22 Mineralogy, Volcanology and Magmatism
Friday, 20 March 2015
8:00 AM - 9:40 AM
Walker
DISTRIBUTION AND COMPOSITION OF URANIUM MINERALS AT COLES HILL PITTSYLVANIA COUNTY, VIRGINIA
Paper number: 22-1
Program: Technical Sessions
Time: 8:00 AM – 8:20 AM
Authors
-
James BeardVirginia Museum of Natural History, Martinsville, VA
Abstract
The Coles Hill uranium property is located at the southeastern edge of the Paleozoic Smith River Allochthon (SMA) in the Western Piedmont Province, adjacent to the fault-bounded Danville Triassic Basin. Uranium mineralization at Coles Hill is restricted to brittlely deformed granite and diorite of the Ordovician Leatherwood granite and Rich Acres gabbro-diorite in the footwall of the basin-bounding Chatham fault. The brittle deformation overprints an earlier ductile deformation. Rocks that have only experienced the ductile event are barren. Uranium minerals occur primarily within late, sinuous fractures that border, but do not cut, matrix mineral grains. These fractures largely postdate a Na-metasomatic event that resulted in widespread albitization of feldspar and replacement of green amphibole by riebeckite. In addition to uranium minerals, the fractures contain chlorite, albite, fluorapatite, iron oxides/hydroxides and microcrystalline quartz. Electron microprobe and SEM analysis of the uranium minerals shows that whatever the original host mineral was, it has now been replaced by an inhomogenous and finely divided patchwork of hydrous uranium and uranium silicate phases. These patchworks are commonly associated with galena. The presence of silica in many microprobe spot analyses suggests that the original U host mineral may have been, at least in part, coffinite.