Upper Caribou Creek Mines, Kantishna Mining District, Denali Borough, Alaska, USAi

Regional Level Types
Upper Caribou Creek Mines	Group of Mines
Kantishna Mining District	Mining District
Denali Borough	Borough
Alaska	State
USA	Country

Caribou Creek, the most productive placer creek in the Kantishna district, is in Denali National Park and Preserve. It has not been mined since about 1985.
Location: Caribou Creek rises below Kankone Peak (Cobb, 1980 [OFR 80-363], 1973 [B 1374]). Major tributaries, all from the south, are Crevice (MM046), Last Chance (MM050), and Snowshoe creeks. They enter an upper segment of Caribou Creek that flows west-southwest and west for about six miles, then turns northerly for about three miles. As defined in this record, the upper Caribou placer deposit begins about in the middle of section 16, T. 15 S., R. 16 W., and ends in the north part of section 7, T. 15 S., R. 18 W., Fairbanks Meridian. The location is about at the midpoint of this segment of the creek, near where Snowshoe Creek enters from the south. It is about the same as number 48 of Cobb (1972 [MF 366]). Upper Caribou Creek, as defined in this record, also corresponds to block C-3 of Levell (1984 [v. 2]).
Geology: Caribou Creek below Crevice Creek cuts into Birch Creek Schist bedrock (Bundtzen, 1981); above Crevice Creek, several headward drainages cut into the Spruce Creek sequence. Caribou Creek rises below Kankone Peak. Initially, it is in a fairly steep canyon, dropping about 500 feet in a mile and a half. It begins to flatten out about in the center of section 16, T. 15 S., R. 16 E. The valley is fairly narrow, but at most places there is at least a 100 foot width of valley- bottom alluvium. In section 17 of R. 15 W, there are prominent south-valley benches. The valley begins to broaden in section 17, R. 16 W., but the north side of the creek continues to crowd the hills for about 3 more miles (Hawley and Associates, 1978; fig. 4.1-A(1)); Thornsberry, McKee, and Salisbury, 1984, fig. K-3). Gravel thickness gradually increases downstream, from a minimum of about 2 feet to about 12 to 14 feet. The earliest extensive mining was of the relatively thin, 2- to 7-foot-thick gravel section in and near modern Caribou Creek. The thin deposits were probably mined out before 1920 (Capps, 1919). Subsequent operations mined gravel sections mainly on the south side of the modern creek. These sections, which probably produced most of the gold mined in the creek, are as much as 300 feet wide. Locally, the south-side pay is bordered by higher benches. These benches apparently are frozen and have not been mined extensively. Gold in the upper Caribou deposit was uniformly silver-rich, with an average fineness of about 675. It was primarily bright and flaky, although the gold on bedrock was stained. It was accompanied by pebble- to sand-sized magnetite, ilmenite, and scheelite; near Last Chance Creek, the concentrate contained stibnite. Wolframite was tentatively identified at one locality, and Joesting (1942, 1941-1943) reported graphite. Although most of the gold is in fine flakes, nuggets up to about 5 ounce size are not uncommon. Crystallinity of gold increased upstream (Prindle, 1907; Capps, 1919; Joesting, 1942; Levell, 1984). Fairly extensive mining in Caribou Creek from 1939 to1948 suggests a fairly constant amount of gold on a bedrock-foot basis. The apparent grade is about 0.02 ounce per bedrock-foot; fluctuations in grade more or less reflect the depth of the deposit. In 1939-40, Caribou Creek gravel 10 to12 feet thick was mined downstream from Last Chance Creek; this gravel averaged about 0.013 fine ounce of gold per cubic yard. In 1941-42, the operation moved upstream of Crevice Creek, into gravel only 6 to7 feet thick. This material contained about 0.020 to 0.022 fine ounce of gold per cubic yard (calculations by C. C. Hawley from production records, 1939-1948). Some grades calculated in 1984 (Levell, 1984, v. 2) were significantly higher--nearly 0.03 fine ounce per cubic yard. These grades can be multiplied by about 1.5 to convert them to as-mined placer gold, based on an average gold fineness of about 675 for Caribou Creek. The difference between the grades computed from 1930-40s and 1980 records appears to reflect gold contained in the upper bedrock part of the pay section. The 1980s operations used excavators that could dig bedrock to a depth of about 3 or 4 feet, compared to a foot or less of bedrock dug by the tractors and draglines of the earlier operations. Gold from the Caribou Creek placer is the most silver-rich (average silver fineness 311) in the Kantishna Hills area (MM084). Only Stampede (MM142) and Little Moose (MM140) creeks, in the eastern outlying part of the Kantishna district, contain placer gold richer in silver. The difference in silver content suggests a difference in the source of the gold. The source of the gold in upper Caribou Creek appears to be argentiferous gold lodes in the Spruce and Kankone Peak areas. Creeks containing higher-fineness gold drain the southern part of the area, featuring such auriferous lodes as the one at the Banjo mine (MM097).
