ORE MINERALS OF THE COFER VOLCANOGENIC MASSIVE SULFIDE DEPOSIT, LOUISA COUNTY, VIRGINIA

The Cofer stratiform volcanogenic massive sulfide deposit is located n ear Mineral, Louisa County, Virginia. It consists of four major en ech elon lenses that are essentially stratabound, with characteristics of both Cu-Zn and Zn-Pb-Cu types of volcanogenic massive sulfide deposits . Ore minerals include coarsely recrystallized pyrite with sphalerite and minor chalcopyrite, galena, arsenopyrite, and tetrahedrite-series minerals. Trace minerals include bornite, marcasite, pyrrhotite, macki nawite, molybdenite, covellite, digenite, chalcocite, gudmundite, boul angerite-bursaite, kobellite-tintinaite, meneghinite, cosalite, magnet ite, ilmenite, rutile, native bismuth, and electrum. Major and minor o re minerals and most oxides were syngenetic with the host lower Cambri an Chopawamsic Formation and were subsequently recrystallized during m etamorphism up to the lower amphibolite facies. Changes in the ore flu id after initial deposition resulted in a crude Zn/Pb versus Cu zoning and probably caused tetrahedrite-freibergite to be replaced by an ars enic-and iron-rich graphic integrowth. Further re-equilibration during metamorphism resulted in exsolution of many sulfosalts, including tet rahedrite-freibergite associated with galena. The peak of metamorphism appears to have been at approximately 470 degrees C, with sulfur acti vity in the range of -4.5 to -6.3 atmospheres.