Road Cut II

Prospect, Inactive

Commodities and mineralogy

Main commodities Cu; Zn
Other commodities Ag; Au
Ore minerals chalcopyrite; pyrite; sphalerite
Gangue minerals epidote

Geographic location

Quadrangle map, 1:250,000-scale SK
Quadrangle map, 1:63,360-scale A-2
Latitude 59.19
Longitude -135.43
Nearby scientific data Find additional scientific data near this location
Location and accuracy This prospect occurs along the Mud Bay Road between mileposts 4 and 5 (from Haines). It is approximately 1 mile south of the Road Cut prospect (SK006) along the Mud Bay Road (Still, 1988). It is in the SE1/4, section 11, T. 31 S., R. 59 E. of the Copper River Meridian.

Geologic setting

Geologic description

According to Still (1988), spotty gold-copper-zinc mineralization extends for at least a mile, between mileposts 4 and 5 on the Mud Bay Road. Mineralization consists of epidote-altered metabasalt and epidote bands up to 2 feet thick that contain pyrite, chalcopyrite, and locally sphalerite. Samples contain up to 0.21 ppm gold, 2.5 ppm silver, 0.69% copper, and 1.83% zinc. This mineralization may be continuous with the Road Cut prospect (SK006). From the descriptions of Still (1988), it appears that mineralization at both prospects occurs along fault and shear zones that are subsidiary shears and splits of the Chilkat fault. If so, then the age of the mineralization is probably Tertiary or younger since most movement along the Chilkat Fault has probably been post-Mesozoic (Lanphere, 1978). Plafker, Hudson and Silberling (1979) and Plafker and Hudson (1980) cite fossil evidence for a Late Triassic (Karnian) age for the metabasalts on the Chilkat Peninsula. The age of a nearby ultramafic body is probably 108-109 m.y. based on potassium-argon ages from a pyroxenite at Battery Point (MacKevett and others, 1974).
Geologic map unit (-135.431828153259, 59.1896745314002)
Mineral deposit model Base metal sulfides with some precious metal values along a shear zone in metabasalt.
Age of mineralization The age is not well established. It can be no older than the Late Triassic age of the metabasalt that hosts the prospect (Plafker, Hudson and Silberling, 1979; Plafker and Hudson, 1980). If the structures that localize the mineralization are related to the Chilkat Fault, then the age of the mineralization is probably Tertiary or younger as most movement on the Chilkat Fault has been post-Mesozoic (Lanphere, 1978).
Alteration of deposit Epidotization.

Production and reserves

Workings or exploration In 1986-1987 the U.S. Bureau of Mines made shallow excavations and sampled the bedrock and rubble. They also ran two 440-foot-long magnetometer lines across the beach and road and up the escarpment that forms the eastern edge of the Chilkat Fault near milepost 5 of the Mud Bay Road. A prominent magnetic low indicates a fault zone that strikes N37W about 35 feet east of the Mud Bay road (Still, 1988). An approximately 30-foot-long adit in metabasalt is located several hundred feet southeast of milepost 4 on the Mud Bay road. No mineralization was seen in the adit, but a band of metabasalt adjacent to the adit contains chalcopyrite (Still, 1988).
Indication of production None

Additional comments

This prospect is within a mile of the Chilkat State Park.

References

MRDS Number 10308236

References

Lanphere, M.A., 1978, Displacement history of the Denali fault system, Alaska and Canada: Canadian Journal of Earth Sciences, v. 15, p. 817-822
Plafker, George, and Hudson, T., 1980, Regional implications of Upper Triassic metavolcanic and metasedimentary rocks on the Chilkat Peninsula, southeastern Alaska: Canadian Journal of Earth Sciences, v. 17, p. 681-689.
Reporters T.C. Crafford (T. Crafford & Associates, Anchorage)
Last report date 2/4/2001