Rum South

Prospect, Active

Commodities and mineralogy

Main commodities Ag; Pb; Zn
Other commodities Au; Cu
Ore minerals arsenopyrite; chalcopyrite; galena; gold; magnetite; pyrite; pyrrhotite; sphalerite
Gangue minerals actinolite; chlorite; quartz

Geographic location

Quadrangle map, 1:250,000-scale MH
Quadrangle map, 1:63,360-scale A-1
Latitude 63.2362
Longitude -144.117
Nearby scientific data Find additional scientific data near this location
Location and accuracy The Rum South prospect is at an elevation of about 5,900 feet about 2 miles east of Rumble Creek and one-half mile west-southwest of peak 7405 and in the SW1/4 section 20, T. 17 N., R. 7 E., Copper River Meridian. The location is accurate.

Geologic setting

Geologic description

The Rum South prospect is in a west-northwest-trending, steeply south dipping sequence of metavolcanic and metasedimentary rocks that have been intruded by gabbroic sills in the central and basal part of the Drum sequence. The Rum North (MH342) occurrence is about 1,000 feet away from this prospect (R.A. Blakestad and others, unpublished Resource Associates of Alaska Inc. report, 1978). The Drum unit that hosts the Rum prospects consists of white to pale gray-green, rusty weathering, quartz-sericite(-chlorite-pyrite) schist with minor gray to black carbonaceous phyllite and rare interbeds of chloritic phyllite. The schist commonly contains 1 to 5 percent quartz eyes but may contain more. The protoliths of the schist are about two-thirds of volcanic origin and one-third of sedimentary origin. The schist has a phyllitic parting in many places (Dashevsky and others, 2003).
The Rum South prospect is stratigraphically below the Rum North prospect and separated from it by a major fault. The base of the footwall of the Rum South deposit is a fine-grained gabbroic body of unknown thickness. Immediately above the gabbro body, felsic metavolcanic rocks crop out; they consist of quartz-sericite schist, sericite-quartz schist, and quartz-sericite-chlorite schist with abundant quartz eyes and banded and disseminated pyrite. Ferricrete masses more than 8 feet thick are present, indicating considerable oxidation. The contact between the rhyolites and overlying graphitic schists displays considerable 'S' style folding and shearing. The layering generally has a southeast dip, and fold axes strike S73E. The quartz-graphite schist contains abundant interbedded lenses and beds of metarhyolite and arenaceous tuffs as much as 15 feet thick. Massive pyrite bands as much as a half-inch-thick are common along the margins of these units (R.A. Blakestad and others, unpublished Resource Associates of Alaska Inc. report, 1978).
The hanging wall rocks are similar to the footwall rocks. They are mostly fairly thin bedded felsic tuffs, crystal tuffs, and arenaceous tuffs that overlie the dark massive sulfide-bearing metasiltstone and arenites (R.A. Blakestad and others, unpublished Resource Associates of Alaska Inc. report, 1979).
The mineralization is exposed in three major and several smaller trenches over a strike length of 260 feet at Rum South. The westernmost occurrences is composed of several massive pyrrhotite boulders as much as 30 inches in diameter. This sulfide is composed of crudely banded fine- to coarse-grained (1 to 2 millimeter) sphalerite and blebs and veinlets of chalcopyrite set in a matrix of medium-grained pyrrhotite with subordinate pyrite. The gangue is quartz, chlorite, and actinolite (?). Chalcocite, hematite, and gypsum are locally present along fractures, and fine-grained galena is disseminated throughout. A grab sample from these boulders contains 0.85 percent copper, 5.8 percent lead, 7.6 percent zinc, and 5.5 ounces of silver per ton (R.A. Blakestad and others, unpublished Resource Associates of Alaska Inc. report, 1979). The main Rum South massive sulfide is commonly higher grade and has values that average 0.7 percent copper, 12.3 percent lead, 14.4 percent zinc, 180 parts per million (ppm) silver, and 1.8 ppm gold (Dashevsky and others, 2003).
Geologic map unit (-144.119249110018, 63.235823367637)
Mineral deposit model Kuroko massive sulfide (Cox and Singer, 1986; model 28a).
Mineral deposit model number 28a
Age of mineralization The Drum unit, which is part of the metamorphic sequence that includes the rocks at this deposit, has been dated at the Devonian-Mississippian boundary on the basis of one SHRIMP U-Pb zircon age of 359 +/- 6 Ma at the nearby DD South prospect (MH325).

Production and reserves

Workings or exploration As of 1979, a total footage of 725 feet of drilling in two holes had been completed at the Rum South prospect; there is no information on any more recent drilling. No significant thickness of sulfide was reported from the drilling, though poor recovery may have been a factor (S.S. Dashevsky, written communication, 2003). In addition, field work has included detailed geologic mapping, trenching, and detailed magnetic and soil geochemistry surveys over the mineralized areas (Rodney A. Blakestad and others, unpublished Resource Associates of Alaska Inc. report, 1979).
Indication of production None

Additional comments

The unpublished data that is cited can be seen by contacting Grayd Resources Inc. in Vancouver, B.C., Canada (www.grayd.com), or Northern Associates Inc. in Fairbanks, Alaska.

References

References

Lange, I. M., Nokleberg, W.J., Newkirk, S. R., Aleinikoff, J.N., Church, S.E., and Krouse, R.H., 1993, Devonian volcanogenic massive sulfide deposits and occurrences, southern Yukon-Tanana terrane, eastern Alaska Range, Alaska: Economic Geology, v. 88, p. 344-376.
Reporters W.T. Ellis (Alaska Earth Sciences), A.S. Wyatt and S.S. Dashevsky (Northern Associates, Inc. ), and W.J. Nokleberg(USGS)
Last report date 3/20/2003