Workings: Except for an operation near Crevice Creek in 1905-6 (Prindle, 1907, 1911), the earliest extensive mining in Caribou Creek seems to have been on the gravel in and near the modern creek. A 1200-foot-long section of upper Caribou Creek between Last Chance and Crevice creeks mined in 1916 ranged from 10 to 70 feet wide. The gravel section was generally 2 to 3 1/2 feet thick, but was as much as 7 feet thick in some bars. Gold occurred throughout the section, but was concentrated on and just above bedrock. Gold in the gravel was bright and flaky; gold on bedrock was somewhat stained. Some nuggets up to about 5 ounces were recovered, and the fineness of the gold was about 655. Pebble-size magnetite, ilmenite, and scheelite, accompanied by large garnets accumulated with the gold in the sluice boxes (Capps, 1919, p. 92), and Prindle (1907) reported stibnite in the concentrates near Crevice Creek. Exploration in the early 1920s included gravels on the south side of the modern creek. Grades reported in 1921-1922 on upper Caribou Creek near Snowshoe Creek reportedly were about 0.01 to 0.03 ounce of gold per cubic yard. A fairly large hydraulic cut made in 1922 in this area apparently recovered less gold than that and the operation failed (Davis, 1923; Buzzell, 1988). Testing with churn drills in about 1924 and 1925 indicated ground with significantly less value (Charles G. Bigelow for Hammon Consolidated Dredging, written commun., 1925). Value on a bedrock- foot basis was reported as about 11 cents; this value is equivalent to about 0.012 ounce of gold per cubic yard in typical Caribou gravel about 7 feet thick. Testing of this ground with caissons in 1937 and 1938 suggested that the small- diameter churn drilling had underestimated the grade, and that it actually was about 0.02 ounce of gold per cubic yard. Similar values were obtained during medium-scale mining in 1939-1942 (Smith, 1941 and 1942; Bundtzen, Smith, and Tosdal, 1976; Bundtzen, 1978). In 1939 and 1940, a dragline mine operated below Last Chance Creek on gravel about 10 to 12 feet thick; computed grade of this ground in 1940 was 0.013 ounce of gold per cubic yard. In 1941-42, the operation moved upstream, above Crevice Creek, where the gravel was only about 6 to 8 feet thick. The respective average grades in those years were 0.0198 and 0.022 ounce of gold per cubic yard. These values are for fine gold; using an assumed fineness of about 660, the corresponding grades for placer gold respectively are about 0.030 and 0.033 ounces per cubic yard. Successful mining on the creek was by innovative methods. Caribou Mines (1939-1942) used a mobile Washington Iron Washing Plant fed by a dragline. Tractors were also used in the pit. That operation processed about 1,000,000 bedrock feet of placer material in each of three seasons before World War II, probably about the same amount in 1946, and lesser amounts in 1947-48. The operation was innovative for its time. Several of the 1975 and later operations used a mining technique developed by Sam and Jerome Koppenberg of KLK, Inc. A mobile washing plant was fed by a tracked, 2-cubic-yard excavator (back shovel). After stripping and pushback of overburden, the excavator cut a slot the length of the pit. This material was not processed, but spread over the surface to be mined. Mining commenced from a second parallel slot; water was discharged through tailings and recirculated. Slots were backfilled during mining, then overburden returned when the operation was completed. Water returned to the creek was not noticeably turbid. Kragness-Hayhurst used the same methods but substituted a jig for sluice processing in their operation on Caribou Creek.
Age: Pleistocene or Holocene.
Production: Small placer mines on upper Caribou Creek produced some gold from shovel-in operations before 1916. In 1916, these operations probably recovered about 300-500 ounces of gold from 1200 feet of the creek (Capps, 1919). Upper Caribou had small, subeconomic gold production in 1922 and 1923 from an ill-fated, large-scale hydraulic mine. W. E. Dunkle began exploration of Caribou Creek in 1937. He prospected by sinking caissons to bedrock and processing the material. Substantial production began in 1939 and continued until 1948, interrupted in 1943-45 by World War II. The 1939-42 operation was carried out by Caribou Mines, a partnership of Glen Carrington of the Carrington Company, W. E. Dunkle, L. C. Thomson of Montreal, Quebec, and W. B. Kluckhohn of Seattle. Dunkle sold his interest in the operation to Carringon after the war. Caribou Mines operated a Washingon Iron Works washing plant fed by about a one and a half cubic-yard dragline. Reported production, in fine ounces, from upper Caribou Creek from 1939 to 1948 was: 1939, 1657 ounces; 1940, 2935 ounces; 1941, 2373 ounces; 1942, 3203 ounces; 1946, 2327 ounces; 1947, 920 ounces; and 1948, 1300 ounces (Company records and Annual Production and Development of Metal Mines forms of the U. S. Bureau of Mines, National Archives, Anchorage) The total production of gold was 14,715 fine ounces, corresponding to about 21,800 ounces of placer gold. Approximately 6,800 ounces of silver were recovered. Operations in 1946-1948 were not profitable, although 1946 could have been, except for an early freeze-up that halted production. The rise in gold price in the early 1970s caused renewed interest in Caribou Creek. Placer gold production in this period probably was several thousand ounces. The total production of placer gold from the creek is probably between 25,000 and 30,000 ounces, corresponding to about 20,000 fine ounces.
Reserves: Levell (1984) calculated gold-bearing placer resources for upper Caribou Creek. He measured 1,980,000 cubic yards of high-potential alluvial gravel with estimated grades of 0.012 to 0.032 ounce of gold per cubic yard. The range in possible gold content is 23,760 to 63,360 ounces. The bench gravels comprise about 1,200,000 cubic yards. They have not been extensively mined or explored, and Levell assigned them only moderate potential. Their grade is uncertain. Assuming a grade of of 0.018 ounce per cubic yard, the calculated gold resource in the bench deposits of upper Caribou Creek is about 21,600 ounces.

Commodities (Major) - Ag, Au; (Minor) - Sb, W
Development Status: Yes; medium
Deposit Model: Au-PGE placer (Cox and Singer, 1986; model 39a).

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Link to USGS - Alaska:	MM042

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