Sora, Sorsk

Siberia, Russia

Main commodities: Mo Cu
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The Sora, Sorskoe or Sorsk porphyry molybdenum-copper deposit is located approximately 350 km SSW of Krasnoyarsk in central Siberia in eastern Russia and occurs within the northeastern segment of the Caledonian Uibat Pluton. This pluton is comprises three magmatic series: i). Kogtakh (490 to 480 Ma), ii). Martaiga (466 to 452 Ma) and iii). Tygertysh (433 to 422 Ma) all of which are represented by monzodiorite-granosyenite-leucogranite associations.

The Uibat pluton intrudes late Proterozoic to Cambrian carbonates, which pass upwards into volcanics. The pluton lies within and along a north-easterly trending anticlinorium developed within the enclosing succession. Within the vicinity of Sora the country rock includes diorite, syenodiorite, syenite, granite, aplite, pegmatite and dolerite. Granite predominates to the south-east, overlain by diorite in the upper, or roof sections of the pluton. This roof phase forms the principal outcrop to the north-west of the deposit

The Uibat pluton hosts irregular, mineraslised, sub-alkaline, leucocratic porphyries, the Sora Porphyry Series which consist of monzodiorite, diorite, granosyenite and sub-alkaline granite porphyries and associated breccias. Granite porphyries are dominant. 40Ar/39Ar dating has shown the age of the porphyries to be 405 to 388 Ma. The porphyries and breccias are apparently largely extrusive, overlying the pluton roof. However, they are also observed to grade into a series of steeply dipping, sub-volcanic dykes cutting both the granite and diorite. The porphyries are composed of albite (41 to 54%); K-feldspar (sanidine-orthoclase, 30 to 37%); and quartz (9 to 18%), but contain minor biotite locally. Phenocrysts are K-feldspar, plagioclase and minor quartz. These porphyries both predate and cut the mineralisation.

The locus of mineralisation at Sora is the intersection of an east-west and a NNW trending fault trends, where jointing and fracturing is most intense. This intersection is just to the north-east of the main body of sub-volcanic, sub-alkaline porphyry. The contours of Cu and Mo geochemical levels are broadly coincident, centred on the same intersection. The internal structure of the stockwork is complex, with zones of mineralised and barren rock alternating. The granite of the batholith is the principal host to ore. The more mafic intrusives, the diorite and syeno-diorite are generally poorly mineralised, while the sub-alkaline porphyries and post-ore dykes are barren. This is interpreted to having largely been due to variations in the mechanical properties of the individual lithologies. Granite is the most brittle and hence was preferentially fractured and mineralised (Smirnov, 1977).

Several ore-forming stages have been recognised in the porphyry stock.

An early stage of mineralisation, characterised by disseminated chalcopyrite and molybdenite, is related to quartz-biotite-K feldspar and intense K feldspar alteration, principally within the granites, with associated quartz-feldspar veins that contain disseminations and irregular 'lumpy' aggregates of pyrite, chalcopyrite, sphalerite and magnetite, with minor molybdenite. Veins vary from a few cm's in thickness, up to 1 to 1.5 m. The earliest of the sub-alkaline porphyries cut this alteration stage.

The dominant and most economically significant Mo mineralisation consists of disseminated, stockwork and breccia ores. It followed the emplacement of the sub-alkaline porphyries, occurring as quartz-molybdenum veins and veinlets, breccia ores and segregations/ disseminations. The veinlets and veins vary from <1 cm, up to 50 to 100 cm in thickness, distributed the same as the earlier Cu veining, but with a predominance of NW strikes. The main minerals in the veins and segregations are molybdenite, pyrite, bornite, and chalcopyrite. Molybdenite forms large segregations while the other minerals are finer. Stockwork ores contain 0.04 to 0.10% Mo and 0.02 to 0.20% Cu.

Two breccia bodies are outlined, one a planar, NNW trending and steeply dipping zone, the other pipe like. The breccia ore consists of intensely K feldspathised and albitised angular fragments of diorite, granite, diorite porphyry, sub-alkaline porphyry and aggregates of microcline-perthite, cemented by a quartz-fluorite matrix containing molybdenite, pyrite and chalcopyrite. The breccia ores contain from 0.1 to 0.5% Mo and 0.02 to 0.3% Cu. Quartz-fluorite-galena-sphalerite veinlets, hosted by sericitised and pyritized rocks, are the final products of the ore-bearing paragenesis.

The final stages of mineralisation involved weak quartz, pyrite, sphalerite, galena, chalcopyrite, fahlore and bismuth, rare uraninite and trace gold and silver.

The deposit has been worked for several decades. Production in 1992 was 9.35 Mt @ 0.06% Cu, 0.051% Mo.

Remaining reserves in 2008 (Seltmann et al., 2009) were:
    233 Mt @ 0.058% Mo, 0.055% Cu, 2.3 g/t Ag containing 135 000 t of Mo,

The most recent source geological information used to prepare this summary was dated: 1996.    
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:
Berzina, A.N., Berzina, A.P. and Gimon, V.O.,  2016 - Paleozoic-Mesozoic Porphyry Cu(Mo) and Mo(Cu) Deposits within the Southern Margin of the Siberian Craton: Geochemistry, Geochronology, and Petrogenesis (a Review): in    Minerals   v.6,  doi:10.3390/min6040125
Berzina, A.N., Sotnikov, V.I., Economou-Eliopoulos, M. and Eliopoulos, D.G.,  2005 - Distribution of rhenium in molybdenite from porphyry Cu-Mo and Mo-Cu deposits of Russia (Siberia) and Mongolia : in    Ore Geology Reviews   v.26 pp. 91-113.
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.

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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