Mineral resource studies of national forest roadless areas in Idaho

Abstract

Within the group 1 study area, there are tracts permissive for the occurrence of undiscovered deposits of five types: Tertiary low-fluorine porphyry molybdenum, Cretaceous low-fluorine porphyry molybdenum, Comstock-type epithermal veins, polymetallic quartz veins and lodes, and radioactive black sand placers. One tract permissive for Tertiary low-fluorine porphyry molybdenum (fig. 3) has a 10 percent chance of containing at least one undiscovered deposit of a type that has a median size of 94 million tonnes of ore and a median grade of 0.085 percent molybdenum. Estimated mean metal endowment for this tract is 50,000 tonnes of contained molybdenum. One tract permissive for Cretaceous low-fluorine porphyry molybdenum (fig. 4) has a 50 percent chance of containing at least one and a 10 percent chance of containing at least two undiscovered deposits of a type that has a median size of 94 million tonnes of ore and a median grade of 0.085 percent molybdenum. Estimated mean metal endowment for this tract is 200,000 tonnes of contained molybdenum. One tract permissive for Comstock-type epithermal veins (fig. 5) has a 50 percent chance of containing at least one and a 10 percent chance of containing at least two undiscovered deposits of a type that has a median size of 770,000 tonnes of ore and a median grade of 7.5 grams/tonne gold and 110 grams/tonne silver. Estimated mean metal endowment for this tract is 25 tonnes of contained gold and 1,700 tonnes of contained silver. One tract permissive for polymetallic quartz veins and lodes (fig. 6) has a 10 percent chance of containing at least one undiscovered deposit of a type that has a median size of 12,000 tonnes of ore and a median grade of 14 grams/tonne gold. Estimated mean metal endowment for this tract is 0.2 tonnes of contained gold. Tracts permissive for radioactive black sand placers (fig. 7) were defined, but no estimate was made of the number of undiscovered deposits present. There is not adequate information on this deposit type to develop descriptive or grade/tonnage models. Group 1 Group 1 8 Polymetallic quartz veins and lodes Deposits are in veins of vuggy brecciated quartz within and next to massive composite quartz veins that commonly form prominent topographic features. Some of the massive quartz veins are exposed for distances exceeding 2 mi. This is a common deposit type in this region, occurring throughout the Idaho batholith. Examples within the map area include the Atlanta and Rocky Bar deposits. The ore zones constitute only a portion of the extensive quartz veins and lodes and are often separated by several tens to hundreds of feet of barren quartz. Most of the production was for gold and silver, although some veins contain significant amounts of lead, zinc, copper, and antimony. Individual ore bodies range from a few tonnes in isolated pods to pipe-like lenses as much as 450 ft long, 8 ft wide, and more than 1,000 ft deep. Ore grades vary considerably but across the larger ore bodies average 11-16 grams/tonne gold and 34-58 grams/tonne silver. Radio...

A compilation of spatial digital databases for selected U.S. Geological Survey nonfuel mineral resource assessments for parts of Idaho and Montana

“…This report compiles areas of mineral potential and their degree of potential from published mineral resource maps into consistent spatial databases. The 13 USGS mineral resource assessment areas included in this compilation are (1) the Absaroka-Beartooth study area, Custer and Gallatin National Forests (Hammarstrom and others, 1993); (2) the Dillon BLM Resource Area (Hammarstrom and others, 1999;Van Gosen and others, 1998a;Van Gosen and others, 1998b); (3) the Gallatin National Forest (Wilson and others, 2005); (4) the Helena National Forest (Tysdal and others, 1996;Green and Tysdal, 1996); (5) the National Forest roadless areas in Idaho (Johnson and Worl, 1991); (6) the Payette National Forest (Bookstrom and others, 1998); (7) the Custer National Forest in the Pryor Mountains (Van Gosen and others, 1996); (8) the Butte 1° x 2° quadrangle (Elliott and others, 1992a;Elliott and others, 1992b;Elliott and others, 1993b); (9) the Challis 1° x 2° quadrangle (Fisher and Johnson, 1995); (10) the Challis National Forest (Worl and others, 1989); (11) the Choteau 1° x 2° quadrangle (Earhart and others, 1981b); (12) the Dillon 1° x 2° quadrangle (Pearson and others, 1990;Pearson and others, 1991;Pearson and others, 1992a;Pearson and others, 1992b); and (13) the Wallace 1° x 2° quadrangle (Harrison, Cressman, and others, 1986;Harrison, Domenico, and Leach, 1986a;Harrison, Domenico, and Leach, 1986b;Harrison and others, 1986a;Harrison and others, 1986b).…”

“…Johnson and Worl (1991) id1ctevg.e00 Comstock epithermal vein do 634 do id1pqvnlg.e00 polymetallic quartz vein and lode (mixed base-and precious metal veins) do 1267 do id1rbsdpg.e00 radioactive black sand placers do 634 do id1tlfmog.e00 Tertiary low-fluorine porphyry molybdenum deposits do 697 do id2clfmog.e00 Cretaceous low-fluorine porphyry molybdenum do 845 do…”