Skinner BJ (eds.) The Kuroko and related volcanogenic massive sulfide deposits. Economic Geology Monograph 5: 365-386 Doyle GM, Allen RL (2003) Subsea-floor replacement in volcanic-hosted massive sulfide deposits. Ore Geology Reviews, v. 23: 183-222

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Evensen NM, Hamilton PJ, O'Nions RK (1978) Rare-earth abundance in chondritic meteorites. Geochimica et Cosmochimica Acta, v. 42: 1199-1212 Franklin JM, Sangster DM, Lydon JW (1981) Volcanic-associated massive sulfide deposits. In: Skinner BJ (ed.) Economic geology; Seventy-fifth anniversary volume; 1905-1980, pp 485-627 Galley AG (2003) Composite synvolcanic intrusions associated with Precambrian VMS-related hydrothermal systems. Mineralium Deposita, v. 38: 443-473 Gibson H, Morton RL, Hudak GJ (1999) Submarine volcanic processes, deposits and envrionments favorable for the location of volcanic-associated massive sulfide deposits. In: Barrie CT, Hannington MD (eds.) Reviews in economic geology, v. 8: 13-51 Grip E (1978) Mineral deposits of Sweden. In: Bowie SH, Kvalheim A, Haslam HW (eds.) Mineral Deposits of Europe, v. 1. The Institution of Mining and Metallurgy/The Mineralogical Society of London, London, pp 93-198 Hannington MD, Bleeker W, Kjarsgaard I (1999) Sulfide mineralogy, geochemistry, and ore genesis of the Kidd Creek Deposit: Part I, North, Central and South orebodies. In: Hannington MD, Barrie CT (eds.) The giant Kidd Creek volcanogenic massive sulfide deposit, western Abitibi Subprovince, Canada. Economic Geology Monograph 10: 163-224 Hashiguchi H, Yamada R, Inoue T (1983) Practical application of low Na2O anomalies in footwall acid lava for delimiting promising areas around the Kosaka and Fukazawa kuroko deposits, Akita Prefecture, Japan. In: Ohmoto H, Skinner BJ (eds.) The Kuroko and related volcanogenic massive sulfide deposits. Economic Geology Monograph 5: 387-394 Jonsson R, Nordin R, Schlatter DM (1995) The Petiknäs Proterozoic volcanic-hosted massive sulfide deposits: case history and a comparative genetic study. Unpublished report, Boliden Mineral AB, 50p. Kokelaar BP (1982) Fluidization of wet sediments during the emplacement and cooling of various igneous bodies. Journal of the Geological Society of London, v. 139: 21-33 Le Bas MJ, Le Maitre RW, Streckeisen A, Zanettin BA (1986) Chemical classification of volcanic rocks based on the total alkali-silica diagram. Journal of Petrology, v. 27: 745-750 Lowe DR (1982) Sediment gravity flows; II, Depositional models with special reference to the deposits of high-density turbidity currents. Journal of Sedimentary Petrology, v. 52: 279-297 MacLean WH (1990) Mass change calculations in altered rock series. Mineralium Deposita, v. 25: 44-49 MacLean WH, Barrett TJ (1993) Lithogeochemical techniques using immobile elements. Journal of Geochemical Exploration, v. 48: 109-133 McPhie J, Doyle M, Allen R (1993) Volcanic textures; a guide to the interpretation of textures in volcanic rocks. Hobart, University of Tasmania, Centre for Ore Deposit and Exploration Studies, 198 pp Montelius C, Allen RL, Svenson SÅ (2004) Polymetallic massive and network sulfide deposits hosted by a crystal-rich rhyolite pumice deposit, Maurliden, Skellefte district, Sweden. Society of Economic Geologists Guidebook Series, v. 33: 95-109 Mullen, Ellen D (1983) MnO/TiO2 /P2O5; a minor element discriminant for basaltic rocks of oceanic environments and its implications for petrogenesis. Earth and Planetary Science Letters, v. 62: 53-62 Rickard DT; Zweifel H (1975) Genesis of Precambrian sulfide ores, Skellefte District, Sweden. Economic Geology, v. 70: 255-274

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Rona PA, Hannington MD, Raman CV, Thompson G, Tivey MK, Humphris SE, Lalou C, Petersen S (1993) Active and relict sea-floor hydrothermal mineralization at the TAG hydrothermal field, Mid-Atlantic Ridge. Economic Geology, v. 88: 1989-2017 Schlatter DM, Allen RL, Jonsson R, and Barrett TJ (2004a) Volcanic and chemical stratigraphy of the Petiknäs South Zn-Cu-Au-Ag-Pb VMS deposit, Skellefte district, Sweden. 26th Nordic Winter Meeting, Uppsala, Sweden, January 6-9 2004, Abstracts volume, Geologiska Föreningens i Stockholm Förhandlingar, v. 126: 151 Schlatter DM, Allen RL, Jonsson R, and Barrett TJ (2004b) Stratigraphy of the Petiknäs South volcanic-hosted massive sulphide deposit, Skellefte district, Sweden. IAVCEI International Volcanological Congress 2004, Pucon-Chile, November 14-19 2004. Abstracts volume 67. Scott SD, Yang K, Xu Q (2005) Magmatic fluids: A key to forming 'giant' volcanogenic massive sulfide deposits. GAC-MAC meeting and IGCP-502 workshop, Halifax, Canada. Abstracts Volume. Shervais JW (1982) Ti-V plots and the petrogenesis of modern and ophiolitic lavas. Earth and Planetary Science Letters, v. 59: 101-118 Simpson K, McPhie J (2001) Fluidal-clast breccia generated by submarine fire fountaining, Trooper Creek Formation, Queensland, Australia. Journal of Volcanology and Geothermal Research, v. 109: 339-355 Stewart AL, McPhie J (2004) An upper Pliocene coarse pumice breccia generated by a shallow submarine explosive eruption, Milos, Greece. Bulletin of Volcanology, v. 66: 15-28 Trepka-Bloch C (1985) Cyclic ore formation of some volcanogenic massive sulfide deposits in the Skellefte District, Sweden. Mineralium Deposita, v. 20: 23-29 Vivallo W, Claesson LÅ (1987) Intra-arc rifting and massive sulphide mineralization in an early Proterozoic volcanic arc, Skellefte district, northern Sweden. In: Pharaoh TC, Beckinsale RD, Rickard D (eds.) Geochemistry and mineralization of Proterozoic volcanic suites. Geological Society Special Publication, v. 33: 69-79 Weihed P, Bergman J, Bergström U (1992) Metallogeny and tectonic evolution of the Early Proterozoic Skellefte district, northern Sweden. Precambrian Research, v. 58: 143-167 Winchester JA., Floyd PA (1977) Geochemical discrimination of different magma series and their differentiation products using immobile elements. Chemical Geology, v. 20: 325-343

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Chemostratigraphy of the Petiknäs South volcanic-hosted massive sulfide deposit, Skellefte district, Sweden

D. M. Schlatter 1*, T. J. Barrett 1,2 R. L. Allen1,3 1

Division of Ore Geology and Applied Geophysics Luleå University of Technology SE-971 87 Luleå, Sweden * 2

3

[email protected]

Ore Systems Consulting 29 Toronto St. S. Markdale, Ontario Canada N0C 1H0

Volcanic Resources Limited Strömforsvägen 57 936 91 Boliden, Sweden

ABSTRACT The Petiknäs South volcanic-hosted massive sulfide deposit is a producing underground mine in the eastern part of the Paleoproterozoic Skellefte district. The deposit consists of several ore lenses (A, B, C and D) and prior to mining contained 6 Mt of ore grading 5 % Zn, 1 % Cu, 1 % Pb, 2.5 g/t Au and 105 g/t Ag. The deposit occurs on the southern limb of a tight, steeply plunging, upright, anticline. The mine stratigraphy dips subvertically and youngs consistently southwards. A major thrust fault truncates the downdip portion of the deposit at the 700 m level. The volcanic rocks of the mine sequence generally have one penetrative tectonic foliation and have been metamorphosed to greenschist facies, although garnet-biotite bearing rocks are present locally. Immobile-element-based lithogeochemical methods were used to classify 469 lithogeochemical samples into rhyolites A, B, B/C, C, dacite II, andesite, basaltic andesite, and a distinct andesite that occurs as sills. Rhyolite AA, dacite I, low-Ti mafic volcaniclastics, and post-ore mafic dykes occur as minor rock types at Petiknäs South. The felsic volcanic rocks dominate the mine sequence and are of transitional to mildly calc-alkaline affinity. The andesite sills, some of the basaltic andesite volcaniclastic rocks and the mafic dykes are of tholeiitic affinity. The mine sequence has been divided into 6 chemostratigraphic units (Units 1 to 6). The footwall complex (Unit 1) consists of rhyolite B and minor rhyolite C, B/C, and dacite, and is overlain by rhyolitic volcaniclastic rocks hosting the B/C ore lens (Unit 2). The B/C ore lenses formed a single lens prior to intrusion of the late andesite sills. Unit 2 is overlain by basaltic andesite volcaniclastic rocks (Unit 3). Above this, Unit 4 is host to the D and A ore lenses. This unit comprises mainly rhyolitic volcaniclastics with several thin andesitic intercalations A WNW-ESE trending fault 1

separates Unit 4 from Unit 5, which comprises volcaniclastic rocks and coherent volcanic felsic rocks. The lower part of Unit 5 is a mass flow deposit of distinctive low-Ti mafic composition that can be traced for 700m eastwards from the proximal part of the mine. Unit 6 comprises the post-ore andesite sills and mafic dykes. A portion of the chemostratigraphic sequence (Units 1 and 2) has also been recognized on the northern limb of the Petiknäs South anticline. In summary, 6 chemostratigraphic units can be identified at the Petiknäs South mine and these can be correlated throughout and beyond the mine, even where they are strongly altered. Two good chemostratigraphic marker horizons were identified: one is of basaltic andesite and andesite composition (unit 3) and one is of low-Ti mafic composition (unit 5a) and both markers can be correlated on the mine-scale and semi-regional scale. The chemostratigraphic results show that ore lenses (B/C, D and A) occur at different stratigraphic positions within clastic stratigraphic intervals of dominantly rhyolitic composition. The most favorable exploration horizon (the B/ C ore horizon) is located at the contact between a felsic clastic and a basaltic-andesitic clastic unit. Based on identification of magmatic affinity, chemostratigraphy revealed that the volcanic succession at Petiknäs South comprises calc-alkaline to transitional footwall rocks representing a proximal facies association and this succession is overlain by tholeiitc juvenile volcaniclastic rocks which were derived from a different and relatively distal volcanic center. In terms of ore location chemostratigraphy revealed that the main ore body at Petiknäs South is located at the contact between rhyolitic calc-alkaline to transitional and basaltic-andesitic tholeiitic rocks.

