Val

Prospect, Active

Commodities and mineralogy

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

Geographic location

Quadrangle map, 1:250,000-scale MH
Quadrangle map, 1:63,360-scale B-1
Latitude 63.2574
Longitude -144.1074
Nearby scientific data Find additional scientific data near this location
Location and accuracy The Val prospect is approximately 3.5 miles south-southeast of the confluence of Robertson River and Rumble Creek at an elevation of about 5,300 feet. It is a about a mile south-southeast of peak 6,220 in the NE1/4 section 17, T. 17 N., R. 7 E., Copper River Meridian. This prospect is concealed by glacial debris. The location is accurate.

Geologic setting

Geologic description

The Val massive sulfide deposit is in felsic metavolcanic rocks of the upper Lagoon unit of Devonian age. The deposit is a sheet-like body as much as 17 feet thick. The prospect is one block in what was once part of a single continuous massive sulfide sheet that extended more than 2 miles along strike and is more than 40 feet thick. The massive sulfide bodies are now offset by high-angle faults into six deposits (Dashevsky and others, 2003).
The rocks around the Val prospect are part of the Tiger unit; however, the massive sulfide mineralization was intersected by drilling into the underlying metavolcanic rocks of the upper Lagoon unit. Drilling has defined an inferred resource of 1.3 million tons that average 0.3 percent copper, 0.6 percent lead, 4.4 percent zinc, 27 parts per million silver (ppm) and 1.2 ppm gold, accompanied by high arsenic and antimony values.
The Lagoon unit is a succession of dark gray, rusty, phyllitic metamorphosed mudstones interbedded with light-gray to white to pale-green siliceous quartz-sericite(-chlorite) schist. Locally the rocks contain coarse-grained blue quartz eyes and rare fragmental volcanic textures preserved as chloritized lithic fragments. The upper part is dominated by white to pale green, massive to laminated quartz-eye-bearing quartz-sericite(-chlorite-pyrite) schist; finely laminated schist with minor metamorphosed black mudstone; and thin intercalations of quartzite and fine-grained metamorphosed grit. The protoliths of the volcanic rocks of the upper Lagoon unit are mainly rhyodacite and dacite, but they also include rare rhyolite and minor andesite and basalt (Dashevsky and others, 2003).
Geologic map unit (-144.10965082598, 63.2570243633389)
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).
Alteration of deposit Development of sericite, quartz, pyrite, and carbonate in the hanging wall; extensive chlorite and magnesium enrichment and sodium depletion in the footwall.

Production and reserves

Workings or exploration The Val prospect was discovered by finding massive sulfide float boulders during stream-sediment reconnaissance in 1976 (Rodney A. Blakestad and others, unpublished Resource Associates of Alaska Inc. report, 1976). The deposit is a buried target that is covered by glacial ice and moraine. Extensive geological, geochemical, and geophysical surveys were conducted from 1976 to 1998. Electromagnetic geophysical surveys were instrumental in recognizing this deposit. Three core holes totaling 2,018 feet have been drilled (Dashevsky and others, 2003).
Indication of production None
Reserve estimates The Val deposit has an inferred resource of 1.3 million tons that averages 0.3 percent copper, 0.6 percent lead, 4.4 percent zinc, 27 parts per million (ppm) silver and 1.2 ppm gold. The resource calculation includes only those contiguous bodies with a true thickness greater than 8 feet and a gross metal value of greater than $80.00 per ton at 1998 prices (Dashevsky and others, 2003).

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) and A.W. Wyatt and S.S. Dashevsky (Northern Associates Inc.)
Last report date 3/20/2003