About
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 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
[email protected]
Data released on July 14, 2017
DNR Open-File Project 392: Regional Survey of Gold in Till, Cook Area, St. Louis County
Summary and Data:
The DNR is releasing new gold grain counts from twenty-five (25) glacial sediment samples collected in an area southeast of Soudan in Northern St. Louis County, at locations where State- or County-controlled surface ownership overlies State-owned or State-administered mineral rights. This new data set includes duplicate samples that confirm the anomalously high gold grain counts from samples collected in 2015 within the Murray Road South Project Area, and provide additional support for the presence of gold within the focus area’s underlying bedrock. This mineral exploration method, which is used in areas where bedrock is covered by glacial sediments, cannot be used to determine the economic value of that bedrock gold; a comprehensive mineral exploration program would be required to determine whether there was a potentially developable ore deposit.
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 glacial till and other glacially-derived sediments. These are ideal geological conditions for using gold grain counts and heavy mineral geochemistry to search for gold within bedrock that is covered by glacial deposits.
The 25 glacial sediment samples were collected in May 2017 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 reported to the DNR in a laboratory report dated June 20, 2017 (see this data release for a sample location map). More than 97% of the recovered gold grains were 100 microns in size or less, and barely visible to the naked eye. These grain sizes are typical for gold in Archean granite-greenstone terranes.
Today’s data release includes the June 20, 2017 laboratory report, maps, and associated spreadsheet files. These documents, and a more detailed description of the project, are available below.
Report 20177493, from Overburden Drilling Management, Ltd, dated June 20, 2017 »
(20177493_mdnr_elsenheimer_cats_gold_hmc_june2017_contractor_report.pdf)
This ODM laboratory report documents total gold grain counts and magnetic/non-magnetic heavy mineral concentrate weights in 25 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 the DNR in May, 2017. 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.
Report 20177493, from Overburden Drilling Management, Ltd, dated June 20, 2017 »
(20177493_mdnr_elsenheimer_cats_gold_hmc_june2017_contractor_spreadsheet.xlsx)
This ODM-authored MS-Excel spreadsheet provides the content of the related PDF laboratory report in spreadsheet format.
Data table with sample locations and normalized gold grain counts »
(cats_attribute_july2017.xlsx)
This DNR data table provides locations as UTM coordinates and normalized gold grain counts (10kg sample weight) for the 25 samples identified in the ODM report. It also includes the results for the 191 Cook Area till samples previously collected from 2012 to 2014.
Data table with grain size distributions for recovered gold »
(cats_grainsize_july_2017.pdf)
This DNR data table and plot summarizes the grain size distributions for gold recovered in the 25 CATS glacial sediment samples collected in May 2017.
GIS data as shapefile for gold-in-till analysis of 216 CATS-series samples (dnr392_gold_in_till_gis.zip) »
This DNR data available in GIS shapefile format combines the field data and ODM results for the 25 samples collected in May 2017 with the results for the 191 Cook Area till samples previously collected from 2012 to 2014.
Map of the Cook Project Area »
(cats_location_map.pdf)
This DNR map shows the location of the Cook Project Area in Northern St. Louis County, Minnesota, and highlights the location of the Murray Road South Project Area.
Detailed Map of Cook Area sample locations within the Murray Road South Focus Area »
(cats_murray_road_south_locations_july_2017.pdf)
This DNR map displays sample locations and sample names for the 25 till samples collected in May 2017.
Map of Gold Grain Counts Within the Murray Road South Focus Area »
(cats_murray_road_south_gold_grains_july_2017.pdf)
This DNR map displays normalized total and pristine gold grain counts in the Cook Area’s Murray Road South Focus Area, where the 25 till samples collected in Fall 2015 were located. Results from samples collected within this area during previous phases of till sampling are also shown.
For questions about this data release, please contact:
Project Leader - Don Elsenheimer, Ph.D
500 Lafayette Road
St. Paul, Minnesota 55155-4045
tel. 651-259-5433
fax 651-296-5939
[email protected]
Past Data Releases
Click on date for information
- April 27, 2017
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April 27, 2017 - DNR Open-File Project 392: Regional Survey of Gold in Till, Cook Area, St. Louis County
Summary and Data: This is a release of a report that integrates different types of geological data from pebbles collected in surface soils at 11 different sample sites in St. Louis County. It also presents recommendations for future work in the sampled area. This report is the result of a small study examining the gold content of pebbles and is based on the pre-existing work of the larger Regional Survey of Gold in Till, Cook Area, St. Louis County project. Gold assays for this report were previously released in July 2016.
