Berezitovoe, Berezitovy

Siberia - Amur Oblast, Russia

Main commodities: Au Ag Zn Pb
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The Berezitovoe or Berezitovy gold-polymetallic deposit is located in the headwaters of the Amur River in the Amur Oblast of the Russian Federation, ~50 km north of the town of Urusha, ~550 km NNW to NW of the Oblast capital Blagoveshchensk and ~750 km ENE of Chita (#Location: 54° 28' 15"N, 122° 58' 23"E).

The Berezitovoe gold-polymetallic deposit is located in one of the side creeks of Haikta Creek, a the tributary of the Bolshoi Oldoi River which discharges into the major Amur River. It lies within the Urusha-Oldoi gold-placer district where >47 t of placer gold have been recovered since placer development began in the late 19th century. The richest placers have been found in the valleys of the Bolshoi Oldoi River and its tributaries, including Haikta Creek. The hard rock Berezitovoe deposit was discovered in 1932. Scientific geological investigations of the deposit were undertaken in several stages during 1934 to 1936, 1960 to 1962 and 1974 to 1980. Trial mining was attempted in 1936-37 with a pilot plant gold amalgamation operation, but gold recoveries were poor, ranging from only 22 to 32% from ore with grades of 2 to 4 g/t Au in pyrite-galena-sphalerite and 0.1 to 2 g/t Au in the pyrite-pyrrhotite-sphalerite associations. In the 1950s the deposit was again studied, but as a polymetallic deposit to primarily exploit its base metal content, but again without sufficiently encouraging results. However, from 1960 to 1962 and from 1974 to 1980, Amurskaya Geological Expedition undertook geological mapping, surface and extensive exploration drives and crosscuts at several levels and further evaluation of the Berezitovoye Deposit. This work culminated in Berezitovyi Rudnik Ltd. commencing mining in 2007 as a joint venture between OAO Buryatzoloto of Russia and High River Gold of Canada. In late 2008 Nordgold acquired High River Gold. Between 2007 and 2016, >15 t of Au were been mined, with continued mining going on currently (2021). In the first four years of mining production increases from 0.6907 Mt @ 2.49% Au in 2008, to 1.391 Mt @ 2.62 G/t Au in 2011. The principal metals produced from the deposit are Au, Ag, Pb, Zn and Cd, mined from an open pit operation, with approval for the development of a decline for underground mining received in 2019. Metallurgical recoveries have improved from 85.9% in 2008 to 89.8% in 2011 (Newell et al., 2012).

Geological Setting

Berezitovoe and a series of other Au, Ag, Cu, Pb, Zn, Bi, Mo, W and U occurrences and deposits define the generally east-west trending, 250 x 60 to 90 km Sergachi Metallogenic Zone and coincident placer gold province. This zone straddles the Mongol-Okhotsk Suture Zone, and extending into the adjacent southern Selenga-Stanovoi Terrane to the north and northern Erguna Terrane to the south. Basement to the north in the Selenga-Stanovoi Terrane, where the Berezitovoe deposit is located, is composed of Archaean metamorphic and magmatic rocks that were intensely reworked by magmatic events, mainly in the Palaeoproterozoic, but also in the Riphean (Meso- to early Neoproterozoic) and late Palaeozoic. The Sergachi Metallogenic Zone is characterised by two orthogonal systems of deep-seated faults, trending ENE and NW, that were active during both the Middle Cambrian and Late Palaeozoic when the Malkhan-Yablonovaya arc and the Selenga-Vitim volcano-plutonic belt respectively were formed (Gusev and Khain, 1995; Larin et al., 2011). Magmatic complexes in this zone are represented by both Palaeoproterozoic gabbro-diorite-granodiorite bodies, and by Late Permian to Early Triassic volcanic and pyroclastic rocks, and coeval calc-alkaline and alkaline massifs. These are overlain by a 1500 to 2000 m thick Jurassic to Cretaceous stratified sedimentary-volcanogenic sequences deposited in localised basins and depressions of up to 120 x 60 km (Vasil'ev et al., 1976). These sequences comprise repeated cycles of continental molassic conglomerate, gritstone, sandstons and siltstone, overlapped by lower lavas and tuffs of andesite-dacite and upper rhyolite layers. These volcanic rocks are approximately coeval with the Great Xing'an Range Large Igneous Province immediately to the south in China. Coeval subvolcanic stocks and dykes are composed of diorite porphyrite, micro-syenite-porphyry, feldspar porphyrie, syenite-granite porphyry and quartz porphyry. Late-orogenic I-type Jurassic to Cretaceous granitoids massifs are widespread, with to two phases represented by i). quartz monzodiorites and granosyenite and ii). subalkaline granodiorite and granite. These are, in turn, cut by dykes of granite-porphyries, granosyenite porphyries and spessartites (after Vakh et al., 2016).

