Rock Glacier

Prospect, Active

Commodities and mineralogy

Main commodities Au
Ore minerals gold
Gangue minerals quartz

Geographic location

Quadrangle map, 1:250,000-scale CH
Quadrangle map, 1:63,360-scale C-3
Latitude 67.5428
Longitude -148.1872
Nearby scientific data Find additional scientific data near this location
Location and accuracy The Rock Glacier prospect consists is based on abundant float of cobbles and boulders of auriferous quartz-vein material in an area about 800 feet long and 150 feet wide on the lower west side of a prominent rock glacier in the cirque at the head of Little Squaw Creek. The coordinates are at about the center of the prospect. It is about 0.2 mile north of the center of section 3, T. 32 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 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). 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 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 [83 p.]). 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. This prospect in the cirque at the head of Little Squaw Creek is covered by alluvium, landslide material, glacial deposits, and thick soil with much solifluction. However, the rocks on both sides of the cirque are part of the Upper Plate unit and the rocks under the surficial material in the cirque probably are mostly Mikado Phyllite.
Before 2002 there was no record of mineralization on the prominent rock glacier in the cirque at the head of Little Squaw Creek. During the work by Little Squaw Mining Company (Barker and Bundtzen, 2004; Barker, 2006; Barker, 2007; Barker and others, 2009) an area about 800 feet long and 150 feet wide on the western side of the lower part of the rock glacier was found to be littered with cobbles and boulders of quartz-vein material and of altered argillized and brecciated schist similar to that found at many of the veins in the Chandalar area. A random chip sample of the white quartz contained 4.06 parts per million gold. The quartz float is so abundant that it points to an undiscovered zone of mineralization in the cirque.
Reconstruction of the source of the float indicates that it probably is associated with one of the west-northwest-trending shear zones along which most of the gold deposits in the Chandalar district are located. In this case, it is probably a fault that extends from the Eneveloe Mine (CH046) to the northwest and the Rachet Ridge prospect (CH114) to the southeast. Ground magnetic surveys and geochemical surveys over the likely site of the source of the float suggest that it consists of at least 4 and perhaps 6 veins. In 2011, Goldrich Mining Corp. drilled 5 holes on the Rock Glacier prospect that totaled 850 meters. Of the 15 intercept 0.3 to 11.3 meters long that contained more than 0.5 gram of gold per tonne, the best were 2.1 meters with 6.02 grams of gold per tonne and 1.5 meters with 4.17 grams of gold per tonne.
Geologic map unit (-148.189933109048, 67.5424177614698)
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 is no definitive data for the age of the veins of the Chandalar area.
Alteration of deposit Abundant quartz-vein float associated with rubble of argillized schist.

Production and reserves

Workings or exploration The work on the Rock Glacier prospect from 2004 to 2009 included sampling and geophysical and geochemical surveys. In 2011, Goldrich Mining Corp. drilled 5 holes on the Rock Glacier prospect that totaled 850 meters.
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).
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).
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, 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 D.J. Grybeck (Contractor, USGS)
Last report date 4/1/2012