Explained by Michael F. Diggles
On the choice of deposit models
Northeastern California contains intermediate to felsic Tertiary and bimodal volcanic rocks and associated high-level intrusions. The region contains appropriate through-going fracture systems, major normal faults, and fractures related to doming (Rytuba, 1988; 1989). Classification of deposits as Comstock or Sado type requires information on basement geology that is not available (Klein and Bankey, 1992). Therefore, a combined Comstock-Sado model was used
On the delineation of permissive tracts
The tract encompasses all Tertiary volcanic rocks in northeastern California, and was delineated using the geologic map of California (Jennings, 1977). Volcanic sequences include andesite and rhyolite domes of Tertiary age and other manifestations of volcanic centers where magmatic events might generate ore-depositing hydrothermal systems.
Important examples of this type of deposit
There are no known quartz-adularia deposits in the area. The Skedaddle Mountain Wilderness Study Area on U.S. Bureau of Land Management land east of Susanville had over 280 lode claims for epithermal deposits (Diggles and others, 1987; Munts and Peters, 1987).
On the numerical estimates made
The estimators thought that there was an even chance of one or more undiscovered districts. For the 90th, 50th, and 10th percentiles, the team estimated 0, 1, and 2 or more quartz-adularia epithermal-vein districts consistent with the grade and tonnage model.
Diggles, M.F., Frisken, J.G., Plouff, Donald, Munts, S.R., and Peters, T.J., 1988, Mineral resources of the Skedaddle Mountain Wilderness Study Area, Lassen County, California, and Washoe County, Nevada: U.S. Geological Survey Bulletin 1706-C, 27 p.
Jennings, C.W., 1977, Geologic map of California: California Division of Mines and Geology, scale 750,000.
Klein, D., and Banky, V., 1992, Geophysical model of Creede, Comstock, Sado, Goldfield and related epithermal precious metal deposits, Cox and Singer models 25b Creede, 25c Comstock, 25d Sado, and 25e quartz-alunite Au, in Hoover, D.B., Heran, W.D., and Hill, P.L., eds., The geophysical expression of selected mineral deposit models: U.S. Geological Survey Open-File Report 92-0557, p. 98-106.
Munts, S.R., and Peters, T.J., 1987, Mineral resources of the Skedaddle study area, Lassen County, California and Washoe County, Nevada: U.S. Bureau of Mines Open-File Report MLA 022-87, 52 p.
Rytuba, J.J., 1988, Volcanism, extensional tectonics, and epithermal systems in the northern Basin and Range, CA, NV, OR, and ID [abs.]: Geological Society of Nevada Newsletter, May, 1988.
Rytuba, J.J., 1989, Volcanism, extensional tectonics, and epithermal mineralization in the northern Basin and Range Province, California, Nevada, Oregon, and Idaho, in Schindler, K.S., ed., U.S. Geological Survey Research on Mineral Resources —1989 Program and Abstracts, Fifth Annual V.E. McKelvey Forum on Mineral and Energy Resources [abs.]: U.S. Geological Survey Circular 1035, p. 59-61.