Kathleen-Margaret

Mine, Inactive

Alternative names

K-M

Commodities and mineralogy

Main commodities Cu
Other commodities Ag; Au; Hg; Sb; Sn; W
Ore minerals bornite; chalcocite; chalcopyrite; malachite; native copper; pyrite; sphalerite; stibnite
Gangue minerals calcite; epidote; quartz

Geographic location

Quadrangle map, 1:250,000-scale MH
Quadrangle map, 1:63,360-scale B-6
Latitude 63.2821
Longitude -146.5513
Nearby scientific data Find additional scientific data near this location
Location and accuracy The Kathleen-Margaret or K-M mine (Cobb, 1979 [OFR 79-238, p. 39-40]) is at an elevation of about 4,100 feet on the north side of what is locally named Discovery Creek, a tributary of the Maclaren River. (Discovery Creek is not named on the Mount Hayes B-6 quadrangle, 1973 edition.) The mine is in the NW1/4SW1/4 section 11, T. 19 S., R. 6 E., Fairbanks Meridian. The site corresponds to locality 17 of Kaufman (1964), Kardex site number KX68-4 (Heiner and Porter, 1972), locality 33 in table 2 of Nokleberg and others (1991), and locality A13 of Kurtak and others (1992). The location is accurate within 250 feet.

Geologic setting

Geologic description

Rock at the Kathleen-Margaret or K-M mine consists of basalt of the Nikolai Greenstone of Late Triassic age (Nokleberg and others, 1991). The rock is generally weakly cupriferous, and a 1- to 3-foot-thick layer of olivine basalt near the mine contains disseminated native copper and bornite (Saunders, 1961, p. 39 [report for the year]). The basalt is faulted and is cut by diabase and intermediate porphyry dikes of probable Late Cretaceous or early Tertiary age. A porphyry dike occupies a fissure a few feet from, and subparallel to, the main vein of the mine. Characteristic alteration minerals in the deposit include epidote, which occurs in quartz veins and in the vein walls.
Copper occurs mainly in a swarm of veins that strike nearly north and dip steeply. Most of the veins in the swarm are less than 3 feet thick and can only be traced for 100 feet or less (Chapman and Saunders, 1954; Kaufman, 1964). The main vein of the mine, which has been developed in open cuts and underground workings, is locally more than 10 feet wide. This vein contained an ore shoot about 60 feet long, 5 feet wide, and 100 feet high. Material in the ore shoot was rich in copper. A shipment of about 15 tons of high-grade ore from the shoot assayed about 16.15 percent copper, 1.5 ounces of silver per ton, and 0.066 ounce of gold per ton.
Copper-bearing veins, including the main vein, are either cut off or are weaker south of an east-west cross-structure. Veins consist mainly of quartz, calcite, bornite, chalcopyrite, and, where oxidized, malachite; locally they contain chalcocite, and barren parts of the veins are pyritic (MacKevett, 1964; Kurtak and others, 1992).
Anomalous levels of trace elements suggest that other minerals are present in small amounts. Antimony is generally present in assay quantities; its maximum detected concentration is 0.43 percent, an amount that led Kurtak and others (1992) to speculate that stibnite is present in the veins. Zinc content of about 500 parts per million (ppm) in a few samples suggests the presence of sphalerite. Mercury was detected in a few samples; the mercury content of the high antimony sample (sample 1124) is 721 ppm. Samples of vein material contain as much as 230 ppm tungsten, and 700 ppm tin was found in a sample that contained 13 percent copper (Nokleberg and others, 1991, 79IL036 sample series).
Most vein samples contain at least small amounts of gold and silver (Kurtak and others, 1992, table A13). It appears that the main ore shoot, described above, contained about 1.5 ounces of silver per ton and 0.066 ounce of gold per ton on an average basis. A 7-foot vein segment sampled by Chapman and Saunders (1954) assayed 0.18 ounce of gold per ton, 1.2 ounces of silver per ton, and 8.99 percent copper. An adjacent 1.75-foot copper-rich vein segment contained no gold, but it assayed 2.55 ounces of silver per ton and 30.45 percent copper. The high tin (700 ppm) sample of Nokleberg and others (1991) cited above also contained 300 ppm silver and 3.2 ppm gold.
Geologic map unit (-146.553566049896, 63.2816693603158)
Mineral deposit model Copper-bearing quartz vein in cupriferous metabasalt host. Basaltic Cu (Cox and Singer, 1986; model 23).
Mineral deposit model number 23
Age of mineralization The age is uncertain; judged from parallelism of the main vein and a porphyry dike of hypabyssal character, implying occupation of the same set of faults, the deposit is significantly younger than its Late Triassic host rock. The deposit could be as old as mid-Cretaceous, correlating with the regional metamorphism of the greenstone (Nokleberg and others, 1991), or as young as early Tertiary, correlating with emplacement of hypabyssal dikes. Stout (1976) proposed that copper deposits of Triassic basalt series were younger than Late Triassic and postdated a pre-Late Jurassic period of folding. It appears possible, probably likely, that copper was mobilized from the relatively copper-rich Nikolai Greenstone in more than one episode.
Alteration of deposit Formation of epidote; alteration of vein walls.

Production and reserves

Workings or exploration The Kathleen-Margaret was probably rediscovered by F.S. Pettyjohn, Jr., in 1952 after an original discovery in about 1918 (Stout, 1976; Martin, 1920). The property was examined in August 1953 by the U.S. Geological Survey and the Alaska Territorial Department of Mines (Chapman and Saunders, 1954). The outcrop of the main vein was sufficiently attractive to promote development. By 1961, more than 800 feet of workings had been driven and more than 2,000 feet of exploratory holes drilled (Saunders, 1961 [report for the year]). The U.S. Bureau of Mines determined that the copper minerals could be concentrated by flotation. A concentrate of 36.7 percent copper was made from ore grading 1.2 percent copper; copper recovery was more than 95 percent (Wells, 1956). Some geobotanical work was done on the property; only a copper-tolerant moss, Rhacomitrium sudeticom, grew on the copper-rich vein outcrops (Shacklette, 1965). Although surface exposures encouraged exploration, the small size of the ore shoot and possible loss of vein to faulting discouraged further work after about 1961.
Indication of production None
Reserve estimates Indicated and inferred reserves calculated at the close of a government-supported exploration program comprised 15,000 tons grading 3.5 percent copper (Zoldak and Albee, 1959). Mainly on the basis of geologic criteria, MacKevett (1964) calculated a copper resource of 46,000 tons grading 5.2 percent copper.
Production notes Total production is reported to be 15 tons of ore that contained 4,900 pounds of copper, 23 ounces of silver, and 1 ounce of gold (Kurtak and others, 1992, p. 108).

References

MRDS Number A011814

References

Heiner, L.E., and Porter, Eve, 1972, Alaska Mineral Properties, volume 2: University of Alaska, Mineral Industry Research Laboratory Report 24, 669 p.
Zoldak, S.W., and Albee, H.F., 1959 Final Report, DMEA Contracts IDM-E667 and E1093, Kathleen-Margaret claims, Alaska: Unpublished report, 11 p.; available from J.M. Kurtak, U.S. Bureau of Land Management, Anchorage, Alaska.
Reporters W.T. Ellis (Alaska Earth Science), C.C. Hawley (Hawley Resource Group), and W.J. Nokleberg (USGS)
Last report date 7/31/2001