Geologic description
The Rainbow quartz (-calcite) fissure vein occurs in the part of the Reid Inlet gold area (Kimball and others, 1978) underlain by granodiorite of Cretaceous age (Rossman, 1959, B 1058-B; Brew and others, 1978). Minor amounts of alaskite are present near the mine (MacKevett and others, 1971, p. 59). The Rainbow vein-bearing fault zone strikes about N 30 E, and dips 70 southeast to nearly vertical. The vein is narrow, generally 1 foot or less in thickness, but it is well mineralized. Arsenopyrite is common; galena and locally sphalerite are present up to a few percent each. Free gold is locally present. The vein was traced upslope for at least several hundred feet, and the vein-fault zone, nearly free of quartz, could be traced an additional 2000 feet up hill by subcropping bright red (hematitic?) altered rocks (Rossman, 1959, p. 52). The mineralization is similar to the LeRoy mine (MF022), moderately abundant auriferous sulfides in a quartz-calcite rich vein matrix. Locally the vein was rich. MacKevett found some rich parts of the vein when he sampled the Rainbow adit in 1966 (MacKevett and others, 1971, p. 59-60, table 11). Three samples collected below overhand-stoped quartz veins in the adit contained from 1.518 to 10.208 ounces per ton gold. The richest sample also contained about 2 ounces per ton silver, 1000 ppm arsenic, 100 ppm copper, 15 ppm molybdenum, 500 ppm lead, and 2000 ppm zinc. All the mineralized samples had trace amounts of molybdenum. (Bismuth, antimony, and tungsten were looked for but not found). Major elements contained in the veins include calcium up to 2 percent and magnesium up to 0.8 percent, along with iron, suggesting the possiblity of ankerite or dolomite in the gangue. |
Alteration of deposit |
Alteration was not described specifically at the Rainbow. In general for the Reid Inlet area, Rossman (1959, p. 43) says that the vein walls are altered for up to 10 to 15 feet from the veins. Oxidation formed a rust-red color, consistent with either sulfides or ankerite disseminated in the altered zone. MacKevett and others (1971, p. 59) noted abundant secondary iron minerals, gouge, and scattered free gold in the altered vein zones. |