Coal Creek

Prospect, Active

Commodities and mineralogy

Geographic location

Quadrangle map, 1:250,000-scale TK
Quadrangle map, 1:63,360-scale D-6
Latitude 62.9909
Longitude -149.8633
Nearby scientific data Find additional scientific data near this location
Location and accuracy The Coal Creek prospect is at an elevation of about 2,800 feet, approximately 2 miles east of lower Eldridge Glacier and about 0.4 mile northwest of hill 2650. It is near the head of an unnamed, small south- flowing tributary of Coal Creek in the SW1/4 sec. 21, T. 22 S., R. 12 W., Fairbanks Meridian. The location is accurate and it is approximately at the center of 15 claims staked on the prospect in 2005.

Geologic setting

Geologic description

Tin-silver mineralization was discovered at Coal Creek in 1972 by C. C. Hawley (Clark and others, 1972). The deposit was staked by Houston Oil and Minerals in 1980 and they explored the deposit until 1985. Their work included geologic mapping, trenching, surface sampling, and airborne and ground geophysics; they also drilled 42 holes totaling 17,193 feet. The U.S. Bureau of Mines examined the deposit in 1984 and 1988 (Parker, 1991, Kurtak and others, 1992). In 2005, Brett Resources staked 15 State of Alaska claims over the deposit and commissioned a NI 43-101 report (Ellis, 2006) on the property. The report relied heavily on the previous studies, drill hole information, and analytical data, but also involved relogging of the old core, analysis of old core that had not previously been analyzed, and reanalysis of selected portions of the old core with more modern methods to get a better definition of its metal content. In the late summer of of 2006, Brett drilled 4 holes to confirm historic values; their results were 'significantly lower than from earlier work' (Brett Resources, Inc., 2006).
The Coal Creek silver-tin deposit is a barely eroded, sheeted tin greisen (Reed, 1978; Thurow, 1983; Parker, 1991; Ellis, 2006). The deposit is at the top of a multiphase, 50-55 Ma granitic body made up of seriate granite porphyry that is intruded at depth by fine-grained equigranular porphyritic granite. The granite intrudes Devonian clastic sedimentary rocks and limestone that is altered to skarn near the granite. The mineralization is in steeply dipping, tabular sheeted greisen bodies in the granite that are characterized by quartz, tourmaline, topaz, sericite, and minor fluorite.
The mineralization consists mainly of coarse-grained sphalerite, cassiterite, arsenopyrite, and pyrrhotite in quartz veins in the greisen; disseminated ore minerals also are in the silicified margin of the granite and in the hornfels. The veins vary in width from hairline to 1 cm, are nearly vertical, and reach a density of 10 veins per meter in the most intensely fractured zones. The veins form a stockwork along a fracture zone in granite in an area of about 4,000 square meters (Thurow, 1983). The mineralization extends to the bottom of the drill holes, about 700 feet. In addition to the primary minerals, bismuthinite, chalcopyrite, galena, loellingite, marcasite, pyrite, stannite, and wolframite also occur and samples collected by Reed (1978) contained up to 4.3 ounces of silver per ton. Selected samples collected by Balen (1990) have up to 65 ppm silver, 0.5 ppm gold, 328 ppm lead, 720 ppm tungsten, and 4.86 percent zinc. In the limited drilling in the late summer of 2006 (Brett Resources Inc., 2006), the best intercepts were were: 1) 9.4 meters with 18.21 ppm silver, 0.41 percent tin, and 0.81 percent zinc; and 2) 9.3 meters with 11.95 ppm silver, 0.45 percent tin, and 0.29 percent zinc.
Thurlow (1982) estimated that the deposit as drilled by Houston Oil and Minerals contain 4.85 million tons of mineralized greisen with an average grade of 0.27 percent tin. However Ellis (2006) emphasized that these figures are more conceptual than adhering to modern standards for defining mineral resources.
Geologic map unit (-149.865583231228, 62.9904166780969)
Mineral deposit model Tin greisen (Cox and Singer, 1986; model 15c).
Mineral deposit model number 15c
Age of mineralization Probably genetically related to the 50-55 Ma granite that hosts the deposit.
Alteration of deposit Sericitization and greisenization of the granite host rock; hornfels developed at the borders of the granite.

Production and reserves

Workings or exploration Tin-silver mineralization was discovered at Coal Creek in 1972 by C. C. Hawley (Clark and others, 1972). The deposit was staked by Houston Oil and Minerals in 1980 and they explored the deposit until 1985. Their work included geologic mapping, trenching, surface sampling, and airborne and ground geophysics; they also drilled 42 holes totaling 17,193 feet. The U.S. Bureau of Mines examined the deposit in 1984 and 1988 (Parker, 1991, Kurtak and others, 1992). In 2005, Brett Resources staked 15 Alaska claims over the deposit and commissioned a NI 43-101 report on the property (Ellis, 2006). The report relied heavily on the previous studies, drill hole information, and analytical data, but also involved relogging of the old core, analysis of old core that had not previously been analyzed, and reanalysis of selected portions of the old core with more modern methods to get a better definition of its metal content. In the late summer of of 2006, Brett drilled 4 holes to confirm historic values; the results were 'significantly lower than from earlier work' (Brett Resources, Inc., 2006).
Indication of production None
Reserve estimates Thurlow (1982) estimated that the deposit as drilled by Houston Oil and Minerals contain 4.85 million tons of mineralized greisen with an average grade of 0.27 percent tin. However Ellis (2006) emphasized that these figures are more conceptual than adhering to modern standards for defining mineral resources.

Additional comments

MAS/MILS number 20760063.

References

MRDS Number A012176

References

Alaska: Field Report for the U.S. Dept. of the Interior, Bureau of Mines, p. 1-36.
Brett Resources Inc., 2006, Brett Announces Assays From Coal Creek, Alaska: http://www.brettresources.com/s/NewsReleases.asp?ReportID=159520&_Type=News-Releases&_Title=Brett-Announces-Assays-From-Coal-Creek-Alaska (News Release, November 23, 2006).
Ellis, W.T., 2006, Technical report on the Sleitat Mountain tin-silver deposit, southwest Alaska, NI 43-101 report: Unpublished Technical Report for Brett Resources, Inc., 57 p. (posted on www.sedar.com, April 10, 2008)..
Parker, Tracy V.L., 1991. Mineralization in the Coal Creek Tin Prospect, South-Central
Thurow, Gregory, Dec. 1983. Geology of Coal Creek Tin Prospect South-Central, AK: The Alaska Miner, vol. 11, #12, p. 24.
Thurow, Gregory E. 1982. Coal Project Annual Report: Internal Report for Houston Oil and Minerals, Inc. p. 1-10.
Reporters R.K. Rogers (U. S. Geological Survey); D. J. Grybeck (Port Ludlow, WA)
Last report date 6/5/2008