The Vasilkovskoye deposit is a typical example of a large intrusion-related gold system of the stockwork type. The deposit is located in North Kazakhstan, in the.
Mineralogical and Geochemical Characteristics of the Vasilkovskoye Gold Deposit (North Kazakhstan) Alla Dolgopolova, Reimar Seltmann CERCAMS, Department of Earth Sciences, Natural History Museum, Cromwell Road, London SW7 5BD, UK Anastassiya Miroshnikova, Marina Mizernaya East Kazakhstan State Technical University, 69 Protozanov Str., Ust-Kamenogorsk 070004, Kazakhstan Abstract. The Vasilkovskoye deposit is a typical example of a large intrusion-related gold system of the stockwork type. The deposit is located in North Kazakhstan, in the Kokshetau Massive - a large block of Precambrian metamorphic rocks, with anatexis and Paleozoic magmatism comprising gabbro and granodiorite series. The Vasilkovskoye deposit is situated at the contact of gabbrodiorite and diorite with hornblende-biotite granodiorite and plagiogranite. The deposit is characterized by concentric metasomatic, mineralogical, and geochemical zoning. The mineralogical zoning is expressed by distinct paragenetic assemblages and characteristic minerals. The gold grade is irregular and varies from 1.5 to 3.6 g/t (cut-off 0.8 g/t). Native gold is fine grained (up to 0.12 mm) and associated with pyritearsenopyrite-quartz and bismuthinite-pyrite-arsenopyritequartz assemblages.
Complexity of intrusive phases, transitions of textural variations and alteration facies, frequent alternation of rock types with banding, schlieren and branching offsets, hybridisation zones, resorbed migmatites and enclaves are typical, further complicated by shearing and thrusting. Results of our geological, geochemical and mineralogical study allow to reconstruct the intrusive sequence and to distinguish the sequence of the different intrusive phases and mineral associations within the Vasilkovskoye gold deposit.
Keywords. Intrusion-related gold deposit, stockwork, Vasilkovskoye, Kazakhstan
1 Introduction The Vasilkovskoye intrusion-related gold deposit is located 17 km north of the city of Kokshetau in Akmola Oblast, northern Kazakhstan. The deposit was discovered in 1963, and a pilot open pit mining project undertaken from 1980 to 1986. Mining commenced in 1995 until the end of 2007, mining the oxide ores which were treated by heap leach. Production to 2011 was 14 Mt of ore. The Vasilkovskoye deposit is localised within the western part of the NW-trending Shatskaya metallogenic zone of the Altai-Sayan orogenic belt. It lies within a Proterozoic metamorphic basal complex, intruded by Ordovician granitoids, and overlain by later Palaeozoic sediments. The area has been subjected to a Mesozoic weathering regime, and is overlain by Cenozoic sand and clay sediments (Newall 2011; Porter GeoConsultancy 2013). The main structural elements of the Vasilkovskoye gold district are the northeastern margin of the Kokshetau Terrane; intersection of the regional NWtrending Dongulagash and Akekseevka faults; the NEtrending Vasilkovskoye-Berezovka Fault and the Latitudinal Fault; and the North Kokshetau ellipsoid domal-ring structure 55×30 km within an area affected by domes of the second order (Figure 1). The most of the Vasilkovskoye district is occupied by the Ordovician North Kokshetau domal pluton of the Zerenda Complex (gabbro, gabbrodiorite, diorite, granodiorite, plagiogranite, monzonite) elongated in the northwestern direction (Rafailovich 2009, 2011).
