Volcanic rock-hosted gold and base-metal mineralization, associated with Neoproterozoic-Early Paleozoic, back-arc extension in the Carolina terrane, southern Appalachian Piedmont

Abstract

Volcanogenic mineral deposits in the Carolina terrane, southern Appalachian Piedmont,include Kuroko-type polymetallic massive sulfide deposits and disseminated gold-pyrite deposits associated with propylitic, silicic, argillic, and advanced argillic alteration. Host rocks are metavolcaniclastic and metaepiclastic rocks of a Neoproterozoic-Early Cambrian magmatic arc. The favorable gold horizon is the transition from a lower succession of andesitic and rhyolitic pyroclastic rocks with basal mafic lavas to an upper sequence of epiclastic sedimentary units and minor lava and ash flows. Kuroko-type deposits are associated with mafic to bimodal volcanic rocks in the upper sequence. Whole-rock oxygen isotope analyses indicate that gold mineralization is associated with a transition from hydrothermal systems dominated by isotopically relatively light (δ18O = -6‰ to -10‰) waters, typical of high-latitude subaerial systems, to seawater (δ18O = 0‰). Plots of δ18O vs. SiO2 of the host rocks show a compositional gap associated with mineralization at the subaerial to submarine transition. Values of δ18O for the hydrothermal waters, lithostratigraphic analyses, and tectonic models of the Carolina terrane demonstrate that mineralization coincided with extension in a rifted arc.