DNR Open-File Project 389: Heavy Mineral Concentrate Assays, St. Louis and Lake Counties

Map of platinum concentrations in total HMC
Click for full size PDF

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 (DNR 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:

Sample Location Map

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.

July 1, 2013 slide presentation from McSwiggen and Associates

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.

July 1, 2013 data table from McSwiggen and Associates

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, 12mb)

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.

Excel file with locations, assay results, and microprobe analytical results

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 ArcGIS; table and column header abbreviations are provided in a separate sheet.

Data released on March 13, 2013

February 2, 2012 laboratory reports from Overburden Drilling Management, Ltd

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 the DNR in October and November, 2012. The sample locations are 20-30 miles east of the known areas of metallic mineral deposits. The DNR has a contract with ODM to process the till samples that it collects.

June 17, 2012 laboratory report from ALS Minerals

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 the DNR for geochemical analysis.

Excel file with analytical results, provided by ALS Minerals

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.

Data table for 96 DC-series samples with locations, HMC concentrate weights and assay results

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.

Map of Project 389 platinum concentrations

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.

Disclaimer and Copyright Protection: Maps, Reports, Data, and Other Information - The State of Minnesota makes no representations or warranties express or implied, with respect to the use of the information contained herein regardless of its format or the means of its transmission. There is no guarantee or representation to the user as to the accuracy, currency, suitability, completeness, usefulness, or reliability of this information for any purpose. The user accepts the information “as is." The State of Minnesota assumes no responsibility for loss or damage incurred as a result of any user’s reliance on this information. All maps, reports, data, and other information contained herein are protected by copyright. Permission is granted to copy and use the materials herein for any lawful noncommercial purpose. Any user of this information agrees not to transmit or provide access to all or any part of this information to another party unless the user shall include with the information a copy of this disclaimer.