The Cook Area Gold in Till survey is a DNR geological investigation that began in July 2012. It lies within an approximately 200 square mile area of historical gold and base metal exploration located between the towns of Cook and Tower. In this region, relatively thin layers of Rainy Lobe glacial till and other glacially derived sediments overlie an Archean granite-greenstone terrane. These are ideal geological conditions for using gold grain counts and pebble studies to search for gold within bedrock covered by glacial deposits.
This smaller study took advantage of pre-existing duplicate till samples collected for the Gold in Till survey. Sample sites for the Gold in Till survey are located where State- or County-controlled surface ownership overlies State-administered mineral rights. Pebbles were separated from the duplicate glacial sediment samples using sieves. The pebble separates were rinsed free of sediment and were examined to determine the size fractions, rock type, and angularity. After examination, rock types from each sample were sent to Activation Laboratories, Ltd (a state vendor) for Fire Assay with Instrumental Neutron Activation Analysis (INAA) to determine if any gold is present in the rocks.
After studying the results from the pebble separates, it appears that there are no definite correlations between assay values of specific rocks types and gold grain counts. However, the results do suggest that a change in bedrock type might be important for hosting a gold deposit in the area. Studying glacial dispersal trains of pebbles may help narrow down locations for changes in bedrock type. A large dispersal train study combined with gold grain counts, could help indicate where bedrock changes occur as well as identify if there is gold associated with the changes.
Today’s data release includes the April 2017 report. The report and a more detailed description of the project, are available below.
Report - DNR Open-File Project 392: Regional Survey of Gold in Till, Cook Area, St. Louis County— Pebble Counts and Assay Data »This PDF document includes both the April 2017 report and its appendices.
- July 15, 2016
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July 15, 2016 - Regional Survey of Gold in Till, Cook Area, St. Louis County
Summary and Data: This is a release of new gold assay data from pebbles collected at 11 different glacial sediment sample sites. This data represents a small study examining the gold content of pebbles and is based on the pre-existing work of the larger Regional Survey of Gold in Till, Cook Area, St. Louis County project (which is focused on gold grain counts in glacial sediment samples). Pebbles were separated from stored duplicate glacial sediment samples from the Gold in Till survey using sieves. Duplicate glacial sediment samples used for this study were gathered in northern St. Louis County at the same time as the original samples in the Gold in Till survey. Sample sites are primarily located southeast of Soudan; two sample sites are located to the southeast of Tower and one site is located to the east of Lost Lake. Sample sites are located where State- or County-controlled surface ownership overlies State-administered mineral rights.
The ultimate goal is to find gold in the bedrock. This is an indirect exploration method used in areas where glacial sediments cover bedrock. By examining the gold grains, the content of gold in rocks, and types of rock in the glacial sediment, it helps identify what might be going on in the bedrock under the cover of glacial sediments. This new data set attempts to narrow down the bedrock types that may be hosting the gold mineralization in some of the more promising areas, as indicated by the Gold in Till survey. The pebble separates were rinsed free of sediment and were examined to determine the size fractions, rock type, and angularity. After examination, rock types from each sample were sent to Activation Laboratories, Ltd (a state vendor) for Fire Assay with Instrumental Neutron Activation Analysis (INAA) to determine if any gold is present in the rocks.
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 the towns of Cook and Tower. In this region, relatively thin layers of Rainy Lobe glacial till and other glacially derived sediments overlie an Archean granite-greenstone terrane. These are ideal geological conditions for using gold grain counts and pebble studies to search for gold within bedrock covered by glacial deposits.
Today’s data release includes the June 1, 2016 laboratory report, a map, and a spreadsheet file summarizing the information collected. These documents and a more detailed description of the project, are available below.
