DNR Open-File Project 392: Regional Survey of Gold in Till, Cook Area, St. Louis County

Map showing sample locations for Gold in Till sampling DNR project 392, Cook area, St. Louis County, Minnesota

Map of Sample Locations (click for detailed PDF This is a PDF file. You will need Adobe Acrobat Reader to download it.)

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.

For more information:

Project Leader - Don Elsenheimer, Ph.D
500 Lafayette Road
St. Paul, Minnesota 55155-4045
tel. 651-259-5433
fax 651-296-5939
donald.elsenheimer@state.mn.us


Data released on June 30, 2015

June 30, 2015 - DNR Open-File Project 392: Regional Survey of Gold in Till, Cook Area, St. Louis County

Summary and Data: The DNR is today releasing gold grain counts and associated analytical results from thirty-three (33) 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 33 glacial sediment samples were collected in Fall 2014. Sample locations were based on previous results from 139 glacial sediment samples that were collected within the project area in October 2012 and October 2013, processed by Overburden Drilling Management, Ltd (ODM), and assayed by Activation Laboratories Ltd (ActLabs). The DNR has previously released those results to the public.

The 33 glacial sediment samples were sent to ODM for heavy mineral concentrate (HMC) separation and gold grain counts The results of this processing and gold grain analysis were reported to the DNR in a laboratory report dated June 10, 2015 (see this data release for a sample location map). More than 90% of the recovered gold grains were less than 100 microns in size, and barely visible to the naked eye. These grain sizes are typical for gold in Archean granite-greenstone terranes.

Representative splits of the silt+clay fraction and magnetic HMC from each of the samples were sent to ActLabs for analysis. This data release includes the ActLabs analytical results, provided in reports dated June 15, 2015 and June 29, 2015. Note that silt+clay fraction analytical results were also obtained from 105 archived Cook Area samples that were collected in 2012.

Today’s data release includes June, 2015 laboratory reports, maps, and associated spreadsheet files. These documents, and a more detailed description of the project, are available below.

Report 20156936, from Overburden Drilling Management, Ltd, dated June 10, 2015 (.pdf) »

This ODM laboratory report documents total gold grain counts and magnetic/non-magnetic heavy mineral concentrate weights in 33 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 DNR in October, 2014. 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 DNR has a contract with ODM to process the till samples that it collects.

Certificate of Analysis/Laboratory Report A15-04300, from Activation Laboratories, Ltd, dated June 15, 2015 (.pdf) »

This laboratory report and certificate of analysis from ActLabs provides geochemical results from the analysis of magnetic HMC from the 33 Rainy Lobe till samples collected by DNR in Fall 2014. The representative split samples were analyzed using instrumental neutron activation analysis (INAA); the report also contains quality control (QC) results tied to the sample analysis.

ActLabs data table for geochemical analysis of magnetic HMC (excel, .xlsx) »

This ActLabs-authored data table provides the results of the INAA analysis of the 33 samples collected by DNR in Fall 2014 in a spreadsheet format. 

Certificate of Analysis/Laboratory Report A15-04151, from Activation Laboratories, Ltd, dated June 29, 2015 (.pdf) »

This ActLabs laboratory report provides analytical and quality control results for the multi-element analysis of bulk and silt+clay fractions (-63micron) from the 33 samples collected by DNR in Fall 2014, and 105 archived samples collected in Fall 2012. Analytical packages included whole rock analysis of major elements, and ICP/MS trace element analysis. This laboratory report was dated and submitted by ActLabs to MnDNR on June 29, 2015.

Rare Earth Element Plot (.pdf) »

This PDF figure, provided by ActLabs, plots rare earth element (REE) distributions for the silt+clay fraction (-63micron) samples. These distributions are of scientific value only; there is no significant economic value associated with the plotted concentrations.

ActLabs data table for geochemical analysis of silt+clay fractions (excel, .xlsx) »

This ActLabs-authored data table provides the results of the geochemical analysis of the 33 samples collected by DNR in Fall 2014, and 105 archived samples collected in Fall 2012, in a spreadsheet format. The data table identifies analytical methods and method detection limits for each analyzed element.

