A mineral resource assessment was performed by the U.S. Geological Survey (USGS) to assess the potential of undiscovered skarn-hosted tungsten resources in the Northern Rocky Mountain region of eastern Idaho and western Montana. This region has seen moderate tungsten trioxide (WO3) production in the past from a variety of mineralization styles including skarn, vein and replacement, and wolframite-quartz veins. The geology of the area is dominated by large plutons of Cretaceous to Tertiary age, emplaced into a belt of sedimentary rock ranging from Mesoproterozoic to Permian age, and affected by tectonism related to the Sevier and later Laramide orogenies. Known tungsten (W) skarn mineral sites are associated with contacts between Cretaceous plutons and calcareous and argillaceous (meta)sedimentary rocks. Two permissive tracts were delineated: the Great Falls Tectonic Zone (GFTZ)-Cretaceous tract and the Bitterroot tract. For the GFTZ-Cretaceous tract, a quantitative assessment was performed in August 2019 using a three-part form of mineral resource assessment following the methods of Singer (1993) and Singer and Menzie (2010). The results of the quantitative assessment indicated that undiscovered W resources might exist in skarn-type deposits within the study area. The Bitterroot tract was assessed qualitatively.
The geographic information systems (GIS) data presented here were assembled as part of the W resource assessment. They are divided into assessment data and supporting data. The assessment data include the permissive tracts (W_Tracts) and mineral sites (MineralSites) in the study area compiled from seven different data sources: U.S. Geological Survey Mineral Resource Data System (MRDS) (McFaul and others, 2000), Tungsten Deposits of the United States (USMIN) (Carroll and others, 2018), Montana Bureau of Mines and Geology Abandoned and Inactive Mines Database (MBMG) (Montana Bureau of Mines and Geology, 2006), Idaho Geological Survey Database of the Mines and Prospects of Idaho (IGS) (Tate and others, 2018), Inventory of significant mineral deposit occurrences in the Headwaters Project Area in Idaho, Western Montana, and extreme Eastern Oregon and Washington (SPANSKI) (Spanski, 2004), Mineral deposit data for epigenetic base- and precious-metal and uranium-thorium deposits in south-central and southwestern Montana and southern and central Idaho (KLEIN) (Klein, 2004), and Exploration for critical and strategic minerals in Idaho, Montana, Oregon, and Washington, conducted under the DMA, DMEA, and OME programs, 1950-1974 (DMEA) (Kiilsgaard, 1996; Kiilsgaard, 1997). The supporting data include: Geologic units selected from Spatial Databases for the Geology of the Northern Rocky Mountains - Idaho, Montana, and Washington (Zientek and others, 2005) and State Geologic Map Compilation (SGMC) (ver. 1.1, Horton, 2017) geologic maps; stream sediment geochemistry selected from the National Uranium Resource Evaluation (NURE) Hydrogeochemical and Stream Sediment Reconnaissance (HSSR) project (Smith, 1997; ver. 5.0, Smith and others, 2018); whole rock chemistry selected from EarthChem PetDB (Lehnert and others, 2000), du Bray and others (2012), and the National Geochemical Database (U.S. Geological Survey, 2008); airborne radiometric data from the North American compilation of airborne radiometric data (Duval and others, 2005); and airborne magnetic data from the Magnetic Map of North America (U.S. Geological Survey and National Geophysical Data Center, 2002) and the lower frequency content EMAG2 data (Maus and others, 2009). Assessment and supporting data are included in a file geodatabase and are also made available in shapefile and CSV format.
