Rachet Ridge

Prospect, Active

Commodities and mineralogy

Main commodities Au
Other commodities As; Pb
Ore minerals arsenopyrite; galena; gold; pyrrhotite
Gangue minerals quartz

Geographic location

Quadrangle map, 1:250,000-scale CH
Latitude 67.5395
Longitude -148.1825
Nearby scientific data Find additional scientific data near this location
Location and accuracy The Rachet Ridge prospect is at the east side of the pass between the head of Little Squaw Creek and Big Creek. It is about 0.8 mile southeast of Little Squaw Peak, about 0.3 mile southeast of the center of section 3, T. 31 N., R. 3 W. The location is accurate.

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 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 and in early 2010, that effort continued (Goldrich Mining Company, 2010).
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, 2009a, 2009b). 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 rocks in the Rachet Ridge prospect area are part of the Upper Plate.
There was no record of work at the Rachet prospect until it was explored by Little Squaw Gold Mining Company in 2006. They found a short adit and several hand-dug pits that probably date to the early days of the district. In 2006, they excavated a trench on the prospect and drilled three reverse-circulation holes.
The rocks at the prospect are similar to those at the nearby Summit Mine (CH041), black carbonaceous schist overlain by light-gray, muscovite-chlorite-quartz schist. The Summit fault, one of the west-northwest-striking regional faults, is along the south side of the prospect. The veins at the prospect splay from the Summit fault and strike about N70E. There are at least 5 veins; where exposed they are about 2 feet thick. A quartz-vein sample with arsenopyrite and galena contained 2.88 parts per million (ppm) gold. One drill hole showed considerable pyrrhotite, arsenopyrite, and pyrite for 20 feet. Another had a 5-foot intercept with 0.28 ppm gold and a 10-foot interval with 0.32 ppm gold.
Geologic map unit (-148.185232680481, 67.53911776944)
Mineral deposit model Low-sulfide Au-quartz veins (Cox and Singer, 1986; model 36a).
Mineral deposit model number 36a
Age of mineralization Possibly Middle Cretaceous based on the assertion of Dillon (1982) that the gold-quartz veins of the central Brooks Range are that age. However, there is no definitive data for the age of the veins of the Chandalar area.
Alteration of deposit Not specifically mentioned.

Production and reserves

Workings or exploration An old adit and several pits probably date to the early 1900s. No record of any work until Little Squaw Gold Mining Company examined and sampled the prospect, did a magnetic survey, dug a trench, and drilled three, reverse-circulation holes in 2006.
Indication of production None
Reserve estimates None.
Production notes None.

References

References

Barker, J.C., 2006, Chandalar Mining District, a report of findings and recommendations, 2005: Unpublished report for Little Squaw Gold Mining Company, 93 p. (on the Internet at http://www.goldrichmining.com/Files/corporate/2005AnnualReport011906.pdf, as of February 14, 2010).
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).
Buzzell, R.G., 2007, History of the Caro-Coldfoot trail (RST 262) and the Coldfoot-Chandalar trail (RST 9): Alaska Office of History and Archaeology, Report 17, 138 p.
Goldrich Mining Company, 2010, Chandalar, Alaska; Project overview: http://www.goldrichmining.com/pages/prop_chan_over.htm (as of February 16, 2010).
Reporters D.J. Grybeck (Contractor, U.S. Geological Survey)
Last report date 4/2/2010