Figure 1. Geological-structural position of the Vasilkovskoye gold district (after Rafailovich 2009) (1–10) Geological complexes: (1) terrigenous-carbonate (C1), conglomerate-sandstone molasses (D2-3), (3) terrigenous and volcanic-terrigenous (O), (4) Upper Riphean-Vendian quartzitic sandstone Kokshetau Formation, (5) Upper RipheanVendian carbonaceous terrigenous-carbonate Sharyk Formation, (6) Lower-Middle Riphean metavolcanic Kuuspek Formation, (7) Paleoproterozoic amphibolite and gneiss of Zerenda Group, (8) leucogranites of the Dal'nensky and Zolotonosha intrusive complexes (D2), (9) Zerenda intrusive complex (O3), (10) gabbro and gabbrodiorite intrusions; (11) domal and ring structure; (12) regional fault; (13) second- and third-order faults; (14-16): gold-sulfide-quartz stockworks: (14) giant Vasilkovskoye deposit, (15) small deposits and occurrences, (16) Berezovka gold–silver–barite–base-metal deposit (17) line of geological-geophysical section. Regional faults: I, Vasilkovka–Berezovka; II, Dongulagash; III, Alekseevka; IV, Latitudinal.
2 Magmatism The North Kokshetau pluton cuts through metamorphic rocks of the Paleoproterozoic-Mesoproterozoic Zerenda Group and Neoproterozoic carbonaceous terrigenous and carbonate rocks of the Sharyk Formation. Geodynamics, Orogenic cycles and mineral systems
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The Zerenda Group consists of eclogite, garnetbiotite gneisses, cordierite-garnet-biotite gneisses, and quartz-mica gneisses, crystalline schists, cordieritespinel-quartz granulite with elevated W, Bi, Mo, and Sn contents. These rocks correspond to the high-temperature granulite-amphibolite metamorphic facies. The Sharyk Formation consisting of carbonaceous phyllite, dolomite, and marmorized limestone occurs in the northwestern, northeastern, and southwestern frameworks of the North Kokshetau pluton. The epigenetic ore-magmatic stockworks (Vasilkovskoye, Turan deposits), the Chaglinka uranium deposits with gold as a by-product, and the Berezovka gold-silverbase-metal massive sulfide deposit are conjugated with the rocks of the Sharyk Formation. The early intrusive phases composed of gabbro and gabbrodiorite are characterized by elevated alkalinity with prevalence of sodium over potassium. The late felsic intrusive phases are depleted in CaO, MgO, total FeO, and Al2O3 along with enrichment in SiO2, high Na2O + K2O (10-12 wt %) and predominance of K over Na (4:1); granodiorite is affected by K-feldspathization. Red to pinkish-grey and grey microcline porphyroblasts occupy 5-10 and 45-70% of rock volume, respectively. Fine-grained granite, aplite-like granite, and pegmatite dikes are abundant. Pegmatites also occur as sills and schlieren. Most typical igneous textures are shown on Figure 2.
Figure 3. Tectonic discrimination diagram (Pearce et al. 1984) for sample series of the Vasilkovskoye deposit, age sequence: G - gabbro, GD - gabbrodiorite, D - diorite, QD - quartz diorite PG - plagiogranite, GRD - granodiorite, GR - granite.
Overall, granodiorite and gabbro series show similar enrichment resp. depletion patterns. The chondrite normalized spider diagram of the Vasilkovskoye rock suite exhibits pronounced negative K, Nb, P and Ti anomalies, but lesser Sr anomaly (Figure 4). Negative Nb anomalies are also characteristic of the continental crust and may be an indicator of crustal involvement in magma processes. Notable is the significant enrichment in U, Ta and La that is more profound in granodiorite series compared to gabbro series. There are also some notable differences between the two series. For example, granodiorite series are enriched in Rb, Th, Ce and Zr, whereas gabbro series show depletion in these elements.
Figure 2. Igneous textures of typical rock suites at the Vasilkovskoye deposit. A. Gabbrodiorite. B. Plagiogranite. C. Granodiorite. D. Granite.
Major and trace elements were analysed for 27 samples. Based on geological observations, samples were grouped in seven distinct rock types, here listed in sequence of formation: gabbro, gabbrodiorite, diorite, quartz diorite, plagiogranite - that form a combined group (called collectively here “gabbro series”) and granodiorite, granite (called here “granodiorite series”). All sample series plot within the volcanic arc granite + syn-collision granite setting on the tectonic discrimination diagram (Figure 3). This supports a formation of Vasilkovskoye and several other stockwork gold deposits in the Kokshetau-North Tien Shan lithotectonic zone in the Late Ordovician simultaneously with collision granites of the Zerenda, Qryqquduk, and Qorday-Shatyrkol intrusive complexes (Abishev et al. 1972).
