Regional distribution of mineral deposits beneath the pre-middle Ordovician unconformity in the southern Appalachians

Abstract

Most geologists working in the Southern Appalachian Valley and Ridge mineral districts now believe the deposits formed in Early to Middle Ordovician time. If this is correct, the present distribution of the mineral deposits reflects disordering of the original patterns both vertically and areally by the Late Paleozoic orogeny. Because the ores are now in allocthonous blocks the original plumbing and relations to basement rocks are obscured.Regionally there are ore deposits of barite, copper, fluorite, iron, lead, manganese, and zinc in rocks ranging in age from Precambrian to early Middle Ordovician, and in crystalline to metasedimentary, clastic, and little altered carbonate rocks. However, the major barite-manganese-lead- and zinc-producing hosts are thick dolomitic limestones or residual clays derived from them. Specifically the Shady Dolomite (Lower Cambrian) and the upper part of the Knox Group (Lower Ordovician) are the chief ore hosts.The modes of the deposits show them to be epigenetic and chiefly open-space fillings. The importance of the carbonate hosts is interpreted to derive from the extensive development of open spaces in them.The deposits exhibit variations in their mineralogy that seem to be a function of stratigraphic position and geography. This may imply differences in ore sources and various mineralizing episodes. Mineral zonation in the classic sense is obscure, and if it ever existed is now disrupted by post-ore deformation. Similarly, post-ore history casts doubts on some genetic parameters and obscures genetic explanations.