2

INTRODUCTION The Petiknäs South VMS deposit is located about 17 km west of Boliden in the Renström area of the 1.9 Ga Skellefte district, which contains over 85 pyritic Zn-Cu-Au-Ag VMS deposits. Most of the VMS deposits occur within and especially along the top of a regional volcanic unit known as the Skellefte Group and Allen et al. (1996) have attributed the Skellefte Group to extension and intense volcanism in a marine arc developed on continental or mature arc crust. The VMS deposits are associated with this extension and volcanism. The Renström area hosts five VMS deposits within an area of 4 km2: Renström, Kyrkvägen, Renström East, Petiknäs North and Petiknäs South. The Renstöm and Petiknäs South deposits are currently in production as underground mines. The Petiknäs South orebody was discovered in 1988 by Boliden Mineral AB using a combination of alteration mapping, deep drilling, downhole electromagnetic surveys (EM3) and geological modeling. The deposit consists of four stacked sulfide lenses that are hosted by a complex sequence of rhyolitic to andesitic volcanic rocks (Fig. 1). In recent years, lithogeochemical techniques have been widely applied to the study and exploration of VMS deposits of various types, ages and metamorphic grade (Bernier and MacLean 1993; Hodges and Manojlovic 1993; Barrett and MacLean 1994; Skirrow and Franklin 1994; Galley 1995; Lentz 1996; Lentz and Goodfellow 1996; Lentz et al. 1997; Lentz 1999; Roberts et al. 2003). Lithogeochemical studies have been carried out on volcanic successions in the Skellefte district by Claesson (1985), Vivallo and Cleasson (1987), Bergström (1997, 2001) and Hannington et al. (2003) and at several mines within the district: Kristineberg (Barrett et al. 2003; Barrett et al. 2005), Kristineberg West and Rävliden (Schlatter et al. 2003), Storliden (Imaña et al. 2004), Maurliden (Montelius et al. 2005), Renström (Allen and Svenson 2004), and the Petiknäs mine (Allen et al. 2004; Schlatter et al. 2004a, b). Rock classifications based on major elements are not suitable for altered rocks due to the mobility of many of these elements (Franklin et al. 1975; Floyd and Winchester 1978; Le Bas et al. 1986). As most of the volcanic rocks at the Petiknäs deposits are chemically altered, we have used immobileelement techniques, following MacLean and Kranidiotis (1987), MacLean (1990), and Barrett and MacLean (1991, 1994). These techniques involve elements such as Al, Ti, Zr, Y, Nb, Th and the heavy REE, which remain immobile under typical conditions of VMS alteration and greenschist to amphibolite facies metamorphism. The objectives of this study are to identify the chemostratigraphy of the host rocks of the Petiknäs South VMS deposit using immobile-element lithogeochemical methods and to define the stratigraphic position of the different ore lenses. Comprehensive lithogeochemical sampling (469 samples) covering the entire volcanic sequence was carried out mainly from drill cores. Samples were also collected from the 300 m mine level and from outcrops to the east of the mine. Because many of the rocks were altered, identifications were based on immobile-element ratios. Chemostratigraphic units were defined largely on this basis, but were also linked to volcanic facies in the less altered areas. The chemostratigraphic units can be correlated between sections, even where the rocks are strongly altered. In this study we provide a robust chemostratigraphy at the mine-scale and show that the main ore body at Petiknäs South is located at the contact between a rhyolitic and a basalticandesitic volcaniclastic unit.

3

O

16

O

24

O

58O

60

O

64O

68O

Petiknäs South

8

Unit 4

1900Y

Petiknäs South D

Petiknäs South B/C

1800Y

Petiknäs North

1700Y

Unit 5b

Unit 6

B/C ore horizon

Unit 1d

2300Y

Unit 2

2200Y

PMFZ

2100Y

Petiknäs South A

2000Y

Unit 3

80

BH 9

Unit 1b

2700Y

85

60

85

3000Y

9

3200Y

86 Unit

Outline of Skellefte and Petikån rivers Road from Renström (SE) to Petiknäs village (NW)

Outcrops

1c

85

100 m

31.9o


3100Y

Bore hole from surface (BH) with BH start (o)

Diverse

Unit 1b

Strike and dip of S2 foliation

F2 Anticline (steeply east plunging)

Stratigraphic younging

2900Y

Unit 1a

2800Y

PMFZ Petiknäs Main Fault zone

Fault

Structural geology

Unit 5a

Unit 2

86

2600Y

BH 111

2500Y

87

BH 22

2400Y


Ore horizon of the C+B ore lens

Massive sulfide

Chlorite-altered rock


Hydrothermal alteration

Fire fountain breccia

Silty matrix Pumice-rich Angular clasts

Sandy matrix

Primary volcanic textures

Quartz-feldspar phyric rhyolitic mass flow unit

Rhyolitic mass flow unit

Strongly porphyritic dacite

Petiknäs North Stratigraphy

Andesite to dacite v’clastic sandand siltstone (U1a)

Mudstone-turbidite unit Low Ti mafic mass flow unit minor felsic intercalations (U5a) Rhyolitic volcaniclastic (U4 and U5b) sandy and silty matrix Basaltic andesite v’clastic sandstone and siltstone (U3) Rhyolitic volcaniclastic (U2 of southern limb) Rhyolitic volcaniclastic (U2 of northern limb) Strongly feldspar porphyritic rhyolite (U1d and U5b) Weakly to moderately porphyritic dacite (U1c) Dacitic volcaniclastic sandstone (U1b)

Strongly porphyritic dacite (Storåliden intrusion) Rengård granodioritic synvolcanic intrusion Weakly to moderately feldspar and qz porphyritic rhyolite Strongly feldspar and quartz porphyritic rhyolite Andesitic post-ore sill (U6)

Petiknäs South Stratigraphy

Fig. 1. Simplified geology around the Petiknäs South mine modified after Allen et al. 1996; Allen and Svenson 2004 and Boliden Mineral AB unpublished data. The geology of the mine area has been projected from the 300 m level of the mine to surface, as the bedrock is covered by glacial till and the Skellefte River. The ore lenses are hosted in the southern limb of the F2 anticline. Drillhole BH 9 intersected the B/C ore horizon, whereas BH 22 and BH 111, located north of the F2 anticline, intersected only deep footwall rocks. The Petiknäs North deposit is located north of PMFZ. X and Y coordinates are given in the local “Petiknäs coordinate system” which is used by Boliden Mineral AB; for coordinates of the Swedish national grid see appendix 1.

2000X

2100X

2200X

2300X

2400X

2500X

2600X

2700X

2800X

2900X

3000X

3100X

.ORW AY

3200X

1600Y

3WEDEN

3300X

1500Y

D

4

&INLA N

3400X

1400Y 3500X

Petiknäs N

LOCAL GEOLOGY AND MINE SEQUENCE The ore at Petiknäs South is mainly pyritic massive sulfide. Prior to mining, the deposit contained 6 Mt grading 5% Zn, 1% Cu, 1% Pb, 2.5 g/t Au and 105 g/t Ag. The orebody lies below the 250 m mine level and is truncated between the 600 and 700 m mine levels by a major reverse fault (PMFZ = Petiknäs Main Fault Zone). The PMFZ, which dips moderately to the south, separates rocks of the Petiknäs South block from those of the Petiknäs North block. The volcanic and subvolcanic rocks have been subjected to regional deformation and greenschist facies metamorphism. Major folds in the Petiknäs area (F2) are related to the second regional tectonic foliation and comprise a set of large-scale, tight, steeply east plunging, upright folds with west-northwest-trending axes. The Petiknäs South deposit occurs on the southern limb of a major F2 anticline and dips subvertically; the stratigraphy youngs consistently southwards (Fig. 1). Major N-S trending folds (F3) and an associated penetrative cleavage are superimposed on the regional F2 folds in the Renström area, 2 km to the east, but are not developed at Petiknäs. Earlier, first generation folds appear to be restricted to local small folds observed in some outcrops (Allen and Svenson 2004). At the Petiknäs mine, sedimentary structures indicate that the mine sequence youngs constantly to the south. Excluding post-ore andesite sills, the mine sequence comprises from oldest to youngest (north to south): (1) feldspar-porphyritic rhyolitic sill; (2) the B and C ore lenses, which are hosted by rhyolitic tuffaceous sandstone; (3) andesitic pumiceous mass flow deposits; (4) felsic and intermediate tuffaceous sandstones and siltstones hosting the D and A ore lenses; and (5) a fault followed by rhyodacitic feldspar-quartz porphyry and felsic volcaniclastic rocks. Prior to intrusion of the post-ore andesite sills, the B and C ores formed a single massive sulfide lens within a thin interval of rhyolitic volcaniclastic rocks. The D and A ores formed at a stratigraphically higher level, in an interval of alternating rhyolitic and andesitic mass flow deposits. Weakly altered feldspar-porphyritic rhyolite sills with peperitic margins (Unit 1) were then intruded into the felsic volcaniclastic rocks directly below the B/C ore lens. The mine sequence is summarized in Table 1. TABLE 1. Simplified geological description of the 6 mine scale units. Based on geological and volcanic facies mapping the mine sequence was divided into 6 stratigraphic intervals: Units 1 to 6. The table also gives the relations between sills and dykes and their host rocks. Mine sequence

Unit 6 (x) Unit 6 (+)

description post-ore sills: andesitic post-ore sills/dykes: mainly Hi-Mg-Cr-Ni-basalt

principal lithology dark-green, even fine to medium grained granular andesitic sill with fgr margins green-yellowish soft, chlorite-talc altered, calcareous mafic volcanic

Unit 5b Unit 5a Unit 4

faulted HW-complex lowest sub-unit of faulted HW-complex A+D ore lens package

Unit 3 Unit 2 Unit 1d Unit 1c Unit 1b Unit 1a

Basaltic andesite clastic HW Felsic clastic hosting B/C ore lens

various lithologies, rhyolitic coherent and volcaniclastic mass flow breccia of low Ti-mafic composition with fgr pale-pink lithics rhyolitic pumice breccia, siltstone-sandstone with thin basaltic-andesitic and rhyolitic mudstone intercalations basaltic andesite pumice-lithic mass flow breccia with sandy and silty matrix rhyolitc volcaniclasitc sandstone and siltstone, presence of pumice-lithics strong 20 %, 2-3 mm, feldspar porphyritic coherent rhyolite with peperitic contacts dacitic coherent sill mainly dacitic volcaniclastic, minor basatic andesites and andesites andestic, basaltic-andesitic and dacitic volcaniclastic

shallow footwall complex (thins out towards east) deep footwall complex (east of Petiknäs S mine) deep footwall complex (east of Petiknäs S mine) deep footwall complex

post-ore sills

x x x x x

+ + +

The Petiknäs North deposit (Fig. 1) contains 1.3 Mt grading 5.6% Zn, 1.3% Cu, 0.9% Pb, 5.6 g/t Au and 103 g/t Ag. Its potential for mining is currently being evaluated. The deposit is hosted by pumice-lithic mass flow breccias and is interpreted by Allen et al. (1996) and Doyle and Allen (2003) to have formed by replacement. Although Allen and Svenson (2004) suggest that the Petiknäs South and Petiknäs North deposits are both associated with the proximal parts of small to moderate size rhyolite volcanoes, it has not yet been determined if the deposits are stratigraphically equivalent.