Certificate of Analysis/Laboratory Report A16-03812, from Activation Laboratories, Ltd., dated June 1, 2016 »
This certificate of analysis and laboratory report from ActLabs provides gold assay results for the pebble samples collected by the DNR. The pebbles were assayed using the fire assay method with instrumental neutron activation analysis (INAA). The report also contains quality control (QC) results tied to the sample analysis.Data table with sample locations and laboratory results - printable »
This DNR data table provides sample locations as UTM coordinates, pebble characteristics, and gold assay results. It is formatted for easy printing.Data table with sample locations and laboratory results - GIS friendly »
This DNR data table provides sample locations as UTM coordinates, pebble characteristics, and gold assay results. Formatting is removed and metadata is included on a separate tab to aid understanding.Map of the Cook Area and Pebble Sample Locations »
This DNR map displays the general location of the Cook area, two areas of focus, and the locations of where the pebble samples came from. - February 2, 2016
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February 2, 2016 - Regional Survey of Gold in Till, Cook Area, St. Louis County
Summary and Data: The DNR is releasing Scanning Electron Microscope (SEM) data and high-resolution backscatter electron images of gold grains from glacial sediment samples collected in an area southeast of Soudan in Northern St. Louis County, at locations where State- or County-controlled surface ownership overlies State-owned or State-administered mineral rights. SEM imaging of these gold grains was performed by Overburden Drilling Management, Ltd (ODM), a third-party contractor. The SEM observations confirm the accuracy of previously reported shape classifications of “pristine” and “modified” gold grains, made using a lower-resolution binocular microscope. The high numbers of pristine and modified gold grains led ODM to conclude in their January 26, 2016 letter report that “...a bedrock source (or sources) must be present within or near the surveyed area.” That said, neither these results nor previous results obtained using the gold-in-till mineral exploration method can determine the precise location of a bedrock gold source (or sources). The data also cannot be used to determine the economic value of that bedrock gold; a comprehensive mineral exploration program would be required to do that.
Backscatter SEM Images of Gold Grains from Glacial Sediment: DNR Sample CATS-406, Cook Project Area, Northern St. Louis County (click for detailed PDF )
This data release also includes geochemical data from the analysis of the 19 glacial sediment samples that were collected by the DNR in October, 2015, and previously analyzed for gold grain counts by ODM. Activation Laboratories Ltd (ActLabs) analyzed representative splits of the silt+clay fraction and magnetic HMC from the 19 samples, and reported the results to the DNR in a laboratory report dated January 28, 2016. The distribution of metals and associated pathfinder elements within these samples will be compared against the geochemical results from 172 previously-collected Cook Area sediment samples, and evaluated within an open-file report that is currently under preparation.
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 glacial till and other glacially-derived sediments. These are ideal geological conditions for using gold grain counts and heavy mineral geochemistry to search for gold within bedrock that is covered by glacial deposits.
Today's data release includes the ODM letter report, digital images of individual gold grains, the ActLabs laboratory report, and associated spreadsheet files. These documents, and a more detailed description of the project, are available below.
Letter Report from Overburden Drilling Management, Ltd, dated January 26, 2016
(odm_letter.pdf) »This ODM letter report documents SEM observations and analyses of gold grains from three (3) Rainy Lobe glacial sediment (till) samples collected in a focus area southeast of Soudan, in Northern St. Louis County, Minnesota. These samples were collected on State-owned or State-administered mineral rights by the DNR in October, 2015. The report contains fineness data (i.e. information on the purity of the gold grains), and ten (10) backscatter SEM images of representative gold grains of each shape class. The DNR has a contract with ODM to perform this type of analysis.
Zip file collection of digital images within ODM letter report
(odm_images.zip) »This compressed zip file contains stand-alone digital images (.tif format) provided to DNR by ODM of each of the 10 gold grain images shown in ODM’s January 26 report. Each digital image is approximately 1Mb in size.
Shape comparisons of representative gold grains and conceptual cross-section of a dispersal train
(gold_grains_shape_comparisons_feb2016.pdf) »This pdf document contains two figures:
- Backscatter electron images of five representative goal grains from a single Cook Area glacial sediment sample (CATS-406). These gold grains have distinct forms (e.g. “leaf) and shape classifications (i.e. “pristine,” “modified,” and “re-shaped); and,
- Conceptual cross-section of a dispersal train of gold grains, liberated from mineralized bedrock and transported by glacial flow.
