- GeoRef, Copyright 2006, American Geological Institute. Abstract, Copyright, Society of Economic Geologists
Most gold deposits of the northern Piedmont of Georgia are within the Dahlonega gold belt and the Carroll County gold belt. Together these belts can be traced across Georgia from Alabama to North Carolina and consist of at least 217 abandoned mines and prospects. The overwhelming majority of the gold deposits occurs within the New Georgia Group, with a small number occurring within the western belt of the Sandy Springs Group. Important host rocks for the gold deposits include mafic and felsic metavolcanics of the Pumpkinvine Creek Formation, metasediments and metavolcanics of the Canton Formation, metavolcanics of the Mud Creek Formation, meta-igneous rocks of the Kellogg Creek mafic complex, and metavolcanics and metasediments of the Univeter Formation. Most gold deposits of the Dahlonega and Carroll County belts can be grouped into six districts: the Villa Rica district, the Burnt Hickory Ridge district, the South Canton district, the Auraria district, the Dahlonega district, and the White County district. Gold was mined intermittently from the Dahlonega and Carroll County belts from 1829 to 1935. Production from these belts accounted for the majority of the recorded statewide production of just over one-half million ounces.An extrapolation of metamorphism dates from the southern Piedmont suggests that rocks in the Dahlonega and Carroll County gold belts were metamorphosed to at least greenschist facies (biotite subfacies) and as high as amphibolite facies (kyanite subfacies) in the Late Devonian approximately 365 million years ago and were affected by four fold generations. Rocks of the New Georgia Group are interpreted as the oldest rocks in the Dahlonega and Carroll County belts. The New Georgia Group is composed predominantly of metavolcanic rocks and grades upward into the overlying Sandy Springs Group, a predominantly metased-imentary sequence.Whole-rock and trace element chemistry of mafic metavolcanic host rocks and the presence of abundant interlayered metasediments strongly suggest that rocks of the Dahlonega and Carroll County gold belts were deposited in a back-arc basin environment. Contemporaneous with the deposition of the rocks within the back-arc basin, convecting thermal waters leached gold from underlying rocks. Upon reaching the sea floor in the vicinity of a vent, gold was precipitated in siliceous horizons (exhalites) or was incorporated into contemporaneous tuffs, flows, and sediments. Subsequently, during metamorphism and deformation of the host rocks, gold and other elements were remobilized and redeposited in structurally controlled ore shoots in the siliceous horizons. Gold originally incorporated into contemporaneous tuffs, flows, and sediments migrated to structurally controlled sites (fold hinges, shear zones, cleavages, etc.) in these host rocks, thus giving rise to two types of deposits: ore shoots in metamorphosed, auriferous siliceous horizons, and gold-bearing quartz bodies ("sweat-outs") derived from metamorphosed auriferous host rocks. Exposure and weathering of the gold deposits resulted in a supergene enrichment of gold in the weathered horizon (saprolite) and a mechanical and chemical concentration of gold in placers.