REPORT 284 INTRODUCTION A pilot study using heavy mineral concentrate samples from glaciofluvial sediments was conducted over a broad area of Minnesota by the Minnesota Department of Natural Resources, Division of Minerals, in cooperation with the U.S. Geological Survey, Branch of Geochemistry in Denver, Colorado. The study examined the heavy mineral fraction of eighty glaciofluvial samples collected from a number of geologically distinctive areas of the state. It evolved from a similar eight-sample test study that was completed in the previous year through a contract with the USGS.
The overall goals of the project were to educate DNR staff in heavy mineral investigative techniques that have been developed and refined by the USGS and to begin to develop heavy mineral baseline data for a portion of the state. The specific pilot study objectives were threefold: 1) to determine reliable, cost-effective sampling methods, concentration techniques, and analytical methods to use in future heavy mineral studies; 2) to determine the presence of heavy minerals of economic value, either semi- or precious metals and stones or industrial minerals, in glaciofluvial deposits that are currently being mined for sand and gravel; and 3) to determine the presence of heavy minerals in glacigenic sediments that could be used as indicator minerals in regional heavy mineral surveys or used to complement future geochemical terrain surveys.
This open-file report summarizes the sampling strategy and the methods of sample preparation and analysis for the pilot and test study samples and presents the results in table format.
REPORT 284-1 INTRODUCTION (First 3 Paragraphs) This report presents an interpretation of the results of a study that analyzed the heavy-mineral content of samples collected in Minnesota northeastern-provenance glaciofluvial sediments. Since it's inception, this study has been a cooperative project between the U.S. Geological Survey, Branch of Geochemistry, Colorado, and the Minnesota Department of Natural Resources, Division of Minerals. The project began with an eight-sample test study to determine whether there was enough geochemical and mineralogical variation in the heavy-mineral content of surficial glaciofluvial sediments to observe differences between samples. Test study results showed substantial variation between samples, which led to an eighty-sample pilot study to evaluate whether this variation would show any anomalous values or geographic distribution patterns that could be related to inferred regional bedrock or glacial geology.
The study area traverses Minnesota from the northeast to the southwest and encompasses an area approximately 60 miles wide by 230 miles long (Fig. 1). This area lies on the southern edge of the Canadian Shield and includes several of Minnesota's Precambrian bedrock terranes. Unique lithologic, tectonic, and structural characteristics of the various terranes create an area with diverse mineral potential. The northeast-southwest orientation of the study area was chosen because it is parallel to the major glacial flow and includes glacigenic sediments with a variety of genetic origins, glacial transport paths, and glacial and fluvial transport distances.
Within the study area the primary sampling strategy was to collect samples from late Figure 1. General location of study area in Minnesota. Wisconsinan northeastern-provenance glaciofluvial sand and gravel deposits; these deposits have been sorted by currents, which removed most of the silt and clay and produced some concentration of heavy minerals. Preference was given to sites where the depth to bedrock was 100 feet or less, because glacigenic sediments in these areas are more likely to reflect regional bedrock. Most samples were collected in gravel pits; with sampling preference given to ice-contact stratified sediments over outwash sediments...
Report 284: Chemical and Mineralogical Analyses and Geological Characteristics of Heavy Minerals from Glaciofluvial Sediments in Minnesota: Test and Pilot Study Data
(108 pages, 8.5 x 11 inches, 3.66 MB)
Authors: S.L. Nelson, 1S.J. Sutley, and 1R.B. Tripp
Report 284-1: An Interpretation of the Results of a Study of Heavy Minerals in Minnesota Northeastern Provenance Glaciofluvial Sediments
(123pages, 8.5 x 11 inches, 5.09 MB)
Authors: S.L. Nelson Russell, 1P.K. Theobald, J.D. Lehr, R.L. Johnson, 1J.L. Ryder, and T.L. Lawler
1United State Geological Survey, Geochemical Branch, Denver, Colorado
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