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Van Tuyl Lecture: Kaleb Scarberry, Montana Bureau of Mines and Geology
December 6 @ 8:00 am - 5:00 pm
Kaleb Scarberry, Montana Bureau of Mines and Geology
241 Berthoud Hall, 4PM
Topic: Mesozoic – Cenozoic Igneous Geology and Related Mineral Deposits in the Butte North 30’ X 60’ Quadrangle, Southwestern Montana
Abstract: The Butte North 30′ x 60′ quadrangle in southwestern Montana has been subject to extensive geologic research since the 1890’s, and detailed U. S. Geological Survey (USGS) investigations began over one hundred years ago (e.g. Weed, 1912) (Appendix A). Mineral resource exploration associated with the Butte, Welcome Creek, and Rock Creek mining districts was the focus of early geologic investigations (e.g. Weed, 1912; Blackwelder and Atwood, 1917). The Butte district contains two world-class porphyry Cu-Mo deposits, which are cut by polymetallic lode veins (e.g. Houston and Dilles, 2013a). Geologic mapping efforts in the 1960’s and 1970’s by the USGS focused on the Boulder batholith (Fig. 1), in part to explore for mineral deposits (Becraft, 1960a; Becraft, 1960b; Becraft and Pinkney, 1961; Smedes and others, 1962; Ruppel, 1963; Wanek and Barclay 1966; Weeks, 1974). Mapping efforts were limited from the 1960’s onwards with the Montana Bureau of Mines and Geology (MBMG), completing one quadrangle (Derkey and Bartholomew, 1988), and a 1:250,000 compilation (Lewis, 1998) before the initiation of large scale geologic mapping as part of the USGS STATMAP program in 2004.
In conjunction with the STATEMAP advisory committee, the MBMG selected the Butte North 30′ x 60′ quadrangle for a new map compilation project because STATEMAP-funded mapping at 1:24,000 and 1:50,000 scale over the preceding twelve years had significantly advanced knowledge of structural and igneous development of the area (Berg and Hargrave, 2004; Hargrave and Berg, 2013; Elliott and others, 2013; Scarberry and Elliott, 2016; Scarberry, 2016a; Scarberry, 2016b; Scarberry and others, 2017; Scarberry, in review (a) and (b)). The Butte North 30′ x 60′ quadrangle not only contains numerous active and abandoned mining properties, but also areas of structural and stratigraphic complexity, populated intermountain valleys, geologic interest, and vital transportation corridors. Other important contributions to mapping in the quadrangle include: (1) a geologic hazard assessment at 1:50,000 scale for Silver Bow County (Elliott and McDonald, 2009), (2) three 7.5′ quadrangle maps produced as student EDMAP projects (Feeney and others, 2009; Olson and others, 2016; Olson and others, 2017), and a detailed map of the Butte mining district (Houston and Dilles, 2013b).
The Butte North quadrangle lies in a geologically complex area of southwestern Montana. Archean and Paleoproterozoic crystalline basement rock, Mesoproterozoic through Cretaceous metasedimentary and sedimentary rock, Cretaceous through Tertiary intrusive and volcanic rock, and Tertiary and Quaternary valley-fill and surficial deposits are all exposed in the quadrangle. The Late Cretaceous Boulder batholith and co-magmatic Elkhorn Mountains Volcanic Field, and the Eocene-Oligocene Lowland Creek and Elliston volcanic fields (Fig. 1 and location figure on map) are the dominant rock types in the quadrangle. Glacial deposits are particularly abundant in the northeastern corner of the quadrangle, and on the western margin of the Deer Lodge Valley. The quadrangle is characterized by high elevation, low relief topography in the Boulder Mountains, and rugged alpine topography in the Flint Creek and Anaconda ranges at it western edge. The continental divide runs across the central portion of the quadrangle, separating the Clark Fork and Missouri watersheds.