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Figure 4. Spider diagram of rock/chondrite (Sun and McDonough 1989) with symbols as in Figure 3
Granodiorite series with highest REE abundances show a distinct pattern with enrichment in light REE relative to heavy REE and strongest developed negative Eu anomaly compared to gabbro series that display much flatter REE patterns and a positive Eu anomaly (Figure 5). Positive Eu anomalies suggest plagioclase accumulation. REE pattern of one plagiogranite sample differs from other rock suites reflecting strong potassic alteration.
MINERAL RESOURCES IN A SUSTAINABLE WORLD • 13th SGA Biennial Meeting 2015. Proceedings, Volume 1
Different patterns for behaviour of REEs with negative vs. positive Eu anomalies respectively, as well as contrasting behaviour of other elements as discussed above and shown on Figure 4, indicates either derivation of the granodiorite and gabbro series from different sources or variable melting mechanisms.
Figure 5. Rare earth element plots for rock series of the Vasilkovskoye deposit with symbols as in Figure 3. Data are chondrite normalized (Sun and McDonough 1989)
3 Mineralization Mineralisation has been divided into a series of stages, all of which include some sulphides, particularly arsenopyrite (Porter GeoConsultancy 2013): Pre Ore Phase - corresponds to the earliest sulphide introduction, comprising chalcopyrite-pyrrhotite-pyrite, arsenopyrite-pyrite and Au assemblages, which are best developed within the gabbro suite, especially adjacent to the contact with the granites, and in strongly fractured areas. The chalcopyrite-pyrrhotite-pyrite assemblage is generally ore when closely associated with rocks rich in mafic minerals. Early Ore Phase - dominated by the introduction of quartz, carbonates, sericite and pyrite (i.e., carbonate and phyllic alteration). Main Ore Phase - essentially a quartz, carbonate and chalcophile mineral assemblage accompanied by the introduction of complex copper, bismuth, antimony, arsenic and tellurium minerals. Post Ore Phase - representing a waning of the system with the introduction of silica, carbonate and minor complex sulphides, as well as the deposition of uranium.
The concentration of gold mineralization is controlled by hybrid intrusive rocks within the Dongulagashsky fault and is hosted mainly by altered, intensively fractured, and occasionally brecciated porphyroblastic hornblende granodiorite and gabbrodiorite. The mineralised area of about 1.5 km2 contains 8 gold bearing linear zones, which are 8-10 to 100 m wide, are spatially separated at the flanks but form a single conelike main stockwork at the centre of the deposit that narrows with depth (Figure 6) (Levitan 2008). The oval shaped main stockwork zone measuring 400 x 150 m at the surface pinches out at a depth of 1300-1500 m (Kazhgeldin 1996).
