|Quadrangle map, 1:250,000-scale||SO|
|Quadrangle map, 1:63,360-scale||C-4|
|Nearby scientific data||Find additional scientific data near this location|
|Location and accuracy||The Saddle prospect is an area about 800 meters long by 300 meters wide. It was originally defined by anomalous arsenic and gold in soil samples; later 14 scattered holes were drilled in it. The center of the area is about 1.0 mile northeast of the abandoned settlement of Bluff. It is about 0.2 mile southwest of the center of section 32, T. 10 S., R. 25 W. The location is accurate.|
The Saddle prospect was first identified by BHP-Utah in 1995 as an area anomalous in arsenic and gold in soils. Subsequently they drilled 10 holes in the area before they dropped the property in 1990. In 2008, Millrock Resources Inc. (2010) began exploring in the area under an agreement with Bering Straits Native Corporation. Millrock's work on the Saddle prospect included geologic mapping and sampling, reanalysis of some of the BHP core, and geochemical soil surveys.
The Saddle prospect is near the center of an arcuate band of Paleozoic schist about three miles long and up to a half mile wide that extends from the mouth of Koryana Creek to the mouth of Daniels Creek (Herreid, 1965; Mulligan, 1971; Till and others, 1986; Stevens, 2010)) . This schist unit hosts most of the lode deposits in the Bluff area, including the Koryana (SO176), Daniels Creek (SO177), and Idaho (SO135) prospects. The schist is bordered to the north and south by thick, extensive marble; the schist-marble contacts are probably thrust faults.
There is little outcrop in the Saddle area and most of the information about it comes from the 10 BHP-Utah drill holes. As described by Ford (1993) and Ford and Snee (1996), the mineralization at the Saddle prospect is localized in extensional joints that strike easterly and dip moderately to the south in quartz-muscovite schist. The veins are discontinuous and commonly less than 3 inches thick. Gold grades are irregularly distributed; vein intersections up to 3.3 feet across contain up to 1.8 ounces of gold per ton. The quartz veins frequently contain a few percent of ore minerals, mainly arsenopyrite, but marcasite, pyrite, and pyrrhotite occur in small amounts. The veins are commonly bordered by altered zones with plagioclase, chlorite, carbonate, white mica, biotite, titanite, and tourmaline. A sample of white mica from a quartz vein gave an Ar/Ar plateau date of 109.1 +/- 0.2 Ma and metamorphic white mica in the host schist gave Ar/Ar total gas dates of 122.6 +/- 0.4 Ma and 122.4 +/- 0.2 Ma (Ford and Snee, 1996). This indicates that the mineralization at Saddle is Late Cretaceous and probably related to regional metamorphism as are many other deposits on the Seward Peninsula (Apodoca, 1994; Ford, 1993, Ford and Snee, 1996; Goldfarb and others, 1997).On the basis of their drilling, BHP-Utah concluded that the resources of the Saddle prospect was 1,500,000 tons of material with a grade of 7.77 grams of gold per tonne, or a total resource of 165,000 ounces of gold (Heine and Kell, 1991; Stevens, 2010). (However, Stevens also emphasized that the BHP-Utah 'resource' for Saddle was not 43-101 compliant.)
