The junior is drilling 11,000m at the Kalaba target at Zamsort and all 46 holes so far have hit metal, it said, with thicknesses up to 144m and an average between 60m to 80m.
Surface indications point to a 5km system extending over a strike of 2km, added the company.
Grades were also higher in this set of results at 1.3% copper and 0.19% cobalt with continuous cobalt dissemination.
Nick von Schirnding, executive chairman, said the dimensions so far has exceeded all initial internal expectations and bore the hallmarks of a typical large deposit in the Domes region in north-west Zambia.
Arc Minerals has three drill rigs running at Zamsort currently, with a pilot processing plant on schedule to be commissioned by the fourth quarter.
Arc has a 66% interest in Zamsort.