Explained by Stephen E. Box and Arthur A. Bookstrom

On the choice of deposit models

This deposit type consists of massive quartz-gold veins that typically are low in sulfide minerals (<5 percent), are vertically and horizontally persistent, and are deformed into pinch-and-swell structures due to compressive deformation (Berger, 1986). These mesothermal veins occur in belts of regionally metamorphosed, low- to moderate-grade, marine sedimentary and volcanic rocks, penetratively deformed, and cut by high-angle regional-scale faults . Rocks of the Quesnellia terrane and the Covada Group of northeastern Washington (Stoffel and others, 1991) fit this description.

On the delineation of permissive tracts

The tract outlines the rocks of the Quesnellia terrane and the Covada Group in northeastern Washington (Stoffel and others, 1991). The tract boundaries were drawn to include areas that are covered by less than a km of younger rocks. Younger cross-cutting granitic plutons were excluded.

Important examples of this type of deposit

No major low-sulfide Au-quartz deposits are recognized in this tract in northeastern Washington. Small deposits north of Republic, Washington near Danville are considered by some to be examples of this type of deposit (Tschauder, 1989). However several deposits are known in correlative rocks in British Columbia less than 100 km to the north.

On the numerical estimates made

The lack of known low-sulfide Au-quartz deposits or prospects led the team to give a very low estimate for the occurrence of an undiscovered deposit here. For the 90th, 50th, 10th, 5th, and 1st percentiles, the team estimated 0, 0, 0, 0, and 1 or more deposits consistent with the grade and tonnage model of Bliss (1986).

References

Berger, B.R., 1986, Descriptive model of low-sulfide Au-quartz veins, in Cox, D.P., and Singer, D.A., eds., Mineral deposit models: U.S. Geological Survey Bulletin 1693, p. 239.

Bliss, J.D., 1986, Grade and tonnage model of low-sulfide Au-quartz veins, in Cox, D.P., and Singer, D.A., eds., Mineral deposit models: U.S. Geological Survey Bulletin 1693, p. 239–243.

Stoffel, K.L., Joseph, N.L., Waggoner, S.Z., Gulick, S.W., Korosec, M.A., and Bunning, B.B., 1991, Geologic map of Washington-Northeast quadrant: Washington Division of Geology and Earth Resources, Geologic Map GM-39, scale 1:250,000.

Tschauder, R., 1986, Gold deposits in northern Ferry County, in Joseph, N.L., ed., Geologic guidebook for Washington and adjacent areas: Washington Division of Geology and Earth Resources Information Circular 86, p. 239-254.