The Berezitovoe deposit lies within the eastern section of the Selenga–Stanovoi Terrane, in the upper reaches of the Ol'doi River. Nearby basement rocks belong to the Mogocha Group, composed of granulite facies reworked Archaean rocks dated at 1873 ±8 Ma (Gavrikova et al., 1991) and 2400 ±13 Ma (Ahang et al., 2017), intruded by 1866 ±6 Ma gabbro and gabbro–anorthosites (Buchko et al., 2006, 2008), as well as relatively small enclaves of Proterozoic stratified rocks (Vakh et al., 2016). The deposit is hosted within Palaeozoic 379 ±1.1 Ma (U-Pb zircon; Vakh et al., 2011, 2013) gneissose biotite-feldspar granitoids of the Pikansky Complex, intruded by Early Cretaceous porphyritic granites of the 137 ±0.67 Ma (U-Pb zircon; Vakh et al., 2013) Haikta Pluton and late Cretaceous dykes of porphyrite, porphyry and lamprophyre which all intrude the older basement suites (Sorokin et al., 2014). Vakh et al. (2016) show three main facies of the Pikansky Complex, an eastern porphyritic granodiorite and granite, a western granite porphyry and smaller masses of quartz diorite that intrudes the former. Mineralised zones traverse the first two of these. The Haikta Pluton is composed of two phases, leucocratic and porphyritic granites (Vakh et al., 2016).

The main deposit is almost exclusively hosted within the Mid Palaeozoic granitoid of the Pikansky Complex and comprises a NNW-SSE elongated, ~950 m long, intensely metasomatised zone with a thickness that varies from 10 to 15 m on the southern and northern extremities, to as much as 110 m in the centre. This mineralised alteration represents the ore zone, and lies within a large fault complex that is well-defined in magnetic and gravity data. It is bound in the south by a 7.5 km long gold-scheelite-skarn vein system that traverses both the granite porphyry and the porphyritic granodiorite and granite facies. At ~100 to 200 m below the present surface, the steeply 70 to 75°W dipping altered ore zone of the main deposit splits into two separate, downward tapering 'roots' that pinch out at a depth of 700 to 800 m below the surface. Whilst Vakh et al. (2016) describe the main deposit as a fault controlled zone of metasomatic alteration and mineralisation, Newell et al. of Wardell Armstrong (2012) in a Competent Person's Report for the then titl, Nord Gold, describe the deposit as a "north-northwest trending and steeply southwest dipping zone of brecciated and hydrothermally altered granodiorite. In addition, gold mineralisation is associated with metasomatic alteration and quartz flooding in granitic and granodioritic rocks". The same authors also describe "The overall outline of the mineralised zone is due to the juxtaposition of two inverted cone shaped structures (breccia pipes), which have provided channel ways to the hydrothermal alteration and the associated gold-polymetallic mineralisation".

