Map of of Gold in Till, Cook Area, St. Louis County

Map of of Gold in Till, Cook Area, St. Louis County

Source: http://www.dnr.state.mn.us/lands_minerals/mpes_projects/project392.html

Local Copy of files: Click here to download a zip with all of the files from this article (including the map)

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:

December 5, 2013 laboratory reports from Overburden Drilling Management, Ltd This is a PDF file. You will need Adobe Acrobat Reader to download it.

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 link leads to an Excel document.
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 link leads to an Excel document.
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 is a PDF file. You will need Adobe Acrobat Reader to download it.
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.

Lode Gold in Minnesota

This post comes in response to some questions that have popped up on the forum/facebook regarding lode gold in Minnesota.

  • Is gold this size even possible in our area? (refers to photo below)
  • Doesn’t lode gold mean there is a mother or source? There is no native source of gold in MN.
  • Isn’t lode gold is indicative of fault lines such as California, china, Canada, ect?
  • From what I’ve read our geology doesn’t support lode gold, volcanic eruptions can only produce alluvial gold.
5 Gram Minnesota Gold Nugget

5 Gram Minnesota Gold Nugget

Is gold this size even possible in our area?
Yes, gold that large is not only possible but probable. The problem is finding it as you probably already know.

The subsurface geology in most of Northern Minnesota is conductive to containing large amounts of metal. The surface geology is the problem. Glacial sediment covers most of the region and even if there is not much glacial sediment, the region is heavily forested making testing and mobility a problem. In addition, The lack of elevation change is probably the most damaging factor for placer deposits as it causes the rates of erosion to be so slow that soil can actually build faster than it is removed. The actual basement rock that contains lode gold is usually protected from direct erosive process, and even if exposed the speed of the streams in our region are so slow that they can not move gold very far.

In contrast
In mountainous regions chunks of gold bearing material break off the sides of the mountain and are rolled down the hill. As the boulders are pushed down stream they break up and any gold contained within is dropped out along the way. Prospectors/geologist use magnification to check the condition of the gold. The more jagged it gets the less distance it has traveled. As soon as you quit seeing gold in the stream you backtrack and start working your way up the mountain testing rocks until you find the lode/source deposit.

The Minnesota DNR is using a modification to this technique to search for lode deposits by analyzing till and checking the condition of the gold grains. The process is harder because you have to factor in ice flow, but the DNR appears to have identified at least two areas that contain lode gold in Minnesota. One is South of Big Fork East and the other is Southeast of Lake Vermilion. I do not think the DNR has the exact location of the lode deposit, but they have narrowed down the area to look for commercial entities.

If there were mountains in Minnesota there would be gold in just about every stream.  (There is more information below on this)

Next Question

  • Doesn’t lode gold mean there is a mother or source? There is no native source of gold in MN.

I basically already covered this above, but we will take a 1 step further.  There are native sources of gold in Minnesota. They are same kind of rocks as what you find in Canada, but most of the overburden in Canada was removed during the last glacial period and dumped in the lower 48.  The result is that it is much easier to test for lode gold deposits in much of Canada than Minnesota.

Gold-Mines-and-Locations-Ontario-and-Minnesota

Gold-Mines-and-Locations-Ontario-and-Minnesota

Next Question

  • Isn’t lode gold is indicative of fault lines such as California, china, Canada, ect?

You mean like these?

MN Major Faults

MN Major Faults (inferred)

Keep in mind those are major fault lines.  There would be thousands of smaller faults to go along with each major black line. Most of those lines are inferred by changes in magnetic studies of Minnesota.  A few have been mapped in outcrop.

Minnesota has a very long geologic history.  At one time some of the boulders near Sauk Centre were dated as being the oldest rocks in the world. That title did not stand for long, but what it means is that what we see today is nothing like what the area looked like in the past.  The rocks in Northern Minnesota are billions of years old. The major faults would have been active more than 1.8 billion years ago, and at that time Minnesota had ocean front property (not inland seas they came later).  Small continents were smashing into the side of the craton (protocontient) and getting stuck to the side which later became north America. At the time there would have been massive mountain ranges that would probably put all modern mountain ranges to shame. Geologist call mountain building events “orogenies” (usually gets a chuckle) The one we are talking about specifically was the Penokean Orogeny which happened ~1.84 Billion years ago. Depending on climate conditions it only takes a few hundred millions years to completely erase mountain ranges. For perspective much of the rocky Mountains underwent mountain building as little as 40 million years ago while the Appalachians underwent mountain building about 260 million years ago.

