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Ozernoe

Russia

Main commodities: Zn Pb Ag
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Ozernoe, is an important, large, low grade, pyritic, polymetallic Zn-Pb deposit located to the east of Lake Baykal in the Russian Federation. A resource of 126 Mt @ 6.6% Zn, 1.17% Pb, 35 g/t Ag has been quoted. It is hosted by a 5 to 6 km thick sequence of Cambrian volcano-sedimentary rocks and carbonates preserved in an outlier on the margin of the Aldan Shield. This sequence is overlain by middle Cambrian red-bed molasse and is cut by lower Palaeozoic and Mesozoic granitoids (Smirnov, 1977).

The mineralisation at Ozernoe is hosted by the lower Cambrian Oldynda Group which is around 1500 m thick. It is subdivided into a lower and upper sub-group. The lower is characterised by a predominance of tuffaceous rocks with subordinate carbonates; while the upper has significant carbonate sediments containing archaeocyathids and algae. The lower sub-unit has two members, the upper has only one. The lower section of each of the three members consists mainly of tuffs and lavas of andesitic to dacitic composition, while the upper portions comprise tuffs, bedded tuffs and carbonates. The amount of lava is insignificant, and is mainly of dacite flows up to several tens of metres in thickness. Tuffaceous-carbonates predominate within the sequence, with a varying ratio of tuffaceous andesite-dacite, dacite, carbonate and coarser terriginous to pelitic material. The entire sequence to a greater or lesser degree has been saturated with finely dispersed sulphides, mainly globular pyrite. The sulphide content increases locally to form the ore lenses (Smirnov, 1977).

Intrusives include sub-volcanic bodies which are comagmatic with the lower Cambrian volcanics and comprise auto-magmatic breccias of rhyodacite, dacite porphyry, dolerite and quartz-dolerite. Permo-Triassic quartz porphyries and granosyenite porphyries also cut the sequence, as do Triassic to Jurassic alkaline dolerites and trachy-dolerite (Smirnov, 1977).

Two productive horizons are recognised in the main ore bearing Ozernova Member. These together total between 140 and 230 m in thickness, and are composed of rhythmically stratified tuffs, tuffaceous sediments, calcareous breccias (often with a tuffaceous matrix), tuffaceous-calcareous conglomerates, limestones and pyritic orebodies. They are characterised by calcareous breccias, with fragments of red jasperoid and a framework of reefal limestone. Locally the carbonates of the productive horizons have been entirely sideritised (Smirnov, 1977).

The Ozernoe orebody is a multi-stage layered accumulation of massive and segregated pyritic-polymetallic ores with conformable banded structures and lesser superimposed veinlet overprinting. In the main ore sequence ten conformable layers of ore have been recognised. In sections of the deposit, complex siderite lenses which in places are interlacing, accompany and overprint the volcanics, carbonates, tuffaceous sediments and ore. The sulphide orebodies are confined to a limited number of stratigraphic levels and are layer like, arranged one above the other, separated by layers of sediments and volcaniclastics 5 to 30 m thick. They commonly separate underlying finely clastic rocks from overlying coarsely clastic beds. The lower boundaries of the sulphide bands are generally sharp, the upper often being more diffuse (Smirnov, 1977).

The bulk of the ores have a banded structure and a fine grained crypto-crystalline texture. The main sulphide minerals are pyrite, sphalerite and to a lesser degree, galena, while the principal gangue minerals forming a rhythmic alternation with the sulphides, are siderite, calcite, ankerite, dolomite and minor quartz. The superimposed veinlets are varied, including barite-sulphide-siderite and barite-sulphide ore. In all, the sulphides include sphalerite, pyrite, galena, native gold, native silver and its sulphosalts. Sporadic gypsum, pyrrhotite, rutile, arsenopyrite and muscovite are found in segregations within the orebody. Chalcopyrite and barite are only present in the vein mineralisation, not in the finely banded sulphides. All of the volcanogenic and pyroclastic rocks have been affected by sericitisation, K-feldspar alteration, hornfels development and to a lesser degree by hydro-biotitisation (Smirnov, 1977).

The most recent source geological information used to prepare this summary was dated: 1994.    
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.


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

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