VMS

Miner Deposita DOI 10.1007/s00126-015-0612-1

ARTICLE

Geology, alteration, and lithogeochemistry of the Hood volcanogenic massive sulfide (VMS) deposits, Nunavut, Canada Hannah K. Mills 1 & Stephen J. Piercey 1 & Trish Toole 2

Received: 18 December 2014 / Accepted: 13 August 2015 # Springer-Verlag Berlin Heidelberg 2015

Abstract The Hood volcanogenic massive sulfide (VMS) deposits are hosted by the ~2.68 Ga Amooga Booga volcanic belt (ABVB) in the northwestern Archaen Slave Craton and consist of three deposits (Hood 10, 41, and 41A) and three occurrences (46, 461, and 462). The mineralized zones consist of massive to semi-massive pyrrhotite, pyrite, chalcopyrite, sphalerite, and galena hosted predominantly by felsic volcanic flows within the predominantly mafic ABVB. The mineralized lenses occur at different stratigraphic levels and have textural, alteration, and stratigraphic features consistent with formation via subseafloor replacement. The felsic volcanic rocks in the Hood deposits can be subdivided into groups based on immobile trace element geochemistry. The main felsic types (A and B) are petrographically indistinguishable. Type A has higher high field strength element (HSFE) and rare earth element (REE) contents than type B, suggesting a higher temperature of formation. Type A rocks also have higher Nb/Ta values indicative of a greater mantle input in their genesis compared to type B rocks. Mineralization is more closely associated with type A than type B rocks. The two mafic volcanic rock types previously identified in the ABVB,

Editorial handling: K. Kelley and G. Beaudoin Electronic supplementary material The online version of this article (doi:10.1007/s00126-015-0612-1) contains supplementary material, which is available to authorized users. * Hannah K. Mills [email protected] 1

Department of Earth Sciences, Memorial University of Newfoundland, 300 Prince Philip Drive, St. John’s, NL A1B 3X5, Canada

2

MMG Resources Inc., Vancouver, Canada

type I and type II, both occur within the Hood deposits. The type II mafic group is interpreted to be the result of variable crustal contamination of type I magma. The volcanic rocks of the ABVB are interpreted to have formed in a continental margin arc/back-arc setting. The genesis of these magmatic suites involved magmatic underplating and emplacement through pre-existing sialic basement that resulted in crustal melting, mantle-crust mixing, and contamination leading to the aforementioned geochemical features in both mafic and felsic suites. This type of extensional tectonic environment was likely associated with high heat flow and is similar to global VMS environments proximal to extending continental margins (e.g., Sturgeon Lake, Bathurst, and Finlayson Lake). The similarities of the ABVB to other Slave Craton greenstone belts further highlights the overall potential for greenstone-hosted VMS mineralization in the Slave Craton. Chlorite-sericite (+/− quartz) is the dominant hydrothermal alteration assemblage in the Hood deposits and is typical of VMS-style mineralization. Mass change calculations illustrate that elemental changes are typical of VMS environments with gains in Fe2O3, MgO, and base metals associated with chlorite alteration near mineralized zones; K2O gains associated with sericite alteration; and losses of Na2O in both alteration types. Keywords Volcanogenic massive sulfide . Archean . Petrogenesis . Slave Craton

Introduction Volcanogenic massive sulfide (VMS) deposits are a significant global source of Zn, Cu, Pb, Ag, and Au, as well as numerous other metals. They have been extensively studied, and syntheses and summaries are provided by Franklin et al. (2005) and Galley et al. (2007). In spite of hosting numerous

Miner Deposita

VMS deposits, the Archean Slave Province (referred to as Slave Craton) in northern Canada is underexplored and understudied compared to well-known Archean VMS camps such as those within the Yilgarn Craton, Australia or the Superior Craton, Canada. The Slave Craton VMS deposits include both bimodal-mafic deposits (e.g., Hood, High Lake, and Homer Lake) and bimodal-felsic deposits (e.g., Izok Lake, Hackett River, and Gondor; Bleeker and Hall 2007). The purpose of this study is to characterize the Hood VMS deposits in the Slave Craton and to contribute descriptions of individual Slave Craton deposits. The Hood VMS belt consists of several Cu-Zn-Pb mineral deposits and occurrences in a ~9 km2 area hosted by the ~2.68 Ga Amooga Booga volcanic belt (ABVB). This paper focuses on (1) a documentation of the stratigraphy, lithofacies, alteration, and emplacement mechanisms for the deposits; (2) evaluation of the primary and secondary lithogeochemical attributes of the host rocks to the deposits; (3) assessment of the tectonic setting of formation; and (4) discussion about the relationships between host rocks, geochemical evolution and alteration, and tectonic setting of formation, and how these relate to deposit genesis and exploration. In addressing the above, we have utilized detailed lithofacies and stratigraphic mapping of diamond drill core for the various lenses within the Hood deposits, which have been augmented by lithogeochemistry, mineralogy, and mass change calculations. These results are integrated to enhance the understanding of these poorly understood Archean VMS deposits.

