DNR Open-File Project 392: Regional Survey of Gold in Till, Cook Area, St. Louis County
About this project
The DNR is conducting a regional survey of gold in till in the Cook Area of St. Louis County. In this region, an Archean granite-greenstone terrane is overlain by relatively thin layers of Rainy Lobe till and other glacially-derived sediments. In comparable portions of the Archean Superior Province, the quantity and morphology of gold grains within samples of glacial till has led to the identification of associated bedrock gold deposits.
The results of this survey will support land management decisions in the region of high mineral potential, and may provide useful guidance for private mineral exploration companies that are considering gold exploration programs on State lands.
Note: While the identification of gold grains in glacial sediment samples may bolster the assessed mineral potential of an area, it is not a determinable test (either positive or negative) for bedrock mineralization. This type of geological investigation should be considered only the first step in determining whether there are bedrock gold deposits in the area. The DNR uses this data for land management purposes.
Project Manager: Don Elsenheimer
Data released on December 19, 2013
December 19, 2013 - DNR Open-File Project 392: Regional Survey of Gold in Till, Cook Area, St. Louis County
Summary and Data: The DNR is today releasing preliminary results from the processing and analysis of thirty-four (34) glacial sediment samples collected in Northern St. Louis County, at locations where State- or County-controlled surface ownership overlies State-owned or State-administered mineral rights. This is the latest data release for a DNR geological investigation that began in July, 2012, within an approximately 200 square mile area of historical gold and base metal exploration that lies between Cook and Tower. In this region, an Archean granite-greenstone terrane is overlain by relatively thin layers of Rainy Lobe till and other glacially-derived sediments. These are ideal geological conditions for using gold grain counts and heavy mineral geochemistry in glacial sediment samples to explore for proximal bedrock mineralization.
The 34 glacial sediment samples were collected in October 2013, and sent to Overburden Drilling Management, Ltd, (ODM) for heavy mineral concentrate (HMC) separation and gold grain counts. Sample locations were based on initial results from 105 glacial sediment samples that were collected within the project area in October 2012, processed by ODM, and assayed by Activation Laboratories Limited (ActLabs). The DNR released those results to the public on February 4, 2013 and July 2, 2013.
Today’s data release includes an ODM report dated December 5, 2013 that documents HMC separation and gold grain count work for the 34 new samples, a sample location map, and associated spreadsheet files. These documents, and a more detailed description of the project, are available below:
This laboratory reports from Overburden Drilling Management, Ltd, (ODM) documents total gold grain counts and magnetic/non-magnetic heavy mineral concentrate weights in 34 Rainy Lobe glacial sediment (till) samples that overlie an Archean greenstone belt in the Cook Area of Northern St. Louis County, Minnesota. These samples were collected on State-owned or State-administered mineral rights by Mn DNR in October, 2013. The approximately 200 square mile Cook Area is an area of historical gold and base mineral exploration, located in between areas of active gold exploration to the Northeast (Vermilion District) and West (Linden Grove Area). The Mn DNR has a contract with ODM to process the till samples that it collects.
Data table for 34 Phase 2 CATS samples with locations and normalized gold grain counts
This data table provides locations as UTM coordinates and normalized gold grain counts (10kg sample weight) for the 34 samples identified in the ODM report.
Attribute data table for 139 CATS series samples
This data table combines the field data and ODM results for the 34 samples collected in October 2013 with the results for the 105 Cook Area till samples collected in 2012 (see February, 2013 monthly data release.
Map of Cook Area sample locations and gold grain counts
This map displays sample locations, normalized total and pristine gold grain counts and areas of active and historic mineral exploration, overlain on a 2010 aerial photograph of the Cook Area. Results from the previous phase of till sampling (105 samples) are also shown. The State of Minnesota has a dominant land position within this accessible greenstone terrane.
Next data release: Geochemical analyses
ODM-prepared representative splits of the silt and clay fraction (<63 micron), the non-magnetic HMC and magnetic HMC have been forwarded to Activation Laboratories (ActLabs) for geochemical analysis. The results will be posted as a separate data release.
Data released on July 2, 2013
This Certificate of Analysis and Laboratory Report provides analytical and quality control results from the multi-element neutron activation analysis (NAA) of the heavy mineral concentrate (HMC) from 105 samples and 4 duplicate samples of glacial till from the Cook Area. The HMC samples were previously processed by Overburden Drilling Management, Ltd. (see February 4, 2013 data release below).
This MS-Excel spreadsheet, created by ActLabs and converted to PDF, provides the analytical and quality control results from NAA analysis of 105 samples and 4 duplicate samples of HMC in a data table format. Non-detect values are reported as text strings (e.g. “< 5”).
This MS-Excel spreadsheet adds sample locations as UTM coordinates to the NAA results for the 105 HMC samples. Information provided in the ActLabs data table on analyte detection limits, units of measure, and analytical methods was stripped from this data table in order to create a format suitable for import into Arc-GIS. The “less than” non-detect values reported in the ActLabs data table are replaced by values that are one-half the method detection limit. The original ActLabs data table and QC results are archived in this file as separate sheets.
Data released on February 4, 2013
These laboratory reports from Overburden Drilling Management, Ltd, (ODM) document total gold grain counts and magnetic/non-magnetic heavy mineral concentrate weights in 105 Rainy Lobe till samples that overlie an Archean greenstone belt in the Cook Area of Northern St. Louis County, Minnesota. These orientation survey samples were collected on State-owned or State-administered mineral rights by Mn DNR in September and October, 2012. The approximately 200 square mile Cook Area is an area of historical gold exploration, located in between areas of active gold exploration to the Northeast (Vermilion District) and West (Linden Grove Area). The Mn DNR has a contract with ODM to process the till samples that it collects.
This MS-Excel electronic spreadsheet converted to PDF, provided to MnDNR by ODM, compiles the results presented in the three separate laboratory reports into a single file.
This data table provides locations as UTM coordinates and normalized gold grain counts (10kg sample weight) for the 105 samples identified in the ODM report. Five relatively small (<5 square miles) clusters of anomalously high gold grain counts were identified. Three of these five clusters are located in areas of the Archean granite-greenstone terrane that have not been previously explored for gold mineralization.
This map displays sample locations, normalized total gold grain counts and areas historically offered by the State of Minnesota for mineral exploration, overlain on a 2010 aerial photograph of the Cook Area. The State of Minnesota has a dominant land position within this accessible greenstone terrane.
Future data release: ArcGIS File Geodatabase
ArcGIS data files will be released separately that incorporate the data into a geodatabase alongside associated mineral exploration and mineral rights ownership information. The Cook Area gold-in-till data will also be integrated into a separate ArcGIS compilation of MnDNR till sample data collected in Northern Minnesota from 2005-2013.
For more information:
Project Leader - Don Elsenheimer, Ph.D
500 Lafayette Road
St. Paul, Minnesota 55155-4045
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