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Brandberg West |
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Namibia |
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Sn W
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Super Porphyry Cu and Au
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IOCG Deposits - 70 papers
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All papers now Open Access.
Available as Full Text for direct download or on request. |
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The Brandberg West tin-tungsten mine is located in the Omaruru district, approximately 230 km north of Walvis Bay and 370 km NW of Windhoek in north-western Namibia (#Location: 21° 14'S, 14°. 37'E).
The ore deposit lies within a sequence of poly-deformed turbidite and carbonate rocks of the Neoproterozoic Damara Supergroup, specifically the Khomas Series of the Swakop Group. The host rocks embracing the orebody are well bedded alternating quartzites and biotite schists (after shales) with lesser dolomite and marble interbeds. The quartzites are present as more resistant beds from a few cms to a few tens of metres thick. In detail, both the quartzites and schists are generally finely laminated with individual laminae from l to 10 mm thick, although, some less well laminated beds are also present.
Within the mine area, the local sequence is exposed in the core of a tight anticline and two adjacent synclines. The core of the north-south trending anticline is occupied by a hard dark quartzite which lenses out to the north into a red muddy schistose shale. A biotitic schist occurs immediately above the quartzite, developed from a schistose, sandy to silty shale. It is laminated with 0.5 to l mm laminae of biotite or chlorite alternating with silty quartzose bands up to 1 to 2 mm thick with interspersed biotite. The schist is some 200 m thick and is overlain in turn by a 30 m thick, lensoid marble unit followed by more interbedded biotite schist and quartzite. The sequence is cut by three Karoo age dolerite dykes in the open pit.
Ore grade mineralisation occurs as Damaran age hydrothermal quartz veins carrying Sn-W mineralisation. The veins are composed of poorly crystalline, coarse grey and white quartz aggregates forming planar, but irregular, veins from a few cms to a maximum of 4.5 m in thickness. These veins make up 15% of the total rock volume in the pit. They are almost exclusively restricted to the biotite schist, only penetrating the quartzite and marble by a few cms. They are not developed in the schists above the marble unit, although mineralised veins are present in the same unit in the adjacent synclines, the density of veining is markedly lower as is the resultant bulk grade. The main ore zone is made up of a series of east-west striking and vertically dipping veins which range from a few metres up to 50 to 80 m in lateral extent, and are localised in zones of up to several hundred metres in diameter on the limbs of the anticline, enclosing smaller higher grade shoots.
The orientation of the veins varies through the mine area and have 2 to 3 cm wide muscovite selveges. The country rock between the veins has been noticeably bleached. The principal ore minerals are cassiterite and wolframite which are present as crystals and aggregates from l to 30 mm across, often averaging around l0 mm.
Isotope and fluid inclusion studies suggest the ore fluids were of magmatic origin, possibly related to a shallow granite pluton. It is considered likely that mineralisation was caused by a combination of an impermeable marble barrier and interaction of the fluids with the marble.
Head grades when the deposit was being mined averaged approximately 0.12% Sn, 0.08% WO3 with around 0.4 Mt of ore being mined per year.
Total production of tungsten between 1933 and 1980 amounted to approximately 5510 tonnes of W, with a remaining resource in 1985 of 2.4 Mt of ore at a grade of 0.2% WO3 equivalent. Open pit mining commenced in 1946, with production peaking in 1978, with 1249 tonnes of Sn and W concentrate, before closing in1980. The total output from the mine amounted to 12 000 tonnes of tin and tungsten concentrate.
The most recent source geological information used to prepare this decription was dated: 2006.
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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Macey P and Harric C, 2006 - Stable isotope and fluid inclusion evidence for the origin of the Brandberg West area Sn–W vein deposits, NW Namibia : in Mineralium Deposita v41 pp 671-690
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