Regional geology The Archean Slave Craton consists of Hadean to Mesoarchean basement rocks, Neoarchean greenstone belts, plutonic suites, and sedimentary basins (Fig. 1; Bleeker et al. 1999; Davis and Bleeker 1999; Bleeker and Hall 2007; Ootes et al. 2009). It is bounded on the west by the Wopmay Orogen and to the east by the Thelon Orogen (Fig. 1; Hoffman 1988). The oldest rocks of the craton comprise the >2.9 Ga Central Slave Basement Complex (CSBC), which is overlain by the Mesoarchean Central Slave Cover Group (CSCG) and the Neoarchean supracrustal Yellowknife Supergroup (Bleeker et al. 1999). The CSCG is a thin package of volcanic rocks, quartzite, conglomerate, and banded iron formation (BIF; Bleeker et al. 1999). The overlying Yellowknife Supergroup includes two volcanic sequences (2.73–2.70 and 2.70– 2.66 Ga), referred to as the Kam and Banting groups, respectively (Helmstaedt and Padgham 1986), and the 2.66–2.63 Ga Duncan Lake Group turbidites (Bleeker et al. 1999; Ootes et al. 2009). These rocks are intruded by several (2.63–2.62 and 2.59–2.58 Ga) plutonic phases and were affected by 2.66– 2.63 Ga and 2.61–2.59 Ga deformation and metamorphism

(Relf 1992; Davis et al. 1994; Isachsen and Bowring 1994; Davis and Bleeker 1999; Bleeker and Hall 2007). Stratigraphic terminology for the volcanic belts is mostly defined in the Yellowknife area (Helmstaedt and Padgham 1986). The Kam Group is the stratigraphically lower volcanic sequence and consists of >2.7 Ga tholeiitic mafic volcanic rocks (Helmstaedt and Padgham 1986; Fyson and Helmstaedt 1988; Isachsen and Bowring 1994, 1997; Cousens 2000; Bleeker and Hall 2007). The Kam Group is overlain by the 3.0 Ga) tonalitic and gabbroic basement occurs in three locations in the Hanikahimajuk Lake area (Fig. 2; Gebert 1995; Jensen 1995). The overlying supracrustal rocks of the ABVB are 10 km thick, and though there is limited lateral continuity of units, the overall stratigraphy is presently interpreted to young to the northwest, with local variations in the younging direction (Gebert 1995). Geographically, the ABVB forms a small central area of felsic volcanic rocks surrounded by more voluminous mafic flows and both mafic and felsic volcaniclastic rocks (Fig. 2; Gill 1977). Mafic to intermediate volcanic rocks include pillowed mafic flows, laminated volcaniclastic rocks, and quartz-filled amygdaloidal mafic rocks (Gebert 1995). Mafic rocks have two REE signatures (type I and type II) that represent variable crustal contamination of MORB-like magmas in an ensialic back-arc basin setting (Gebert 1995; Jensen 1995; Yamashita

Miner Deposita 116ºLegend Map Felsic Intrusives (2.68 - 2.58 Ga) 68º Metasedimentary Rocks (2.68 -2.58 Ga) Syn-volcanic Intrusives (2.73 - 2.66 Ga) Felsic Volcanic Rocks (2.73 - 2.66 Ga) Intermediate Volcanic Rocks (2. 73 - 2.66 Ga) Mafic Volcanic Rocks (2.73 - 2.66 Ga) Undivided Gneiss (>2.9 - 2.58 Ga) Basement Gneiss (>2.9 Ga)

112°

68°

High Lake NSBC

st ur u Fa

VMS Deposit

W o Or pm og ay en

lt

ABVB

Fault 66º

104°

108°

Coronation Gulf

th Ba

Fig. 1 Simplified geology of the Slave Craton, showing main volcanic belts and selected VMS deposits (Bleeker and Hall 2007). Labeled greenstone belts are the Amooga Booga volcanic belt (ABVB), Izok Lake volcanic belt (ILVB), Point Lake volcanic belt (PLVB), Yellowknife volcanic belt (YVB), Cameron River volcanic belt (CRVB), and the Beaulieu River volcanic belt (BRVB; modified after Stubley 2005)

