Monte Carlo

Mine, Probably inactive

Alternative names

Chesna
Sunshine

Commodities and mineralogy

Main commodities Au
Other commodities Pb
Ore minerals arsenopyrite; galena; gold; pyrite
Gangue minerals carbonate minerals; chlorite; quartz; white mica

Geographic location

Quadrangle map, 1:250,000-scale VA
Quadrangle map, 1:63,360-scale A-7
Latitude 61.2288
Longitude -146.3453
Nearby scientific data Find additional scientific data near this location
Location and accuracy This mine is east of the Johnson Glacier and west of Mineral Creek. It is about nine-tenths of a mile northwest of the Smith Mill on Mineral Creek. The USGS Valdez A-7 topographic map (1996) shows this location with adit symbols and identifies it as the Big Four mine. However, this record follows Cobb and Matson (1972, locality 24), who showed this location to be the group of mines named above.

Geologic setting

Geologic description

An irregular body of quartz and an offshoot vein to it (the Monte Carlo claim) and quartz veins and stockworks (the Chesna claim) cut metaflysch of the Valdez Group (Johnson, 1915). The Monte Carlo quartz vein is as much as 5 feet thick and contains free gold, pyrite, and galena. This deposit was developed by two adits, and 4 tons of ore were mined in 1913. The lower adit was driven 145 feet and did not find the quartz vein. The upper adit intersected the vein about 36 feet in from the portal (Johnson, 1915). The quartz vein on the Chesna claim is 3 to 4 feet thick on the surface but narrows underground where it merges into a stockwork zone of quartz stringers (Johnson, 1915). The Chesna deposits were developed on three levels by adits that totaled about 750 feet in length. A thin quartz vein was explored by a 25-foot adit on the Sunshine claim (Brooks, 1912).
These veins are probably similar to other gold-bearing quartz veins cutting metaflysch of the Valdez Group in the southern Valdez quadrangle. Data summarized by Goldfarb and others (1997) show that gold-bearing quartz veins in the Valdez Group commonly contain pyrite, arsenopyrite, carbonate minerals, chlorite, and white mica and formed from water-rich fluids with 5 to 15 mole percent CO2 and significant amounts of CH4, N2, and H2S. The vein-forming fluid salinities were less than 8 percent, vein formation temperatures ranged from 225 to 375 degrees centigrade, and emplacement depths varied from 3 to 10 kilometers. The vein-forming fluids were produced by metamorphic devolatilization reactions. Radiometric dating indicates that the veins formed from 57 to 49 Ma (Goldfarb and others, 1997, p. 171), when deep parts of the accreted Valdez Group flysch underwent high-grade metamorphism and partial melting (Hudson, 1994).
Geologic map unit (-146.347356674177, 61.2282818335422)
Mineral deposit model Low-sulfide Au-quartz veins (Cox and Singer, 1986; model 36a)
Mineral deposit model number 36a
Age of mineralization Radiometric dating indicates that the gold-bearing quartz veins in the Valdez Group formed from 57 to 49 Ma (Goldfarb and others, 1997, p. 171), when deep parts of the accreted Valdez Group flysch underwent high-grade metamorphism and partial melting (Hudson, 1994).
Alteration of deposit Country rocks to gold-bearing quartz veins in Valdez Group metaflysch can be variably silicified, carbonitized, and sericitized (Goldfarb and others, 1997).

Production and reserves

Workings or exploration The Monte Carlo deposit was developed by two adits, and 4 tons of ore were mined in 1913. The lower adit was driven 145 feet and did not find the quartz vein. The upper adit intersected the vein about 36 feet from the portal (Johnson, 1915). The Chesna deposits were developed on three levels by adits that totaled about 750 feet in length. A 25-foot adit was driven on a thin vein on the Sunshine claim (Brooks, 1912).
Indication of production Yes; small

References