Prospect Resources (ASX:PSC) said around 20% of the phase 3 diamond drilling for 16,000 meters was completed at the Mumbezhi copper project in Zambia, according to a Tuesday Australian bourse filing.

Ten resource extension holes were completed at the southern end of the flagship Nyungu Central deposit. Copper mineralization was visually observed in several holes outside existing defined mineral resources.

Two diamond rigs continue to target shallow, up-plunge extensions at the southern end of the deposit.

Its shares fell 3% in recent trading on Tuesday.