Introduction extracted from Report 308:
GENERAL INFORMATION B-horizon soil samples were collected at 1385 sites along roads, rivers and lakeshores by the USGS during 1971 - 1975 at a depth of 30-45 cm. The <80 mesh fraction was analyzed in 1993 for Pt, Pd, and Au on behalf of the MDNR-Minerals by Bondar-Glegg & company Ltd Ontario, Canada using a fire assay lead collection direct current plasma atomic emission spectroscopic technique. An interpretation of this data as well as data from USGS analyses will be presented by the authors as a USGS bulletin (in preparation). Precious-metal concentration ranges in these B-horizon soils are shown below:
Pt concentration range: <5 through 75 ppb - 9.6% (134) of samples ~5 ppb
Pd concentration range: <1 through 140 ppb - 26% (360) of samples ~ 3 ppb
Au concentration range: <1 through 156 ppb - 41 % (568)'of samples ~ 1 ppb
REPORT 308 INTRODUCTION The Duluth complex encompasses approximately 6500 km2 of late to Upper Precambrian (1.1 Ga) anorthositic, troctolitic, gabbroic, granodioritic and granitic intrusive rocks (Phinney, 1972) in northeastern Minnesota. The study area of this report (Fig. 1) incorporates approximately 1798 km2 in the northwestern part of the Duluth complex between latitude 47°20'00" - 47°55'00" and longitude 91°30'00" - 92°20'00" within St. Louis and Lake counties.
The climate in this part of the Duluth complex is markedly continental with annual precipitation ranging from 66 cm to 79 cm. About 40 percent of this occurs as snow. Average annual temperatures are in the 38-40° F. The topography is primarily bedrock controlled in the general 360 to 485 m range.
Pleistocene glacial materials mantle the area to a greatly varying depth. These are the parent materials of the sampled B-horizon soils.
The area is extensively forested with pines, spruce, fir, aspen, and birch.
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Report 308: Platinum, Palladium and Gold Distribution in B-Horizon Soils in the Northwestern Part of the Duluth Complex, Minnesota; A cooperative project with the United States Geological Survey
(26 pages, 8.5 x 11 inches, 2.74 MB)
Authors: E. H. Dahlberg and 1Alminas, H.V.
1United State Geological Survey Branch of Geochemistry
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