Figure 6. Vasilkovskoye gold deposit: A. Geological scheme. B. Geological section (after Rafailovich 2009). (1) clay-rubble weathering mantle; (2, 3) intrusive rocks: (2) gabbrodiorite and diorite, unspecified and (3) granodiorite and plagiogranite; (4) contact between gabbrodiorite-diorite and granodioriteplagiogranite; (5) faults; (6) contour of stringer and stringerdisseminated gold mineralization; (7, 8) ore stockwork in (7) plan view and (8) section; (9, 10) gold contents in stockwork: (9) high and medium, (10) low; (11) line of geological section
Mineralization is controlled by faults and fracture zones with NW, NE and latitudinal directions. A distinct zonal distribution of ore and gangue minerals, gold and accompanying ore elements is typical (Rafailovich 2009). Paragenetic mineral associations of the ore stage are: early pyrite-pyrrhotite-marcasite-quartz; gold-pyritearsenopyrite-quartz (with pyrrhotite, loellingite and chalcopyrite), gold-bismuth-pyrite, arsenopyrite-quartz (with molybdenite, cubanite, native Bi, bismuthinite, tetradymite, and mixed tennantite-tetrahedrite) and goldpolymetallic (with chalcopyrite, sphalerite, galena and tennantite); late quartz-carbonate-stibnite-tetrahedrite. The pyrite-pyrrhotite-marcasite-quartz association is predominantly developed at the intermediate and deep horizons; gold-pyrite-arsenopyrite-quartz and goldbismuth-pyrite-arsenopyrite-quartz associations are found in the central part of mineralization; goldpolymetallic and quartz-carbonate-stibnite-tetrahedrite associations are typical of the upper horizons. Arsenopyrite is enriched in gold (up to a few hundreds g/t), Ag (5-50 g/t), Bi (up to 100-300 g/t), Pt (0.3-0.5 g/t), Cu, Pb, Zn, Co (up to 0.01-0.1%). Gold is closely correlated with Bi, As, Ag, Pb, and Cu. The primary geochemical halos are zoned (Figure 7). The highest contents are characteristic of Au, As, and Bi Geodynamics, Orogenic cycles and mineral systems
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halos. The outer boundaries of Ag, Pb, and Cu are remote from ore lodes for a few to tens of meters. The Mo, W, Ni, and Co halos are mostly characteristic of intermediate and low levels, whereas Ag, Cu, Sb, and Hg halos are localized at the upper levels.
4 Conclusions The Vasilkovskoye gold deposit is characterized by longterm ore-forming processes from ore generation to ore deposition; the combined mantle-upper crustal magmatism and ore-bearing fluids; the distinct tectonic dislocations and magnetic and gravity geophysical anomalies; and the regular metasomatic, mineralogical and geochemical zoning. These characteristic features are pivotal for assessing the ore potential of the still unexplored flanks and deeper parts of the deposit and to detail the guidelines for focused prospecting of similar targets elsewhere. In North Kazakhstan, the most promising ones are the slightly eroded Turan and Orlovskoye gold stockworks, located at a distance of 25 km to the northwest and 80 km to the southeast from the Vasilkovskoye deposit, respectively.
Acknowledgements This is a contribution to Project IGCP 592 funded by IUGS and UNESCO. We dedicate this paper to the late Mikhail Rafailovich. The help of Kazzinc is appreciated.
References Figure 7. Distribution of As, Bi, Ag, and Mo in section across ore stockwork of the Vasilkovskoye gold deposit (after Rafailovich 2009). (1) gabbrodiorite and diorite and (2) granodiorite and plagiogranite; (3) contour of ore stockwork; (4) boreholes; (5-7) concentrations of elements: (5) < 0.6% As, < 30 ppm Bi, < 0.3 ppm Ag, < 3 ppm Mo; (6) 0.6–1.0% As, 30100 ppm Bi, 0.3-1.0 ppm Ag, 3-30 ppm Mo; (7) 1-3% As, 100300 ppm Bi, 1-3 ppm Ag
Native gold forms micron-sized to 0.06 mm particles as accretions with quartz, arsenopyrite, pyrite and bismuthinite but 80% of the gold is free (Levitan 2008). Native gold is fine grained (up to 0.12 mm) and associated with the pyrite-arsenopyrite-quartz and the bismuthinite-pyrite-arsenopyrite-quartz assemblages. Non-metalliferous mineral veins form complicated relationships with the bodies of gold-bearing sulphide mineralization. Quartz veins of the ore stage (finegrained dark-grey and grey quartz with sulphides and native gold) form the substance of the ore-bearing stockwork. Post-ore associations are calcite-quartzsericite, fluorite-carbonate, quartz-tourmaline and carbonate-epidote-prehnite (Halls 2004). Medium and high grades of gold are found in the central part of the ore-bearing stockworks, low grades occur in the periphery. Charts of gold distribution in the weathering crust and bedrocks are identical. Gold grades of 0.6-3.3 g/t are more widespread and control the currently applied cutoff grade of 0.8 g/t. Gold shows a positive correlation with Bi, As, Ag, Pb, Cu. Endogene aureoles of Bi define the spatial limit of the gold ore bodies. The outer boundary of the Ag, Pb, and Cu aureoles extends beyond the ore bodies for a few metres up to a few tens of metres.
