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Baimka Trend - Peschanka, Nakhodka, Pryamoy, Malysh, Vesenny III, Vesenny |
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Siberia - Chukotka, Russia |
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Au Cu
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Super Porphyry Cu and Au
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The Peschanka porphyry style Cu-Au(-Mo) deposit is located to the west of the root of the Chukotka Peninsula, some 150 km south of Bilibino in far north eastern Siberia of the Russian Federation and lies within the Circum-Pacific orogen (#Location: 66° 34' 8"N, 164° 27' 15"E).
Peschanka is the largest of a group of deposits which define the NW-SE trending Baimka Trend. Others include the Vesenny gold deposit and the Malysh, Nakhodka, Vesenny III and Pryamoy porphyry Cu deposits that together constitute the Nakhodka ore district, ~20 km to the SE of Peschanka.
Other mineralisation in the surrounding area include the Kekura intrusion related gold deposit ~120 km to the NE in the subparallel South Anyui suture zone, and the Kupol high sulphidation epithermal gold-silver deposit ~240 km to the east in the younger Okhotsk-Chukotka Cretaceous magmatic belt.
For an outline of the regional setting and context of the structural elements mentioned below, see the Kekura record. The 20 to 25 km wide and 200 km long Baimka Trend corresponds to the NW-SE trending 'Baimskaya Shear Zone', which was formed in two stages in the Late Jurassic to Early Cretaceous between 144 and 137 Ma and largely lies within the broader Oloy Zone tectonic collage. This collage is a Palaeozoic and Mesozoic active margin complex, bordered to the SW by the Omolon cratonic block and to the NE by the Mesozoic South Anyui suture zone. The first stage of the development of the regional Baimskaya Shear Zone comprised NW trending sinistral strike-slip and reverse faults. The second stage involved reactivation as a dextral shear zone in which meridional extensional faults, normal faults, strike-slip faults and extensional fractures were formed. The shear and extensional structures controlled the emplacement of Early Cretaceous intrusive bodies and multistage linear stockwork porphyry-copper mineralisation. At the end of the second stage, the porphyry copper deposits were partially eroded. North-south dextral and conjugated east-west sinistral strike-slip faults produced local extensional structures in which low-temperature epithermal gold-bearing quartz veins and linear stockworks were formed (Chitalin, 2021). To the SE, the 'Baimskaya Shear Zone' is truncated by the younger NE-SW trending Cretaceous Okhotsk-Chukotka magmatic belt, whilst to the NW it passes into Late Jurassic to Early Cretaceous clastic sediment basins and Early Cretaceous (Aptian) volcanic complexes (Chitalin, et al., 2022).
Peschanka
Mineralisation at Peschanka is confined to a north-south trending, eastward dipping, sheet-like stock of Late Jurassic quartz monzonite porphyry which splits into a series of dyke-like apophyses. Two other groups of dykes are found in the deposit area associated with the ore related intrusives, namely: i). thin, pre-mineralisation, bodies of fine-grained sub-alkaline and leucocratic granite and granosyenite, and ii). monzonite porphyry, ganodiorite porphyry and gabbro-diorite porphyry which cross-cut the mineralised porphyry stock.
The intruded country rock comprises plutonic rocks of the Ekdykchich Pluton which includes early gabbro, gabbro-diorite and diorite, and later monzodiorite, syenite-diorite, granodiorite and leucocratic porphyritic monzonite.
Mineralisation is present as disseminated and stockwork molybdenum-copper sulphides within the host quartz monzonite porphyry and extending for tens to several hundreds of metres into the surrounding country rock. Overall the mineralised body follows the shape of the host stock and the dyke like apophyses to form a layered like set of sheets which branch, swell and pinch-out.
The core of the deposit includes columnar breccia bodies with clasts of mineralised monzonite and quartz-monzonite porphyry cemented by barren quartz. These late breccias lie within the early K-silicate alteration zone which is characterised by secondary biotite and silicification. Weak K feldspar alteration is observed on the fringes of pre-ore quartz and quartz-sulphide veinlets, while K feldspar alteration is ubiquitous within the mineralised intrusive stock. Late phyllic alteration overprints the potassium silicate zone, manifested by chloritisation of biotite, sericitisation of plagioclase and albitisation of K feldspar. Alteration is most intense on the contact zone of the mineralised stock, while in the upper parts of the deposit kaolinitisation is observed. Propylitic alteration is mapped on the outer fringes of the system, represnted by actinolite-epidote and chlorite-epidote.
The following mineralisation assemblages have been identified, from early to late: i). quartz-(magnetite)-pyrite; ii). quartz-molybdenite; iii). quartz-pyrite-chalcopyrite; iv). quartz-chalcopyrite-bornite-tennantite; v). quartz-carbonate-sphalerite-galena-chalcopyrite-pyrite; vi). post-ore carbonate-anhydrite-zeolite.
The quartz-pyrite-chalcopyrite assemblage is the most widespread, although the highest grades are provided by the quartz-chalcopyrite-bornite-tennantite phase
The deposit is zoned from the core outwards from quartz-chalcopyrite-bornite-tennantite confined to the central phyllic altered zone, grading outwards to quartz-pyrite-chalcopyrite association an then to a marginal halo of pyrite in the propylitic periphery of the alteration system. A quartz-molybdenite association is found in the central part of the orebody, associated with quartz-sericite alteration, and increasing with depth. Linear carbonate-rich crush zones carry the quartz-carbonate-Pb-Zn suite.