5

METHODOLOGY Lithogeochemical sampling At Petiknäs South, drillcore logging and lithogeochemical sampling were carried out on two main cross-sections: a proximal section through the orebody at 2030 East, and a distal one at 2300 East (Figs. 1, 3). In addition, plan maps were constructed for the 300 m (Fig. 2) and 550 m mine levels. About 10,000 m of core from 40 bore holes (BH) were logged in detail (see appendix 2 for details), and 445 core samples and 24 surface and underground samples were taken for lithogeochemical analysis. Each major rock type and alteration facies were sampled along each drillcore resulting in about one 0.5 kg sample (25 cm length of whole drillcore) per 15 to 20 meters. Where rock types could not be identified due to strong alteration samples were taken every 15 to 20 m. Volcaniclastic mass flow units were consistently sampled in the middle of the bed, using the sampling protocol recommended by Allen and Svenson (2004). Analytical methods and quality control All samples were crushed to less than 10 mm and milled to 90% less than 200 mesh (see appendix 3a for details). Pulps of 50 grams were sent to ACME Laboratories in Vancouver where 20 gm splits were subsequently analyzed. Major elements and certain trace elements were determined by ICP-ES following a lithium borate fusion and nitric acid digestion; REE and refractory trace elements by ICP-MS following the same fusion and digestion; and the precious and base metals by ICP-MS after aqua regia digestion. Total carbon and sulfur were determined by the Leco method. Analytical quality was monitored by use of internal standards. All data presented in this study fall within ±5% of mean values. Database In the text, Zr/TiO2 and Zr/Al2O3 are used in place of Zr x 10,000/TiO2 and Zr x 10.000/Al2O3, respectively. The X-Y locations of samples are the coordinates of the local Petiknäs mine grid, which is used by Boliden Mineral AB in the Petiknäs area. For the Z (vertical mine level) coordinates, 0 Z equals 210 m above sea level (see appendix 1 for details of coordinate transformations and appendix 3b for the details regarding the lithogeochemical database). A second lithogeochemical database, comprising >1500 whole-rock analyses from Petiknäs South and Petiknäs North, was also used for selected drill holes and outcrops. These samples were collected by Boliden Mineral AB geologists and analyzed by XRAL in Toronto using XRF methods.

6

1900 Y

2000 Y

2900 X

2100 Y

2200 Y

2300 Y

2400 Y

54

314

31.9o

315

Petiknäs N


50 m

291

267 207/209

2800 X

(292 is just below 291 and both BH have the same drill direction)

FW

266

262 B/C

Drift 356 330 m 273 49

2700 X

72 68 2600 X

A

54

314 315 267 304 207/209

2500 X

266

262


238

291

Unit 1: FW-complex Drift 356 330 m 273

Unit 3: 72 Bas. Andesite clastic HW

49

70 71


679

HW

68

207 233

69

238

70 71

Unit 5: faulted HW-complex 679 69

2400 X

206



distal section (2300Y)

206

100 m 2300 X

Weakly to moderately feldspar porphyritic rhyolite Strongly feldspar porphyritic rhyolite Strongly feldspar and quartz porphyritic rhyolite Peperite

273

Andesite sill Pumice rich Fiamme rich Angular clasts

Autobreccia Felsic mass flow unit, poorly sorted with angular clasts (occurs in BH70&71) Felsic mass flow unit with angular clasts Rhyolitic volcaniclastic sandstone


Rhyolitic volcaniclastic siltstone

Strongly dissiminated sulfides

Mudstone Basaltic andesite and andesite mass flow unit (faulted HW) Basaltic andesite volcaniclastic sandstone Basaltic andesite volcaniclastic siltstone Weakly to moderately porphyritic dacite Strongly porphyritic dacite

Fault

Bore hole (BH)

Chlorite-talc rock Massive sulfide Semi-massive sulfide

PMFZ Petiknäs Main Fault zone Ore horizon of the C/B ore lens FW-Rhyolite intrusive contact Stratigraphic younging FW HW

Footwall complex Hanging wall complex

Fig. 2. Detailed Geology of the 300 m level of the mine. Stratigraphic younging is north-south and at the 300 m level of the mine the ore lenses B/C and A occur. X and Y coordinates of fig. 2 are given in the local “Petiknäs coordinate system” which is used by Boliden Mineral AB; for coordinates of the Swedish national grid see appendix 2.

7

0Z

2800 X

2700 X

2600 X

2500 X

2400 X

NE

SW 68

72 Overburden


100 Z

200 Z

FW

300 Z

291+292

356 69

315 400 Z

291

HW 500 Z

677 676 600 Z 68

69

72


291+292 356 315


700 Z

677

673 B/C 291


Unit 1: FW-complex

Unit 5: faulted HW-complex 676

673

800 Z

441

441


662

662

100 m 900 Z

Fig. 3. Detailed Geology of the distal cross-section (2300 East). Stratigraphic younging is north-south. For legend see figure 2.

8

LITHOGEOCHEMICAL RESULTS Primary rock types and fractionation trends A set of 21 least altered samples from Petiknäs South has been selected on the basis of having 2% Na2O, and lacking sericite, chlorite, carbonate and secondary quartz in hand specimen. Of these samples, 14 are coherent (non-clastic) volcanic rocks and 7 are juvenile volcaniclastic and sedimentary volcaniclastic rocks. In standard discrimination diagrams (Winchester and Floyd 1977; Le Bas et al. 1986), the least altered samples are andesites, rhyodacite/dacites and rhyolites (Fig. 4). 80 Rhyolite

SiO2 % vf

75 70

schematic magmatic fractionation trend Rhyodacite/Dacite

least altered volcanic rocks from Petiknäs South (n=21) Rhy AA (volcaniclastic) Rhy A (coherent and volcaniclastic) Rhy B (coherent) Rhy B/C (coherent) Rhy C (coherent) Dacite II (coherent) Bas. Andesite (volcaniclastic) Andesite (volcaniclastic) Andesite sill (coherent)

65 60

Andesite

55 50

Sub-AB

45 .001

(a)

.01

.1

Zr/TiO2

1

16 Phonolite

14

Tephriphonolite

Na2O + K2O % vf

12 10

PhonoTephrite

8 6 4

Trachybasalt

Trachyandesite

Trachydacite

Rhyolite

Basaltic trachyandesite Dacite Basaltic andesite

Basalt

Trachyte

Andesite

2 0 45

(b)

50

55

60

65

70

75

80

SiO2 % vf

Fig. 4. Discrimination plots for 21 least altered samples from Petiknäs South. (a) SiO2 versus Zr/TiO2 (Winchester and Floyd 1977); (b) Na2O+K2O versus SiO2 (Le Bas et al. 1986). In (a), samples of the andesite sill and basaltic andesite volcaniclastics plot way from the fractionation trend, and probably belong to a different magmatic suite. In (b), several rhyolite samples that probably have been slightly silicified contain >77 % SiO2. vf = volatile free.

These samples, with exception of the andesite sill, basaltic andesite and dacite II rock, were used to estimate a schematic primary fractionation trend in plots involving the immobile elements Al, Ti and Zr (Fig. 5). These samples were selected to define one fractionation trend because on the Zr vs. Y diagram and binary (Harker) diagrams involving the immobile elements Al, Ti and Zr they scatter along one broad curve which suggests that they form one broad magma series or fractionation series. These samples represent the majority of samples and rock types from the Petiknäs South area. In these plots, Zr remains incompatible during fractionation, whereas Al is weakly compatible 9

(Fig. 5b), and Ti is compatible in the andesitic to rhyolitic part of the spectrum (Figs. 5a, 5c). Samples from post-ore andesitic sills and basaltic andesites are not plotted in Figure 5 as they belong to another volcanic suite as seen from Zr vs. Y diagram and Harker diagrams where andesitic sills and basaltic andesites form a separate curve. However, one least altered sample of dacite II is plotted on these diagrams. This sample suggests that Dacite II belongs to a separate volcanic suite to the other felsic rocks at Petiknäs South. Allen and Svenson (2004) from a larger database of least altered samples in the Renström-Petiknäs area interpreted 2 main felsic volcanic suites based on Harker diagrams: a high-Ti dacite suite and a low-Ti suite. The high-Ti dacites were shown to lie on a separate fractionation curve to the other felsic rocks and the high-Ti dacites defined by Allen and Svenson (2004) correspond to the dacite II rocks from Petiknäs South. 1.2

Polynomial second order: y=0.000025x2- 0.0114x + 1.45 R2 = 0.86

1.0 0.8

(a)

least altered volcanic rocks from Petiknäs South Rhy AA (volcaniclastic) Rhy A (coherent and volcaniclastic) Rhy B (coherent) Rhy B/C (coherent) Rhy C (coherent) Dacite II (coherent) Andesite (volcaniclastic)

TiO2 % vf

hi-Ti suite magmatic fractionation trend

0.6 0.4

Schematic magmatic fractionation trend

0.2 0.0

0

25

100

150 Zr ppm vf

200

250

Polynomial second order: y=0.0002x2- 0.1x + 23.7 R2 = 0.81

20

Al203 % vf

50

300

(b)


15

least altered volcanic rocks from Petiknäs South Rhy AA (volcaniclastic) Rhy A (coherent and volcaniclastic) Rhy B (coherent) Rhy B/C (coherent) Rhy C (coherent) Dacite II (coherent) Andesite (volcaniclastic)

10 5 0

0

50

100

25

Al203 % vf

20 15

150 Zr ppm vf

200

250

300

(c)

Polynomial second order: y=-0.0737x2+ 9.4647x + 10.38 R2 = 0.89


least altered volcanic rocks from Petiknäs South


10

Rhy AA (volcaniclastic) Rhy A (coherent and volcaniclastic) Rhy B (coherent) Rhy B/C (coherent) Rhy C (coherent) Dacite II (coherent) Andesite (volcaniclastic)

5 0 0.0

0.2

0.4

0.6 0.8 TiO2 % vf

1.0

1.2

1.4

Fig. 5. Immobile-element plots (a, b, c) for the 18 least altered samples outline a magmatic fractionation trend from andesite to rhyolite. The best-fit curves are second-order polynomial regressions. Coherent volcanic rocks: rhyolites B, B/C, C and A (except one sample); volcaniclastic rocks: rhyolite AA, andesites, and one rhyolite A. vf = volatile free.

