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Kondyor, Konder, Anomalnyi |
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Khabarovsk Kray, Russia |
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PGE PGM Pt Cu Pd Cr Au
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Super Porphyry Cu and Au
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The Kondyor (or Konder) placer and Anomal'nyi hard rock PGE-chromite deposits are developed within, over and downstream of the circular Kondyor mafic to ultramafic massif in the Ayan-Maya District, northern Khabarovsk Kray, far eastern Russia, ~1000 km north of Khabarovsk and ~250 km NW of the Sea of Okhotsk coast (#Location: 57° 35' 3"N, 134° 37' 49"E).
Kondyer is the largest of a number of similar complexes that are quite common in various Siberian terranes (Seltmann et al., 2010).
This Kondyor intrusive complex is located on the southeastern Aldan Shield, intruding Archaean to Palaeoproterozoic metamorphic and unconformably overlying Neoproterozoic platformal metasedimentary successions. It forms the core of a local dome in which the intrusion is surrounded by a ring of Archaean to Palaeoproterozoic rocks, that are, in turn, surrounded by the Neoproterozoic sequence. The latter dips at ~40° outward at the contact with the older metamorphics, to <10° 1 to 2 km from that contact.
The Kondyor massif comprises a well defined circular and regular concentrically zoned structure with a 6 km diameter core of dunite-(peridotite), which accounts for ~90% of the complex. The core is surrounded by an up to 500 m wide concentric ring zone in the periphery of the massif, containing metadunites, wehrlites, olivine clinopyroxenite, olivine-free clinopyroxenite, clinopyroxenite locally hosting apatite-magnetite-biotite veins, and melanocratic gabbro of normal alkalinity (Cabri and Laflamme, 1997; Nekrasov et al., 2005; Seltmann et al., 2010; Malitch et al., 2012; Barkov et al., 2017).
The outer ring and surrounding country rocks are intruded by a complex of dykes and irregular masses of Mesozoic alkaline rocks, accompanied by contact-related and metasomatic aureoles (Emelynenko et al., 1989). The Mesozoic alkaline rocks include diorite and nepheline syenite containing eudialite, lamprophyllite, lovozerite, murmanite and ramzaite which are essentially Ti and Zr bearing silicate minerals. These rocks locally contain abundant chrome-diopside (Seltmann et al., 2010).
The PGE mineralisation is generally hosted in dunite, where dense disseminations, schlieren and veinlets of ferrochromite are also present, and is represented by monominerallic grains or their aggregations, cementing chrome spinelides and olivine. Isoferro-platinum (Pt3Fe) is the major platinum mineral, often containing a significant admixture of Ir and Os and/or Ir- Os alloys. This mineralisation is distributed throughout the dunite, although the most significant is concentrated in the Anomal'nyi Cu-PGE deposit, as described below.
The Anomal'nyi Cu-PGE deposit occurs in the southwestern 'pie slice' segment of the circular dunite core, extending from the centre of the complex to near the southwestern outer margin of the dunite intrusion. The 'pie slice' is bounded to the north by the east-west radial 'cut' and to the south by the NE-SW 'cut'. This section of the dunite is intruded by subparallel vein-like bodies to dykes that range from centimetres to tens of metres in thickness. These bodies are composed of pegmatoid to coarse-, medium- and fine-grained apatite-biotite-magnetite clinopyroxenites and medium- to fine-grained magnetite clinopyroxenites which Barkov et al. (2017) identifies as kosvite. The ‘kosvite’ dykes are closely associated with a vein-like system of phlogopite-rich highly micaceous masses up to ∼20 m thick that contain Cu, Pd and Pt as grains of base metal sulphides, together with a variety of platinum group metals (PGM). Veins of alkaline pegmatite are also present. Locally, these veins and dykes have discordant relations to the host, although they generally conform to the observed pattern of sandwich-like interlayering of 'kosvite' with the phlogopite-rich orebodies and veins (Barkov et al., 2017).
