Western Montana and northern Idaho, showing locations of study area, major faults, and stratabound copper-silver deposits in the Revett Formation (from figure 1).
The western Montana copper belt in western Montana and northern Idaho contains several large stratabound copper-silver deposits in fine- to medium-grained quartzite beds of the Revett Formation of the Mesoproterozoic (1,470-1,401 Ma) Belt Supergroup. Production from the deposits at the Troy Mine and lesser production from the Snowstorm Mine has yielded 222,237 tons Cu and 1,657.4 tons Ag. Estimates of undeveloped resources, mostly from the world-class Rock Creek-Montanore deposits, as well as lesser amounts at the Troy Mine, total more than 2.9 million tons Cu and 2,600 tons Ag in 406 million tons of ore.
The Rock Creek-Montanore and Troy deposits, which are currently the most significant undeveloped resources identified in the copper belt, are also among the largest stratabound copper-silver deposits in North America and contain about 15 percent of the copper in such deposits in North America. Worldwide, stratabound copper-silver deposits contain 23 percent of all copper resources and are the second-most important global source of the metal after porphyry copper deposits.
The Revett Formation, which consists of subequal amounts of argillite, siltite, and quartzite, is informally divided into lower, middle, and upper members on the basis of the proportions of the dominant rock types. The unit thickness increases from north to south, from 1,700 ft near the Troy Mine, 55 mi north of Wallace, Idaho, to more than 5,300 ft at Wallace, Idaho, in the Coeur d'Alene Trough south of the Osburn Fault, a major right-lateral strike-slip fault.
Mineral deposits in the Revett Formation occur mostly in the A-D beds of the lower member and in the middle quartzite of the upper member. The deposits are concentrated along a preore pyrite/hematite interface in relatively coarse grained, thick quartzite beds that acted as paleoaquifers for ore fluids. The deposits are characterized by mineral zones (alteration-mineral assemblages) that are a useful guide to the locations of mineral deposits. In particular, the gradational zone between the chalcopyrite-ankerite and pyrite-calcite zones is the site of most mineral deposits.
Detailed information on the geology and mineral deposits of the Revett Formation is presented in the accompanying files that include (1) a tab-delimited text file providing details of the geologic and mineral-resource data for 57 Revett-subtype stratabound copper-silver deposits, occurrences, and prospects; (2) the stratigraphic records of 40 diamond-drill cores and 86 measured sections, totaling 150,752 ft of true thickness, which are provided in Excel spreadsheet and Adobe Portable Document Format files; and (3) spatial geologic data consisting of geologic maps of the Revett Formation, the subsurface locations of resources in Revett-subtype stratabound copper-silver deposits based on diamond-drill-core data, and the locations of diamond-drill holes and measured sections. The spatial data are contained in Arc/Info interchange files. Spatial information derived from these data includes the locations of mineral zones, a digital database showing untested exploration areas, and a digital database of permissive tracts for undiscovered mineral deposits.
Download the text for Scientific Investigations Report 2005-5231 as a 66-page PDF file (sir2005-5231_text.pdf; 27.1 MB)
Download Plate 1 for Scientific Investigations Report 2005-5231, Map of the Revett Formation, western Montana and northern Idaho, showing the locations of mineralized strata, diamond-drill holes, and measured sections as a ~35" x 44" PDF file (sir2005-5231_plate1.pdf; 1.3 MB)
Download Plate 2 for Scientific Investigations Report 2005-5231, Lithologic cross sections A-B and C-D, showing stratigraphic relations and mineral zones in the Revett Formation of western Montana and northern Idaho as a ~38" x 18" PDF file (sir2005-5231_plate2.pdf; 936 KB)
Download Plate 3 for Scientific Investigations Report 2005-5231, Maps showing pyrite-calcite zones in the upper and lower members of the Revett Formation, western Montana and northern Idaho, untested exploration areas, and permissive tracts for the occurrence of undiscovered Revett-subtype stratabound copper-silver deposits as a ~20" x 24" PDF file (sir2005-5231_plate3.pdf; 2.8 MB)
Download the logbook for Scientific Investigations Report 2005-5231 as a set of 127 up-to-11" x 17" pages in a PDF file (sir2005-5231_logbook.pdf; 7.8 MB)
Download the spreadsheets as a set of 126 Excel files in a zip file (sir2005-5231_spreadsheets.zip; 1.7 MB)
View the metadata files (9 .htm files; 352 KB total)
Download the spatial data as a set of three folders in a zip file (ArcInfo export files (6 .e00 files), metadata files (9 .htm files), and textfile (a .txt file and a .xml file); 1 MB)
For questions about the content of this report, contact Dave Boleneus or Mike Zientek
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URL of this page: http://pubs.usgs.gov/sir/2005/5231/
Maintained by: Michael Diggles
Created: April 24, 2006
Last modified: December 19, 2006 (mfd)