Mount Casca; VABM Casca Prospects, Black District, Southeast Fairbanks Borough, Alaska, USA

This prospect lies on Doyon, Limited selected or conveyed land. For more information, contact Doyon, Limited. This site is within the Yukon-Charley Rivers National Preserve.
Location: The Mount Casca prospects are on the northern and southern flanks of 7,874-foot Mount Casca in section 13, T. 6 N., R. 32 E. Additional Mount Casca prospects are located on the southern flank of Mount Casca in section 18, T. 6 N., R. 33 E., of the Fairbanks Meridian. The prospects cover approximately 2 square miles. The coordinates are for the northernmost prospect. The locations are accurate. These prospects are located on Doyon, Limited selected or conveyed land.
Geology: The main geologic unit in the Mount Casca area is a massive boulder-conglomerate of the Ordovician to Devonian Road River Formation (Dover and Miyaoka, 1988). The massive conglomerate is overlain by thin wedges of algal limestone of the Devonian Ogilvie Formation and underlain by the Cambrian Funnel Creek Limestone. The massive conglomerate is clast supported with an unsorted matrix. Clasts are mostly silicified oolitic limestone, chert pebbles, granular apatite, and fossil fragments. In some places, phosphate nodules as much as 5 inches in diameter were reported (DiMarchi and others, 1993). The conglomerate also contains limestone breccias. The conglomerate contains anomalous phosphorous and uranium geochemical values. The phosphorous is located in phosphate nodules and apatite, and the uranium is in collophane and uranium-bearing apatite (DiMarchi and others, 1993). The limestone breccias contain 400 parts per million uranium, and 16.5 percent P2O5 (Doyon, Limited, 1986). Alteration in the conglomerate appears as pervasive silicification with chalcedony-lined vugs and irregular quartz veining. Within breccia zones, many iron and manganese oxides are present (DiMarchi and others, 1993). The Mount Casca prospect was explored by WGM Inc. in 1975 and 1976, by Union Carbide in 1977, and by ASA Inc. in 1993. WGM Inc. conducted a soil sampling and trenching program, and Union Carbide took soil and rock samples, and also did some petrographic analysis. ASA Inc.'s program consisted of selective rock sampling and mapping of the prospect (DiMarchi and others, 1993).
Workings: The Mount Casca prospects were explored by WGM Inc. in 1975 and 1976, by Union Carbide in 1977, and by ASA Inc. in 1993. WGM Inc. conducted a soil sampling and trenching program, and Union Carbide took soil and rock samples and also did some petrographic analysis. ASA Inc.'s program consisted of selective rock sampling and mapping of the prospect (DiMarchi and others, 1993).
Age: Cambrian or younger, based on the age of the host rocks.
Alteration: Alteration at Mount Casca prospect consists of pervasive silicification with chalcedony-lined vugs and irregular quartz veining. Iron and manganese oxides are present within breccia zones (DiMarchi and others, 1993).

Commodities (Major) - P, U
Development Status: None
Deposit Model: Upwelling-type phosphate deposit? (Cox and Singer, 1986; model 34c)

References:
DiMarchi, J.J., Weglarz, T.B., Adams, D.D., Hubert, J.A., and West, A.W., 1993, 1993 annual report--Reconnaissance program, Doyon option lands: ASA Inc., 120 p. (Report held by Doyon, Limited, Fairbanks, Alaska.) Dover, J.A., and Miyaoka, R.T., 1988, Reinterpreted geologic map and fossil data, Charley River quadrangle, east-central Alaska: U.S. Geological Survey Miscellaneous Field Studies Map MF-2004, 2 sheets, scale 1:250,000. Doyon, Limited, 1986, Mines, prospects, and geochemical anomalies on Doyon, Limited, regional overselection lands, Alaska: Fairbanks, Alaska, Doyon, Limited Report 86-01A, v. 1, 150 p. (Report held by Doyon, Limited, Fairbanks, Alaska.)