Miller Gulch

Mine, Active

Commodities and mineralogy

Main commodities Au
Other commodities Ag; Cu; Hg; PGE
Ore minerals cinnabar; chalcopyrite; gold; native copper; osmiridium
Gangue minerals garnet; magnetite

Geographic location

Quadrangle map, 1:250,000-scale MH
Quadrangle map, 1:63,360-scale A-2
Latitude 63.1748
Longitude -144.8266
Nearby scientific data Find additional scientific data near this location
Location and accuracy
The Miller Gulch mine is in a southwest-flowing, mile-long tributary of Slate Creek. The gulch begins in the S1/2 section 14, T. 20 S., R. 15 E., Fairbanks Meridian, where it trends generally westward. The gulch then turns south in the NW1/4 section 23, T. 20 S., R. 15 E., where it enters Slate Creek. Almost the entire gulch has been mined. The location is about the midpoint of the gulch and is accurate as the center of the placer deposit.
The Miller Gulch mine was approximately located by Cobb in several publications, including 1972 (MF-414), 1973 (B 1374), and 1979 as locality 15 in figure 6 (OFR 79-238). The approximate location of three placer mine operations in the gulch is shown by Rose (1967). The Miller Gulch mine is locality 65 of MacKevett and Holloway (1977) and appears to be included with Slate Gulch in locality 9 in table 3 of Nokleberg and others (1991).

Geologic setting

Geologic description

The lower part of Miller Gulch is incised in argillite of the Eagle Creek Formation of Pennsylvanian age (Richter and Dutro, 1975). This unit was previously mapped as Mankomen Formation of Permian age by Rose (1967). The upper part of the gulch is cut into a Tertiary conglomerate locally termed 'round wash' that unconformably overlies the Eagle Creek Formation. Gabbro of Triassic (?) age crops out on the west side of Miller Gulch, and fault-controlled (?) breccia, which trends northwest, crops out near the head of Miller Gulch (Rose, 1967). The 'round wash' possibly is correlative with the Gakona Formation of Eocene (?) age. It has been deformed and dips about 20 degrees north. The conglomerate is largely composed of diorite and gabbro clasts with lesser granodiorite, slate, graywacke, white quartz, and peridotite. Finer grained facies of the 'round wash' are predominantly schist and slate with some white quartz (Rose, 1967). The unit has been altered or weathered in place, and cobbles are covered with a rind of clay or hematite; some of the cobbles are slickensided (Chapin, 1919; C.C. Hawley, unpublished field mapping, 1967). The conglomerate resembles white channel gravels of the Klondike district, Yukon Territory, which have been extensively altered since their deposition.
Gold was discovered in Miller Gulch in about 1900, and mining commenced immediately. By 1903, the total production of the Chistochina district was about $365,000, of which about $175,000 came from Miller Gulch or nearby Slate Creek (Mendenhall and Schrader, 1903). Miller Gulch has been mined fairly continuously until the present.
The placer deposits in the creek vary from about 5 feet wide near the head of Miller Gulch to 200 to 300 feet wide near the mouth of the gulch. The thickness of the gravel ranges from 4 to 8 feet; most of it is derived from argillite of the Eagle Creek Formation. Some of the gravel is composed of granitic material derived from the 'round wash' (Mendenhall, 1903; Mendenhall and Schrader, 1903). Gold-bearing benches are present irregularly along the creek on both walls of the canyon of Miller Gulch to as high as about 200 feet above the canyon floor.
The gold in Miller Gulch is mainly flat, stained with iron and manganese, and only rarely found with remnant quartz. In the early days of the district, nuggets weighing as much as 1 ounce were common; some were as heavy as 4 ounces. The fineness of the gold varies from about 870 to 895 (Mendenhall and Schrader, 1903; Purington, 1905).
Placer concentrates consist of cinnabar, native copper, and small nuggets of osmiridium with major magnetite and minor garnet. Cinnabar and native copper are probably derived locally because they occur in veinlets with chalcopyrite in the argillite bed rock (Walt Ashwill, oral communication, November 2001).
The bulk of the gold in the creek appears to have been reconcentrated from the 'round wash' (Chapin, 1919; Rose, 1967; Cobb, 1973 [B 1374]; Yeend, 1981 [C 823-B, OFR 81-355]). Other sources include auriferous glacial deposits and mineralized veinlets in bedrock. Moffit (1912) proposed that most of the gold was derived from the older bedrock. The ultimate source of the 'round wash' is speculative; Rose (1967) proposed that most was from derived from an area north of the Denali Fault.
Geologic map unit (-144.828828781688, 63.1744041838882)
Mineral deposit model Placer Au-PGE (Cox and Singer, 1986; model 39a).
Mineral deposit model number 39a
Age of mineralization Eocene (?), Pleistocene, Holocene.
Alteration of deposit The 'round wash' has been extensively weathered or altered in place; it was argillized and cobbles are coated with hematite or clay (Chapin, 1919).

Production and reserves

Workings or exploration Miller Gulch was discovered in 1900. By 1903 about $175,000 (almost 8,500 fine ounces of gold) had been mined from Miller Gulch and nearby Slate Creek (Mendenhall and Schrader, 1903). The gravels along the gulch were mined extensively between 1903 and 1910 when mined slowed temporarily to allow exploitation of deposits in Slate Creek that could be covered by tailings from Miller Gulch (Moffit, 1909; Brooks, 1910; Moffit, 1912). In subsequent years production began on the higher level benches. Mining was reported in 1915 and 1916, although production in 1916 was limited by a shortage of water (Brooks, 1916). Mining activity increased in the 1930s; production was reported in 1932, 1938, and 1939 (Smith, 1934 [B 857-A], 1939 [B 917-A], 1941). The importance of the creek was recognized in summary papers by Moffit (1944, 1954). Mining on the creek was intermittently active in the 1960s (Rose, 1967). Activity increased again in the late 1970s to the mid-1980s as the price of gold rose.
Indication of production Yes; medium
Reserve estimates No reserves have been published, but some gold still exists in bench deposits and unmined remnants of the creek gravels.
Production notes Total production of Miller Gulch is uncertain but considerable. According to Koschmann and Bergendahl (1968), the Chistochina district produced about 141,000 ounces of gold between 1900 and 1959. This figure is minimal because the records are incomplete between 1931 and 1945, a period of active mining. Miller Gulch and Slate Creek produced most of the gold mined in the Chistochina district, although no definite amount is assignable to Miller Gulch. It seems likely, however, that Miller Gulch has produced at least about 50,000 ounces of gold. Approximately 1 ounce of platinum group metals was produced for every 100 ounces of gold.

References

MRDS Number A011774; M045390

References

Reporters W.T. Ellis (Alaska Earth Sciences), C.C. Hawley (Hawley Resource Group), and W.J. Nokleberg (USGS)
Last report date 7/2/2003