Mikado

Mine, Active

Alternative names

Little Mikado
Big Tobin
Carter
Eclipse
Overlook
Engineers Exploration Syndicate
Idaho-Alaska Corp.
St. Mary's

Commodities and mineralogy

Main commodities Au
Other commodities Ag; As; Pb; Sb; Zn
Ore minerals arsenopyrite; galena; gold; pyrite; sphalerite; stibnite
Gangue minerals dolomite; quartz; siderite

Geographic location

Quadrangle map, 1:250,000-scale CH
Quadrangle map, 1:63,360-scale C-3
Latitude 67.5335
Longitude -148.2528
Nearby scientific data Find additional scientific data near this location
Location and accuracy 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 1.6 miles southwest of Little Squaw Peak and about 0.6 mile south-southeast of the center of section 5, T. 31 N., R. 3 W., of the Fairbanks Meridian. The location of the mine is well known and accurately located. The Mikado vein extends up to a mile to the southeast where it is known as the St. Mary's vein (CH113).

Geologic setting

Geologic description

Placer gold was discovered in the Chandalar area on Little Squaw Creek (CH039) in 1902 (Barker and Bundtzen, 2004; Barker, 2007; Barker and others, 2009). By 1909, four quartz veins including the Mikado vein had been discovered and many more were located prior to WWI. Most of the important properties in the district were consolidated by William Sulzer from 1909 to 1941; the Mikado Mine was one of the prominent deposits of the Chandalar area and was included. Those properties were taken over in 1946 to form the Little Squaw Mining Company in 1959, which in turn became the Little Squaw Gold Mining Company in 1968. From 1967 to 1999, Little Squaw Gold Mining Company leased some of their Chandalar lode and placer ground for mining and/or exploration to a succession of companies, notably the Chandalar Gold Mining and Milling Company (1967-1971), Noranda Mining (1974-1976), the Chandalar Development Corporation (1980-1983), and Gold Dust Mines (1989-1999). There was some earlier small lode production from the district but the first documented gold produced from the lodes was 870 ounces produced from 1967 to 1971 from the Mikado and Summit mines by the Chandalar Gold Mining and Milling Company. Subsequently, Chandalar Development produced 8,169 ounces of lode gold from the Mikado and Summit Mines but recovery was poor. In 2003, Little Squaw Gold Mining Company and its direct descendent Goldrich Mining Company began an aggressive exploration program for lode and placer deposits over a large block of land that covers almost all of the known deposits in the Chandalar area. As of early 2012 that effort continued (Goldrich Mining Company, 2012).
The geology of the Chandalar area is dominated by a system of west-northwest-trending regional faults including a prominent thrust fault in the southern part of the district and a series of major high-angle faults through the center of the area (Bundtzen and Laird, 2007 [map], 2007 [technical report]). These faults separate the rocks into two principal units: a west-northwest-trending Upper Plate unit about 3 miles wide in the center of the area and a Lower Plate unit to the north and south. The contact of the two units is a thrust fault on the south side of the Upper Plate rocks and a high-angle fault on the north side. Most of the Upper Plate rocks consist of Devonian upper-greenschist-facies metamorphic rocks, mainly carbonaceous schist, quartz-chlorite-muscovite schist, schist and phyllite derived from turbidites that comprise the Mikado Phyllite, metamorphosed calcareous sandstone, and quartz-muscovite schist. The Lower Plate rocks consist of Devonian, upper-greenschist-facies metamorphic rocks, mainly metamorphosed volcanic agglomerate, chlorite-rich tuffaceous schist, quartz-mica schist derived from mudstone, mica-quartz schist, and quartzite. Both the Upper and Lower Plate rocks are cut by irregular masses, dikes and sills of greenstone, metagabbro, and metadiorite of unknown age. Most of the mineral deposits in the Chandalar area are in the Upper Plate rocks and the deposits often are along the regional, steep-to-vertical, west-northwest-trending faults. There is an additional conjugate set of north-northeast-trending faults that offset the Upper Plate rocks and at least some of the mineralization may be localized at the intersections of the regional west-northwest-trending faults and the conjugate faults.
