The company said the Kili Teke prospective site had a resource of 1.2 million ounces of gold, 506,000 tonnes of copper and 22,000 tonnes of molybdenum.
Chief executive officer Graham Briggs said the inferred mineral resource estimate for Kili Teke of four million ounces of gold equivalent was a positive development.
“Additional significant drill intercepts have already been obtained at depth below and along strike,” he said.
“The declaration of a maiden resource is step one in growing a magnificent resource base – which is wholly owned by Harmony.
“Our exploration discovery cost is less than US$10 (K28) per gold ounce equivalent – one of the lowest world-wide.
“We are thrilled at the prospect of turning Kili Teke into a major new deposit, further enhancing the value of our world class copper-gold portfolio in PNG.”
The inferred mineral resource has been defined over a zone 600m long, 300m wide and 400m deep.
An inferred mineral resource is a deposit which had been sampled usually by drilling to a point at which an estimate of its grade and tonnage is made with low confidence.
The company said at this stage, the resource was constrained by the drill density and limits of the drill pattern.
Harmony Gold owns 100 per cent of the exploration license.