Data table with sample locations and normalized gold grain counts (excel, .xlsx) »

This DNR data table provides locations as UTM coordinates and normalized gold grain counts (10kg sample weight) for the 33 samples identified in the ODM report.

Data table with grain size distributions for recovered gold (.pdf) »

This DNR data table and plot summarizes the grain size distributions for gold recovered in the 33 Phase 3 CATS samples.

Attribute data table for gold-in-till analysis of 172 CATS-series samples (excel, .xlsx) »

This DNR data table combines the field data and ODM results for the 33 samples collected in October 2014, combined with the results for the 139 Cook Area till samples previously collected in 2012 and 2013.

Attribute data table for geochemical analysis of magnetic HMC (excel, .xlsx) »

This DNR data table adds sample location information to the results of INAA analysis of the magnetic HMC in 33 CATS-series samples, and organizes the data provided by ActLabs in a GIS-friendly format. Non-detect “less than” values were replaced by one-half of the method detection limit, where applicable. The original ActLabs spreadsheet data and a compilation that includes previous magnetic HMC results from the Cook Area are also provided.

Map of Cook Area sample locations and gold grain counts (.pdf) »

This DNR 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 phases of till sampling (139 samples) are also shown. The State of Minnesota has a dominant land position within this accessible greenstone terrane.

Detailed Map of Cook Area sample locations (.pdf) »

This DNR map displays sample locations and sample names for the 33 till samples collected in Fall 2014.

Detailed Map of Cook Area gold grain counts (.pdf) »

This DNR map displays normalized total and pristine gold grain counts in the northeastern corner of the Cook Area, where the 33 till samples collected in Fall 2014 were located. Results from the previous phases of till sampling (139 samples) are also shown. The State of Minnesota has a dominant land position within this accessible greenstone terrane.


Past Data Releases

Click on date for information

June 13, 2014

Summary and Data: The DNR is today releasing geochemical analytical results from the silt and clay fraction and magnetic and non-magnetic heavy mineral concentrates from 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.  The results of this processing and gold grain analysis were released by the DNR on December 19, 2013 (see this data release for a sample location map). 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 a January, 2014 analytical report from Activation Laboratories, Ltd. (ActLabs) and associated spreadsheet files.  These documents, and a more detailed description of the project, are available below:

January 14, 2014 A13-14909 analytical report from ActLabs »

This laboratory report from Activation Laboratories, Ltd, (ActLabs) identifies the concentrations of several elements of geochemical interest within both the silt/clay fraction (<63 microns) and the magnetic and non-magnetic fractions of heavy mineral concentrate from 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 DNR has a contract with ActLabs to provide geochemical analyses of rock and soil samples.

The analytical package for each of these samples included fire assay with an ICP/MS finish (Au, Pt, Pd), infrared analysis of sulfur concentrations, multi-element neutron activation analysis of the HMC, and major/trace element analysis of the silt/clay fraction using whole rock analysis (fusion ICP) and ICP/MS methods.

January 14, 2014 A13-14909 LithoPlots from ActLabs »

This PDF document contains rare earth element (REE) diagrams that plot elemental concentrations against increasing atomic number for the silt/clay fractions of the 34 Phase 2 samples.

A13-14909 Data Table from ActLabs »

CATSPhase2_geochem Data Table »

This DNR data table combines the ActLabs analytical results with sample locations (identified using UTM coordinates), and breaks down the data by providing separate data pages for each analytical fraction.

December 19th, 2013

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:

December 5, 2013 laboratory reports from Overburden Drilling Management, Ltd »

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

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.

July 2nd, 2013

June 27, 2013 Laboratory Report from Activation Laboratories, Ltd. (ActLabs) »

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).

ActLabs June 27, 2013 data table for NAA analysis of 105 HMC samples »

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”).

Data table for 105 HMC samples with locations »

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.

February 4th, 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.

January 24, 2013 ODM data table for 105 CATS series samples »

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.

Data table for 105 CATS series 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 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.

Map of Cook Area sample locations and gold grain counts »

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.

 

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