The Mikado Mine is the most productive lode deposit in the Chandalar area and has been a center of attention from the earliest days of the Chandalar district (Barker and Bundtzen, 2004; Barker and others, 2009). The Mikado vein was discovered in 1909. Soon after, 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, were completed by 1913. In the following decades, the Mikado was frequently visited by industry and government. The underground workings were reopened in 1960, and over the next 24 years, there was considerable underground exploration, surface exploration and trenching, exploration and mining. Chandalar Gold Mining and Milling Company operated the Mikado Mine from 1967 to 1971 and produced 685 ounces of gold from ore that averaged 1.64 ounces of gold per ton (Barker and others, 2009); Callahan Mining mined in 1975 and recovered 185 ounces of gold from ore that averaged 0.85 ounce of gold per ton. Chandalar Development produced 6,822 ounces of gold from 1980 to 1983 from ore that averaged 0.93 ounce of gold per ton, although the mill recovery was poor. Since 2004, Little Squaw Gold Mining Company and its successor Goldrich Minerals have continued to explore the property (Barker and others, 2009; Goldrich Mining Company, 2011).
In 2011, Goldrich drilled 11 holes totaling 2,127 meters on the Mikado vein near the main portal of the old mine and about a half mile to the southeast on the vein's extension that is often called the St. Mary's vein (Goldrich Mining Company, 2011). The best intercepts were 0.9 meters with 4.58 grams of gold per tonne, 0.9 meters with 4.64 grams of gold per tonne, 0.9 meters with 10.25 grams of gold per tonne, 0.9 meters with 9.44 grams of gold per tonne, and 0.9 meters with 14.7 grams of gold per tonne.
As described by early workers, the Mikado vein is along a shear zone about 50 feet wide that contains sub-parallel, highly faulted and brecciated, steeply dipping gold-quartz veins and lenses 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 of the gouge-filled Mikado fault. The vein there appeared to be approximately 35 inches or less in width in the upper levels and narrowed 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 $20.67 per ounce of gold), and one ore shoot averaged $49.50 per ton over a 35-inch width (Chipp, 1970). Chipp 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: arsenopyrite, galena, sphalerite, stibnite, and pyrite. Native gold, as flakes or wires, is common in the Mikado; the gold typically occurs along the borders of sulfide grains or in quartz near sulfides. Sulfides generally form less than 5 percent of the main-stage veins. The gold veins in the Chandalar district are considered mesothermal (Barker and Bundtzen, 2004; Barker, 2006; Barker 2007; Barker and others, 2009) by comparison with similar deposits elsewhere and from fluid inclusion and oxygen and lead isotope studies of the Chandalar mineralization (Ashworth, 1983; Rose and others, 1988; Gacetta and Church, 1989).
The Mikado Mine is in a distinctive band of gray, carbonaceous phyllite, a major part of the Mikado Phyllite unit. Barker and Bundtzen (2004) note that the Mikado deposit is distinct in the district in that the structure in which the vein occurs, which may be tens of feet thick, is unusually thick and intensely sheared with abundant gouge. They also emphasize several generations of quartz veining, accompanied by faulting during, prior to, and after the mineralization event(s). Barker and others (2009) suggests that while rich pockets of ore were mined at the Mikado, they might better be considered as rich lenses along a 4,000-foot zone of mineralization that extends to the St. Marys deposit (CH113) and is open at both ends. The potential of this zone may be the extensive lower grade and probably more continuous mineralization that surrounds and extends beyond the smaller rich segments of the belt such as those that were mined in the Mikado.
Geologic map unit (-148.255531938926, 67.5331158907186)
Mineral deposit model Low-sulfide Au-quartz veins (Cox and Singer, 1986; model 36a).
Mineral deposit model number 36a
Age of mineralization Possibly mid-Cretaceous based on the assertion of Dillon (1982) that the gold-quartz veins of the central Brooks Range are that age. However, there are no definitive data for the age of the veins of the Chandalar area.
Alteration of deposit Oxidation of vein material produces scorodite and limonite.

