DNR Open-File Project 389: Heavy Mineral Concentrate Assays, St. Louis and Lake Counties
About this project
In 1989, the Minnesota DNR identified anomalously high platinum and palladium concentrations in the heavy mineral concentrates within glacial sediment samples collected 20-30 miles east of the known areas of metallic mineral deposits (MnDNR Project 262). The goal of DNR Project 389 was to confirm these results, and determine whether similar anomalies can be linked to bedrock map units or features in the general area. A total of 127 glacial sediment samples were collected in Fall 2011; the heavy mineral concentrates from 96 of these samples were separated, and analyzed by ALS minerals for Pt, Pd, and Au concentrations.
Project Manager: Don Elsenheimer
Data released on July 9, 2013
In June 2013, the DNR selected 10 Project 389 samples for electron microprobe analysis by McSwiggen & Associates. Polished grain mounts were prepared using the magnetic fraction of the HMC from each sample (previously processed by Overburden Drilling Management, Ltd) and examined using backscatter electron imagery. Oxide compositions were determined by point analysis of 25-30 grains within each mount. McSwiggen & Associates provided the results of its investigations to DNR on July 1, 2013. These results, and an associated map and data table, are now released:
This map shows the locations of the ten samples selected for microprobe analysis. Samples were selected based on geographic distribution, assay results, and the amount of magnetic fraction HMC available for analysis.
This slide presentation from McSwiggen & Associates includes backscatter electron images (BSI) of the grain mounts from each sample, ternary plots of spot oxide TiO2, FeO and Fe2O3 compositions for each sample, and representative BSI images of single grain internal textures (e.g. symplectites, weathered rims, ex-solution lamellae, overgrowths). Summary notes are provided within a concluding slide.
This MS-Excel spreadsheet file from McSwiggen & Associates provides spot chemistry results (including Cr2O3 wt%) for the analysis of individual grains of magnetic fraction HMC from each of the ten samples selected for electron microprobe analysis. Normalized TiO2, FeO and Fe2O3 concentrations are calculated for each oxide spot analysis and plotted on a ternary diagram.
Sample Imagery (.zip, 12 mb)
This zip file contains the photomicrographs used in the McSwiggen & Associates slide presentation. These stand-alone TIFF files are formatted for both MacOS and Windows-based computers.
This MS-Excel spreadsheet file compiles the spot microprobe analytical results into a single data table, along with sample location information (UTM coordinates) and associated assay results (i.e. Au, Pt, Pd concentrations in a total HMC split sample). This data table is formatted for import into Arc-GIS; table and column header abbreviations are provided in a separate sheet.
Data released on March 13, 2013
This laboratory report from Overburden Drilling Management, Ltd, (ODM) document total gold grain counts and magnetic/non-magnetic heavy mineral concentrate weights in 96 till samples that overlie portions of the Duluth Complex in St. Louis and Lake Counties, Minnesota. These samples were collected on State-owned or State-administered mineral rights by Mn DNR in October and November, 2012. The sample locations are 20-30 miles east of the known areas of metallic mineral deposits. The Mn DNR has a contract with ODM to process the till samples that it collects.
This PDF laboratory report from ALS Minerals (ALS) documents sample weights, and gold, platinum and palladium assay results from the total heavy mineral concentrate fraction of the 96 till samples sent to ODM for processing. ODM sent the sample material directly to ALS, which had a contract with MnDNR for geochemical analysis.
This excel file was saved from a comma delineated (CSV) spreadsheet file, provided by ALS Minerals, provides the assay results in a spreadsheet data file.
This data table combines the ODM and ALS analytical results with sample location information (UTM coordinates) and normalized gold grain counts (10kg sample weight) for the 96 samples. The data table is provided as a MS-Excel spreadsheet, with the table and column header abbreviations provided as separate sheets.
This map displays sample locations and platinum concentrations for the 96 total HMC samples within the Boulder Lake Intrusion and Houghtaling Creek Troctolite areas. The data is plotted alongside Project 262 sample locations and areas of active State leases, and overlain on a DEM topographic image.
Next data release: ArcGIS File Geodatabase
ArcGIS data files will be released separately that incorporate the data into a file geodatabase and shapefiles.
For more information:
Project Leader - Don Elsenheimer, Ph.D
500 Lafayette Road
St. Paul, Minnesota 55155-4045
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