Cokriging to assist metallurgical modelling at the Nena copper-gold deposit, Frieda River, PNG

Mineral system understanding

Mr James Carpenter


This paper provides an update of the Mineral Resource for the Nena copper-gold deposit, located in the Frieda River Igneous Complex in the northern foothills of the Central Range in western Papua New Guinea. A description of the deposit’s estimation domains, and results of cokriging of its iron and sulphide sulphur content are also provided.

The Nena copper-gold deposit is a high-sulphidation epithermal deposit. Since its discovery, the deposit has been drilled and investigated by multiple owners who identified a significant challenge with the efficient extraction of copper in the presence of the deleterious elements arsenic (As) and antimony (Sb).

To overcome this challenge, a new hydrometallurgical process – the Albion Process – was developed to selectively extract the copper metal. Modelling the Process requires estimating minerals present, including pyrite (FeS2) (required to generate ferric ions which selectively leach the copper from the sulphide minerals).

The proportions of minerals, including pyrite, are calculated using stoichiometry. Typical minerals in the hypogene are enargite (Cu3AsS4), dimorph mineral luzonite (Cu3AsS4) and famatinite (Cu3SbS4) with minor amounts of primary covellite (CuS). Varying amounts of native sulphur (S) and pyrite are present throughout.

To effectively calculate the proportions of minerals in the presence of native sulphur, iron and sulphide sulphur estimates are required. Around 20 per cent of the previously drilled diamond core holes of the Nena deposit have been tested for iron, sulphide sulphur and total sulphur, while the remainder have an assay suite including total sulphur, but not iron and sulphide sulphur.

Iron and sulphide sulphur have strong linear relationships with the total sulphur (r>0.9). This means the iron and sulphide sulphur grades can be cokriged using the total sulphur as a secondary variable. The cokriged estimate is more rigorous than independently estimating the otherwise widely spaced iron and sulphide sulphur variables.

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