Mineralogical studies of the Matanagata, Matanagata East, and R1 ore bodies at the Emperor Gold Mine, Fiji

Gold is found in three different forms in the Emperor gold deposit: as invisible or submicrometer-size inclusions of gold in arsenian pyrite, as visible native gold, and as tellurides (calaverite, krennerite, sylvanite, and petzite). Similarly, Te occurs as invisible tellurium or submicrometer-size inclusions of tellurium in arsenian pyrite, as visible native tellurium, and as tellurides. The bulk of the visible proportion of the ore is dominated by gold-bearing tellurides. The estimated contribution of tellurides to the gold budget is between 10 and 50%. Ores studies of the more recently discovered orebodies, Matanagata, Matanagata East, and R1 reveal that tellurium-bearing minerals, sylvanite, calaverite, krennerite, petzite, hessite, empressite, coloradoite, altaite, melonite, native tellurium, and rare benleonardite and nagyagite, formed during various hydrothermal stages and are hosted in primarily in quartz. Sylvanite is the most common telluride in these ore bodies. Paragenetic and mineralogical studies show twelve tellurium-bearing minerals form in three (II, III, and IV) of the eight hydrothermal stages in the paragenetic sequence. Tellurides show no systematic spatial distribution within flatmakes but there appears to be a higher concentration of tellurides where the flatmake intersects steep structures. Scanning electron microscopy (SEM), electron probe microanalysis (EPMA), and secondary ion mass spectroscopy (SIMS) show that pyrite from Emperor is among the most Au- (up to 11,057 ppm Au), Te- (up to 5,796 ppm Te), and As-rich (up to 16.60 wt % As) yet reported from any mineral deposit type. Arsenian pyrite is manifested as uniformly distributed grains, as As-rich rims on pre-existing grains, or as As-rich cores. SIMS depth concentration profiles and element-specific maps suggest Au is essentially found as structurally-bound gold in pyrite and submicrometer-sized inclusions of native gold and gold tellurides are relatively uncommon. Profiles and maps also indicate submicrometer-size inclusions of native tellurium and gold tellurides are also present in arsenian pyrite. Paragenetic studies indicate the highest concentrations of As, Au, and Te in pyrite occur in stages II and IV, which are also the stages containing the highest proportion of visible precious metal tellurides