An Addendum to: Geology and Sulfide Content of Archean Rocks Along Two Proposed Highway 169 Relocations to the North of Sixmile Lake, St. Louis County, Northeastern Minnesota and Geologic Investigations in the Armstrong Lake Area
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An Addendum to: Geology and Sulfide Content of Archean Rocks Along Two Proposed Highway 169 Relocations to the North of Sixmile Lake, St. Louis County, Northeastern Minnesota and Geologic Investigations in the Armstrong Lake Area
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2012
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University of Minnesota Duluth
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Technical Report
Abstract
This report summarizes the geochemical results pertaining to the sulfur contents of rock
samples collected in the Sixmile Lake area, and thusly, serves as an addendum to a previous
report by Severson and Heine (2010). Geologic mapping in the Sixmile Lake area was initiated
at the request of the Minnesota Department of Transportation (Mn/DOT) and concentrated on
areas where Highway 169 could potentially be re-routed. The second purpose of this addendum
is to provide the appropriate GIS-related shape files that were omitted from the initial report by
Severson and Heine (2010). These shape files have been finalized and are provided in this report.
In addition, reconnaissance geologic mapping took place along other Highway 169 relocations in
the Armstrong Lake/McComber Mine area. The results of that endeavor are provided in this
report.
The results of sulfur analyses for samples collected from the Sixmile Lake area show that
most of the samples with ≥ 0.15% analyzed sulfur contents were correctly mapped as
“anomalous sulfide zones” by Severson and Heine (2010). However, there were several instances
where the visually-estimated pyrite contents did not compare well with the actual sulfur contents
due to a “nugget effect” variation in the third dimension. This “nugget effect” variability is
troublesome and suggests that some form of drilling should take place in the areas of future road
cuts in order to obtain more representative S% values.
Examination of rock exposures and recent drilling of the iron-formation in the vicinity of
Shaft #2 in the McComber Mine area indicates that pyrite is present in much higher amounts
when compared to Sixmile Lake. Thus, additional drilling will be needed in the McComber
Mine/Shaft #2 subarea, and possibly in the Clear Lake subarea, in order to obtain a better
understanding of the amount of pyrite present.
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Severson, Mark J; Heine, John J. (2012). An Addendum to: Geology and Sulfide Content of Archean Rocks Along Two Proposed Highway 169 Relocations to the North of Sixmile Lake, St. Louis County, Northeastern Minnesota and Geologic Investigations in the Armstrong Lake Area. Retrieved from the University Digital Conservancy, https://hdl.handle.net/11299/187173.
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