Abstract

The Carolina slate belt consists of Precambrian-Cambrian, metamorphosed, mafic to felsic flows, volcaniclastics, and derived sediments which filled in a volcanic trough presumed to have formed along the leading edge of the North American continent during the early closing of the proto-Atlantic Ocean. Within the slate belt, in central North Carolina, South Carolina, and on the South Carolina-Georgia line, there are volcanigenic massive sulfide deposits of Kuroko affinities and their metamorphically remobilized sulfide and Au quartz deposits.A total of 296 chemical analyses of volcanic rocks and associated dikes (of which 227 are in unpublished theses, dissertation, and reports) are plotted on alkali-SiO 2 , K 2 O-Na 2 O, AFM, and Na 2 O-K 2 O-CaO diagrams. In addition, selected subsets are compared with standard discriminant plots, such as TiO 2 -SiO 2 , MgO-FeO total -Al 2 O 3 , and Y-Zr-Ti. Generally speaking, the volcanics of the slate belt define a bimodal suite of calc-alkaline to tholeiitic rocks with strong affinities to volcanic suites described in the lesser Antilles and with the volcanics of the coastal volcanic belt of Maine. A subduction-related orogenic environment is most probable.In addition, the major element analyses strongly suggest that a pervasive, postdepositional alteration process has taken place. In general, this alteration appears to have affected the fine-grained matrix of the volcaniclastics, but flows and dikes were not immune. An overall alkali depletion and MgO enrichment is characteristic, with significant, but variable, mobility of Na 2 O, K 2 O, CaO, and SiO 2 . Thus, characterization of the magmatogenesis by major element composition alone is not easily done. Alteration associated with massive sulfide mineralization in the Gold Hill district, North Carolina, and the Lincolnton-McCormick district, South Carolina-Georgia, is similar to, but more intense than, the pervasive secondary alteration. Strong silicification, alkali addition or subtraction, and MgO enrichment is characteristic. In general, a significant proportion of the mineralization-associated alteration falls outside the normal range of compositional variability of typical slate belt suites and, thus, has a notable signature.

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