10

Magmatic affinity Magmatic affinity of volcanic rocks can be assessed using Zr/Y and (La/Yb)n ratios (Barrett and MacLean 1999). Broad magmatic affinities are interpreted for Petiknäs South rocks and each of the magmatic affinity categories can include more than one volcanic suite as suggested by Allen and Svenson (2004) who showed that the andesite sills, dacite II and the other felsic rocks form 3 separate volcanic suites. On the basis of Zr/Y ratios, all least altered samples except two plot in the transitional field, whereas (La/Yb)n ratios suggest that the same samples are calc-alkaline or transitional (Fig. 6a). Rhyolites tend to have somewhat higher Zr/Y ratios than dacites and andesites. 10

5.5 4 2.5

0

Tholeiitic Transitional

(La/Yb)n

8

Transitional

4

5

Zr/Y

Rhyolite AA Rhyolite A Rhyolite B Rhyolite B/C Rhyolite C Dacite II Andesite Bas. Andesite Andesite sill

(a)

Not plotted: one Bas. Andesite

3

Least altered volcanic rocks from Petiknäs South

Calcalkaline

Calc-alkaline

Tholeiitic

6

7

8

70 60

c iiti ole h T

50

Y ppm vf

Coherent volcanic rocks from Petiknäs South Rhyolite A Rhyolite B Rhyolite B/C Rhyolite C Dacite I Dacite II Andesite-Dacite Andesite Bas. Andesite Andesite sill

al tion nsi a r T line lka lc-a Ca

40 30 20 10 0

(b) 0

70

50

100

Not plotted: -31 schist samples -4 Rhyolite AA samples -and Rhy B/C at (190,92)

60

Y ppm vf

50

150 200 Zr ppm vf

250

300

Volcaniclastic rocks from Petiknäs South c iiti ole h T

40

(schistose rocks are not plotted)

al tion nsi Tra

Rhyolite A Rhyolite B Rhyolite B/C Rhyolite C Dacite I Dacite II Andesite-Dacite Andesite Andesite "A" Andesite "B" Bas. Andesite Low-Ti mafic

line lka lc-a Ca

30 20 10 0

(c) 0

50

100

150 200 Zr ppm vf

250

300

Fig. 6. Magmatic affinity of Petiknäs South samples based on Zr/Y and (La/Yb)n ratios. (a) Least altered samples are mainly of transitional magmatic affinity; only a few are slightly tholeiitic. Altered coherent volcanic rocks (b) and altered volcaniclastic rocks (c) are transitional or mildly calc-alkaline. Andesite sills and most of the basaltic andesite volcaniclastic rocks are tholeiitic. Strongly altered schists were omitted in these plots, as minor mobility of REE may have occurred. La and Yb data were normalized to the chondrite values of Evensen et al. (1978). vf = volatile free.

11

In binary plots involving elements that are immobile as well as incompatible, such as Zr, Y, Nb and the REE, slightly to moderately altered samples lie along “alteration lines” and pass through the origin (McLean and Barrett 1993) and as “alteration lines” are parallel to fractionation trends they do not cross each other. Y vs. Zr plots for the entire Petiknäs South data set except the strongly altered samples are shown in Figures 6b and 6c. The felsic volcanic rocks are nearly all of transitional to mildly calc-alkaline affinity, whereas the andesitic sills and some of basaltic andesites are of tholeiitic affinity. The dacite II samples straddle the boundary between tholeiitic and transitional affinity. Typical chondrite-normalized REE patterns are shown for the main rock types in Figure 7. REE plots are steep for felsic rocks of calc-alkaline to transitional magmatic affinity (Fig. 7a-h), but they are flat for intermediate rocks of tholeiitic to transitional magmatic affinity (Fig. 7i-l). REE patterns of coherent volcanic rocks are generally very similar to those of the corresponding volcaniclastic rocks, although the rhyolite A volcaniclastic rocks show a more pronounced negative Eu anomaly than their coherent equivalents (Fig. 7b). Due to the greater depletion of light REE relative to heavy REE during hydrothermal alteration (for more detail see paper II of this thesis), altered rocks can have flatter REE patterns than their unaltered equivalents. Such an effect could shift an original transitional REE pattern towards a tholeiitic pattern. To avoid this possible complication, none of strongly altered samples were used for the assessment of magmatic affinity based on REE and Zr/Y plots. Immobile-element plots of altered samples Immobile-element plots for the altered Petiknäs South samples are shown in Figure 8 (TiO2 versus Zr) and Figure 9 (Al2O3 versus TiO2). Samples have been grouped into coherent volcanic rocks (Figs. 8a, 9a) and volcaniclastic rocks (Figs. 8b, 9b). The latter group also includes strongly altered samples which are commonly foliated and have lost their primary textures, and are best described as schists. Alteration lines are shown for the main rock types in Figures 8 and 9. The wide spread of points along each alteration line results from net gains or losses of mobile elements during alteration. Also shown in these figures are the estimated schematic magmatic fractionation trends for the calc-alkaline to transitional rocks and for the hi-Ti volcanic suite based on the least-altered sample set. Although best-fit alteration lines are shown for each chemical group in Figures 8 and 9, each sample lies on its own alteration line. The intersection of a given alteration line with the schematic magmatic fractionation trend defines the Zr and TiO2 contents of the precursor rock. The post-ore andesite sills plot in a cluster somewhat removed from the estimated fractionation trends (Figs. 8a, 9a). As noted earlier, these andesite sills, which are relatively unaltered, belong to a different magmatic suite relative to the juvenile volcaniclastic andesite to coherent rhyolite series. Samples of volcaniclastic rocks and schist tend to show more spread from the best-fit lines, particularly in the dacite to andesite part of the compositional spectrum. This is probably due to processes such as mechanical sorting of crystals during eruption and transport. Evidence for this proposed sorting process is given by physical facies characteristics such as e.g. graded beds with more crystal rich bases.

12

(a)


(e) 1

10

(b)

(d)

(f) La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb Lu

Rhyolite C: 15 volcaniclastic rocks


Rhyolite B and B/C: 24 volcaniclastic rocks


Rhyolite A: 10 volcaniclastic rocks

100

1000

1

10

100

1000

100

1000

1

10

1

10

(g)

(k) La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb Lu

Basaltic Andesites: 4 coherent volcanics


(i)

Andesite sill: 22 coherent volcanics


Dacite II: 5 coherent volcanics

1

10

100

1000

1

10

100

1000

1

10

100

1000

(h)

(j)

(l) La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb Lu

Basaltic Andesites: 63 volcaniclastic rocks


Andesite: 14 volcaniclastic rocks


Dacite II: 19 volcaniclastic rocks

Fig. 7. Chondrite-normalized plots for the main rock types at Petiknäs South samples. A given chemical rock type shows very similar REE patterns regardless of whether it is a coherent or volcaniclastic rock. Rhyolites and dacites (a-h) have steep REE patterns, which is typical of rocks of calc-alkaline magmatic affinity, whereas andesites and basaltic andesites (i-l) have flatter REE patterns that indicate they are more tholeiitic. REE data were normalized to the chondrite values of Evensen et al. (1978).

1

10

100

1000

1

100

Rhyolite C: 30 coherent volcanics


(c)

10

Rock/Chondrites

1000

1

10

100

1000

1

10

100

1000

100

Rhyolite B and B/C: 33 coherent volcanics


Rhyolite A: 7 coherent volcanics

Rock/Chondrites

1000

1

10

Rock/Chondrites

100

1000

Rock/Chondrites Rock/Chondrites Rock/Chondrites

Rock/Chondrites Rock/Chondrites Rock/Chondrites

Rock/Chondrites Rock/Chondrites

Rock/Chondrites

13

1.4

alteration lines (a) schematic magmatic fractionation trend

1.2


TiO2 % vf

1.0

Rhyolite A Rhyolite B

Dacite II y = 0.0037x

Rhyolite B/C Rhyolite C Dacite I

0.8 Dacite I y = 0.0033x

0.6 0.4 0.2 0.0

50

100

150 Zr ppm vf

1.4 Bas. Andesite y = 0.0139x

1.2

Andesite y = 0.0069x

1.0

200

250

300

(b) alteration lines schematic magmatic fractionation trend hi-Ti suite magmatic fractionation trend

Volcaniclastic rocks and schistose rocks from Petiknäs South Rhyolite AA Rhyolite A

Dacite II y = 0.0037x

0.8

Dacite I y = 0.0033x Rhy C y = 0.0023x

0.6

Rhy B and B/C y = 0.0016x

0.4

0

50

100

150 Zr ppm vf

200

250

Rhyolite B Rhyolite B/C Rhyolite C Dacite I Dacite II Andesite Bas. Andesite Low-Ti mafic

Rhy A y = 0.001x

0.2 0.0

Rhy A y = 0.001x

Theoretical Rhy B and B/C precursor

0

Dacite II Andesite sill

Rhy C y = 0.0022x

Rhy B and B/C y = 0.0016x Mass Loss

Mass Gain

TiO2 % vf

Coherent volcanic rocks from Petiknäs South

300

Fig. 8. Plots of TiO2 versus Zr showing (a) 159 coherent volcanic rocks; and (b) 263 volcaniclastic rocks and 25 schists (b) Selected alteration lines are shown, as is the schematic fractionation trend from Figure 5a. Samples are displaced from the fractionation trend due to net gains or losses of mobile mass during alteration, as shown for rhyolite B and B/C in (a). The intersection of an individual alteration line with the fractionation trend yields the TiO2 and Zr content of the precursor rock. The andesite sills form a tight cluster, which indicates that these rocks are little altered. vf = volatile free.