66° Hackett River

HOOD DEPOSIT

NUNAVUT Izok Lake PLVB

Gondor

ILVB

Wopm

ay Fau

lt Zone

Acasta Gneiss

Thelo

n Fro

nt

CSBC

CRVB

64°

NWT

Kennedy Lake Sunrise

YVB Homer Lake

ult

Yellowknife BRVB

ld na

Fa

Do

Mc

62° 116°

Great Slave Lake 112°

et al. 2000). Both type I and type II pillowed mafic flows occur within tens of meters stratigraphically (Gebert 1995). Sedimentary rocks of the ABVB form thin layers between flows and include discontinuous Fe-formation, pelite, psammite, quartzwacke, and conglomerate (Gebert 1995). Synvolcanic gabbro and diorite and post-volcanic granitoids intrude the ABVB (Gebert 1995). The term Bmixed rock^ has been given to amphibolite-grade rocks that are likely supracrustal in origin, but which have been extensively intruded by diorite and granitoid rocks (Gebert 1995). Four different sets of fine-grained gabbro dykes and a single type of pegmatite intrude ABVB rocks in the Hanikahimajuk Lake area (Jensen 1995).

62º

Map 108º Location

Neodymium isotopic signatures (εNdt) of the ABVB volcanic rocks range from −1.2 to +2.5 (Jensen 1995). Although the mafic rocks have mostly positive εNdt, their trends in εNd–147Sm/144Nd space are consistent with mantle melts contaminated by sialic crust (Jensen 1995; Yamashita et al. 2000). All felsic and some intermediate rocks have lower εNdt signatures, indicating more evolved rocks with a crustal component involved in their genesis (Jensen 1995). There is no correlation between mafic geochemical type (I or II) and εNdt signature (Jensen 1995). The volcanic rocks of the Hood deposits surround the Rim granite, which is believed to be roughly coeval with ABVB volcanism (Fig. 2; Yamashita et al. 2000). Granitoid rocks have εNdt signatures that fall

Miner Deposita 414000

Fig. 2 Geology of the Hanikahimajuk Lake area and locations of Hood deposits and mineral occurrences (Gebert 1995)

418000

420000

Map Legend Diabase Dyke Pegmatitic Dyke Iron Formation Shear Zone Fault - known Fault - assumed

Lithology Granitoids and associated pegmatites

Syn-volcanic Intrusions 7332000

7332000

Rim Granite Diorite Gabbro and Leucogabbro

Yellowknife Supergroup- Supracrustal Rocks Metasedimentary Rocks Felsic Volcanic Rocks Intermediate Volcanic Rocks

Hood-46

7328000

Tonalite and Gabbro Basement

Hanikahimajuk Lake 7328000

Mafic to Intermediate Volcanic Rocks

>3.0 Ga Basement

Hood-461

Napaktulik Lake

Hood -10 Hood-462

Hood-41A

7324000

7324000

Hood-41

metres 414000

within the western granitoid field for the Slave Craton (Davis and Hegner 1992). In the vicinity of the Hood deposits, calc-alkaline felsic volcanic rocks make up 25 % of the volcanic sequence (Bruce 1991). They consist of rhyolite, dacite, and fragmental volcaniclastic rocks (Jensen 1995). These rocks are subdivided and variously named in exploration company reports, but are equivalent to regionally described units in the ABVB. The detailed structural setting of the deposits is uncertain (Hassard 1983). Regional metamorphic grade in the Hood area is greenschist facies (Thomas and Glenn 1994). Hydrothermally altered rocks are more commonly altered to chlorite-sericitequartz and Na2O depletions compared to the volcanic rocks surrounding the Hood deposits (Bruce 1991), typical of volcanic rocks associated with VMS deposits (e.g., Spitz and Darling 1978).

418000

420000

Stratigraphy, alteration, and mineralization of the hood VMS deposits Exploration of the Hood deposit has identified three main deposits (Hood 10, 41, and 41A) comprising in total 3.2 Mt of sulfide grading 3.2 % Zn and 2.6 % Cu, and several small mineral occurrences (Hood 46, 461 and 462; Fig. 2). The deposits were discovered in 1972 during regional exploration. Intermittent shallow (