Unico Silver (ASX:USL) said reverse core drilling found "significant extensions" to its La Negra silver resource in its Joaquin project in Argentina, according to a Monday Australian bourse filing.

Assay results include 17 metres at 258 grams per tonne silver equivalent, comprised of 238 g/t silver and 0.26 g/t gold from 63 metres, including one meter at 1,213 g/t silver equivalent comprised of 1,161 grams per tonne silver and 0.66 g/t gold from 65 metres.

The company said the second drill rig is mobilised, with diamond drilling underway to test deeper extensions and support a maiden mineral resource at Joaquin.

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