GENETIC IMPLICATION OF SULFIDE MINERALIZATION IN EMERALD- AND SPODUMENE-BEARING ALPINE-TYPE FISSURE VEINS AT HIDDENITE, NORTH CAROLINA, USA

The Hiddenite area of western North Carolina constitutes the most significant emerald-producing district in North America and is the world's only confirmed locality for the chromium-bearing variety of spodumene known as hiddenite. Both minerals occur in cavities in steeply dipping Alpine-type fissure veins that crosscut highly deformed migmatitic schists and quartz-biotite gneiss of the Inner Piedmont Belt. Preliminary fluid inclusion data from quartz crystals in the cavities constrains the crystallization temperature and pressures of the fissure veins mineralization to <250°C and near 1 kbar. Sulfide mineralization occurs in two separate vein assemblages: (1) beryl-bearing fissure veins that carry accessory pyrite (FeS₂), pyrrhotite (Fe_1-xS), sphalerite (ZnS), chalcopyrite (CuFeS₂), and trace amounts of galena (PbS) and (2) spodumene-bearing veins that host pyrite, pyrrhotite, molybdenite (MoS₂), and trace gersdorffite (NiAsS). The sulfides generally form as part of the last stage of mineralization in the cavities. The crystal morphology and chemical composition of pyrite reflect slightly different fluid chemistries of the two vein types. Pyrite cubes are characteristic of the spodumene-bearing veins whereas octahedra are typical of the beryl-bearing veins. Pyrites of the beryl-bearing veins contain higher As and Ni values compared to those from spodumene veins. Pyrite from the spodumene assemblage is enriched in Cu and Mn relative to pyrite from the beryl assemblage. The physical and chemical properties of pyrite and associated sulfides may serve as an important exploration tool for identifying emerald- or hiddenite-bearing veins in the Hiddenite area.