Igneous-Rock Hosted Orogenic Gold Deposit at Hog Mountain, Tallapoosa County, Alabama

Abstract

The Hog Mountain gold deposit is located in northern Tallapoosa County, Alabama and is part of the historic Goldville mining district. Hog Mountain is geologically located in the eastern Blue Ridge consisting of phyllites, schists, and a Carboniferous tonalite pluton. The Hog Mountain deposit has been mined for gold episodically since 1893 producing ~17,000 troy ounces. Gold at Hog Mountain is hosted in quartz veins within the tonalite pluton and are thought to be orogenic in origin. Sixteen major veins have been identified and successfully mined in the past. Three of these quartz veins, namely the Blue, Kennedy, and Sugar Quartz veins were analyzed for this study. In particular, geochemical studies were carried out on the Blue vein, which is the largest in Hog Mountain. Several quartz textures including planar deformation lamellae, undulose extinction, and polygonal grains were identified using transmitted light microscopy studies. Petrographic studies of the samples were conducted in both reflected and transmitted light. Based on the reflected light studies on polished sections, gold is associated with sulfide minerals including pyrrhotite, pyrite, chalcopyrite, arsenopyrite, and galena. The most dominant sulfide mineral is pyrrhotite, which occurs as big masses, remobilized grains, and filling fractures. Geochemical analyses from the Blue Vein indicate that there are strong correlations between gold (Au) and tellurium (Te), gold (Au) and bismuth (Bi), and bismuth (Bi) and tellurium (Te). Alteration types, geochemistry, and general geologic setting of the Hog Mountain mine have many similarities compared to typical other quartz vein-hosted gold systems including Otago schist, New Zealand, and Bendigo-Ballarat area of Victoria, Australia. Newmont Mining Corporation did drilling at the property in the early 1980s, but current exploration at Hog Mountain is being conducted by Wellborn Mining Company. More than a hundred core holes have been drilled since 2010 on the property based on magnetic anomalies apparently caused by elevated pyrrhotite. Drilling continues to date at Hog Mountain and as of yet, no decision has been made concerning the economics of actual mining.