Swanson Uranium project prospect (Cole property; Coles Hill), Pittsylvania County, Virginia, USAi

Regional Level Types
Swanson Uranium project prospect (Cole property; Coles Hill)	Prospect
Pittsylvania County	County
Virginia	State
USA	Country

After Landowner
Commodities (Major) - Uranium
Development Status: Prospect
Host Rock: Gneiss, cataclasite
Tectonic Structure: Piedmont Terrane Of Appalachians

The Cole's Hill uranium deposit is the largest in the United States and the seventh largest in the world. Mineralization is localized within sets of narrow fractures that cut a broader zone of mylonite within the orthogneiss and amphibolite of the Martinsville Igneous Complex. At the hanging wall of the mylonite zone is the silicified breccia of Chatham fault separating the western Piedmont from the Triassic rocks of the Danville Basin. The ore deposit, as currently known from extensive drilling, is wholly within the Martinsville Igneous Complex.

Deposition of uranium occurred in a relatively low temperature, low pressure hydrothermal environment. It is epigenetic relative to the host rocks of the Martinsville Igneous Complex. The ore was deposited in 3 main stages, each occupying a separate set of fractures. The earliest, and main, ore assemblage consists of coffinite – apatite. The apatite contains substantial uranium and may account for as much as 4% of the total uranium. Subsequent sets of fractures contain pitchblende – calcite and pitchblende – zeolite. All 3 stages of uranium deposition were accompanied by hematization. The depositional mechanism appears to be fluid/rock interaction involving the oxidation of reduced iron in the amphibolites and the complimentary reduction of soluble, oxidized uranium complexes.

An unusual, but important, feature of the Cole's Hill deposit is the amount of phosphorous that the ore contains. In the near surface oxidized zone uranium has been immobilized by phosphate thus preventing migration into and natural contamination of the local groundwater (Jerden, et al, 2003) .

Jerden (2001) proposed that during the Jurassic, fluids circulated through the Triassic rocks of the Danville basin and then upward through the border fault fracture complex including the fractures that contain the Cole's Hill ore deposit. In addition it was noted that the Triassic formations near the border fault contained uranium bearing organic matter and phosphate-rich fossil debris. This idea is tempting because of the proximity of the Cole's Hill site to the basin. However, there are many factors as yet unresolved. Therefore, as noted by Tappa, et al. (2014), the age of the ore deposit, the overall extent of the plumbing system, and the agent(s) driving fluid circulation are unclear as is the source of the uranium and phosphorus.

The mineral specimen potential of the Cole's Hill ore deposit is unknown but is likely to be low for reasons ranging from geological to political and economic. The deposit is estimated to be the largest uranium deposit in the United States, containing more than 110 million pounds of U3O8.

Other Regions, Features and Areas containing this locality

References