Production and reserves

Workings or exploration The Mikado is the most productive lode deposit in the Chandalar area and has been a center of attention from the early history of the 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 over the next 24 years, there was considerable underground exploration, surface exploration, trenching, and mining. Chandalar Gold Mining and Milling Company operated the Mikado Mine from 1967 to 1971 (Barker and others, 2009); Callahan Mining mined in 1975; and Chandalar Development mined from 1980 to 1983. In 2004, Little Squaw Gold Mining Company and its successor Goldrich Minerals began an aggressive exploration program in the district that included work at the Mikado (Barker and others, 2009; Goldrich Minerals, 2011). In 2011, Goldrich drilled 11 holes totaling 2127 meters on the Mikado vein in the vicinity of the main portal of the old mine and about a half mile to the southeast on the vein's extension that is often called the St. Mary's vein (Goldrich Mining Company, 2011).
Indication of production Yes; medium
Reserve estimates Over the years, various geologists and engineers people have cited different reserve or resource figures for the Mikado Mine or the Chandalar district where the Mikado was the best known and largest deposit. For examples see Nokleberg and others (1987), Baggs and others (1), and Swainbank and others(1998). However the most recent estimate in 2005 after several periods of mining from 1967 to 1983 was by the Little Squaw Gold Mining Company (now Goldrich Mining Company) was that the Mikado Mine had 110 tons of proven resources with an average grade of 1.10 ounce of gold per ton and 5,200 tons of probable resources with an average grade of 1.05 ounce of gold per ton (Barker and Bundtzen, 2004; Barker and others, 2009).
Production notes The amount of gold produced from the Mikado vein prior to 1960 is unknown. There may have been some early production as a small stamp mill was constructed on Spring Creek by 1913 to process ore from the Mikado and Little Squaw Mines. The Mikado is the most productive lode deposit in the Chandalar area. Chandalar Gold Mining and Milling Company operated the Mikado Mine from 1967 to 1971 and produced 685 ounces of gold from ore that averaged 1.64 ounces of gold per ton (Barker and others, 2009); Callahan Mining mined in 1975 and recovered 185 ounces of gold from ore that averaged 0.85 ounce of gold per ton. Chandalar Development produced 6,822 ounces of gold that averaged 0.93 ounce of gold per ton, although the mill recovery was poor. As of the end of 2011, there had been no additional production (Barker and others, 2009).

References

MRDS Number A010680; A012558

References

Ashworth, K.K., 1983, Genesis of gold deposits at the Little Squaw mines, Chandalar mining district, Alaska: Bellingham, Western Washington University, M.Sc. thesis, 98 p.
Barker, J.C., 2007, Chandalar Mining District, Annual Report of findings for 2006; Unpublished report for Little Squaw Gold Mining Company, 124 p. (On the Internet at http://www.goldrichmining.com/Files/chandalar/chandalar_barker_rpt_2007.pdf, as of February 14, 2010).
Barker, J.C., and Bundtzen, T.K., 2004, Gold deposits of the Chandalar Mining District, Northern Alaska: An information review and recommendations: Unpublished report for the Little Squaw Gold Mining Company, 165 p. (in the files of the Goldrich Mining Company).
Barker, J.C., Murray, R.B., Keener, J.O., and Martin, P.L., 2009, Evaluation of the Chandalar mining property: Unpublished report prepared for Goldrich Mining Company, 165 p. (on the Internet at http://www.goldrichmining.com/Files/chandalar/Chandalar_tech_rept_4_15_09.pdf, as of February 14, 2010
Bundtzen, T.K., and Laird, G.M., 2007, Geologic map of the Chandalar Mining District, Brooks Range, Northern Alaska, 2007: Unpublished map prepared for Little Squaw Gold Mining Company, 1 sheet, scale 1:20,000. (on the Internet at http://www.goldrichmining.com/Files/chandalar/regional_chandalar_geo_map_final_07.pdf, as of February 14, 2010).
Goldrich Mining Company, 2009, Goldrich concludes successful mining test of Chandalar, Alaska placer gold: http://www.goldrichmining.com/Files/press_release/2009/GR_PRESS_Release_05_09.pdf (News release, November 9, 2009).
Goldrich Mining Company, 2011, Goldrich completes Chandalar, Alaska Phase I exploration drilling: http://www.goldrichmining.com/news/45-goldrich-completes-chandalar-alaska-phase-i-exploration-drilling.html (News release, November 30, 2011).
Goldrich Mining Company, 2012, Chandalar gold district: http://www.goldrichmining.com/properties/chandalar-gold-district.html (of of March 25, 2012).
Reporters J.M. Britton (Anchorage, Alaska); Travis Hudson (Applied Geology, Inc.); D.J. Grybeck (Contractor, USGS)
Last report date 4/1/2012