Alteration and Mineralisation

The ore zone of the main deposit is dominantly composed of light-grey and greenish-grey massive, sometimes fissile, muscovite-quartz metasomatic assemblages, in which garnet and up to 6% tourmaline occur as irregularly dispersed porphyroblastic impregnations. Orthoclase, chlorite, biotite, plagioclase and zinc spinel occur, but are relatively rare in this zone, accompanied by minor epidote, prehnite, apatite, fluorite and graphite. These minerals combine to form the following assemblages that make up the main orebody: i) tourmaline-garnet-orthoclase-muscovite-quartz to the south; ii) tourmaline-garnet-muscovite-quartz in the centre; and iii) tourmaline-garnet-quartz-muscovite in the north. The boundaries between these three facies is basically normal to the trend of the ore zone. The main body of the deposit is bound by a relatively thin skin ranging from 2 to 5 m, and rarely up to 10 m, composed of garnet-biotite-orthoclase-anorthite-muscovite and/or garnet-muscovite-biotite-quartz-anorthite. Within the main metasomatic altered ore zone, and sometimes extending into the enclosing rocks, there are unaltered dykes of garnet-bearing metaporphyrite, as well as postore dykes of spessartites and diorite porphyrite. The main metasomatised zone contains accumulations of 10 to 12 vol.% sulphides occurring as disseminations aggregates, thin veins, and streaks. Thin veinlets of fluorite and carbonates also occur locally (Vakh et al., 2016).

The principal ore minerals of the deposit are galena, sphalerite, pyrite and pyrrhotite, with accessory magnetite, chalcopyrite, arsenopyrite, marcasite, ilmenite and native gold. Rare stannite, scheelite, tennantite, molybdenite, hematite, chalcocite, native bismuth, bismuth meneghinite, antimony bursaite-cosalite, jordanite, boulangerite and jamesonite also occur. Patronite, scheelite, argentite, bismuthite, native copper, altaite, calaverite, cinnabar and cassiterite have also been reported. Secondary minerals, which occur within a 5 to 7 m thick zone of oxidation, include jarosite, limonite, hydrogoethite, malachite, covellite, chalcanthite, anglesite, cerussite and smithsonite (Vakh et al., 2016).

Gold mineralisation is irregularly distributed, predominantly concentrated in the central and northern assemblages of the ore-metasomatic zone as described above with Au/Ag ratios that are lower on the northern end, where pyrite-pyrrhotite-sphalerite ores mainly contain 0.1 to 2 g/t Au, 16 to 20 g/t Ag. In contrast that ratio is highest in the centre of the ore zone, where peak concentrations are ~2 to 4 g/t Au in pyrite-galena-sphalerite ores. Much lower concentrations of gold (0.2 to 0.6 g/t Au) are found in pyrite ores of the southern part of the overall alteration zone (Vakh et al., 2016).

