Cliff

Mine, Undetermined

Commodities and mineralogy

Main commodities Ag; Au
Other commodities Pb; Zn
Ore minerals arsenopyrite; gold; galena; pyrite; sphalerite
Gangue minerals albite; carbonate minerals; chlorite; quartz; sericite

Geographic location

Quadrangle map, 1:250,000-scale VA
Quadrangle map, 1:63,360-scale A-7
Latitude 61.1245
Longitude -146.5545
Nearby scientific data Find additional scientific data near this location
Location and accuracy The Cliff mine is on the north shore of Port Valdez, just east of the spit on the east side of the mouth of Shoup Bay. The mine is located on the USGS Valdez A-7 topographic map (1996). It is locality 18 of Cobb and Matson (1972) and locality 15 of Winkler and others (1981 [OFR 80-892-B]).

Geologic setting

Geologic description

The Cliff is one of the major mines in the Valdez area. A system of linked gold-bearing veins cut metaflysch of the Valdez Group here. Individual veins are an inch to 5 feet in thickness and occur in faulted zones with gouge and slickensides, particularly along the footwall (Grant and Higgins, 1910; Johnson, 1915). The veins enclose lenticular masses of country rock and have offshoots of quartz stringers into the hanging wall. The quartz is bluish and banded in places; other gangue minerals include calcite, albite, chlorite, and an unidentified carbonate mineral. Ore commonly contained 3 to 5 percent sulfide minerals, including pyrite, galena, sphalerite, arsenopyrite, and stibnite. The vein system strikes northwest and dips moderately both north and south. It can be traced for more than 1,700 feet along strike and more than 700 feet of vertically, from 442 feet above sea level to 332 feet below sea level (Johnson, 1915; Moffit, 1954). The Cliff mine was developed by more than 8,000 feet of underground workings on 10 levels. The veins were worked over about 775 feet of dip length (Jansons and others, 1984). Deeper levels were commonly flooded during non-operating periods. Production was principally between 1910 and 1918 and between 1936 to 1942, when it closed in response to Public Law 208 (Hoekzema and others, 1986). Total production at the Cliff mine was 51,740 ounces of gold and 8,153 ounces of silver from 29, 695 tons of ore (Hoekzema and others, 1986). The average grade indicated by this production was about 1.7 ounces of gold per ton, consistent with early reports (Grant and Higgins, 1910).
These deposits 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 (-146.556532045183, 61.1239764789037)
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 The deposit is variably oxidized to a depth of 100 feet. 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 Cliff mine vein system was traced for over 1,700 feet along strike land over 700 feet vertically, from 442 feet above sea level to 332 feet below sea level (Johnson, 1915; Moffit, 1954). It was developed by more than 8,000 feet of underground workings on 10 levels. Deeper levels were commonly flooded during non-operating periods. The facilities of the Cliff mine were obliterated by the tsunami that accompanied the Good Friday earthquake of March 27, 1964; the runup of this wave reached an elevation of 170 feet at the site of the Clff mine (Coulter and Migliaccio (1966).
Indication of production Yes; medium
Production notes Production was principally between 1910 and 1918 and between 1936 to 1942 when it closed in response to Public Law 208 (Hoekzema and others, 1986). Total production at the Cliff mine was 51,740 ounces of gold and 8,153 ounces of silver from 29, 695 tons of ore (Hoekzema and others, 1986). The average grade indicated by this production was about 1.7 ounces of gold per ton, consistent with early reports (Grant and Higgins, 1910).

References

MRDS Number A011459

References

Goldfarb, R.J., Miller, L.D., Leach, D.L., and Snee, L.W, 1997, Gold deposits in metamorphic rocks in Alaska, in Goldfarb, R.J., and Miller, L.D., eds., Mineral Deposits of Alaska: Economic Geology Monograph 9, p. 151-190.
Hudson, T.L., 1994, Crustal melting events in Alaska, in Plafker, G., and Berg, H. C., eds., The Geology of Alaska: Geological Society of America, DNAG, The Geology of North America, Vol. G-1, p. 657-670.
Reporters Travis L. Hudson
Last report date 12/14/2001