Petratherm (ASX:PTR) encountered a high-grade heavy mineral sand discovery during a recent drill program at the Rosewood prospect in South Australia, according to a Thursday filing with the Australian bourse.

The new intersections include 28 meters at 13.6% heavy minerals from a depth of 10 meters and 16 meters at 12.1% heavy minerals from 14 meters.

The company expects results from other Muckanippie Project heavy minerals targets within two weeks, the filing said.

Petratherm's shares plunged 20% in recent Thursday trade.