Tungsten

Tungsten mineralisation at Torrington is hosted predominantly within silexite bodies of Permian-Triassic age (230 to 270Ma). The silexite consists of quartz (average ~80%) and topaz (average ~18%) that formed as late stage intrusives related to the surrounding Mole Granite.

The metal mineralisation associated with the Mole Granite includes polymetallic tungsten, tin, gold, silver and base metals, while gem-quality minerals including emerald, beryl and topaz are also present. The metallic mineralisation shows distinct zonation, from a tin rich core, through a tungsten rich and gold zone near the granite margins, to a base metal zone in the surrounding country rock. This zonation often represents a chemical continuum; from tin and tungsten out to base metal rich zones with all the end members represented. This zoning is probably due to the polyphase nature of the Mole Granite with five mineralising events recognized.

Within the Project area, tungsten mineralisation occurs dominantly as the mineral ferberite (FeWO4) and is present either as large euhedral crystals (up to 5cm long) in bungs within quartz or silexite bodies, or as disseminated fine to coarse grained euhedral-anhedral crystals throughout quartz and silexite veins and bodies. Many large multi-tonne wolframite bodies have been recovered from these deposits, with the largest single mass of ferberite recorded being 12.5 tonnes.

The Company will be focusing of the widely occurring finely disseminated style of tungsten mineralisation in the silexite that lends itself to bulk open pit mining (Figure 1). It will be difficult to quantify the coarse-grained and vein-type mineralisation (that often also contains appreciable amounts of bismuth). This is similar to the nugget effect from coarse gold. Where this coarse material occurs it will only add to the defined resources.

Figure 1: Wild Kate Deposit Typical Silexite Body – LiDar Topography over Geology and Mineralisation

Mt Everard Silexite Body – Mined 1979-81

Photos of typical ferberite (tungsten) mineralisation (black mineral)

Finely disseminated ferberite in silexite and Optical microscope image of fine-grained ferberite mineralisation with 1mm scale grading.

Banded fine-grained disseminated ferberite mineralisation in silexite.

Coarse grained ferberite in silexite

Coarse grained vein-type in metasedimentary cover rock

There is strong evidence for some homogeneity of tungsten grade within the silexite bodies, especially those centrally located including Burnt Hut, Fielders Hill & Wild Kate, despite their separation by several kilometres.  The larger sampling size of the historic mining and bulk sampling also gives a more reliable indication of grade. A summary of the results of these programmes is shown in table below.

Location Year Tonnes WO3%
Wild Kate 1915-16 4,000 0.25
Fielders Hill N & S 1977 2,660 0.22
Burnt Hut 1977 3,100 0.22
Fielders Hill North 1979-80 69,425 0.22
Fielders Hill South 1979-80 11,626 0.22
Burnt Hut 1979-80 31,025 0.22
Mt Everard 1979-80 18,680 0.22
Average   0.23

Table 1: Historic mining indicates consistent grade in the main central silexite bodies at Torrington