|Geologic map unit||(-163.722882708259, 64.5758632235706)|
|Mineral deposit model||Discontinuous, irregular to joint-con tolled arsenopyrite-quartz veins and breccia with disseminated arsenopyrite and pyrite in host rocks; low sulfide-Au quartz vein (Cox and Singer, 1986; model 36a).|
|Mineral deposit model number||36a|
|Age of mineralization||Mid-Cretaceous; a sample of white mica from a quartz vein gave an Ar/Ar plateau date of 109.1 +/- 0.2 Ma (Ford and Snee, 1996).|
|Alteration of deposit||Quartz veining; the veins are commonly bordered by altered zones with plagioclase, chlorite, carbonate, white mica, biotite, titanite, and tourmaline.|
|Workings or exploration||The Saddle prospect was first identified by BHP-Utah in 1995 as an area anomalous in arsenic and gold in soils. Subsequently they drilled 10 holes in the area before they dropped the property in 1990. As of early 2010, Millrock's work on the Saddle prospect included geologic mapping and sampling, reanalysis of some of the BHP-Utah core, and geochemical soil surveys.|
|Indication of production||None|
|Reserve estimates||On the basis of their drilling, BHP-Utah concluded that the resource of the Saddle prospect was 1,500,000 tons of material with a grade of 7.77 grams of gold per tonne or a total resource of 165,000 ounces of gold (Heine and Kell, 1991; Stevens, 2010). However, Stevens also emphasized that the BHP-Utah 'resource' for Saddle was not 43-101 compliant.|
Apodoca, L.E., 1994, Genesis of lode gold deposits of the Rock Creek area, Nome mining district, Seward Peninsula, Alaska: Boulder, Colorado, University of Colorado, Ph.D. dissertation, 208 p.
Asher, R.R., 1969, Geological and geochemical study, Solomon C-5 Quadrangle, Seward Peninsula, Alaska: Alaska Division of Mines and Geology Geologic Report 33, 65 p., 2 sheets.
Cobb, E.H., 1978, Summary of references to mineral occurrences (other than mineral fuels and construction materials) in the Solomon quadrangle, Alaska: U.S. Geological Survey Open-File Report 78-181, 185 p.
Collier, A.J., Hess, F.L., Smith, P.S., and Brooks, A.H., 1908, The gold placers of parts of Seward Peninsula, Alaska, including the Nome, Council, Kougarok, Port Clarence, and Goodhope precincts: U.S. Geological Survey Bulletin 328, 343 p., 4 sheets, scale 1:250,000.
Ford, R.C., 1993, Geology, geochemistry, and age of gold lodes at Bluff and Mt. Distin, Seward Peninsula, Alaska: Golden, Colorado School of Mines, Ph.D. dissertation, 302 p.
Ford, R.C., and Snee, L.W., 1996, 40Ar/39Ar thermochronology of white mica from the Nome district, Alaska--The first ages of lode sources to placer gold deposits in the Seward Peninsula: Economic Geology, v. 91, p. 213-220.
Goldfarb, R.J., Miller, L.D., Leach, D.L., and Snee, L.W, 1997, Gold deposits in metamorphic rocks in Alaska, in Goldfarb, R.J., and Miller, L.D., eds., Mineral Deposits of Alaska: Economic Geology Monograph 9, p. 151-190.
Heine, R., and Kell, R., 1991, 1990 Bluff Gold Exploration Summary Report-Parts 1, 2, 3, and 4:
Herreid, G.H., 1965, Geology of the Bluff area, Solomon quadrangle, Seward Peninsula, Alaska: Alaska Division of Geological and Geophysical Surveys Geological Report 10, 21 p., 1 sheet, scale 1:40,000.
Miller, E.L., and Hudson, T.L., 1991, Mid-Cretaceous extensional fragmentation of a Jurassic-Early Cretaceous compressional orogen, Alaska: Tectonics, v. 10, p. 781-796.
Millrock Resources Inc., 2010, Bering Straits Native Corporation Lands: http://www.millrockresources.com/index.php/projects/bering_straits/ (as of Feb 10, 2010).
Mulligan, J.J., 1971, Sampling gold lode deposits, Bluff, Seward Peninsula, Alaska, with a section on petrography by Walter L. Gnagy: U.S. Bureau of Mines Report of Investigations 7555, 40 p.
report prepared for BHP-Utah Minerals Int.
Stevens, D.L., 2010, Bluff Gold prospect, Seward Peninsula, western Alaska: NI43-101 Technical Report for Millrock Resources Inc., 153 p. (posted on www.sedar.com on February 4, 2010).)
|Reporters||Travis L. Hudson (Applied Geology); D.J. Grybeck (Contractor, U.S. Geological Survey)|
|Last report date||4/2/2010|