Topaz

The topaz mineralisation at Torrington is an integral constituent of the silexite (average ~18%) which as described in the separate tungsten section is the host to the bulk of the tungsten mineralisation. In appearance the silexite is similar to a relatively coarse grained white sandstone / quartzite (see photographs below).

Banded fine-grained disseminated tungsten (ferberite) mineralisation in silexite

Mineralised silexite with grey-white quartz, translucent grey topaz, black tungsten (ferberite) and oxidised bismuth pale orange

The topaz (Al2SiO4(FOH)2) appears to be distributed evenly throughout the silexite bodies with a reported average content of ~18% and a grain size average of close to 2mm.

In the 1980’s a consortium of companies focussed on topaz production at Torrington building a pilot plant for topaz recovery with the concentrate product being used to produce mullite, a refractory mineral. Despite proving the high performance of the product, the consortium could not obtain financial support for large scale mining and processing of topaz and eventually the individual companies went their separate ways. During this time, some of the topaz was used in the shipping industry as an abrasive (sand blasting).

There were also extensive studies conducted at CSIRO and later at UNSW (until about 2006) on the potential mullite products that can be produced from the topaz, including fibres before commercial funding ran out.

Topaz has an average SG of 3.5 vs that of quartz with an average SG of 2.65, so in the planned gravimetric spiralling and tabling processing plant the topaz will be recovered either during the initial processing to recover the tungsten, or afterwards by retreating the middling and waste streams.

Recent QEMSCAN studies on tungsten mineralised silexite by ALS Metallurgy (Perth) produced the mineral distribution shown in Figure 1 with topaz content in the sample being in excess of 20%.

Figure 1: Mineral Distribution in Silexite – Quartz and Topaz + Tungsten (Wolframite)

At a processing rate of 500,000tpa of silexite, it is theoretically possible to co-produce in the order of 90,000tpa of topaz as a by-product from tungsten extraction and recovery by gravimetric processing. The sheer volume of topaz that will be produced as by-product warrants research into its potential markets and products as both a bulk industrial feedstock material and / or high-added value small volume commodity. Success in this research endeavour will contribute to the financial robustness on the project and remove the reliance of producing one product (tungsten) only.