Two temporally separated gold-bearing mineral associations have been differentiated in the Berezitovoe deposit, separated by the intrusion of porphyry dykes which lack galena-sphalerite mineralisation, but are crosscut by gold-bearing quartz veinlets (after Vakh et al., 2016):
• An early polymetallic massive type with accompanying Au and Ag. This ore is characterised by an irregular distribution of segregations, veinlets and disseminations of sulphide minerals within the metasomatic altered zone with common replacement textures. The sulphide segregations do not exceed 20 to 30 cm in diameter, whilst the veinlets are <3 to 5 cm. The earliest minerals are coarse-grained granoblastic aggregates of sphalerite and galena. Pyrrhotite is often developed over these as irregular segregations or as microveinlets of pyrrhotite aggregates that crosscut sphalerite. Pyrite also occurs with the galena, sphalerite and pyrrhotite, both as colloform and as two crystalline varieties designated at pyrite I and pyrite II. Pyrite I is marked by the absence of a pronounced crystalline form, and is often replaced by pyrrhotite or colloform aggregates of pyrite and marcasite. Pyrite II predominantly occurs as from 0.2 to 2, up to 4 mm impregnated crystals or as intergrowths. It also occurs as segregations within pyrrhotite and sphalerite or as isolated idiomorphic crystals containing inclusions of the enclosing sulphides.
  Sphalerite and pyrrhotite are ubiquitously replaced by very small (<1 mm), rounded, isometric grains of magnetite. Pyrite II is mostly replaced by magnetite. The last major mineral introduce is chalcopyrite. The paragenetic history, comprises Pyrite I + sphalerite + galena → pyrrhotite → pyrite II + arsenopyrite + magnetite + ilmenite → chalcopyrite, producing two distinct assemblages, namely i). early pyrite I-galena-sphalerite and ii). late pyrrhotite-pyrite II-magnetite-chalcopyrite.
  There is a dependence between gold concentration and sulphide content, with a distinct correlation between Au and Pb + Zn in the richest zones of gold-pyrite-galena-sphalerite ores at the central part of the deposit, although native gold does not occur within either sphalerite of galena. The sulphide segregations and veinlets are generally always richer in gold than the enclosing metasomatic rocks with disseminated sulphide mineralisation. However, the maximum native gold segregations occur in aggregates of pyrite II, and more rarely in pyrrhotite and chalcopyrite. Native gold occurs in sulphides as isolated rounded 0.1 to 0.2 mm droplets. Similar but finer aggregates of native gold are also found in magnetite.
• Late superimposed Gold-ore complex with 'streaky' gold - occurring as quartz veinlets and thin veins that crosscut the gold-polymetallic mineralisation, but are restricted to dislocations in the central and northern sections of the deposit and in the surrounding porphyritic granodiorites. This style comprises three mineral associations with high gold contents:
 - Gold-sulphide, occurring in the main ore-metasomatic zone of the deposit, in porphyrite dykes, as well as in the surrounding granitoids. It is represented by thin, discontinuous, streak-like, sulphide veinlets that rarely exceed 2 to 10 mm in thickness, found within shears or detachment fractures. These streak-like veinlets are usually accompanied by adjacent disseminated mineralisation. Galena is the main ore mineral, amounting to 70 to 90% of the veinlet. Lesser pyrite and chalcopyrite are present, together with pyrrhotite, magnetite, ilmenite, arsenopyrite, lead sulphosalts and native gold. In the northern part of the ore zone, lens-like and streak-like segregations of fine-grained galena crosscut the nest-like separations of first stage massive pyrrhotite-sphalerite ores. Native gold in this association generally occurs as 1 to 2 mm segregations in galena. Large streaky aggregates are also found in microfractures cutting arsenopyrite, pyrite and pyrrhotite.
 - Gold-quartz-sulphide, occurs as streaks and veins of light-grey, locally drusoid quartz with irregularly distributed disseminated sulphide mineralisation and wall rock fragments, together with isolated coarsely imbricated aggregates of biotite and black tourmaline. These veins have distinct wall rock contacts, although in the surrounding granitoids, they have 1 to 3 m thick quartz-muscovite selvages. The principal ore minerals are pyrite and galena, with quartz veinlets sometimes containing far more galena as large, almost monominerallic aggregates or small poikilitic inclusions in other minerals such as quartz. Pyrite is predominantly ~2 mm fine crystals. Secondary minerals are arsenopyrite and chalcopyrite. Arsenopyrite forms small irregular grains between quartz grains, sometimes as close intergrowths with pyrite. Tennantite and jordanite are also present, as are 0.2 to 0.6 mm molybdenite flakes. Native gold predominantly occurs as microscopic fine (0.002, up to 1 to 2 mm) grains, typically in quartz, and more rarely in pyrite, galena and arsenopyrite. Intergrowths of native gold with jordanite are also noted. Inter-relations between gold and sulphide minerals suggest their coeval formation.
 - Gold-quartz-garnet-sulphide, which is only found within the mineralised metasomatic zone, occurring as veinlets no thicker than a few centimetres. The central part of these veinlets is composed of massive or banded sulphides, whilst the margins comprise quartz-garnet aggregates with disseminated sulphides. In some instances, thin veinlets comprise 60 to 70% quartz-garnet with dispersed sulphide mineralisation. Garnet grains are corroded by quartz and carry abundant inclusions of galena, sphalerite, pyrite, marcasite, magnetite, arsenopyrite, ilmenite, lead sulphosalts, stannite and native gold. As such, they are essentially different to the garnets of the ore-bearing metasomatites. Native gold is mostly concentrated in the quartz-garnet margins of these veins occurring as 3 to 5 mm rounded-isometric, foliated and thread-like to crystalline grains. Their color varies from light-yellow to almost white and brown-yellow. Gold fills the interstices between the garnet aggregates, but also occurs as micro-inclusions in the garnet grains, and as close intergrowths or micro-inclusions with or within sulphide minerals.