The mineralised zones at Anomal'nyi are composed of variable amounts of diopside that is moderately magnesian and locally enriched in the aegirine end member (Wo40.9En33.3Fs15.7Ae10.1). Titaniferous magnetite and Sr-bearing fluorapatite are common accessories. The mineralised zones are generally substantially enriched in Cu, up to 4%, occurring as the chalcopyrite-bornite-secondary chalcocite association with fletcherite. Various species and varieties of PGM have been identified, including: isomertieite, Sb-rich arsenopalladinite, sobolevskite, kotulskite, Pb-enriched kotulskite, merenskyite, sperrylite, maslovite or moncheite, mertieite-I, mertieite-II, zvyagintsevite, palarstanide, paolovite, hollingworthite, and Pd-rich phases of arsenide-bismuthide-thallide compositions, and oxides of Pd, Bi, Te and Tl. Grains of PGM minerals typically occur as inclusions in base metal sulphides near their rim, located at grain boundaries of phlogopite with base metal sulphides, or intergrown with apatite hosted by phlogopite (Barkov et al., 2017). The same authors regard these textures as being consistent with deposition from a sulphide melt enriched in Cu, nearly simultaneously or after the associated PGM. However, no strong, invariable, positive correlation has been observed between Cu and the PGE (Pd+Pt). Barkov et al. (2017) regard this as consistent with their observation that many grains of PGM are enclosed entirely within hydrous silicates, commonly in phlogopite, or, occasionally, in titaniferous magnetite. Such grains probably precipitated as separate phases (cf. Kamenetsky et al., 2015) directly from microvolumes of a late-stage fluid rich in noble metals and metalloids at a postmagmatic-hydrothermal stage of crystallisation. This is also consistent with the observed compositionally diverse assemblage of ore minerals, which includes PGM, but also Au-bearing silver (Ag78.8Au16.8Cu4.3). In general, enrichment in Te, Bi and Pb is also characteristic. Thallium accompanies Bi in the form of constituents of the Tl-Bi rich PGM.
Barkov et al. (2017) suggest the following comagmatic series of rocks were developed sequentially in the core of the complex, in the following order:
• Chromite-bearing dunite (+peridotite) forming the core of the Kondyor massif. Crystallisation of the complex began with a high-forsterite [Mg-Fe] olivine fraction in the dunite core accompanied by disseminated and podiform magnesiochromite-chromite with associated weak PGE mineralisation.
• Coarse-grained 'kosvite' (clinopyroxenite rich in magnetite), which is very heterogeneous, and is interpreted to have formed from the strongly fractionated magma that was relatively rich in Fe, Cu, alkalis and volatiles, and was the residue after the crystallisation of >90% of the igneous complex to form the dunite-peridotite core. An inferred build-up of oxygen fugacity in the remaining volume of magma led to the deposition of abundant magnetite. Barkov et al. (2017) argue that the crystallisation of an evolved melt is indicated at Anomal'nyi by: i). the enriched ferrosilite [Mg-Fe] and [Na-Fe] aegirine composition of pyroxene, which is inconsistent with a closed-system crystallising with phlogopite; ii). depletion in Cr and Ni, which is generally characteristic of Anomal’nyi, with diopside that has a more magnesian composition having been crystallised earlier than the [Na-Fe] aegerine pyroxene; iii). the enrichment of Pd at Anomal'nyi in contrast to the Pt-Os-Ir-Ru rich character of the mineralised dunites of the core.
• Vein-like pegmatitic mafic rocks of the Anomal'nyi deposit, which are anomalously rich in phlogopite, apatite, Cu-rich base metal sulphides, and contain
the Pd-based species of PGM. The pegmatitic textures are interpreted to imply the presence of elevated levels of volatile components accumulated in the 'kosvite zone' during formation of the vein-type Pd-Pt deposit at Anomal'nyi. It is further suggested that a buildup of S and Cu, resulted in the deposition of droplets of Cu-enriched sulphide melt, most likely formed during crystallisation of the fractionated magma of the 'kosvite zone' late in the history of the core of the complex. Barkov et al. (2017) also infer this stage of the ore-forming system remained relatively open, allowing recrystallisation and metasomatic activity (e.g., pegmatitic alkaline veins) at late magmatic and sub-solidus stages in the 'kosvite zone'. The abundance of phlogopite at Anomal'nyi may well be a reflection of an influx into the local system of aqueous fluid that is genetically related to the ultramafic core of the complex.
• Alkali-enriched mafic pegmatite veins that were emplaced into the 'kosvite' dykes to form the sandwich-like structured system.
Cabri et al. (1998) dated biotite from crosscutting veins in dunite and in a dyke of 'kosvite' at 120 ±1 Ma (40Ar/39Ar).