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Abishev VM, Bakhanova EV, Zorin YuM et al. (1972) Geology, composition and geochemistry of the Vasilkovskoye gold deposit. Geology, geochemistry, and mineralogy of the gold districts and deposits of Kazakhstan. Alma-Ata:107-162 Halls C, Seltmann R and Dolgopolova A (2004) Atlas of mineral deposit models of the Republic of Kazakhstan. Almaty, 142 p English edition of compilation by Bespaev KhA and Miroshnichenko LA (eds), CERCAMS NHM London 2004 Kazhgendin AM (ed., 1996) Gold deposits of Kazakhstan. Reference book. Almaty (in Russian) Levitan G (2008) Gold deposits of the CIS. Xlibris, USA Lyubetsky VN (1985) Deep criteria of localization of gold mineralization in Kazakhstan based on geophysical data. In: Experience of forecasting and evaluation of gold deposits in Kazakhstan. Alma-Ata:10-19 Newall P (ed, 2011) Competent person’s report for the assets held by Kazzinc Limited in Kazakhstan and Russia; prepared by Wardell Armstrong International, Truro, UK Pearce JA, Harris NBW and Tindle AG (1984) Trace element discrimination diagrams for the tectonic interpretation of granitic rocks. J Petrol 25:956-983 Porter GeoConsultancy (2013) www.portergeo.com.au Rafailovich MS (2009) Gold deposits of Kazakhstan: geology, metallogeny, exploration models. Almaty, 304 p (English translation by CERCAMS NHM London, 2012) Rafailovich MS, Mizernaya, MA and D'yachkov BA (2011) Large gold deposits hosted in black shales: formation conditions and signs of similarity. Almaty (English translation by CERCAMS NHM London, 2012; www.nhm.ac.uk/cercams) Sun SS and McDonough WF (1989) Chemical and isotopic systematics of oceanic basalts: implications for mantle composition and processes. In: Saunders AD and Norry MJ (eds) Magmatism in Ocean Basins. Geol Soc Spec Publ, London pp313-345
MINERAL RESOURCES IN A SUSTAINABLE WORLD • 13th SGA Biennial Meeting 2015. Proceedings, Volume 1
Mineral resources in a sustainable world Proceedings Volume 1
Mineral Resources in a Sustainable World 13th Biennial SGA Meeting 24-27 August 2015, NANCY, FRANCE
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Volume 1 Edited by Anne‐Sylvie André‐Mayer, Michel Cathelineau, Philippe Muchez, Eric Pirard and Sven Sindern
The 13th SGA biennial meeting is organized by the CNRS, and a group of French, Belgian and German universities (Nancy, Liège, Aachen and Louvain). The theme for this 13th edition is “Mineral Resources in a Sustainable World”. The SGA was founded in 1965 in Heidelberg and the 2015 SGA biennial meeting will celebrate the 50th anniversary of the Society.
Suggested citation for the entire volume: André-Mayer AS, Cathelineau M, Muchez Ph, Pirard E, Sindern S (eds) Mineral resources in a sustainable world. Proceedings of the 13th Biennial SGA Meeting, 24-27 August 2015, Nancy, France, 2134 pages Suggested citation for an individual paper: André-Mayer AS, Turlin F, Vanderhaeghe O, Gervais F, Ohnenstetter D, Moukhsil A, Solgadi F (2015) REE mineralizations associated to Late- to PostGrenvillian Orogeny peraluminous pegmatites, Québec. Proceeding of the 13th Biennial SGA Meeting, 24-27 August 2015, Nancy, France
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