14

25

Al2O3 % vf

20

(a) Rhy B/C Dacite I Rhy B y = 44.6x y = 37.1x Rhy A y = 73.3x y = 56.4x Rhy C y =35.6x

Dacite II y = 23.4x

Coherent volcanic rocks from Petiknäs South Rhyolite A Rhyolite B Rhyolite B/C Rhyolite C Dacite I

15

Dacite II Andesite sill

10 alteration lines schematic magmatic fractionation trend

5


0 0.0

25

Al2O3 % vf

20

0.2

0.4

0.6 0.8 TiO2 % vf

Rhy B Rhy C y = 53.7x y =37.7x Rhy A y = 67.1x Rhy B/C y = 44.8x

1.0

Dacite I y = 32.9

1.2

1.4

Volcaniclastic rocks and schistose rocks Bas: Andesite y = 14.7x from Petiknäs South Rhyolite A (b)

Andesite y = 21.9x

Dacite II y = 24.2x

Rhyolite B Rhyolite B/C Rhyolite C Dacite I Dacite II Andesite

15 10

Bas. Andesite Low-Ti mafic

alteration lines schematic magmatic fractionation trend

5


0 0.0

0.2

0.4

0.6 0.8 TiO2 % vf

1.0

1.2

1.4

Fig. 9. Al2O3 versus TiO2 plot showing fractionation trend (Figure 5c) and superimposed alteration lines. Samples of the nearly unaltered andesitic sill do not plot on the fractionation trend, indicating that they belong to a different magmatic suite. vf = volatile free.

15

Chemical identification of altered samples As noted earlier, during alteration immobile elements are either diluted by addition of mobile components to the rocks (in open spaces), or are residually enriched by leaching of mobile components (MacLean and Kranidiotis 1987; MacLean and Barrett 1993; Barrett and MacLean 1999). However, the immobile-element ratios are retained during alteration. Based on the ratios Zr/ TiO2, Al2O3/TiO2 and Zr/Al2O3, eight main chemical groups have been defined (rhyolites A, B, B/ C, C, dacite II, andesite, basaltic andesite and andesite sill), and seven minor chemical groups (Fig. 10). Table 2 summarizes the average values and standard deviations of the immobile-element ratios for each chemical rock type whereas table 3 provides lithgeochemical analysis of representative Petiknäs South rocks. The primary rock names used in Table 2 and 3 are based on the composition of the least-altered samples, in conjunction with several immobile-element ratios, and certain nearimmobile elements such as V and P. The frequency distribution of the main rock types, as given by

TABLE 2. Average immobile-element ratios of the main and minor rock types at Petiknäs South Abbreviations: sed/schist = volcaniclastic rock or schist; coh = coherent Chemical Groups

number of samples

Mean and St. deviation

Zr/TiO2

Rhy AA (5 sed/schist)

n=5

mean st.dev.

1595.8 131.5

Rhy A (14 coh; 17 sed/schist)

n=31

mean st.dev.

Rhy B (45 coh; 58 sed/schist)

n=103

Rhy B/C (17 coh; 37 sed/schist)

Zr/Al2O3

Zr/Y

67.4 6.6

23.7 0.8

4.4 0.7

3.3 0.7

1018.8 148.6

73.2 14.7

14.1 1.5

5.0 1.9

5.0 1.3

mean st.dev.

636.6 51.7

55.2 3.1

11.6 1.0

6.3 1.3

6.3 1.6

n=54

mean st.dev.

585.2 81.8

45.0 2.2

13.0 1.7

5.3 0.9

5.2 1.3

Rhy C (37 coh; 25 sed/schist)

n=62

mean st.dev.

449.1 27.5

36.8 3.5

12.3 1.4

5.0 0.7

5.0 1.0

Dacite I (2 coh; 13 sed/schist)

n=15

mean st.dev.

304.1 54.3

33.7 2.5

9.0 1.4

5.4 0.9

5.3 0.8

Dacite II (5 coh; 28 sed/schist)

n=33

mean st.dev.

272.6 55.2

24.6 2.9

11.0 1.3

4.3 0.7

3.6 0.9

Andesite-dacite (1 coh; 2 sed/schist)

n=3

mean st.dev.

296.3 27.9

47.3 0.7

6.3 0.5

4.3 1.1

4.9 0.4

Andesite (2 coh; 26 sed/schist)

n=28

mean st.dev.

143.3 23.8

22.6 4.5

6.5 1.2

3.9 0.8

3.9 1.1

Andesite "A" 4 sed/schist)

n=4

mean st.dev.

98.7 9.7

23.9 0.4

4.1 0.3

4.1 0.3

3.6 0.1

Andesite "B" 2 sed/schist)

n=2

mean st.dev.

107.5 5.0

20.8 3.2

5.2 0.6

3.3 0.3

3.9 0.5

Basaltic andesite (5 coh; 73 sed/schist)

n=78

mean st.dev.

72.0 15.2

15.0 1.5

4.8 0.8

2.9 0.6

2.8 0.4

Low-Ti mafic (8 sed/schist)

n=8

mean st.dev.

108.2 27.4

45.3 1.7

2.4 0.6

3.7 0.6

3.9 1.0

Andesite sill

n=31

mean st.dev.

68.4 4.4

15.6 0.5

4.4 0.3

3.3 0.4

3.1 0.3

Mafic post-ore sill/dyke

n=9

(4 minor groups)

16

Al2O3 /TiO2

Lan/Ybn

17

BH-9 BH-49 Mine

BH-206 BH-238 BH-262

BH-54 -25.7 BH-291 -146.0 BH-662 -557.8

BH-206 -136.1 2356.9 BH-71 -1.2 2486.7 BH-238 -84.5 2588.1

outcrop 180.0 BH-207 -158.2 BH-292 -274.2

BH-72 BH-51 BH-238

Rhyolite B PETS-BH206-14.1m PETS-BH238-59.05m PETS-BH262-84m

Rhyolite B/C *PETS-BH54-214.6m *PETS-BH291-10.6m PETS-BH662-48.85m

Rhyolite C PETS-BH206-498m PETS-BH71-223.4m PETS-BH238-90.05m

Dacite II Re 76 PETS-BH207-301.7m PETS-BH292-228.6m

Andesite PETS-BH72-62.5m PETS-BH51-78.7m PETS-BH238-17.6m

2558.1

BH-68

BH-207

Low-Ti mafic PETS-BH68-343.25m

Andesite sill PETS-BH207-121.5m

-53.7

2738.5

2648.4 2704.0 2619.4

Basaltic andesite *PETS-BH206-188.85m BH-206 -45.1 PETS-M-60803-02 Mine -132.0 PETS-BH458-30.25m BH-458 -403.2

-149.7

2610.4 2692.4 2642.6

2914.0 2592.9 2672.9

2854.3 2806.0 2594.3

2805.4 2612.5 2757.6

2459.9 2723.1 2655.0

117.0 101.6 -37.4

31.3 -65.6 -49.6

-220.9 -285.3 -120.0

2630.3 2744.3

Rhyolite A PETS-BH9-529.2m PETS-BH49-456.55m PETS-M-60803-05

-49.6 -79.6

BH-238 BH-266

X

Rhyolite AA PETS-BH238-35m PETS-BH266-85.95m

Depth (m asl)

Hole

Sample ID

2035.6

2191.7

2045.7 2164.0 2059.9

2319.3 2061.1 1957.1

3150.0 2023.6 2313.5

2001.6 2043.6 1951.2

1984.4 2198.5 2265.8

2038.9 1953.7 1988.2

2577.0 2033.1 2081.0

1955.7 2058.5

Y

263.7

359.7

255.1 342.0 613.2

93.0 108.4 247.4

30.0 368.2 484.2

346.1 211.2 294.5

235.7 356.0 767.8

178.7 275.6 259.6

430.9 495.3 330.0

259.6 289.6

Z

coherent sill. dark-green. fgr

v'clastic. light-grey. mgr. sandy

v'clastic. dark-grey. layered v'clastic. possibly pumice schist. silica altered. strongly sulfide impreg.

v'clastic. fgr. m-flow v'clastic. dark-grey. clastic breccia v'clastic. silty to muddy. sulfide stringers

coherent dacitic sill schist. chlorite-garnet altered v'clastic. light-grey. fgr. silty

coherent rhyolite. grey. massive coherent rhyolite. fsp and qz pxtals v'clastic. dark-grey. fgr-mgr. sandy. sulfide diss.

coherent. light-grey. fsp pxtals schist. garnet-chlorite altered. sulfide diss. schist. sericite-qz altered

coherent rhyolite. beige. massive. fsp pxtals v'clastic. dark-grey to greenish. mgr. m-flow. sulfide diss. coherent. light-grey. qz and fsp pxtals

coherent rhyolite. grey. fgr. fsp and qz pxtals v'clastic. brownish to greenish. sulfide diss. schist

v'clastic. dark-grey. silty-sandy. weak sulfide diss. v'clastic. grey. silty. chorite altered

Rock description

a

a?

a b c

a b c

a b c

a b c

a b c

a b c

a b c

a b

72.51 64.83 89.08

77.17 39.67 88.15

76.46 61.57 85.08

78.72 51.05 86.95

79.91 60.03

SiO 2 (%)

unit 6

unit 5

unit 3 unit 3 unit 4


58.64

57.93

58.46 51.49 77.25

64.34 54.76 74.16

unit 1c 71.21 unit 4 50.06 unit 4 73.35





unit 4 unit 2

alt. Unit

0.952

0.411

1.004 1.009 0.386

0.662 0.787 0.436

0.639 0.577 0.485

0.362 0.509 0.107

0.258 0.313 0.125

0.243 0.366 0.158

0.164 0.252 0.086

0.158 0.388

TiO2 (%) 1.76 3.08

FeO (%)

0.99 5.56 1.20

15.06

19.01

15.62 15.04 6.54

15.30 14.17 11.61

13.39 14.60 10.69

13.94 18.56 4.55

11.69

6.06

9.77 8.76 9.93

7.21 8.49 5.09

6.24 25.78 7.55

2.03 3.78 1.78

12.52 2.21 12.82 28.31 5.98 1.38

13.43 19.88 7.96

12.36 0.94 17.35 14.64 8.09 1.06

11.45 23.45

Al2 O3 (%)

0.18

0.13

0.15 0.21 0.03

0.14 0.21 0.05

0.15 1.56 0.12

0.06 0.08 0.02

0.03 5.37 0.02

0.02 0.08 0.01

0.02 0.09 0.03

0.06 0.08

3.08

3.72

5.15 5.06 0.23

2.57 4.67 1.00

1.01 5.50 2.64

0.84 1.83 0.50

0.81 5.76 0.24

0.46 5.11 0.26

0.26 3.30 0.67

1.20 2.02

MnO MgO (%) (%)

Cont.

