Abstract

Massive sulfide deposits occur in the Hillabee Greenstone at Pyriton, Alabama. The Hillabee Greenstone represents Devonian tholeiitic arc volcanism and occurs at the stratigraphic top of the Talladega slate belt in the northern Alabama Piedmont. Below the Greenstone, rocks in the lower part of the Talladega slate belt formed in a continental shelf environment. The entire Talladega slate belt has been metamorphosed to lower greenschist grade. The lower contact of the Hillabee is stratigraphic; the upper contact represents a major thrust fault. A zone of sulfide mineralization extends for a lateral distance of several tens of kilometers along strike at the base of the Hillabee. At Pyriton, the sulfide zone is locally over seven m thick and has been mined for pyrite.The Pyriton sulfides are characterized by significant amounts of Cu and Zn, with subordinate amounts of Pb; Au and Ag are of quite low abundance. Dominant minerals are pyrite, chalcopyrite, and sphalerite. Vertical zonation through the sulfide zone is poorly defined. There is strong indication of consistent lateral variations in base metal contents near Pyriton. The host rocks (Hillabee Greenstone) exhibit essentially no evidence of mineralization related chemical alteration, although mineralogic changes in the vicinity of the sulfides can be recognized.The Pyriton deposits are interpreted to represent deposition of sulfides on the sea floor surface, distal from the volcanic and ore sources, which were to the southeast. The deposits are similar to other volcanogenic massive sulfide deposits in arc-type settings with respect to geometry, structural history, associated rocks, base metal abundances, and igneous character of the host rocks. Additional zones of sulfide enrichment might be expected downdip to the southeast, because the Hillabee host rock thickens in the general direction of the volcanic source.

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