Dr. Colin Paterson
Ph.D. (1978), University of Otago
Professor of Economic Geology
Geology and Geological Engineering
South Dakota School of Mines
Rapid City, SD 57701
Homestake-type Iron-Formation-Hosted Gold Deposits
Gold at the Homestake mine is found in quartz veins and adjacent wall rock of the Homestake Formation, a Fe-Mg-carbonate-rich iron formation that was recrystallized to garnet-grunerite assemblage above the garnet isograd. The cause of gold precipitation in iron-formation-hosted gold deposits is generally attributed to alteration of iron-bearing minerals, and association of iron with the sulfur in the gold sulfide complex, thus releasing the gold. Studies are in progress on characterization of alteration across the mine, spanning the biotite and garnet zones. The reason for gold ore being localized only in the synclinal hinges of the intensely folded structure is unknown. Sources of the gold, sulfur, arsenic and water in the hydrothermal fluid remain to be resolved.
Carlin-like Gold and Alkalic Gold DepositsCarlin-like replacement gold-silver deposits and alkalic igneous rock-hosted gold-silver deposits were historically mined in the northern Black Hills in the late 18th and early 19th century, but with the advent of heap leach cyanide leaching, four open pit mines were opened up in the 1980s. The Wharf mine continues to operate and has produced about 2.1 million ounces of gold from replacement ores hosted by carbonate-bearing sandstones of the Deadwood Formation (Cambrian), as well as trachytic sills of Eocene age. The Eocene alkali intrusions occur in a WNW-trending linear zone through the northern Black Hills, and include trachyte, quartz trachyte, phonolite, and rhyolite. Locally, quartz trachytic stocks host stockwork Au-Ag-Te mineralization. Through exposure in the Homestake mine, as well as surface outcrops and mines, a vertical section extending for almost 4 km has been documented for the Eocene hydrothermal systems. Fluid inclusion, alteration, and stable isotopic studies have led to the hypothesis that the metals and fluids have a magmatic source. The question of which magmas are the causative ones has not been resolved.
Rare Earth Elements and Gold in the Bear Lodge Mountains, WyomingThe alkali igneous province in the Bear Lodge Mountains is characterized by trachyte, syenite, phonolite, and carbonatite, and has been known for the occurrence of REE, thorium, gold, and copper. The area has been the focus of mineral exploration since the 1980s. Rare Element Resources is actively developing an REE reserve, and potentially will be opening a mine by 2016. The characteristics of the mineralizations, and the controls on their distributions are topics for further study.
Hyperspectral Remote Sensing and Field SpectroscopySatellite and airborne remote sensing has tremendous potential in exploration for ore deposits. Particularly important are hyperspectral imaging systems which collect reflected visible and near-infrared (VNIR) radiation in 100-200 narrow spectral channels. Many hydrothermal minerals can be mapped with a high degree of confidence at spatial resolutions of 3-5 meters. A complementary technology is portable VNIR spectrometry which can be used to ground-truth remotely sensed spectral data or to conduct independent spectral analyses in the field, mine sites, or of drill core. Students and faculty in the Department of Geology and Geological Engineering have conducted a variety of remote sensing and field spectral studies related to ore deposits in areas such as Goldfield, NV, Darwin, CA, western Death Valley National Park, CA, and several locations in Namibia.
Potential for PGE-Cu-Ni mineralization in the southern margin zone of the Superior Craton, eastern South DakotaNi-Cu-PGE deposits occur within the Superior Boundary Zone (SBZ) in northern Manitoba, Canada, in a region called the Thompson nickel belt. This tectonic setting is not unique to northern Manitoba, however. The SBZ extends from northern Canada southward beneath the Paleozoic cover into the subsurface of eastern North Dakota and eastern South Dakota. Beneath southeastern South Dakota, the SBZ wraps around the southernmost part of the Superior craton and into the subsurface of northwestern Iowa. In eastern South Dakota, several mafic and one ultramafic intrusion have been intersected in drill-holes, all of which are within or adjacent to the SBZ. One mafic-ultramafic layered intrusion, the Matlock or Otter Creek intrusion (Windom et al., 1993), is present in the SBZ in northwestern Iowa. Preliminary petrography suggests the presence of minor Ni-bearing minerals in just a couple of samples from South Dakota intrusions. Limited geochemistry demonstrates some potential for Ni-Cu mineralization within the ultramafic rocks, and in two of the southernmost gabbros (one to the south of the SBZ and one within it in Iowa), Pt is present (up to 40 ppb). We are currently working to obtain radiometric dates, and conduct geochemical modeling on core samples from two drill-holes in which more than 1000 ft of gabbro was intersected in each hole. High resolution geophysics, additional drilling, sampling, chemical analyses, and modeling are necessary to fully investigate the potential for Ni-Cu-PGE deposits in this area. Discovery of mineralization within the southern margin zone of the Superior Craton could lead to economic development in the region as well as a means to help supply our need for Ni, Cu, and most importantly, PGEs.
- Recent Research Projects Completed
The Study of Gabbroic Intrusions, Wakonda, Clay County, South Dakota: What is their Potential for PGE (Ni-Cu) Mineralization? Rachel Haley
Characterization and Distribution of Breccia, Whitetail Ridge, Bear Lodge, WY: Implications for emplacement of carbonatite and REE mineralization. Paul Woods