Polymetals Resources (ASX:POL) reported an increased total mineral resource of 20.7 million tonnes for its Endeavor mine in New South Wales, according to a Monday filing with the Australian bourse.

The updated reading comes after reinterpretation of a historic subsidence zone led to a targeted underground drilling program that has now added 1.3 million tonnes of mineralized material, mainly within the high-grade Upper Main Lode, the company said.

The mineral resource contains about 1.6 million tonnes of zinc, 860,000 tonnes of lead, and 54.3 million ounces of silver, per the filing.

The update incorporates 29 new drill holes, mine depletion, revised surveys and estimation parameters, and historical mine reconciliation, the filing said.

The company's shares gained 2% in recent Monday trade.