Certificate of Analysis/Laboratory Report A15-11277, from Activation Laboratories, Ltd, dated January 28, 2016
(a15_11277_cert_res.pdf) »This laboratory report and certificate of analysis from ActLabs provides geochemical results from the analysis of magnetic HMC and the silt+clay fraction (-0.063mm) from the 19 Rainy Lobe till samples collected by the DNR and processed by ODM in October, 2015. 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 results reported in Laboratory Report A15-11277
(a15_11277_final.xlsx) »This ActLabs-authored data table provides the results contained within Laboratory Report A15-11277 in a spreadsheet format.
Rare Earth Element Plot
(a15_11277_litho_plots.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.
DNR attribute data table for geochemical analysis of magnetic HMC and silt+clay fraction
(cats_400series_geochem_update_01292016.xlsx) »This DNR data table adds sample location information to the results of the geochemical analysis of the magnetic HMC silt+clay fractions in the 19 glacial sediment samples collected in October, 2015, 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 is also provided for comparison.
- January 8, 2016
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January 8, 2016 - DNR Open-File Project 392: Regional Survey of Gold in Till, Cook Area, St. Louis County
Summary and Data: The DNR is releasing new gold grain counts from nineteen (19) glacial sediment samples collected in an area 5 miles southeast of Soudan in Northern St. Louis County, at locations where State- or County-controlled surface ownership overlies State-administered mineral rights. The goal is to find gold in the bedrock. This indirect exploration method is used in areas where bedrock is covered by glacial sediments, and can narrow down the search for gold in the bedrock. This new data set strongly points towards the presence of gold within the focus area’s underlying bedrock. The new samples confirm previously reported results of three samples that had high gold grain counts, and create a new cluster of 18 samples that have high gold content. University Trust mineral ownership exists in what appears as the most prospective area.
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 glacial till and other glacially-derived sediments. These are ideal geological conditions for using gold grain counts and heavy mineral geochemistry to search for gold within bedrock that is covered by glacial deposits.
The 19 glacial sediment samples were collected in Fall 2015 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 reported to the DNR in a laboratory report dated December 18, 2015 (see this data release for a sample location map). More than 97% 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 19 samples have been sent to Activation Laboratories Ltd for analysis. Representative gold grain samples will also be characterized and photographed by ODM using a Scanning Electron Microscope (SEM). The DNR anticipates that these results will be available for public release by early February, 2016.
Today’s data release includes the December 18, 2015 laboratory report, maps, and associated spreadsheet files. These documents, and a more detailed description of the project, are available below.
Report 20157067, from Overburden Drilling Management, Ltd, dated December 18, 2015
(20157067_mndnr_elsenheimer_cats_19_december_2015.pdf) »
This ODM laboratory report documents total gold grain counts and magnetic/non-magnetic heavy mineral concentrate weights in 19 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 the DNR in October, 2015. 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.Report 20157067, from Overburden Drilling Management, Ltd, dated December 18, 2015
(excel, 20157067_mdnr_elsenheimer_cats_19_december_2015_final.xls) »
This ODM-authored MS-Excel spreadsheet provides the content of the related PDF laboratory report in spreadsheet format.Data table with sample locations and normalized gold grain counts
(excel, cats_phase4_samples.xlsx) »
This DNR data table provides locations as UTM coordinates and normalized gold grain counts (10kg sample weight) for the 19 samples identified in the ODM report.Data table with grain size distributions for recovered gold
(cats_phase4_grainsize.pdf) »
This DNR data table and plot summarizes the grain size distributions for gold recovered in the 19 Phase 4 CATS samples.Attribute data table for gold-in-till analysis of 191 CATS-series samples (excel, cats_attribute_dec2015.xlsx)»
This DNR data table combines the field data and ODM results for the 19 samples collected in October 2014 with the results for the 172 Cook Area till samples previously collected from 2012 to 2014.Cook Area location map
(cats_simple_location_map.pdf) »
This DNR map displays the general location of the Cook Area, as well as the two areas of focus.Map of Cook Area sample locations and gold grain counts
(cats_jan2016_big.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 (172 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
(cats_phase4_sampid.pdf) »
This DNR map displays sample locations and sample names for the 19 till samples collected in Fall 2015.Detailed Map of new gold grain counts
(cats_phase4_results_airphoto.pdf) »
This DNR map displays normalized total and pristine gold grain counts in the northeastern corner of the Cook Area, where the 19 till samples collected in Fall 2015 were located. Results from samples collected within this area during previous phases of till sampling are also shown. The State of Minnesota has a dominant land position within this accessible greenstone terrane.Detailed Map of Cook Area gold grain counts
(cats_focus_area_results.pdf) »
This DNR map displays all of the normalized total and pristine gold grain counts in the northeastern corner of the Cook Area, where the 19 till samples collected in Fall 2015 were located. - November 12, 2015
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November 12, 2015 - DNR Open-File Project 392: Regional Survey of Gold in Till, Cook Area, St. Louis County
Summary and Data: The DNR is releasing analytical results from the re-assay of 138 glacial sediment samples collected in the Cook Area of Northern St. Louis County. These results replace a small sub-set of Activation Laboratories (ActLabs) data that was published within a June 30, 2015 data release, involving fire assay-ICP/MS analyses of gold (Au), platinum (Pt) and palladium (Pd) that fell outside of expected distribution ranges for silt+clay fraction sediment samples.