The deposit has a thin supergene zone, generally no more than several tens of metres in thickness, comprising an upper zone with goethite, hematite and lepidocrocite, above an interval with azurite, malachite and chrysocolla, and covellite and chalcocite.
Resources reported are: 940 Mt @ 0.51% Cu, 0.42 g/t Au (Mutschler et al., 1999).
More recent estimates quote a resource of 1350 Mt @ 0.61% Cu, 0.015% Mo, 0.32 g/t Au and 3.7 g/t Ag accounting for total contained metal resources of 8.3 Mt of Cu, 200 000 t of Mo, 425 t of Au and 5000 t of Ag.
Nakhodka Ore Field
The Nakhodka ore field comprises the Vesenny gold deposit and the Malysh, Nakhodka, Vesenny III and Pryamoy porphyry Cu deposits. Both porphyry and epithermal mineralisation are hosted by Early Cretaceous diorite and monzonite intrusions, dated at 139 to 141 Ma (U-Pb zircon) and are structurally controlled.
Mineralisation is associated with a north-south elongated, 3.5 x 10 km Early Cretaceous quartz-diorite porphyry intruding a Upper Jurassic volcano-sedimentary sequence, The marginal rim of this main intrusion is intruded by a complex of dyke-like lenses and stocks of second phase quartz diorite porphyry and monzodiorite to quartz-monzonite porphyry. These younger intrusions form a horseshoe shaped zone in the outer margin of the lower two thirds of the main intrusion which is copper mineralised. The higher grade zones of this rim constitute the Malysh, Nakhodka, Vesenny III and Pryamoy porphyry Cu deposits. The Vesenny epithermal gold deposit is within the same zone of copper mineralisation, on the SW margin of the main intrusion.
The stress field of the Baimka shear zone produced extensional and strike-slip structures that control distinct zones of strong quartz-sericite alteration and sheeted high-grade quartz–sulphide veining, similar to the Peschanka porphyry Cu-Au deposit ~20 km to the NW. Hydrothermal alteration in the Nakhodka ore field includes potassic, propylitic, phyllic, and more rarely argillic assemblages. Two phases of porphyry-style mineralisation are distinguished: i). early-stage quartz-magnetite veining associated with potassic alteration and ii). sheeted quartz-sulphide bornite, chalcopyrite, molybdenite and pyrite veining that is spatially associated with a strong quartz-sericite phyllic alteration assemblage. Epithermal Au-Ag mineralisation, as at Vesenny, is intermediate-sulphidation type and consists of gold-bearing polymetallic quartz-dolomite  rhodochrosite veins and veinlets.
The JORC compliant Inferred Mineral Resources of the main deposits at a cut-off grade of 0.3% CuEquiv. (IMC Montan) are as follows after Chitalin et al. (2013):
Nakhodka and Pryamoy - 917.9 Mt @ 0.34% Cu, 0.0054% Mo, 0.30 g/t Au, 1.2 g/t Ag for 3.1 Mt of Cu, 50 kt of Mo, 278 t of Au, 1130 tonnes of Ag;
Vesenny veins - 4.38 Mt @ 3.4 g/t Au, 31.4 g/t Ag for 14.9 t of gold, 137.6 t of Ag.
Vesenny stockwork at a 1 g/t AuEquiv. cut-off - 65.74 Mt @ 1.48 g/t Au, 13.6 g/t Ag for 97.1 t of Au, 895.5 t of Ag.
The most recent source geological information used to prepare this decription was dated: 2022.
Record last updated: 20/1/2023
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.
Peschanka
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Selected References:
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Chitalin, A.F., Baksheev, I.A., Nikolaev, Y.N., Nagornaya, E.V., Khabibullina, Y.N., Nikolaeva, I.U., Kalko, I.A. and Muller, D., 2023 - Porphyry-epithermal Cu-Mo-Au-Ag mineralization in the Nakhodka ore field, Baimka Trend, Chukotka, Russia: a geological, mineralogical, and geochemical perspective: in Mineralium Deposita v.58, pp. 287-306.
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Marushchenko, L., Baksheev, I., Nagornaya, E., Chitalin, A., Nikolaev, Y., Kalko, I. and Prokofiev, V., 2015 - Quartz-sericite and argillic alterations at the Peschanka Cu-Mo-Au deposit, Chukchi Peninsula, Russia: in Geology of Ore Deposits v.57, pp. 213-225.
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Nikolaev, Y., Baksheev, I., Prokofiev, V., Nagornaya, E., Marushchenko, L., Sidorina, Y., Chitalin, A. and Kalko, I., 2016 - Gold-Silver mineralization in porphyry-epithermal systems of the Baimka trend, western Chukchi Peninsula, Russia: in Geology of Ore Deposits v.58, pp. 284-307.
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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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Zvezdov V S, Migachev I F and Girfanov M M 1993 - Porphyry copper deposits of the CIS and the models of their formation: in Ore Geology Reviews v7 pp 511-549
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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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