Bessie-Maple Prospect, Port Clarence District, Nome Borough, Alaska, USA
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Geology: Polymetallic, sulfide-bearing veins, veinlets, replacements, and fracture fillings in Ordovician limestone are locally present over about 1,200 feet of the east-west trending Rapid River fault zone. Sainsbury (1969, 1972) maps the Rapid River fault as a 12-mile long, east-west trending thrust fault in the southern part of the York Mountains although stratigraphic relations across the fault suggest normal displacement. Fluorite and beryllium-bearing mineralization has apparently developed peripheral to the sulfide veins. Lamprophyre dikes and a small plug are present in the mineralized area. Sulfide vein mineralogy is complex. Knopf (1908, p. 57-58) described a 1-foot wide zone of stringer veinlets containing wolframite, stannite, and galena with topaz and fluorite. Steidtmann and Cathcart (1922) described fractured and kaolinized dike rocks, some with disseminated tourmaline and fluorite, cemented with thin seams of galena, pyrite, and chalcopyrite and in places with 3-inch wide vertical stibnite-bearing veins. Sainsbury (1965; 1969, p. 64) described a 1-foot wide diamond drill intercept of semi-massive sulfides containing stannite, pyrite, arsenopyrite, and galena. Grades reported for sulfide-rich samples include trace to 0.03 opt gold, 4.2 to 25.6 opt silver, 0.5 to 9.1 % Pb, 0.48 to 1.53% Cu, about 3% Zn, 0.3 to 1.6% Sn, up to 3.2% WO3 and 3% Sb (Berg and Cobb, 1967, p. 132). Fluorite, chrysoberyl, white mica, and tourmaline are present in replacements of limestone and dolomite peripheral to the sulfide-bearing veins. One sample from the Bessie-Maple adit dump contained 0.39% BeO and 59% fluorite (Sainsbury, 1963, p. 8). Samples from three short USBM diamond drill holes had up to 0.79% BeO and 75% fluorite (Mulligan, 1965). Five inclined diamond drill holes completed by Lost River Mining Corporation through the near vertical fluorite mineralization had average intersections of 60 feet grading 34% fluorite (WGM, 1972, p. 54). Three of these five holes also intersected sulfide mineralization. These intersections were: (1) 10 feet of 0.18% Sn, 0.11% Pb, 4.9% Zn, 0.15% Cu, and 1.34 opt Ag; (2) 4.5 feet of 0.22 % lead, 1.89 % Zn, and 1 opt Ag; and (3) 2 feet of 0.27% Pb and 2.17% Zn (WGM, 1972, p. 72). Another diamond drill hole drilled vertically at a location north of the main Bessie-Maple prospect encountered 46 feet of 21.2 % fluorite, 0.23% Pb, 0.38 % Cu, and 1.3 opt Ag in the uppermost part of the hole (WGM, 1972, p. 72-73).
Workings: Older workings are a 150-foot adit and various suface pits and trenches. The USBM completed three short diamond drill holes totalling 399 feet on the eastern part of the mineralized area near where it merges with the Lost River valley prospect. Lost River Mining Corporation drilled 8 diamond drill holes totalling 1,905 feet in the prospect area (WGM, 1972, p. 63).
Age: The mineralization is assumed to be related to the development of tin systems in the Lost River area and therefore Late Cretaceous, the age of the tin-mineralizing granites there (Hudson and Arth, 1983).
Alteration: The limestone is commonly dolomitized but the relation of this alteration to sulfide and fluorite mineralization is not clear. Lamprophere dikes are kaolinized and locally contain disseminated tourmaline and fluorite. Fluorite veining and replacement is in effect a type of alteration here that can be thought of as distal alteration to more intense, tin metallization at depth. Mass balance calculations show significant SiO2, Al22O3, alkali, and fluorine enrichment with this type of alteration (Sainsbury, 1968, p. 1567).
Reserves: Not defined
Commodities (Major) - Ag, Cu, Pb, Sn, W., Zn; (Minor) - Au, Be, fluorite
Development Status: None
Deposit Model: Fluorite-, beryllium-, and sulfide-bearing veins, veinlets, and replacements in
11 entries listed. 9 valid minerals.
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Cobb, E.H., 1975, Summary of references to mineral occurrences (other than mineral fuels and construction materials) in the Teller quadrangle, Alaska: U.S. Geological Survey Open-File Report 75-587, 130 p. Cobb, E.H., and Sainsbury, C.L., 1972, Metallic mineral resources map of the Teller quadrangle, Alaska: U.S. Geological Survey Miscellaneous Field Studies Map MF-426, 1 sheet, scale 1:250,000. Hudson, T.L., and Arth, J. G., 1983, Tin granites of Seward Peninsula, Alaska: Geological Society of America Bulletin, v. 94, p. 768-790. Knopf, Adolph, 1908, Geology of the Seward Peninsula tin deposits, Alaska: U.S. Geological Survey Bulletin 358, 71 p. Mulligan, J.J., 1965, Diamond drill sampling data, fluorite-beryllium deposits, Lost River valley, Seward Peninsula, Alaska, 1964, with a section on petrography by Walter L. Gnagy, and a section on laboratory concentration tests by Richard Havens: U.S. Bureau of Mines Open-File Report 7-65, 94 p., 1 sheet. Sainsbury, C.L., 1963, Beryllium deposits of the western Seward Peninsula, Alaska: U.S. Geological Survey Circular 479, 18 p. Sainsbury, C.L., 1968, Tin and beryllium deposits of the central York Mountains, Alaska, in Ridge, J. D., ed., Ore deposits in the United States, 1933-67: American Institute of Mining, Metallurgy, and Petroleum Engineers, v. 2, p. 1555-1572. Sainsbury, C.L., 1969, Geology and ore deposits of the central York Mountains, western Seward Peninsula, Alaska: U.S. Geological Survey Bulletin 1287, 101 p. Sainsbury, C.L., 1972, Geologic map of the Teller quadrangle, Seward Peninsula, Alaska: U.S. Geological Survey Map I-685, 4 p., 1 sheet, scale 1:250,000. Steidtmann, Edward, and Cathcart, S. H., 1922, Geology of the York tin deposits, Alaska: U.S. Geological Survey Bulletin 733, 130 p. WGM Ltd., 1972, Preliminary feasibility report on the Lost River fluorite-tin-tungsten: Toronto, Canada, Lost River Mining Company, Limited, unpublished report, 291 p.