Malitch et al. (2012) dated two main populations of zircons from the intrusive complex. The first were crystals of oval and rounded shapes, characterised by a bimodal distribution of 2477 ±18 and 1885 ±52 Ma (U-Pb SHRIMP-II). These were interpreted to possibly represent remnants from assimilated Archaean country rock metamorphosed during the Palaeoproterozoic. The second population was of idiomorphic crystals and aggregates of prismatic habit, forming two younger age clusters at 176 ±1.2 and 143 ±2.0 Ma).
Shcheka et al. (2004) reported data from G.K. Czamanske, given in Cabri et al. (1998) who determined a 187Os/188Os ratio of 0.1250 ±0.002 (n = 5), which yields a mantle model age of 330 ±30 Ma. The same authors dated biotite from cross-cutting dykes for an age of 120 ±1 Ma (40Ar/39Ar).
Pushkarev et al. (2002) dated biotite from ultramafic and gabbro units at 132 ±8 and 115 ±6 Ma, respectively (K-Ar), and discordant Rb-Sr ages of 123 ±2 and 93 ±47 Ma for pyroxenite and gabbro pegmatite, respectively.
Kondyor placer deposit - Extensive PGE and chromite placer deposit are concentrated in a network of alluvial channels over the intrusive complex, breaching the northern rim of the dome, and persisting for a further ~40 km downstream to the junction with the Reka Omnya river, with widths of 500 m to 2 km and thicknesses generally of from 1 to 1.5 m, locally up to 7 m (Malitch 1999).
The Amur Mining Company commenced exploitation of the placers in 1984. By 2004, ~40% of the total estimated resource of around 60 t of PGE had been mined (Shcheka et al., 2004) at an average grade of 1.6 g PGE/m3, decreasing
from 4 g/m3 over the intrusive body, to ~0.5 g/m3 at its downstream extremity (Yakubchuk and Edwards 2002). In 2003, production amounted to 5 t of PGE for the year (Shcheka et al., 2004).
The Kondyor placer mineralisation is characterised by the platinum-iron alloy (Pt3Fe) occurring as idiomorphic crystals of up to 1.5 cm in size, accompanied by minor Iridium-osmium alloy and gold. The largest PGM nugget found at Kondyor weighs 3.521 Kg. The Kondyor placer ores comprise 85% Pt, 1.7% Ir, 0.7% Os, 0.5% Pd, 0.4% Rh, 0.1% Ru, with other elements, including Au, amounting to 9% (Yakubchuk & Edwards 2002). The creeks draining the Anomal'nyi deposit are characterised by the idiomorphic Pt-Fe crystals mentioned above and by enrichment in gold, whilst creeks over the northwestern segment of the intrusive complex are also characterised by idiomorphic Pt-Fe alloy crystals (Shcheka et al., 2004). In general, the gold content in Kondyor heavy-mineral concentrates is ~1 wt.%, but heavy-mineral concentrates from creeks draining the southern Anomal'’nyi deposit carry 3 to 5 wt.% Au (Nekrasov et al., 1999; Shcheka et al., 2004).
The most recent source geological information used to prepare this decription was dated: 2017.
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.
Kondyor
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Selected References:
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Barkov, A.Y., Shvedov, G.I., Polonyankin, A.A. and Martin, R.F., 2017 - New and unusual Pd-Tl-bearing mineralization in the Anomalnyi deposit, Kondyor concentrically zoned complex, northern Khabarovskiy kray, Russia: in Mineralogical Magazine v.81, pp. 679-688.
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Malitch, K.N., Efimov, A.A. and Badanina, I.Yu., 2012 - The Age of Kondyor Massif Dunites (Aldan Province, Russia): First U-Pb Isotopic Data: in Doklady Earth Sciences v.446, Part 1, pp. 1054-1058.
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Seltmann, R., Soloviev, R., Shatov, V., Pirajno, F., Naumov, E. and Cherkasov, S., 2010 - Metallogeny of Siberia: tectonic, geologic and metallogenic settings of selected significant deposits: in Australian J. of Earth Sciences v.57, pp. 655-706.
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Shcheka, G.G., Lehmann, B., Gierth, E., Gomann, K. and Wallianos, A., 2004 - Macrocrystals of Pt-Fe alloy from the Kondyor PGE placer deposit, Khabarovskiy Kray, Russia: trace-element content,mineral inclusions and reaction assemblages: in The Canadian Mineralogist v.42, pp. 601-617.
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