Reserves and Resources

The deposit is reported to contain >40 t of Au, 190 t of Ag, 0.13 Mt of zinc, and 0.080 Mt of Pb (Vakh et al., 2016) at unspecified grades.
Assuming an average grade of 1.5 g/t Au, as for Resources below, the above figures would infer a mineral resource of very approximately:
  26.7 Mt @ 1.5 g/t Au, 7 g/t Ag, 0.5% Zn, 0.3% Pb.

Remaining JORC compliant resources and reserves at 1 January 2012 were (Newell et al., 2012, Competent Person's Report to Nord Gold):
    Measured Mineral Resource, 0.3 g/t Au cutoff - 10.275 Mt @ 1.66 g/t Au for 17.046 t of gold;
    Indicated Mineral Resource, 0.3 g/t Au cutoff - 12.410 Mt @ 1.38 g/t Au for 17.066 t of gold;
  Measured + Indicated Mineral Resource, 0.3 g/t Au cutoff - 22.685 Mt @ 1.50 g/t Au for 34.112 t of gold;
    Inferred Mineral Resource, 0.3 g/t Au cutoff - 7.362 Mt @ 1.11 g/t Au for 8.15 t of gold,
  Proved + Probable Ore Reserves, 0.5 g/t Au cutoff - 18.351 Mt @ 1.63 g/t Au for 29.966 t of gold.
NOTE: Mineral Resources are inclusive of Ore Reserves.
Between 2007 and 2016, >15 t of Au had been mined, with 1.8 Mt of ore being mined in 2011 (Vakh et al., 2016).

The most recent source geological information used to prepare this summary was dated: 2016.    
This description is a summary from published sources, the chief of which are listed below.
© Copyright Porter GeoConsultancy Pty Ltd.   Unauthorised copying, reproduction, storage or dissemination prohibited.

  References & Additional Information
   Selected References:
Avchenko, O.V., Vakh, A.S., Chudnenko, K.V. and Khudolozhkin, V.O.,   2014 - Genesis of garnet-bearing rocks at the Berezitovoe deposit, Upper Amur Region, Russia: in    Geology of Ore Deposits (Pleiades Publishing)   v.56, pp. 15-34.
Melnikov, A.V., Sorokin, A.A., Ponomarchuk, V.A., Travin, A.V. and Sorokin, A.P.,  2009 - The Berezitovoe gold-polymetallic deposit (East Siberia): mineralogy, age, and relation with magmatism: in    Russian Geology and Geophysics,   v.50, pp. 188-194.
Sorokin, A.A., Ponomarchuk, V.A., Travin A.V., Rogulina, L.I. and Ponomarchuk, A.V.,  2014 - Correlation between the ore formation processes in the Berezitovoe gold-complex-metal deposit (western part of the Selenga-Stanovoy superterrane) and the regional tectonomagmatic events: in    Russian Geology and Geophysics,   v.55, pp. 335-348.
Vakh, A.S., Khomich, V.G., Boriskina, N.G. and Santosh, M.,  2016 - The Berezitovoe gold-polymetallic deposit (Upper Amur region, Russia): Structure, mineralogy and genetic aspects: in    Geoscience Frontiers   v.7, pp. 483-494.
Zhang, G., Yang, Y., Vakh, A.S., Khomich, V.G., Wang, K., Ye, S. and Han, S.,  2017 - Chronology and Geochemistry of the Berezitovoe Polymetallic Gold Deposit in Eastern Siberia, Russia and its Geological Significance: in    Acta Geologica Sinica   v.91, pp. 1733-1750.

Porter GeoConsultancy Pty Ltd (PorterGeo) provides access to this database at no charge.   It is largely based on scientific papers and reports in the public domain, and was current when the sources consulted were published.   While PorterGeo endeavour to ensure the information was accurate at the time of compilation and subsequent updating, PorterGeo, its employees and servants:   i). do not warrant, or make any representation regarding the use, or results of the use of the information contained herein as to its correctness, accuracy, currency, or otherwise; and   ii). expressly disclaim all liability or responsibility to any person using the information or conclusions contained herein.

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