Siberia - Chukotka, Russia

Main commodities: Au Cu
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The Peschanka porphyry style Cu-Au(-Mo) deposit is located on 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 Baimka ore district. Others include the Yuryakh, Nakhodka, Pryamoi and Omchak deposits. Other mineralisation in the area include the Kekura intrusion related gold deposit ~120 km to the NE and the Kupol high sulphidation epithermal gold-silver deposit ~240 km to the east. The district is confined to the marginal zone of the large, multiple intrusive, Late Jurassic to Early Cretaceous, Ekdykchich Pluton. This district is in turn, part of the Baym metallogenic zone which comprises a linear, 20 to 25 km wide structure, traceable for over 200 km, that hosts a number of porphyry deposits, and is located on the western margin of the Okhotsk-Chukotka volcano-plutonic belt, where this belt is superimposed on the Omolon microcontinent.

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.

The most recent source geological information used to prepare this summary was dated: 1999.    
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:
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.
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.
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.
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

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 takes no responsibility what-so-ever for inaccurate or out of date data, information or interpretations.

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