Swanson Uranium project prospect (Cole property; Coles Hill), Pittsylvania Co., Virginia, USA
|Latitude & Longitude (WGS84):||36° 52' 14'' North , 79° 18' 23'' West|
|Latitude & Longitude (decimal):||36.87056,-79.30639|
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.
14 valid minerals.
Rock Types Recorded
Select Rock List TypeAlphabetical List Tree Diagram
Entries shown in red are rocks recorded for this region.
This geological map and associated information on rock units at or nearby to the coordinates given for this locality is based on relatively small scale geological maps provided by various national Geological Surveys. This does not necessarily represent the complete geology at this locality but it gives a background for the region in which it is found.
Click on geological units on the map for more information. Click here to view full-screen map on Macrostrat.org
201.3 - 252.17 Ma
|Newark Supergroup; Triassic Sandstone, Siltstone, and Shale|
Age: Triassic (201.3 - 252.17 Ma)
Stratigraphic Name: Newark Supergroup
Description: Sandstone, very fine- to coarse-grained, reddish-brown to gray, micaceous, minor conglomerate beds. Siltstone, reddish-brown to gray, micaceous. Shale, reddish-brown, greenish-gray, gray, yellowish-brown, laminated, fossiliferous. Upward-fining sequences, discontinuous vertically and horizontally.
Comments: Mesozoic Basins; paper map and digital map have differernt labels: paper map does not have TR prefix, but the digital source has TR as part of the label.
Reference: Horton, J.D., C.A. San Juan, and D.B. Stoeser. The State Geologic Map Compilation (SGMC) geodatabase of the conterminous United States. doi: 10.3133/ds1052. U.S. Geological Survey Data Series 1052. 
Jerden, J.L., Sinha, A.K, and Zelazny, L. (2003). Natural immobilization of uranium by phosphate mineralization in an oxidizing saprolite-soil profile: chemical weathering of the Coles Hill uranium deposit, Virginia. Chemical Geology: 199: 129-157.
Tappa, M.J., Ayuso, R.A., Bodnar, R.J., Aylor, J.G., Beard, J., Henika, W.S. Vazquez, J.A., and Wooden, J.L. (2014), Age and petrogenesis of host rocks at the Coles Hill uranium deposit, Pittsylvania County, Virginia, USA, based on zircon U-Pb geochronology.