Lost River-endogreisen

Mine, Active

Commodities and mineralogy

Main commodities Sn
Other commodities Ag; Cu; Pb; Zn; W
Ore minerals cassiterite; chalcopyrite; galena; sphalerite; wolframite
Gangue minerals arsenopyrite; fluorite; pyrite; quartz; topaz; tourmaline; white mica

Geographic location

Quadrangle map, 1:250,000-scale TE
Quadrangle map, 1:63,360-scale B-5
Latitude 65.474
Longitude -167.156
Nearby scientific data Find additional scientific data near this location
Location and accuracy
The Lost River Mine area includes the Cassiterite dike exogreisen deposit (TE048), the Lost River Mine skarn deposit (TE049), the Lost River Mine endogreisen deposit (TE050), and the Ida Bell dike exogreisen deposit (TE051). The Lost River endogreisen deposit is located in a subsurface granite cupola below the Lost River skarn deposit. The skarn is exposed along and east of Cassiterite Creek at elevations of 275 to 400 feet about 0.9 miles upstream from the creek's confluence with Lost River. The upper part of the endogreisen is within 100 to 200 feet of the surface whereas deeper parts extend to depths of 750 feet or more. This deposit was included as part of locality 8 by Cobb and Sainsbury (1972).
References were summarized under the name 'Lost River' by Cobb (1975).

Geologic setting

Geologic description

The Lost River endogreisen deposit is developed at the roof of a highly differentiated, fine-grained granite cupola and in sheeted zones at depth within the cupola. The Lost River skarn deposit is developed in Ordovician limestone country rocks adjacent to and above the endogreisen deposit. Late hydrothermal breccia, with mica- and clay-rich matrices, have been superimposed on both endogreisen and skarn (Dobson, 1982, figure 4). The age of 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). Fine-grained, leucocratic granite collected from a Lost River Mine dump has been dated at 80.2 +/- 2.9 my (Hudson and Arth, 1983, p. 769).
As described by Dobson (1982), the roof greisen is mica-rich, commonly 30 to 60 percent muscovite and probably zinnwaldite. The mica-rich greisen merges upward with hydrothermal breccias having a mica-rich matrix. Downward the mica-rich roof greisen gives way to quartz-rich greisen that characteristically contains tourmaline and sulfide minerals including pyrite, arsenopyrite, galena, sphalerite, and chalcopyrite. There are gradations from unaltered to completely greisenized granite but in places only thin, quartz-arsenopyrite, quartz-tourmaline, and greisen veins are present in granite. The roof greisen as mapped by Dobson (1982, figures 4 and 5), has dimensions of about 120 x 400 x 1,000 feet. Sainsbury's (1964, plate 9) compilation of grade data for this part of the deposit indicates that the general grade is a few tenths of a percent tin and a few hundredths of a percent WO3.
The deeper sheeted greisen was defined by Dobson (1982, figure 4) but it is primarily known from intercepts in two diamond drill holes completed by Texasgulf Inc. in 1979. Hole TG 2 (collared at 275 feet elevation, azimuth of N 19 E, inclined at 67.5 degrees, and a total depth of 1,012 feet) encountered: (1) 0.19 percent tin, 0.74 percent copper, 0.95 percent lead, 4.32 percent zinc, 2.73 ounces per ton silver, and 0.01 percent WO3 from 633 to 638 feet; (2) 1.21 percent tin, 0.05 percent copper, 0.06 percent lead, 0.03 percent zinc, 0.18 ounces per ton silver, and 0.06 percent WO3 from 638 to 647 feet; (3) 0.84 percent tin, less than 0.03 percent copper, 0.18 percent lead, 0.43 percent zinc, 0.27 ounces per ton silver, and 0.01 percent WO3 from 800.1 to 814.5 feet; and (4) 1.33 percent tin, less than 0.03 percent copper, less than 0.04 percent lead and zinc, 0.04 ounces per ton silver, and 0.05 percent WO3 from 814.5 to 823.6 feet. Hole TG 3 (collared at 321 feet elevation, azimuth of N 19 E, inclined at 64.5 degrees, and a total depth of 1,037 feet) encountered: (1) 0.28 percent tin, 0.08 percent copper, 0.78 percent lead, 0.80 percent zinc, and 1.75 ounces per ton silver (tungsten was not determined) from 778.5 to 789.8 feet; and (2) 0.88 percent tin, 0.08 percent copper, 0.20 percent lead, 2.13 percent zinc, and greater than 3.4 ounces per ton silver (tungsten was not determined) from 796.3 to 801.4 feet. Other zones of weaker tin metallization and weaker to stronger base metal and silver metallization are present in these holes. The metallization is in highly silicified zones with sulfide minerals, tourmaline, and fluorite in granite.
Geologic map unit (-167.158719355121, 65.4732245793714)
Mineral deposit model Endogreisen including roof and sheeted greisen. Tin greisen model (15c) of Cox and Singer, 1986).
Mineral deposit model number 15c
Age of mineralization The age of 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). Fine-grained, leucocratic granite collected from a Lost River Mine dump has been dated at 80.2 +/- 2.9 my (Hudson and Arth, 1983, p.769).
Alteration of deposit There is a well-developed quartz-tourmaline-fluorite greisen at depth, a mica-rich greisen in the roof zone, and both mica- and clay-matrix hydrothermal breccias above the roof zone. The greisen types appear to merge with one another and the breccias are late, overprinting assemblages.

Production and reserves

Workings or exploration This prospect has been explored by 750 feet of underground workings of the Lost River mine (32 and 195 crosscuts, Calcite drift, and 190 raise; Sainsbury, 1964, plate 9). The upper roof greisen has been encountered by many USBM and Lost River Mining Corporation drill holes and the deeper sheeted greisen zones have been encountered by two Texasgulf Inc diamond drill holes.
Indication of production None
Reserve estimates Resource estimates have not been separately determined for the endogreisen deposits; grades are commonly a few tenths percent tin and a few hundreths percent WO3 although some greisen sheets at depth have higher tin grades, base metals, and silver in places.
Production notes Production from the Lost River Mine has been from the Cassiterite dike exogreisen deposit (TE048).

References