The tin lodes and placers in this area were first identified by Asarco in 1975 after a review of geochemical data collected by the U.S. Geological Survey in 1968 and 1969 (Patton and Miller, 1973; Kurtak and others, 2002). From 1975 to 1983 a succession of companies and organizations including the U.S. Bureau of Mines, WGM Inc., British Petroleum, Patino Inc., and Doyon Ltd. mapped and studied the lodes and placers (Bright, 1989; WGM Inc., 1978, 1979a, 1979b, 1980a, 1980b; Patino Ltd., 1981, 1982; Barker and Foley, 1986).
The lode tin prospects are associated with the Early Cretaceous Sithylemenkat granitic batholith (Barker and Foley, 1986; Kurtak and others, 2002). Cassiterite has been identified in chlorite-rich and locally magnetite-bearing greisen zones in the granitic rocks. Mineralized samples exhibit variable effects of greisenization, with tourmaline and magnetite sometimes present. Sericite-quartz veins and altered dikes contain abundant secondary chlorite and may contain up to several percent sulfides. The sulfide minerals include pyrite, arsenopyrite, galena, and molybdenite. The greisen range in color from light to dark green; the highest tin values are in the darker varieties. The extent of the greisen is difficult to determine owing to poor exposures. Some zones have been traced for as much as 1,200 feet, and one greisen zone is up to 10 feet thick (Barker and Foley, 1986).
Thin sections of the greisen show relict porphyritic texture; feldspar phenocrysts are replaced by intergrown quartz and sericite, which in the more altered samples are replaced by chlorite and clay minerals.Greisen samples contained 25 to 2,300 parts per million (ppm) tin (Barker and Foley, 1986). The analyses also showed up to 5,126 ppm arsenic, 326 ppm, bismuth, 253 ppm cesium, 1,808 ppm copper, 3.4 percent lead, 1,156 ppm rubidium, 135 ppm tungsten, and 4,044 ppm zinc. Other samples contained anomalous tin, zinc, copper, and lead, as well as up to 25.9 ppm silver, 75.6 ppm uranium, and 101 ppm thorium (Kurtak and others, 2002).