This report is more or less an atlas with regard to gold exploration in the Archean rocks of northern Minnesota. The main objective of this study is to compile all available information (maps, assays, reports, etc.) from the historical records to produce a “Guidebook” that describes “who did what, where, and how, and what did they find” regarding the gold exploration history of northeastern Minnesota. In essence, detailed “due diligence” checks have been performed in this report, and the results are described for 62 orogenic gold prospects as follows: western Vermilion District with 29 gold prospects; Cook area with nine gold prospects; northeastern Itasca County area with nine gold prospects; Rainy Lake area with four gold prospects; Virginia Horn area with ten prospects; and the Koochiching-Beltrami-Roseau-Lake of the Woods counties area (no significant prospects).
Out of 23 gold prospects that were extensively drilled and/or trenched in the western Vermilion District, the best prospects that returned the highest gold values, and collectively the most mineralized zones, are located in the area bordered by the Vermilion Fault and Mud Creek Shear zone. Most of these prospects are associated with subsidiary shear zones and/or rheological contacts on the edges of iron-formation lenses. Shear zone-hosted gold was also explored for in some detail elsewhere in the western Vermilion District at Spaulding Bay, Murray, and Eagles Nest Shear zones. Exploration for gold took place the most extensively, and for the longest period, at the Shagawa Lake stock. There are very few conclusions that can be drawn from the data that are available for the Cook area. The data suggest that the best gold potential is present at the Linden Grove area, where several faults converge and structural preparation would be increased.
A review of the gold prospects in Itasca County suggests that significant gold shows are associated with an iron-formation trend in the Wilson Lake sequence. In almost all cases, the high gold values are associated with iron-formation, especially structurally-prepared and sulfide-replaced zones. Glacial overburden sampling campaigns have reiterated this gold-to-iron-formation connection. A review of the exploration activities conducted at the gold prospects in the Rainy Lake area suggests that significant gold anomalies are present within both the “iron-formation” unit of Day (1990) and the Rainy Lake-Seine River Fault Zone. However, the gold values obtained during drilling generally occur as isolated values in a select number of drill holes. Exploration to the west of Rainy Lake in the Koochiching-Beltrami-Roseau-Lake of the Woods area is confined to scattered drill holes that targeted geophysical anomalies.
Exploration in the Virginia Horn has to date identified a “small but low-grade” gold deposit associated with a hypabyssal quartzofeldspathic intrusion informally known as the Viking porphyry. Visible gold, often with associated arsenopyrite, is present in quartz veins in the porphyry. However, gold shows are also present in the surrounding rocks, and more drilling is needed to fully assess the potential of the Virginia Horn.
Severson, Mark J.
The History of Gold Exploration In Minnesota.
University of Minnesota Duluth.
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