Explained by Dennis P. Cox, Steve Ludington, and Michael F. Diggles

On the choice of deposit models

Volcanogenic massive sulfide deposits have been an historically important source of Cu, Zn, Ag, and Au. Their relatively high grades, simple metallurgy, and potential for large deposits make these deposits attractive exploration targets. Kuroko massive sulfide deposits form in marine volcanic rocks of intermediate to felsic composition that include marine rhyolite, dacite, and subordinate basalt and associated sedimentary rocks (Singer, 1986). In the West Shasta district, known deposits and host rocks are Devonian in age.

On the delineation of permissive tracts

The permissive tract is based on the extent of the Devonian Copley Greenstone and Balaklala Rhyolite, host rocks for deposits in the West Shasta district (Kinkel and others, 1956; Albers and Bain, 1985).

Important examples of this type of deposit

The West Shasta District, in the Klamath Mountains, has been an important mineral producer in the past. The Iron Mountain mine is one of the larger examples of volcanogenic massive sulfide deposits in the United States, and has produced nearly 11 metric tons of gold.

On the numerical estimates made

In light of the small size of the district, the relative ease of observing altered areas, and the thoroughness with which the area has been explored, low numbers were estimated. For the 90th, 50th, and 10th percentiles, the team estimated 0, 1, and 2 or more kuroko deposits consistent with the grade and tonnage model of Singer and Mosier (1986).

References

Albers, J.P., and Bain, J.H.C., 1985, Regional setting and new information onsome critical geologic features of the West Shasta copper-zinc district, Shasta County, California: Economic Geology, v. 80, no. 8, p. 2072–2091.

Kinkel, A.R., Jr., Hall, W.E., and Albers, J.P., 1956, Geology and base-metal deposits of West Shasta copper-zinc district, Shasta County, California: U.S. Geological Survey Professional Paper 285, 156 p.

Singer, D.A., 1986, Descriptive model of kuroko massive sulfide, in Cox, D.P., and Singer, D.A., eds., Mineral deposit models: U.S. Geological Survey Bulletin 1693, p. 189.

Singer, D.A., and Mosier, D.L., 1986, Grade and tonnage model of kuroko massive sulfide, in Cox, D.P., and Singer, D.A., eds., Mineral deposit models: U.S. Geological Survey Bulletin 1693, p. 190-197.