TABLE 3. Selected chemical analysis of main rock types and two minor rock types at Petiknäs Geochemical whole rock analysis and immobile element ratios of selected rocks from Petiknäs South. All data are on LOI free basis. Column 1: Rock types in bold are main rock types, small asterix = sample with petrographic thin section. Columns 4-6: XYZ coordinates of the local “Petiknäs coordinate system. Column 7: fsp = feldspar, qz = quartz, pxtals = phenocrysts, fgr = fine grained, mgr = medium grained, m-flow = mass flow deposit, Column 8: alteration classes a) least altered samples, b) altered samples with net mass loss, c) altered samples with net mass gain. Column 9: stratigraphic position, Units 1 to 6.

18

2.06 5.82

1.41 5.01 0.52

1.44 1.80 1.75

1.34 6.68 0.96

3.74 3.06 1.41

1.88 1.39 3.04

2.55 13.47 3.84

5.07 15.16 0.23

4.43

4.78

Rhyolite A PETS-BH9-529.2m PETS-BH49-456.55m PETS-M-60803-05

Rhyolite B PETS-BH206-14.1m PETS-BH238-59.05m PETS-BH262-84m

Rhyolite B/C *PETS-BH54-214.6m *PETS-BH291-10.6m PETS-BH662-48.85m

Rhyolite C PETS-BH206-498m PETS-BH71-223.4m PETS-BH238-90.05m

Dacite II Re 76 PETS-BH207-301.7m PETS-BH292-228.6m

Andesite PETS-BH72-62.5m PETS-BH51-78.7m PETS-BH238-17.6m

Basaltic andesite *PETS-BH206-188.85m PETS-M-60803-02 PETS-BH458-30.25m

Low-Ti mafic PETS-BH68-343.25m

Andesite sill PETS-BH207-121.5m

CaO (%)

Rhyolite AA PETS-BH238-35m PETS-BH266-85.95m

Sample ID

P 2 O5 (%)

5.34 0.02 0.134

7.75 0.44 0.033

3.65 0.85 0.141 0.23 2.43 0.291 0.21 1.96 0.058

4.28 2.62 0.126 0.97 2.23 0.080 0.33 3.09 0.081

4.22 0.98 0.182 0.14 0.12 0.056 0.75 1.20 0.067

4.15 2.12 0.074 4.65 2.37 0.113 0.31 0.59 0.017

4.66 0.88 0.062 0.02 0.88 0.058 2.98 0.10 0.028

5.54 1.28 0.033 0.43 4.52 0.051 2.67 0.79 0.038

4.34 1.64 0.023 0.56 5.18 0.029 0.11 2.41 0.011

0.18 3.07 0.020 0.50 4.21 0.056

Na 2 O K2 O (%) (%)

0.000

0.006

0.000 0.000 0.000

0.000 0.000 0.004

0.000 0.000 0.000

0.000 0.000 0.000

0.000 0.001 0.000

0.001 0.000 0.000

0.000 0.000 0.000

0.000 0.000

2.2 5.5 4.3

3.8 2.2 0.7

1.7 6 0.7

1.4 3.6 1.6

1.5 8.7 1.4

2.8 5

0.95

0.8

5.3

4.6

0.79 5.4 3 12.2 0.01 4.8

47

87

326 319 105

999 188 879

212 21 270

420 530 41

164 71 28

402 180 186

543 480 321

455 651

LOI Ba (%) (ppm)

0.52 3.3 2.52 10.8 1.71 3.2

0.42 0.11 0.59

0.7 0.18 0.03

0.27 1.65 0.21

0.27 0.02 0.33

0.25 0.91 0.11

0.52 0.71

Cr2 O3 tot C (%) (%)

100

66

32 189 38

25 31 169

3 80 18

7 5 53

9 32 4

7 21 14

7 2231 5

27 113

Cu (ppm) 163 142

Zn (ppm)

1

5

19 250 6359

3 40 106

1 42 3

2 3 3322

5 89 4

7 335 10

0.03 0.01 0.82

0.01 2.47 0.03

0.01 0.64 0.08

0.01 9.98 0.01

0.16 1.02

108

75

190 1668 13751

99 413 800

0.01

0.48

1.05 0.96 7.31

0.03 0.45 1.94

8

1

11 13 223

3 7 2

0 7 1

3 2 93

2 3 1

3 9 1

2 204 2

1 1

S Au (%) (ppb)

121 0.6. As correlation between the elements Zr, TiO2 and Al2O3 is good we concluded that they remained immobile during alteration and subsequent metamorphism.

TABLE 6. Correlation between immobile elements at Petiknäs South a) Spearman rank coefficient of correlation (r') for rhyolite B/C rocks (n=54) TiO2 %

Al2O3 % Zr ppm

Y ppm

Nb ppm

Yb ppm

Lu ppm

Th ppm

TiO2 %

1.000

Al2O3 %

0.932

1.000

Zr ppm

0.597

0.626

1.000

Y ppm

0.563

0.552

0.911

1.000

Nb ppm

0.576

0.599

0.631

0.592

1.000

Yb ppm

0.550

0.554

0.875

0.935

0.530

1.000

Lu ppm

0.541

0.570

0.868

0.917

0.582

0.921

1.000

Th ppm

0.676

0.674

0.562

0.566

0.748

0.586

0.571

1.000

Hf ppm

0.536

0.591

0.840

0.790

0.639

0.737

0.784

0.554

b) Spearman rank coefficient of correlation (r') for rhyolite A rocks (n=31) TiO2 %

Al2O3 % Zr ppm

Y ppm

Nb ppm

Yb ppm

Lu ppm

Th ppm

TiO2 %

1.000

Al2O3 %

0.770

1.000

Zr ppm

0.794

0.835

1.000

Y ppm

0.260

0.254

0.465

1.000

Nb ppm

0.467

0.628

0.720

0.699

1.000

Yb ppm

0.243

0.234

0.396

0.961

0.709

1.000

Lu ppm

0.214

0.160

0.354

0.899

0.644

0.935

1.000

Th ppm

0.143

0.370

0.441

0.591

0.785

0.659

0.624

1.000

Hf ppm

0.497

0.641

0.775

0.742

0.880

0.756

0.725

0.737

r' ≥ 0.9 r' ≥0.8

31

Temperatures of ore forming fluids Conditions of ore formation from 10 VMS deposits across the Skellefte district can be inferred from fluid inclusion studies by Broman (1987, 1988) and Broman and Lindblom (1991) who showed that the ores were formed at temperatures between 145o and 377oC. These temperature are similar to ore forming temperatures reported from other VMS districts (Huston 1999; Urabe et al. 1983) and are also comparable with temperatures measured at sites of recent and venting black smokers, (250oC to 350oC, Henley and Ellis 1983). Assessment of REE mobility REE can be mobilized by hydrothermal fluids following partial destruction of the host phases (e.g. apatite, Monecke et al. 2003). In general, the amount of depletion or mobilization of REE increases from the heavy to the light REE, a pattern also observed by MacLean (1988) for chloritized felsic volcanics at the Phelps Dodge deposit in Canada. Wells et al. (1998) examined REE behavior in a mineralized alteration pipe within the Troodos ophiolite, and showed that alteration resulted in either no changes of REE patterns or depletion in the light REE. On the other hand, Prior et al. (1999) showed that the REE in strongly sericitized altered rhyolites at the Kidd Creek VMS deposit were relatively immobile, although samples from the chloritized footwall stringer zone showed mobility. In order to investigate the behavior of the REE during alteration at Petiknäs South, six samples of variably altered rhyolite B have been plotted in a chondrite-normalized diagram, together with a least-altered sample of rhyolite B (Fig. 14a). Although the REE patterns are not exactly parallel to each other, it is clear that the chlorite-garnet altered samples have the highest REE contents. This can be attributed in part to the chlorite alteration, which causes net mass loss of mobile elements, and residual enrichment of the relatively immobile REE. In order to test for REE mobility, the altered samples were normalized to the Lu content of the least altered sample, as the heavy REE, including Lu are essentially immobile under typical VMS alteration conditions (MacLean 1988; Barrett and MacLean 1994b). On binary plots Lu forms alteration lines against Zr, TiO2 and Al2O3 (not shown). From table 6 it can be seen that Lu shows good correlation with typical immobile elements (Zr, Y and Yb). The Lu-normalized REE patterns are shown in Figure 14b. The REE patterns of the least altered and the most altered rhyolite B rocks are almost identical which indicates that no significant losses of REE have occurred relative to the least-altered sample. The small variation of the REE patterns between the samples can be explained by variation of REE between different rhyolite B rocks. The strongest Eu depletion is associated with sericite alteration and is caused by feldspar destruction. Chemostratigraphic and alteration synthesis for Petiknäs South On the basis of geological facies mapping, chemostratigraphic relations (for more detail see paper I of this thesis) and mass change calculations, a restored schematic section has been constructed for Units 1 to 4 at Petiknäs South (Fig 15). The stratigraphic younging direction (from NE to SW) is based on primary sedimentary structures in drill core and outcrop. The restored section shows the stratigraphic succession at the time of formation of the A ore lens on the seafloor (near the top of Unit 4). Unit 5, the faulted hanging-wall, has been omitted from the restored section, as have the post-ore andesitic sills and mafic dykes of unit 6. Unit 1: The footwall complex is dominated by cryptodomes and synvolcanic sills (with peperitic contacts) of rhyolite B which probably were intruded into an original dacitic footwall slightly after ore-

32

1000

REE on LOI free basis

(a)

Mass loss effect

Rock/Chondrites

100

10 pattern of Precursor

1 1000


REE corrected for mass changes (normalized to Lu)

Rock/Chondrites

100

(b)

pattern of Precursor

10

1

La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb Lu Petiknäs South; footwall rhyolite B rocks of unit 1: least altered coherent Fsp porphyritic, used for normalization chlorite-garnet schist, gains of MgO, FeO; large losses of SiO2 sericite altered coherent with peperitic contact, gains of K2O silica altered coherent with peperitic contact gains of SiO2

Fig 14. Chondrite-normalized REE patterns for rhyolites from the footwall complex (Unit 1) at Petiknäs South. (a) Raw data for variably altered samples. Some of the vertical range in patterns is due to residual enrichment of the REE caused by large net loss of mobile mass, e.g. the samples of chlorite-garnet schist. REE data were normalized to the chondrite values of Evensen et al. (1978) (b) The same REE data, but normalized to Lu, which is generally immobile under typical conditions of VMS alteration (MacLean, 1988). This plot shows that there has been no mobility in the REE during strong alteration.

