Host Rock Gneiss as a Possible Source of Ore Mineralization at Ore Knob, North Carolina

According to classical theory, most epigenetic mineral deposits in regionally metamorphosed rocks are hydrothermal in origin. The hydrothermal fluids are generally considered to have been end products of cooling magmatic bodies, although in the last few years researchers have stated that hydrothermal fluids also may be metamorphically and meteorically derived ... The absence of magmatic bodies in the vicinity of some mineral deposits in regionally metamorphosed areas, the absence of typical argillic zones around the ore body, and the presence of criteria favoring a metasomatic origin of the host rocks, weakens the classical magmatic-hydrothermal theory in such cases. The Ore Knob copper deposit is epigenetic, occurs in a regionally metamorphosed area and is generally considered to be of magmatic-hydrothermal origin. If the ore body were entirely of epigenetic hydrothermal origin it would be expected that elements in the deposit would have diffused into the wallrock and formed mineral phases relatively rich in these elements adjacent to the ore ... However, the data collected by Brown (1958) and the present writer indicate that as the ore is approached iron in the wallrock biotite decreases rather than increases. The author studied the Ore Knob copper deposit with the hope of determining the source of the metals and the origin of the deposit. The study was primarily geochemical since Brown (1958) had made field and petrographic studies. The biotite in the host rock gneiss was analyzed for iron and copper; samples of the host rock also were analyzed for iron and sulfur. In addition to the chemical investigations, modal analyses of all specimens studied were made, and several polished surfaces were examined in detail.