Phase I fuzzy-logic GIS modeling to evaluate the occurrences of mineral systems in Minnesota

Abstract

Eight mineral systems potentially present in Minnesota have been evaluated using fuzzy-logic modeling utilizing ArcMap® software. Data used from the models was derived from the Natural Resources Research Institute Assembling Minnesota dataset. The eight mineral systems modeled include: 1) Placer; 2) Marine Chemocline; 3) Volcanogenic Seafloor; 4) Orogenic; 5) Metamorphic; 6) Alkalic Porphyry; 7) Magmatic REE; and 8) Mafic Magmatic. Inference nets have been developed to illustrate the fuzzy logic and components of each of the mineral system models. Results of the modeling are summarized below by mineral systems: Placer Mineral System: Based on the modeling, the highest probabilities for the presence of a Placer mineral system occur in northeastern Minnesota and in southwestern Minnesota. These regions correlate with the presence of the Biwabik Iron Formation, metasedimentary rocks associated with the Penokean Orogeny, and the margins of the Sioux Quartzite. Marine Chemocline: Based on the modeling, the highest probabilities for the presence of Marine Chemocline mineral systems occur in northeastern and north-central Minnesota in rocks associated with the Animikie Basin and Penokean Orogeny strata. As well, the model indicates high probabilities for the presence of the Marine Chemocline mineral system in western and southwestern Stearns County associated with interlayered volcanic, volcaniclastic, sedimentary, and hypabyssal intrusive rocks that comprise the Mille Lacs Group, North and South Range Groups, and Glen Township Formation. Volcanogenic Seafloor: High potential for the presence of Volcanogenic Seafloor mineral systems were identified in both the Abitibi-Wawa and Wabigoon subprovinces. In the Abitibi-Wawa subprovince, this includes the Vermilion district and the Wilson Lake sequence (Jirsa, 1990). Within the Wabigoon subprovince, enhanced potential for Volcanogenic Seafloor mineral systems occurs in east-central Lake of the Woods County and in northwestern Beltrami County. A single region of high potential for the presence of a Volcanogenic Seafloor mineral system also occurs in north-central Marshall County. Orogenic: The highest probabilities for Orogenic mineral system-associated gold deposits occur within the Abitibi-Wawa and Wabigoon subprovinces within the northernmost one-third of Minnesota. These regions are closely-associated with regional-scale shear zones. The modeled regions correlate well with the six areas of gold exploration identified by Severson (2011), as well as a weights of evidence model developed by Hartley (2014). Metamorphic: Several regions occur where elevated potential for Metamorphic mineral systems exist in Minnesota. The highest modeled potential for such a system exists in east-central St. Louis County and northwestern Lake County; however, this region of modeled high potential may be a false positive due to anomalously high contents of nickel (and perhaps vanadium) within Mesoproterozoic rocks in the area. Other areas with modeled high potential occur within northeastern Koochiching County and are associated with Quetico subprovince high-grade metamorphic rocks in proximity to the Rainy Lake – Seine River Fault, and in northeastern Itaca County, in proximity to the Coon Lake Pluton. Alkalic Porphyry: Modeling conducted for this study indicates several regions where elevated potential for Alkalic Porphyry mineral systems exist. The areas with the highest modeled probability for having Alkalic Porphyry mineral systems occur in northeastern Minnesota with Lake, St. Louis, and Itasca counties. Magmatic REE: Regions with the highest modeled potential for Magmatic REE mineral systems occur in south-central Lake County, north-central and northwestern St. Louis County, northeastern Itasca County, east-central Koochiching County, southeastern Marshall County, and east-central Stearns County. These are associated with Neoarchean syenite, monzodiorite, granodiorite, and diorite and granite-rich migmatites, Neoarchean gabbro, peridotite, pyroxenite, lamprophyre and metamorphic equivalents, and Paleoproterozoic porphyritic granites. Mafic Magmatic: Fuzzy-logic modeling indicates the highest probability for the presence of Mafic Magmatic mineral systems occurs in northeastern Lake County, east-central St. Louis County, and within eastern Aitkin County. The model identified known disseminated-to-massive Cu-Ni-PGM deposits that occur in troctolitic rocks at the base of the Duluth Complex in Lake and St. Louis counties, as well as Ti-Voxide deposits and prospects associated with oxide ultramafic intrusions (peridotites, pyroxenites) that occur along the western margin of the Duluth Complex in central St. Louis County. As well, the model identified the location of the Tamarack intrusion in eastern Itasca County, the host of the Tamarack Ni- Cu-Co deposit.