33

Fig 15. Restored schematic section for Petiknäs South, showing chemostratigraphic relations and general distribution of alteration at the time of deposition of the A massive sulfide lens on the seafloor (strata above this in the mine have been removed by the hanging-wall fault). Representative rock types as defined by their immobile-element ratios are shown by arrows. Boxes shows representative calculated mass changes. Chlorite-garnet schists in the footwall complex (Unit 1) are interpreted as a discordant upflow alteration zone. The restored section shows how intensity and style of alteration varies between proximal and distal parts of the Petiknäs South deposit. In Unit 1, a rhyolitic sill probably intruded rhyolitic felsic volcaniclastics of the shallow footwall after the B/C ore lens had been deposited and hydrothermal alteration had largely ceased, which would explain the weak alteration under much of this ore lens, and also the “removal” of the upper part of the alteration pipe. Post-ore andesitic sills and mafic dykes are omitted from the restored section.

34

100m

0m

ca 500m above sea-floor

$SiO2 - - $FeO ++ $MgO +++ $MnO + / $K2O ++ $Na2O- - $CaO -

D ore lens

Rhyolitic volcaniclastic siltstone Strongly feldspar porphyritic rhyolite

Unit 2

Unit 1

Unit 3

Unit 3

Mudstone

Unit 2 Unit 4 Basaltic Andesite volcaniclastic siltstone Basaltic Andesite volcaniclastic sandstone

Silica altered

Strongly feldspar and quartz porphyritic rhyolite

Unit 4

rock type as given by Zr/TiO2 - ratio

Chemostratigraphy

100m

$SiO2 - $FeO + / $MgO ++ $MnO + / $K2O + $Na2O- $CaO - -

U 3 proximal

Bas. And. Zr/TiO2=72

in boxes: mass changes caused by alteration (see table 4 and 5 for descriptive terms)

Sericite altered

Chlorite altered

Chlorite-garnet altered

0m

-+ +/+/+ --

U 1 prox. $SiO2 $FeO $MgO $MnO $K2O $Na2O $CaO

Intense Alteration

Rhy B Zr/TiO2=633

Rhy AA Zr/TiO2=1596

B/C ore lens

$SiO2 +++ / - - $FeO +++ $MgO ++ $MnO +++ $K2O +++ $Na2O- - $CaO - - -

Rhy A Zr/TiO2=1019

Proximal

Rhyolitic volcaniclastic sandstone

Simplfied mine sequence

A ore lens


U 4 proximal

sea-floor below wave base

U 2 proximal

Dacite II Zr/TiO2=271

Unit 1

Unit 2

Unit 3

Unit 4


sea-level at about 500 m above the sea-floor

Unit 4

500m

400m

300m

Rhy B Zr/TiO2=633

WNW

300m

U 4 distal

400m

$SiO2 ++ / - - $FeO + $MgO ++ $MnO + $K2O ++ $Na2O- - $CaO -

U 2 distal

$SiO2 - $FeO ++ $MgO ++ $MnO + / $K2O + $Na2O- $CaO - -

U 3 distal

Rhy B/C Zr/TiO2=542

500m

+++ ++ + +/---+++/--++/---

large gain moderate to large gain zero to minor gain minor gain or loss zero to minor loss moderate loss large loss large gain and large loss moderate gain and large loss

Results of mass change calculations

Massive sulfide

ESE

$SiO2 ++ / - - $FeO + $MgO + / $MnO + / $K2O ++ $Na2O- $CaO -

Rhy B Zr/TiO2=633

$SiO2 - $FeO ++ $MgO + $MnO + $K2O + $Na2O+ $CaO -

U 1 distal

Andesite Zr/TiO2=143

Andesite Zr/TiO2=143


Sulfides

200m

$SiO2 - - $FeO +++ $MgO +++ $MnO +++ $K2O ++ $Na2O- - $CaO -

U 1 upflow

Rhy A Zr/TiO2=1019

Distal

Rhy B/C Zr/TiO2=542

formation. Remants of the original dacitic volcaniclastic footwall are present in the deep proximal footwall (dacite II on Fig. 15). This volcaniclastic dacitic footwall extends more than 1000 m east of the mine, where sampled pumiceous outcrops also yielded a dacite II composition. No feldsparporphyritic rhyolite intrusions were noted in the surface exposures east of the mine, thus the felsic sills and cryptodomes that are present in the mine sequence likely thin out towards the east. The original dacitic footwall at Petiknäs South has been correlated with rocks in the upper part of the footwall at the Renström deposit, 2.5 km east of Petiknäs South by Allen and Svenson (2004). They noted that the Renström and Petiknäs South dacitic footwall rocks are distinctive in having higher TiO2, Fe2O and P2O5 contents than other dacites in the region. The proximal footwall complex at Petiknäs South is generally only weakly altered, as indicated by the presence of abundant plagioclase phenocrysts, and supported by mass change calculations (Table 3). However, a narrow but strongly altered chlorite-garnet zone occurs in the distal part of the deposit (Fig. 15). This obliquely discordant alteration zone may have acted as a feeder to the B/C ore lens. Several thin (1 kg were washed and afterward dried in the Swedish sample preparation lab (SGS) in steel buckets at 105oC and subsequently crushed to 10 mm by a Retsch crusher. After each pass the crusher was cleaned with pressed air and after each client the crushing facility was washed with barren material. The entire crushed sample was pulverized using a LM5 pulverizer with pulverizing time adjusted for each sample and calculated as: 2min/kg and the final pulp was 90% less than 200 MESH. After each sample-pass the grinding disk and bowl was cleaned by compressed air. The grinding bowls and disk are of chrome free steel having low levels of minor and trace elements and the maximum levels of these elements in the steel are: Au 0.05ppm, Ag 0.5ppm, Bi 10ppm, Cd 10ppm, Co 500ppm, Cu 500ppm, Cr 300ppm, Mg 300ppm, Mn 1.40%, Mo 50ppm, Ni 300ppm, Pb 10ppm, V 500ppm, Zn 50ppm. In order to assure that the grinding product was 90% less than 200 MESH, regular sieving tests were performed by SGS. Grinding equipment was regularly cleaned with barren rocks. Sample splitting finally provided a 50g portion which was packed into a pre-labeled sample bag and sent in batches containing internal standards to ACME Laboratories in Vancouver. The unused and remaining material of each sample was returned to the mining company Boliden Mineral AB for final storage.

Appendix 3b New Lithogeochemical Database The database comprises 469 samples from Petiknäs South and 93 samples from Petiknäs North. Petiknäs North samples include samples from >1000m long BH 32 which intersects ore and also include the core samples from Petiknäs South bore holes which are located below the PMFZ and consequently belong to the Petiknäs North block (namely BH 231 and BH 314 from the proximal and BH 502 from the distal section). 162 samples from the Petiknäs South are coherent volcanic rocks, 276 samples are volcanic sedimentary rocks and 31 samples are strongly altered volcanic rocks and are lacking any primary texture and thus classified as schists. 206 samples are from the Petiknäs South proximal section, 154 from the distal section, 56 samples from the Z 300 horizontal plan; 17 samples are from surface and 7 samples from underground. A further 29 samples are from a regional bore hole (BH 9) which is drilled around 500m south-east of the Petiknäs South orebody. All Petiknäs North samples are core samples and are equally coherent volcanic and volcaniclastic rocks.

74.79 0.202 13.58 3.14 0.05 3.63 0.70 0.37 3.39 0.014 0.000 340 14 59.8 27.7 64.8 327.5 0.00062

BH207-185.55m Rhyolite AA volcaniclastic Unit 2 2690.0 2030.7 305.2

75.35 0.163 11.23 6.23 0.08 2.00 1.50 0.32 2.92 0.012 0.001 304 22 62.6 21.4 40.3 150.8 0.00108

BH206-236.5m Rhyolite A volcaniclastic Unit 4 2604.1 2043.7 272.2

59.61 0.383 21.42 5.46 0.90 3.11 1.85 0.19 6.19 0.051 0.000 693 24 102.3 41.7 48.8 268.4 0.00143

BH291-15.75m Rhyolite B schist Unit 1 2802.9 2202.2 357.6

Intersection of fractionation curve y= 0.000025x^2-0.0114x+1.45 and alteration lines y=mx Zr of precursor 220.0 184.4 168.5 TiO2 of precursor 0.136 0.200 0.241 Correction factor 0.672 1.223 0.628 Correction factor = Zr precursor/Zr altered y = TiO2. x = Zr

Untreated data (LOI-free basis) SiO2 (%) TiO2 (%) Al2O3 (%) FeO (%) MnO (%) MgO (%) CaO (%) Na2O (%) K2O (%) P2O5 (%) Cr2O3 (%) Ba (ppm) V (ppm) Rb (ppm) Sr (ppm) Y (ppm) Zr (ppm) Slope of TiO2-Zr alteration lines

Sample Chemical Group Description Stratigraphic interval Petiknäs X Petiknäs Y Petiknäs Z

158.3 0.273 1.086

75.04 0.252 14.51 1.95 0.04 0.67 0.74 5.23 1.39 0.052 0.000 371 18 27.1 75.8 19.5 145.8 0.00173

BH315-275m Rhyolite B coherent Unit 1 2741.7 2231.4 602.7

149.2 0.307 0.776

74.68 0.395 12.77 5.71 0.08 0.77 1.08 1.80 2.44 0.069 0.000 574 3 54.0 64.5 36.6 192.2 0.00206

BH54-33.9m Rhyolite C coherent Unit 1 2941.8 1995.7 78.3

148.9 0.308 0.651

71.33 0.473 16.05 2.51 0.05 1.03 1.20 3.62 3.36 0.109 0.001 1064 42 65.7 86.6 41.8 228.8 0.00207