The Gold that is trapped in the rocks of Northern Minnesota and Canada has been there a very long time, and the rocks we see on the surface now were miles underground at one time.  We are looking at the bottom of mountains when we look at the rocks in Minnesota and Canada.
(This might be a mind F for some of the none geology types that find this post)

Next question (not a question just incorrect)

  • From what I’ve read our geology doesn’t support lode gold, volcanic eruptions can only produce alluvial gold.

I’m tired read the following.  :)

Alluvial Gold Vs Eluvial Gold
http://www.gold-prospecting-wa.com/alluvial-gold.html

Additional Thoughts

That nugget in the photo above probably didn’t get far from where it came from it would be interesting to know exactly where it was found.

Photo Above came from here http://metaldetectingforum.com/showthread.php?t=123779

Lode Gold in Minnesota

An explanation of lode gold in Minnesota and what makes it difficult to find.

More Gold Reports for Minnesota (Project 392)

Source http://www.dnr.state.mn.us/lands_minerals/mpes_projects/project392.html

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

Map of gold deposits of gold in Cook County, MN

Map of gold deposits of gold in Cook County, MN

PDF of the image above

Normalized Grain Count Data With Locations

Lab Analysis with locations

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.

Project Manager: Don Elsenheimer

Basic Geology Stuff You May Want to Know

The first thing we will talk about is mohs hardness scale. This is something all geology 101 students are forced to memorize. It can help us prospect because we will know what minerals are likely to survive where we are looking.

Mohs Scale of Gemstone Hardness

Mohs Scale of Gemstone Hardness

The following are the typical field tests. It is not uncommon to see a geologist carrying a few of these items specifically for the following tests.

  • 1 — Soft, greasy, flakes of fingers (talc)
  • 2 — Can be scratched by a fingernail (gypsum)
  • 3 — Can be cut easily with a knife or a nail, scratched by a penny (calcite)
  • 4 — Can be scratched easily by a knife (fluorite)
  • 5 — Can be scratched by a knife with difficulty (apatite)
  • 6 — Can be scratched by a steel file (orthoclase)
  • 7 — Scratches a steel file (quartz)
  • 8 — Scratches quartz (topaz)
  • 9 — Scratches anything lower on the scale (corundum)
  • 10 — Scratches anything lower on the scale (diamond)

Most of us prospect in streams or areas that have seen water flow so we need to be aware of how minerals have interacted up to the point where we find them.

Blond sand is mostly made up of quarts with minor amounts of Feldspars and other minerals. (Feldspars tend to turn into clays minerals over time)

In general we can say that anything that does not have a hardness of 7 or greater is going to get beat up relatively fast because sand grains will slowly eat away anything softer.

Anything softer than sand grains will end up being smaller than the sand grains that surround them. If a mineral is harder than quarts it will likely stand up to the punishment, but it will also become rounded. It is difficult to tell the difference between rounded diamond, corundum, and topaz.
A later post will describe methods you can use at home to tell the difference.

So unless you are after load deposits you should realize that you are probably going to be looking for an elemental metal or something harder than quarts.

The information above seems like enough for now.

Note: I will be adding links to the other posts once I write them. This information is not meant to be complete alone.

V2 of the gold map

V2 of the gold map has been posted. Changes include some extra public data from the USGS and a handful of updates from the MN prospectors.

V2 of the gold map

Made some changes to “the gold map”

More public data for MN, WI, MI regarding historic gold locations.

There were also a handful of updates provided by the MN prospectors. (Thank You)

Updated The gold Map

Updated “The gold Map”

Historical data was put into the Upper Midwest gold map along with a few new user reports out of Minnesota.

Gold in Minnesota

Added some information on the history of gold in MN.

Click the title of this post to be taken to the article.

Gold in Minnesota

Added some information on how to find gold in Minnesota.  The post covers the history of gold discoveries in and explains the most recent glacial advances.  In general sediments from the “Rainy” lob contain the most gold bearing sediment.

Click on the title of this post to see the full article.

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