THE SPATIAL DISTRIBUTION OF PRECIOUS METAL TELLURIDES IN THE EMPEROR GOLD-SILVER TELLURIDE DEPOSIT, FIJI

Alkaline igneous rock-related epithermal gold telluride deposits constitute some of the world’s largest resources of gold. Included in this group is the Emperor gold-silver telluride deposit in Fiji, which contains approximately 11.5 Moz of Au. The deposit, hosted by Tertiary shoshonitic rocks, occurs near Vatukoula in north-central Viti Levu on the western flank of the Tavua caldera. The caldera is situated along the intersection of the northeast trending Viti Levu lineament and the northwest trending Nasivi shear zone. Ore mineralization is characteristic of a "low sulfidation" style and is associated with flat-dipping structures (<45^o), referred to locally as "flatmakes," steeply dipping structures (e.g. dikes and faults), and the intersection of two or more structures referred to as "shatter zones." Petrographic, electron probe microanalysis, and scanning electron microscope studies reveal that eight hydrothermal stages of mineralization occur in the Emperor deposit and that sylvanite ((Au,Ag)Te₄), calaverite (AuTe₂), krennerite (AuTe₂), petzite (Ag₃AuTe₂), hessite (Ag₂Te), empressite (AgTe), coloradoite (HgTe), altaite (PbTe) and melonite (NiTe) and native tellurium are widely distributed throughout the deposit, including the recently discovered Matanagata East and R1 orebodies. Other precious metal minerals include benleonardite (Ag₈(Sb,As)Te₂S₃), andorite (PbAgSb₃S₆), and naumannite (Ag₂Se), which are identified at Emperor for the first time. Calaverite and sylvanite are more common in the eastern portion of Matanagata East flatmake whereas native gold/electrum is more abundant in the Matanagata flatmake. The spatial distribution of sylvanite and calaverite in the Matanagata East flatmake appears to be structurally controlled since they are absent south of the Lololevu and Sam Sorby faults. A zone containing gold-silver tellurides in the Vono and Kava flatmakes (R1 section) parallel the adjacent Crown Cross steep structure. Although precious metal tellurides are an important source of gold, most of the gold at Emperor likely occurs as "invisible gold" in the structure of arsenian pyrite. Secondary ion mass spectroscopy data obtained herein reveal that pyrite contains up to 16.60 wt. % As, 11,057 ppm Au, and 5,796 ppm Te.