BH206-334m Rhyolite C coherent Unit 5 2512.2 2030.5 302.1

131.4 0.385 0.675

72.15 0.570 15.09 3.38 0.05 1.11 1.47 3.69 2.17 0.122 0.000 521 10 48.6 123.0 39.4 194.5 0.00293

BH54-173m Dacite II volcaniclastic Unit 1 2875.8 1989.6 200.5

83.9 0.669 0.877

64.98 0.763 14.08 11.05 0.14 4.88 1.65 0.19 2.00 0.131 0.000 335 52 33.9 20.0 22.9 95.7 0.00798

BH206-154.3m Andesite volcaniclastic Unit 3 2680.0 2045.9 240.9

Appendix 4. Mass change calculations applying a multi precursor approach (MacLean 1990) for representative rocks from Petiknäs South

70.7 0.769 0.815

66.37 0.944 14.26 7.41 0.15 3.65 4.38 0.44 2.12 0.122 0.000 476 214 46.3 59.9 23.7 86.8 0.01087

BH292-166.1m Basaltic andesite volcaniclastic Unit 3 2716.7 2282.2 452.6

75.7 0.730 1.893

77.25 0.386 6.54 9.93 0.03 0.23 0.23 0.21 1.96 0.058 0.000 105 43 26.4 6.6 12.9 40.0 0.00966

BH458-30.25m Basaltic andesite schist Unit 4 2619.4 2059.9 613.2

BH207-185.55m Rhyolite AA volcaniclastic Unit 2

BH206-236.5m Rhyolite A volcaniclastic Unit 4

BH291-15.75m Rhyolite B schist Unit 1

Precursor values (based on Zr precursor values and fractionation trends for each oxide and selected traces) SiO2 (%) 81.8 78.3 76.5 TiO2 (%) 0.14 0.20 0.24 Al2O3 (%) 11.2 12.4 13.0 FeO (%) 1.03 1.47 1.76 MnO (%) 0.02 0.03 0.03 MgO (%) 0.4 0.5 0.6 CaO (%) 1.2 1.6 1.8 Na2O (%) 3.5 4.0 4.3 K2O (%) 2.2 1.9 1.7 P2O5 (%) 0.02 0.04 0.04 Ba (ppm) 640 619 610 Rb (ppm) 36 32 30 Sr (ppm) 77 89 95 Y (ppm) 48 40 37 Zr (ppm) 220 184 168 V (ppm) 5 9 13 Total 101.52 100.57 100.09

Sample Chemical Group Description Stratigraphic interval

Appendix 4. cont.

75.3 0.27 13.3 1.99 0.04 0.7 1.9 4.4 1.6 0.05 604 28 99 35 158 16 99.77

BH315-275m Rhyolite B coherent Unit 1

74.1 0.31 13.7 2.24 0.04 0.8 2.0 4.6 1.6 0.05 599 27 102 33 149 20 99.49

BH54-33.9m Rhyolite C coherent Unit 1

74.1 0.31 13.7 2.25 0.04 0.8 2.0 4.6 1.6 0.05 599 27 102 33 149 20 99.48

BH206-334m Rhyolite C coherent Unit 5

71.6 0.38 14.3 2.89 0.05 1.0 2.3 4.9 1.4 0.07 589 25 109 29 131 33 98.96

BH54-173m Dacite II volcaniclastic Unit 1

62.8 0.67 16.0 7.08 0.11 2.5 3.2 5.6 1.0 0.11 562 19 126 19 84 177 99.08

BH206-154.3m Andesite volcaniclastic Unit 3

59.5 0.77 16.4 9.98 0.15 3.4 3.5 5.8 0.9 0.13 554 18 131 17 71 338 100.67

BH292-166.1m Basaltic andesite volcaniclastic Unit 3

60.8 0.73 16.2 8.72 0.13 3.0 3.4 5.7 0.9 0.12 557 18 129 18 76 262 99.89

BH458-30.25m Basaltic andesite schist Unit 4

37.4 0.24 13.4 3.4 0.57 2.0 1.2 0.1 3.9 0.03 435 64 26 31 168 15 62.32

Reconstituted values (based on untreated data multiplied by the Zr correction factor) SiO2 (%) 50.2 92.1 TiO2 (%) 0.14 0.20 Al2O3 (%) 9.1 13.7 FeO (%) 2.1 7.6 MnO (%) 0.04 0.10 MgO (%) 2.4 2.4 CaO (%) 0.5 1.8 Na2O (%) 0.2 0.4 K2O (%) 2.3 3.6 P2O5 (%) 0.01 0.01 Ba (ppm) 228 371 Rb (ppm) 40 77 Sr (ppm) 19 26 Y (ppm) 44 49 Zr (ppm) 220 184 V (ppm) 9 27 Total 67.14 122.09

BH291-15.75m Rhyolite B

76.5 0.24 13.0 1.8 0.03 0.6 1.8 4.3 1.7 0.04 610 30 95 37 168 13 100.00

BH206-236.5m Rhyolite A

77.8 0.20 12.4 1.5 0.03 0.5 1.6 4.0 1.9 0.04 616 31 89 40 183 9 100.00

80.5 0.13 11.0 1.0 0.02 0.4 1.2 3.4 2.2 0.02 630 35 75 47 217 5 100.00

BH207-185.55m Rhyolite AA

Precursor values normalized to 100 % SiO2 (%) TiO2 (%) Al2O3 (%) FeO (%) MnO (%) MgO (%) CaO (%) Na2O (%) K2O (%) P2O5 (%) Ba (ppm) Rb (ppm) Sr (ppm) Y (ppm) Zr (ppm) V (ppm) Total

Sample Chemical Group

81.5 0.27 15.8 2.1 0.04 0.7 0.8 5.7 1.5 0.06 403 29 82 21 158 20 108.50

75.5 0.27 13.4 2.0 0.04 0.7 1.9 4.5 1.6 0.05 606 29 99 35 159 16 100.00

BH315-275m Rhyolite B

58.0 0.31 9.9 4.4 0.06 0.6 0.8 1.4 1.9 0.05 446 42 50 28 149 2 77.54

74.5 0.31 13.7 2.3 0.04 0.8 2.0 4.6 1.6 0.05 602 27 103 33 150 20 100.00

BH54-33.9m Rhyolite C

46.4 0.31 10.4 1.6 0.03 0.7 0.8 2.4 2.2 0.07 693 43 56 27 149 27 65.01

74.5 0.31 13.7 2.3 0.04 0.8 2.0 4.6 1.6 0.05 602 27 103 33 150 20 100.00

BH206-334m Rhyolite C

48.7 0.38 10.2 2.3 0.03 0.7 1.0 2.5 1.5 0.08 352 33 83 27 131 7 67.48

72.4 0.39 14.4 2.9 0.05 1.0 2.3 4.9 1.4 0.07 595 25 110 30 133 33 100.00

BH54-173m Dacite II

57.0 0.67 12.4 9.7 0.12 4.3 1.4 0.2 1.8 0.11 294 30 18 20 84 45 87.64

63.4 0.68 16.1 7.1 0.11 2.5 3.2 5.7 1.0 0.11 567 20 127 20 85 179 100.00

BH206-154.3m Andesite

Appendix 4. (cont.) Mass change calculations applying a multi precursor approach (MacLean 1990) for representative rocks from Petiknäs South

54.1 0.77 11.6 6.0 0.12 3.0 3.6 0.4 1.7 0.10 388 38 49 19 71 174 81.41

59.1 0.76 16.3 9.9 0.15 3.4 3.5 5.8 0.9 0.13 551 18 130 17 70 335 100.00

BH292-166.1m Basaltic andesite

146.2 0.73 12.4 18.8 0.06 0.4 0.4 0.4 3.7 0.11 198 50 12 24 76 82 183.30

60.9 0.73 16.3 8.7 0.13 3.0 3.4 5.8 0.9 0.12 558 18 129 18 76 262 100.00


BH207-185.55m Rhyolite AA

14.3 0.0 1.4 6.2 0.1 1.9 0.3 -3.6 1.7 0.0 -245 45 -63 9 1 18 22.1

BH206-236.5m Rhyolite A

-39.0 0.0 0.5 1.7 0.5 1.3 -0.6 -4.2 2.2 0.0 -174 35 -69 -6 0 2 -37.7

BH291-15.75m Rhyolite B

6.0 0.0 2.4 0.1 0.0 0.0 -1.1 1.2 -0.1 0.0 -203 1 -17 -14 0 4 8.5

BH315-275m Rhyolite B

-16.5 0.0 -3.8 2.2 0.0 -0.2 -1.2 -3.2 0.3 0.0 -156 14 -53 -5 -1 -18 -22.5

BH54-33.9m Rhyolite C

Iron, reported by the laboratory as iron total was transformed to FeO (ferrous iron) by applying a conversion factor of 0.8998. Major oxides and traces were normalized to a loss on ignition free basis (vf)

Mass changes (reconstituted values minus precursor values) -30.3 SiO2 (%) TiO2 (%) 0.0 Al2O3 (%) -1.9 FeO (%) 1.1 MnO (%) 0.0 MgO (%) 2.1 CaO (%) -0.7 Na2O (%) -3.2 K2O (%) 0.1 P2O5 (%) 0.0 Ba (ppm) -402 Rb (ppm) 5 Sr (ppm) -57 Y (ppm) -3 Zr (ppm) 3 V (ppm) 5 Total mass change (%) -32.9

Sample Chemical Group

-28.1 0.0 -3.3 -0.6 0.0 -0.1 -1.2 -2.3 0.6 0.0 0 0 0 0 0 0 -35.0

BH206-334m Rhyolite C

-23.6 0.0 -4.2 -0.6 0.0 -0.3 -1.3 -2.4 0.1 0.0 -243 7 -27 -3 -1 -26 -32.5

BH54-173m Dacite II

-6.4 0.0 -3.8 2.5 0.0 1.8 -1.8 -5.5 0.8 0.0 -273 10 -109 1 -1 -133 -12.4

BH206-154.3m Andesite

Appendix 4. (cont.) Mass change calculations applying a multi precursor approach (MacLean 1990) for representative rocks from Petiknäs South

-5.0 0.0 -4.7 -3.9 0.0 -0.4 0.1 -5.4 0.9 0.0 -163 20 -81 3 0 -161 -18.6


85.3 0.0 -3.9 10.1 -0.1 -2.6 -2.9 -5.4 2.8 0.0 -359 32 -116 7 0 -180 83.3
