The Silbak Premier orebody lies within Early to Middle Jurassic age Hazleton Group calc-alkaline volcanic rocks in the Intermontane Tectonic Belt of British Columbia. These rocks are intruded by Jurassic and Tertiary granitic stocks and dykes.
On a property scale, the deposit occurs within fine-grained to aphanitic, moderately to well-foliated green andesite. The andesite overlies intensely folded and fractured argillite and siltstone and is in turn unconformably overlain by maroon and green andesite volcaniclastic rocks. This sequence of rocks is intruded by a series of sills and dykes composed of porphyritic dacite. The foliation in the andesite strikes southwest and dips moderately northwest. Four orientations of faults on the property are known.
The orebody occurs in two distinct breccia and vein stockwork zones known as the Main and the West zones which together comprise the Glory Hole deposit. The Main zone trends 230 degrees , dips about 60 degrees to the north near surface and flattens to a dip of about 30 degrees at depth. The proposed open pit area is 390 m long and consists of several sub-parallel zones with an aggregate thickness of 20 to 50 m. It is open to the northeast and to depth. The Main zone is truncated by the West zone, which trends 290 degrees and is steeply dipping. It is 225 m long and occurs as a single 5- to 10-m thick zone which is open to depth and is partially truncated by topography to the northwest.
In the Main and West zones, ore occurs in vein stockwork and breccia and has been interpreted as having been formed in three stages. The early stage breccia (which is crosscut by early-stage, 0.5- to 3-cm-thick tabular, banded veins of quartz and chlorite with pyritic margins) occurs within andesite peripheral to porphyritic dacite. Middle-stage stockwork veins form irregular networks of banded veinlets that vary in thickness from 0.5 to 4 cm. The matrix of the breccia is chalcedonic and contains patches of sulphide mineralization. The middle-stage stockwork veins and breccia contain the bulk of the ore and the highest silver and gold grades. Late-stage veins composed of coarse- grained quartz and chlorite are up to 200 cm thick. In general, base-metal- rich veins which contain 20% to 45% sulphide minerals are more prominent in the lower part of the orebody and in the West zone, whereas the precious-metal-rich veins which have less than 5% sulphide minerals tend to be more prevalent near surface and in the Main zone.
The main gold-bearing mineral is electrum which is associated with galena and silver-bearing minerals. Gold may also occur locally within pyrite. The main silver-bearing minerals include electrum, tetrahedrite, polybasite and less abundant pyrargyrite, argentite and ruby silver. Rare arsenopyrite occurs peripheral to the precious metal zones and small amounts of barite occur with the base and precious metals. The main sulphide minerals are pyrite and galena.
Alteration of the vein stockwork and breccia consists of abundant potassium-feldspar and sericite in the immediate wall rock which grades outwards into an assemblage of chlorite, epidote, calcite and apatite. Sericite and calcite are more abundant in the hangingwall veins. Chlorite is patchy but normally more prominent in footwall areas. Silicious breccia zones, around which the more intense alteration occurs, tend to host the most extensive precious-metal-bearing zones although gold and silver mineralization is not uniformly distributed within these bodies.
Production of 2,000 tonnes per day from the Premier gold project is to begin in early 1989. Initial production emphasizes higher-grade portions of the Silbak Premier pit and mining of two areas of the Big Missouri deposit. Pamela Phillips is a geologist and project co-ordinator for Greenstone Resources. She would like to thank A. W. Randall (project geologist at Westmin) and Dean McDonald of the University of Western Ontario’s Dept. of Geology for their assistance.
]]>
Be the first to comment on "Core Sack SILBAK PREMIER"