In Spring 2015, the DNR requested that ActLabs analyze representative silt+clay fractions from 138 Cook Area sediment samples using two separate data packages: 1) whole rock analysis of major element concentrations and ICP/MS trace element analysis (ActLabs Code 4LITHO), and 2) fire assay-ICP/MS analysis of Au, Pt and Pd concentrations (ActLabs Code 1C-Exp). The results were provided to the DNR in ActLabs report A15-04151, dated June 29, 2015, and included within the June 30, 2015 data release.
The DNR reviewed the data and asked ActLabs to reanalyze a subset of thirty (30) silt+clay fraction samples using the fire assay-ICP/MS method. The results of this partial re-assay were provided to the DNR in an ActLabs report dated September 16, 2015. ActLabs then re-assayed the remaining 108 silt+clay fraction samples using the fire assay-ICP/MS method and provided the results within a report dated October 23, 2015. The ranges of Pt, Pd, and Au concentrations obtained by these re-assays are more comparable to both previous Cook Area results and to results obtained from similar geologic terranes. The DNR considers these replicate analyses to be far more representative than the initial results provided in the June 30 data release, and will only use these replicate analyses within the open file report that is currently under preparation.
The DNR request for reanalysis was limited in scope, and did not involve associated whole rock and trace element analyses of the silt+clay fraction samples. A more detailed analysis of these data sets and a fuller explanation of the methods used to process and geochemically analyze the glacial sediment samples will be provided within an open file report that is currently under preparation.
Today’s data release includes two laboratory reports and two data tables.
Note: This replacement of silt+clay fraction assay results does not impact other data that was included within the June 30, 2015 release. Specifically, the gold grain counts that were reported in that data release were obtained by a different vendor. No issues were identified with this stand-alone gold grain data set.
ActLabs Laboratory Report dated September 16, 2015 (a15_0415_cert_res_reassay.pdf) »
This ActLabs laboratory report provides analytical and quality control results for the re-assay of thirty (30) silt+clay fractions (-63micron) from Cook Area glacial sediment samples. This laboratory report was dated and submitted by ActLabs to the DNR on September 16, 2015.
Data Table for ActLabs September 16, 2015 Laboratory Report (excel, a15_04151_final_reassay.xlsx) »
This ActLabs-authored data table provides the results included in September 16, 2015 Laboratory Report within a spreadsheet file. The data table identifies analytical methods and method detection limits for each analyzed element.
ActLabs Laboratory Report dated October 23, 2015 (a15_04151_cert_res_reassay2.pdf) »
This ActLabs laboratory report provides analytical and quality control results for the re-assay of 108 silt+clay fractions (-63micron) from Cook Area glacial sediment samples. This laboratory report was dated and submitted by ActLabs to the DNR on October 23, 2015.
Data Table for ActLabs October 23, 2015 Laboratory Report (excel, a15_04151_final_reassay2.xlsx) »
This ActLabs-authored data table provides the results included in October 23, 2015 Laboratory Report within a spreadsheet file. The data table identifies analytical methods and method detection limits for each analyzed element.
- June 30, 2015
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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 the 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.
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 the 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 the DNR in Fall 2014 in a spreadsheet format.
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 the 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 the DNR 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 the 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.
- June 13, 2014
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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 the 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
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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 the 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 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
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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
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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 the 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 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 the DNR 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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