Genesis of Gold Deposits at the Little Squaw Mines, Chandalar Mining District, Alaska

The Little Squaw gold mines are located in the Chandalar Mining District, which is in the Brooks Range, 200 miles north of Fairbanks, Alaska. Country rock in the Little Squaw area consists of Devonian clastic and volcanic rocks which were subjected to two periods of upper greenschist facies metamorphism during the Cretaceous. A penetrative schistosity developed during the first metamorphic event, and thrust faulting and the development of a non-penetrative cleavage occurred during the second. Gold-bearing quartz veins in the Little Squaw area crystallized along high angle normal faults which post date thrust faulting and cross-cut the non-penetrative cleavage. Data obtained from the study of fluid inclusions from the gold-bearing quartz were used to determine physical and chemical conditions of ore deposition. It was found that the gold-bearing quartz veins in the Little Squaw area crystallized at about 275 degreesC and 825 bars from boiling fluids containing an average of .18 mole % CO2. Thermodynamic calculations suggest Au(HS)2- was the predominant gold transporting agent and transport as AuCl2- was insignificant. The presence of arsenopyrite, stibnite, and CO2-rich fluid with the gold suggests that arsenothio, antimonothio, and carbonate complexing may have contributed to the transport of gold. A drop from lithostatic to hydrostatic pressure, resulting from tectonic uplift and hydraulic fracturing, induced boiling of the hydrothermal fluids. The physiochemical changes that took place during boiling caused gold to precipitate. The search for additional ore shoots should center on locating the zone of boiling within post- metamorphic quartz-bearing structures in the Little Squaw area.