Siberia, Russia

Main commodities: Mo W
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The low grade Bugdain'sk porphyry Mo-W deposit lies within the Aldan Shield of the Siberian Craton in the Russian Federation 750 km east of Irkutsk.

It lies within a large mass of upper Palaeozoic granite, overlain by lower to middle Jurassic marine sediments and upper Jurassic volcanics, and intruded by plutons of upper Jurassic biotite-hornblende granites. The Jurassic plutons have outer rims which include granodiorite, quartz diorite, diorite and syenodiorite and small bodies of leucocratic granite, dykes of aplite and aplite pegmatites (Smirnov, 1977).

Mineralisation occurs as a stockwork in the upper exo-contact zone of the Jurassic granites, hosted mainly by the Palaeozoic biotite-granite. A small, elongate, downward expanding, vertically dipping stock of granite porphyry occurs in the centre of the stockwork zone. The mineralised stockwork is confined to locations where zones of increased jointing (fracturing?) in a north-south, north-east and north-west direction intersect. The north-south direction is most pronounced, being followed by dykes, veins, veinlets and some brecciation (Smirnov, 1977).

The stockwork has an annular outcrop, elongated in a northerly direction, and tending to dip inwards towards the core. The annular stockwork of molybdenum mineralisation surrounds an un-, or poorly-mineralised zone of silicification developed within both the Palaeozoic biotite granite and the stock of upper Jurassic granite porphyry at the core of the annulus. A relatively narrow zone of quartz-magnetite veining occurs at the outer margin of the silicified core, surrounded by the outer zone of sericitisation which accompanies the molybdenum mineralisation (Smirnov, 1977).

The veinlets of the stockwork vary from a fraction of a mm to 50 mm, rarely reaching 100 to 200 mm. Silicification and barren quartz veining preceded the molybdenite introduction. Mineralisation is present as a number of pulses of quartz-molybdenite. Molybdoscheelite is present in traces in the early veins, and chalcopyrite in the later stages. Molybdenite mineralisation was post dated first by a quartz-pyrite-fluorite vein suite, with minor chalcopyrite and then by the formation of a mineral association which included galena, sphalerite, pyrite, chalcopyrite and arsenopyrite. The gangue vein minerals are quartz, sericite, siderite, calcite, rhodochrosite and dolomite. The sulphide:gangue ratio decreases with depth (Smirnov, 1977).

The most recent source geological information used to prepare this summary was dated: 1997.    
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

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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