Mikado; Little Mikado; Tobin; Carter; Eclipse; Overlook; Engineers Exploration Syndicate; Idaho-Alaska Corp. Mine, Chandalar Mining District, Yukon-Koyukuk Census Area, Alaska, USAi

Regional Level Types
Mikado; Little Mikado; Tobin; Carter; Eclipse; Overlook; Engineers Exploration Syndicate; Idaho-Alaska Corp. Mine	Mine
Chandalar Mining District	Mining District
Yukon-Koyukuk Census Area	Census Area
Alaska	State
USA	Country

Recent literature, and especially news notes, may confuse the Little Squaw and Mikado mines because the Mikado is owned by Little Squaw Mining Co. References to the Little Squaw property thus may refer to either the Little Squaw Mine, the Mikado Mine, or both. The names Idaho-Alaska Corp. and Engineers Exploration Syndicate associated with this property refer to the transaction in 1932 in which the Idaho-Alaska Corp. took over the leases and options formerly held by the Engineers Exploration Syndicate on various properties in the Chandalar district.
Location: The portal of the Mikado mine is on the north side of the upper end of the east branch of Tobin Creek. It is at an elevation of about 4,600 feet, approximately 1 1/2 miles southwest of Little Squaw Peak and 4 1/2 miles south-southwest of the south end of Squaw Lake, in the SE1/4 section 5, T. 31 N., R. 3 W., of the Fairbanks Meridian. The location is accurate.
Geology: The Mikado is the most productive lode deposit in the Chandalar area. Maddren (1913) reported open cuts that exposed auriferous quartz in six places over a strike length of 3,000 feet. Underground workings, including a 100-foot shaft and 160-foot adit, reportedly were completed by 1913. The underground workings were reopened in 1960, and an additional 600 feet of new workings were driven. An additional 800 feet was driven in 1962-63. An unknown amount of work was done in late 1960s, and again in the late 1970s and early 1980s (Bundtzen and others, 1982). Some bulldozer trenching was completed on veins in the area in 1962. The amount of gold produced from the Mikado vein prior to 1960 is unknown; however, a small stamp mill was constructed on Spring Creek by 1913 to process ore from the Mikado and Little Squaw mines. Production between 1960 and 1979 was reported to be approximately 1,000 ounces of gold and 200 ounces of silver (Cobb and Cruz, 1983). In 1979 the Little Squaw Gold Mining Co. resumed development and seasonal production; the ore was processed through a cyanide leach-flotation plant on Tobin Creek at a rate of 100 to 125 tons per day (Bundtzen and others, 1984). Production during 1981 was reported as 4,000 tons of ore worth $1.6 million (Bundtzen and others, 1982). In 1983 it was estimated that 10,000 ounces of gold had been recovered during the previous several years (1979-1982?) (Bundtzen and others, 1984). Lode production apparently ceased in 1983 due to lack of reserves and the high cost of the remote operations. In 2004, Little Squaw Gold Mining Company controlled 8,550 acres of patented and unpatented mining claims in the Chandalar district which includes the Mikado mine. This company contracted a district-scale analysis of the placer and lode gold potential of the district by Pacific Rim Geological Consulting, Inc. This study was completed in April, 2004 (Barker and Bundtzen, 2004). Discovered in 1909, the Mikado vein is one of several auriferous quartz veins in an area approximately 1 mile wide and 2 1/2 miles long between the heads of Tobin and Big creeks to the south and Squaw and Little Squaw creeks to the north. In general, most of the gold-bearing quartz veins in this area are in or near steeply dipping, northwest-trending normal faults in Devonian quartz-muscovite schist, phyllite, and quartzite intruded by Devonian mafic sills and dikes (Chipp, 1970). The intrusions have been metamorphosed to greenstone or greenschist. Major structural features include large-scale northeast-trending anticlines and synclines, northeast-trending thrusts, and the northwest-trending, high-angle cross faults. The Mikado vein/fault system is described as a shear zone about 50 feet wide which contains sub-parallel, highly faulted and brecciated, steeply dipping (generally 80N), auriferous quartz veins up to 6 feet thick which have been exposed for over 3,000 feet along the Mikado fault (Maddren, 1913). Although the Mikado vein is said to average 6 feet in thickness over a 500-foot strike length, most of the ore shoots are discontinuous and generally are a few tens or hundreds of feet long. According to Boadway (1933), the Mikado vein in the underground workings consists of lenses of auriferous quartz, mostly on the hanging wall side of a gouge-filled fault. The vein appears to be approximately 35 inches or less in width in the upper levels and narrows to 16 inches at a depth of 99 feet. Ore shoots in the vein reportedly assayed from $37 per ton to as high as $439 per ton (at $20 per ounce of gold), and one ore shoot averaged $49.50 per ton over a 35-inch width (Chipp, 1970). Drilling has intersected additional quartz in both the hanging wall and footwall of the fault. In a general description of the Chandalar gold-quartz lodes, Chipp (1970) indicated that white, crystalline to microcrystalline quartz is the dominant gangue mineral and that crystals of quartz are commonly found in small vugs. Banding in the quartz veins is produced by shearing and by elongate cavities in the veins parallel to the walls. Siderite occurs in minor amounts. Ashworth (1983) described three generations of quartz in the Mikado deposit: (1) lenses and pods of quartz plus or minus pyrite plus or minus dolomite, these are possibly pre-faulting metamorphic segregations; (2) massive, white, coarsely crystalline quartz with less than 5 percent sulfides and trace gold; and (3) 'main stage' quartz, which is fine grained, white, and in places vuggy. The sulfide assemblage in main stage quartz consists in decreasing order of abundance of arsenopyrite, galena, sphalerite, stibnite, and pyrite. Native gold, as flakes or wires, is common in the Mikado and typically is along the borders of sulfide grains or in quartz near sulfides. Sulfides generally form less than 5 percent of the veins. Early workers postulated the source of the gold-quartz mineralization to be small granitic intrusives, based largely on the presence of monazite and rutile in the placers (Mertie, 1925). Chipp (1970) suggested that there may be a genetic relationship with the the larger greenstone bodies as well. The genesis of these gold deposits is still in question, although various workers have hypothesized some genetic link to a variety of felsic and mafic igneous rocks from which the gold was remobilized during metamorphism (Mertie, 1925; Boadway, 1933; Chipp, 1970; Dillon, 1982).
Workings: Maddren (1913) reported open cuts that exposed auriferous quartz in six places over a strike length of 3,000 feet. Underground workings, including a 100-foot shaft and 160-foot adit, reportedly were completed by 1913. The underground workings were reopened in 1960, and an additional 600 feet of new workings were driven. An additional 800 feet was driven in 1962-63. An unknown amount of work was done in late 1960s, and again in the late 1970s and early 1980s (Bundtzen and others, 1982). Some bulldozer trenching was completed on veins in the area in 1962. In 2004, Little Squaw Gold Mining Company controlled 8,550 acres of patented and unpatented mining claims in the Chandalar district which includes the Mikado mine. This company contracted a district-scale analysis of the placer and lode gold potential of the district by Pacific Rim Geological Consulting, Inc. This study was completed in April, 2004 (Barker and Bundtzen, 2004).
Age: Middle Cretaceous(?) based on arguments by Dillon (1982) that the age of emplacement of the gold-bearing quartz veins of the Koyukuk and Chandalar districts was between the Neocomian metamorphism of the Devonian host rocks and their erosional unroofing and cooling in Albian time.
Alteration: Oxidation of vein material produces scorodite and limonite.
Production: The amount of gold produced from the Mikado vein prior to 1960 is unknown; however, a small stamp mill was constructed on Spring Creek by 1913 to process ore from the Mikado and Little Squaw mines. Production between 1960 and 1979 was reported to be approximately 1,000 ounces of gold and 200 ounces of silver (Cobb and Cruz, 1983). In 1979 the Little Squaw Gold Mining Co. resumed development and seasonal production; the ore was processed through a cyanide leach-flotation plant on Tobin Creek at a rate of 100 to 125 tons per day (Bundtzen and others, 1984). Production during 1981 was reported as 4,000 tons of ore worth $1.6 million (Bundtzen and others, 1982). In 1983 it was estimated that 10,000 ounces of gold had been recovered during the previous several years (1979-1982?) (Bundtzen and others, 1984). Lode production apparently ceased in 1983 due to lack of reserves and the high cost of the remote operations.
Reserves: Various reserve figures, which generally do not define reserves for specific deposits, have been published for the Chandalar area lode properties. Some of these figures are as follows: Bundtzen and others (1982) reported that in 1979 the Mikado property had proven reserves of 30,000 tons of ore with a grade of 1 ounce of gold per ton. Nokleberg and others (1987) reported 12,000 tonnes grading 75 grams of gold per tonne at the Mikado and Little Squaw mines. An inferred lode reserve for the Chandalar district lodes (as a whole) of 45,000 tons with a grade of 2 oz of gold per ton was reported as late as 1997 (Swainbank and others, 1998). Heiner and Wolff (1968) reported proved reserves estimated to be $2,000,000 with the ore valued at $85 per ton. Baggs and others (1988) reported that as of 1980, the district had 13,600 metric tons of measured resources, 4,500 metric tons of indicated resources. and 18,200 metric tons of inferred resources at a grade of 85.2 grams of gold per metric ton.

Commodities (Major) - Au; (Minor) - Ag, As, Pb, Sb, Zn
Development Status: Yes; small
Deposit Model: Low-sulfide Au-quartz veins (Cox and Singer, 1986; model 36a)

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Link to USGS - Alaska:	CH045

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References