Thor increased the resource estimate to 10.7 million tonnes at 0.26% tungsten trioxide, 19.38g/t silver, 0.15% copper and 0.38% zinc.

It said the upgrade represented a 6.5% increase in the deposit's scheelite inventory, which contained 27,700 tonnes of WO₃, 85% of which was in the indicated category.

The news boosted Thor's shares by 8.93% to 1.52p (US1.92c).

The update also added zinc to the estimate for the first time, which added an extra potential by-product stream to Pilot Mountain and Thor expected zinc sulphides in concentrate to be recovered with minimal additional cost by the planned flotation recovery process being trialled.

"The resource inventory still has considerable growth potential via the Gun Metal and Good Hope deposits, as well as further potential upside at both Desert Scheelite and Garnet," Thor said.

Executive chairman Mick Billing said the increased estimate enhanced Pilot Mountain's potential in a country that hadn't seen any primary tungsten production for some years, despite the mineral being classified as critical by the US department of the interior.

The project's scoping study previously outlined a 12-year mine life based on annual throughput of 650,000 tonnes per annum from the Desert Scheelite openpit producing around 1,000tpa of scheelite concentrate, as well as copper-silver and zinc-silver concentrates.