THE EMERALD- AND SPODUMENE-BEARING QUARTZ VEINS OF THE RIST EMERALD MINE, HIDDENITE, NORTH CAROLINA

摘要

We have re-investigated the paragenesis and mineral compositions of the emerald occurrence at the Rist mine, Hiddenite, North Carolina, in order to provide a foundation for fluid-inclusion and isotopic studies, and to examine the possible relationship between emerald and spodumene mineralization and granitic pegmatites. Beryl and chromian spodumene occur entirely within quartz veins and in open cavities that occupy brittle tensional fractures in folded metamorphic rocks. Examination of cavities reveals four assemblages characterized by a specific group of minerals; characteristic minerals in the four assemblages are calcite, amethystine quartz, spodumene and emerald. The early stage of vein development is characterized by the crystallization of massive quartz and followed largely by the precipitation of Ca-Fe-Mg carbonates. The occurrence of Be-, Li-, Ti-, and B-bearing minerals coupled with local contamination by Cr and V is largely penecontemporaneous with the formation of cavities. Late precipitation of pyrite, chabazite-Ca and graphite suggests that low temperatures and reducing conditions were prevalent during the waning stages of mineral precipitation. The presence of cogenetic high- and low-X(CO_2) fluid inclusions in quartz indicates that an aqueous carbonic fluid reached a state of immiscibility during vein formation. No relationship with granitic pegmatite was observed.