Mount Bischoff Mine, Waratah, Waratah district, Waratah-Wynyard municipality, Tasmania, Australiai

Regional Level Types
Mount Bischoff Mine	Mine
Waratah	Town
Waratah district	District
Waratah-Wynyard municipality	Municipality
Tasmania	State
Australia	Country

A famous old tin mine near Waratah, NW Tasmania. It was this mineral discovery the really helped opened up the west coast of Tasmania to exploration and development.

The Mt Bischoff mine was discovered by farmer and part-time prospector James “Philosopher” Smith in 1871, and for many years was one of the world’s richest tin mines (Groves et al., 1972). After 70 years of continuous production, the Mt Bischoff mine finally closed in 1947. Following mining ventures have mostly been small and spasmodic. Open-cut mining restarted in 2008, with a large open pit swallowing most of the old workings, except the western, Slaughteryard Face and Summit workings. Mining reserve estimates as at June 30, 2008 are 845,000t at 1.20% Sn. The ore was trucked some 50km to the mill at the Renison Bell tin mine. Mining finished in 2011 and the pit is now flooded, but exploration continues around the pit and deeper reserves are of great exploration interest.

Mt Bischoff was the first major mineral resource developed in Tasmania, with a total production of around 62,000t of metallic tin. The discovery provided the impetus for exploration of other areas of the west coast and the subsequent discovery of other mining areas such as Mt Lyell and Renison.

Geology
Precambrian quartzite, shale and dolostone at Mt Bischoff have been intruded by a radial group of Devonian quartz-feldspar porphyry dykes and breccia dykes, related to the nearby Meredith granite. Tin +/- base metal sulphide mineralisation accompanies these dykes, and occurs as a replacement of dolomite, as greisenised dykes, and as veins and fracture linings (Groves et al., 1972; Wright & Kwak, 1989, Halley & Walshe, 1995; Sorrell, 1997). Tin mineralisation occurs within a radius of about 1km from the summit of Mt Bischoff, and several silver-lead-antimony deposits also surround the mine. Supergene zones were minor.

Dolomite-Replacement Mineralisation
Dolomite-replacement mineralogy is dominated by sulphides (mostly pyrrhotite), Fe-Mg-Mn carbonates, fluorides (fluorite, sellaite), tourmalines and magnesium silicates (chondrodite, norbergite, clinohumite, phlogopite, talc and serpentine), in part as magnesian skarns and “wrigglite” (banded skarn), largely retrogressed. The highest tin grades were found within a quartz-pyrrhotite-topaz-fluorite assemblage (the most strongly altered dolomite replacement rocks) adjacent to the dykes, (now largely worked out). Dolomite-replacement mineralisation is found at the Greisen Face, where talc-pyrrhotite alteration occurs, and at the Slaughteryard Face, where quartz-pyrrhotite alteration and fluorite “nodules” occur.

Dyke Mineralisation
Greisenised dyke rocks are characterised by a white, fine-grained groundmass of quartz and topaz, with orthoclase phenocrysts variably pseudomorphed by siderite, pyrrhotite, quartz, topaz, pyrite, fluorite and cassiterite. One of the most prominent features of Mt Bischoff is the Western Dyke, a greisenised porphyry with cassiterite both disseminated and coating joint surfaces.

Veins and Fracture Linings
Fissure lodes are a late phase of mineralisation, cross-cutting both Devonian dykes and Precambrian country rocks. They contain variable proportions of quartz, siderite, tourmaline, topaz, fluorite, cassiterite, wolframite and sulphides (pyrite, pyrrhotite, galena, sphalerite, chalcopyrite, bismuthinite, As-Sb-Bi sulphosalts and stannite).

More than 100 mineral species have been recorded from Mt Bischoff, particularly because of the extensive alteration and large amounts of magnesium and fluorine in the system, producing both attractive and uncommon minerals such as sellaite, franckeite, chondrodite, norbergite, wagnerite and fluoborite.

Site is under an active mining lease and permission to enter is required from the Tenement Holders; there is no public access.

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References