Explained by Miles Silberman
On the choice of deposit models
Metamorphosed Proterozoic volcanic rocks, especially felsic volcanic rocks in greenstone terranes show an association of stratabound polymetallic massive sulfide deposits.
On the delineation of permissive tracts
The assessment criteria include: (1) submarine volcanic host rocks of felsic composition; (2) an island-arc tectonic setting, with local extensional deformation at the time of mineralization; and, (3) exhalative horizons within the supracrustal sequence associated with the volcanic rocks (for example, iron-formations or cherty horizons) that indicate the evidence for submarine hydrothermal hot-spring activity during volcanism. Mafic-dominant greenstone belts make up a significant part of Proterozoic terranes in New Mexico. These greenstones consist of metamorphosed submarine basalts and locally important felsic rocks which are the host rocks for volcanic massive sulfide deposits (Silberman, 1994). Robertson and others (1986) indicate where felsic- and mafic-dominant greenstone belts occur within the Precambrian outcrop areas of New Mexico, thus defining the permissive tract for kuroko massive sulfide deposits.
Important examples of this type of deposit
Significant production has come only from the Pecos deposit, a kuroko-type massive sulfide deposit hosted in metarhyolite in the Pecos greenstone belt (Silberman, 1994). Significant reserves have been drilled out at one other deposit, Jones Hill, hosted in similar rocks and only a few kilometers distant from the Pecos mine. Although no other significant deposits are known, there are large numbers of small mines and prospects in New Mexico, some of which produced minor amounts of Ag, Au, Cu, and other base metals.
On the numerical estimates made
Kuroko-type massive sulfide deposits small and tend to form in clusters, so the presence of several large deposits and numerous smaller deposits indicates that this process took place in New Mexico. Although the permissive tract is not large, it could contain a significant number of deposits of various sizes. For the 90th, 50th, 10th, 5th, and 1st percentiles, the team estimated 0, 1, 2, 4, and 6 or more deposits consistent with the grade and tonnage model for kuroko massive sulfide deposits (Singer and Mosier, 1986).
Robertson, J.M., Fulp, M.S., and Daggett, M.D., III, 1986, Metallogenic map of volcanogenic massive sulfide deposit occurrences in New Mexico: U.S. Geological Survey Miscellaneous Field Studies Map MF-1853-A, scale 1:1,000,000.
Silberman, M.L., 1994, Submarine exhalative and related Precambrian deposits of New Mexico: U.S. Geological Survey Administrative Report, 9 p.
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.