Summary:
The Phu Kham deposit represents a copper-gold porphyry system, with mineralisation present in skarn, stockwork and disseminated styles. Significant folding and alteration events have created a complex heterogeneous mineralogy horizon. Weathering and water table contact have created a leached zone, overlying transition zones with supergene chalcocite- dominant secondary copper mineralisation and clay-rich gangue. Primary ore copper mineralisation is mainly chalcopyrite with minor bornite. The major challenges to the copper-gold fl otation process are a wide size distribution of chalcopyrite mineralisation and poor primary grind liberation, a high pyrite content in skarn ore requiring aggressive pyrite depression conditions, clay-rich gangue and nonsulfi de copper mineralisation in weathered zones, and a signifi cant association of gold with pyrite.
Mineralisation is present in iron-rich skarns, silica-rich stockwork, and altered disseminated styles. Chalcopyrite and bornite are the dominant primary copper minerals in skarn, stockwork, and disseminated mineralisation. Gangue mineralogy is mainly quartz, mica and pyrite, with signifi cant kaolinite clay and talc-related magnesium silicate content within the weathered zones.
A gold-enriched oxide zone on the Phu Kham orebody was the resource for the heap leach gold mine which was built and operated by Phu Bia Mining during the 2005 to 2010 period. Below the oxide zone, there is a zone of supergene weathering, with copper leached from the oxide zone re-precipitated in contact with pyrite grains as particles and coatings of chalcocite and covellite, with minor enargite and tennantite copper arsenic sulfi des. Signifi cant copper enrichment in the oxide and supergene zones is also present as oxide and native copper species.
Skarns are present as replacement of carbonate minerals, with disseminated grains of chalcopyrite and bornite in banded to massive pyrite skarns and veinlets containing pyrite, chalcopyrite and bornite in garnet, magnetite, and hematite-chlorite skarns. Pyrite skarns are common throughout the mineralised system.
Stockwork mineralisation is present as fine fractures in quartz veins. The fractures host pyrite, chalcopyrite and bornite sulfi de minerals. Minor chalcopyrite mineralisation is also present in quartz-carbonate veins. Disseminated mineralisation consists of scattered grains of bornite and chalcopyrite in sericite altered host rock.
Gold occurs as small grains associated with pyrite and copper sulfi des throughout the mineralised system.
Mineralisation is present in iron-rich skarns, silica-rich stockwork, and altered disseminated styles. Chalcopyrite and bornite are the dominant primary copper minerals in skarn, stockwork, and disseminated mineralisation. Gangue mineralogy is mainly quartz, mica and pyrite, with signifi cant kaolinite clay and talc-related magnesium silicate content within the weathered zones.