Soil samples for placer indication

[Slatco]

Morning gents, I am looking at some ground in the Yukon that has not had much placer work done on it but there has been soil sampling for hardrock. There are quite a few samples coming up with gold greater than 50 ppb and some over 1000 ppb. From my understanding 1000 ppb is 1g/yd so that should be a pretty good indication.

Just wondering if any of you guys have used soil sampling to find and then prove out a good placer prospect?

[Geowizard]

Hi Slatco,

For clarification, 1 ppm = 1 gram per metric tonne. Because one gram is defined as one cubic centimeter of water, that's 1 cubic meter of water or 2205 pounds (avdp) by weight.

I presume your sample was a bulk sample taken over a wide area. I also presume you are planning on testing the soil for its residual, eroded GOLD content and mapping the results. If that's the plan, you may be able to better define to location of the lode as well as get vectors to the placer in the process! Erosional products from a lode deposit are referred to as Colluvial. Colluvial sands and gravels are generally low grade because of the dilution of GOLD that is widely scattered in the gravels.

https://en.wikipedia.org/wiki/Colluvium

Geomorphing:

Outcropping Lode deposits always produce a placer deposit. If GOLD is found at the surface, it's a matter of "geomorphing". Use a quality topographic map (i.e. an online map like caltopo.com ) and draw down-slope vectors that represent the probable flow of erosion products to a nearby drainage. There-in will lie the concentration of GOLD from millions of years of erosion!

Caltopo is recommended because you can draw lines and get accurate terrain profiles with angle of slope in degrees and something called "Aspect". Aspect is the direction of the slope in degrees relative to true north. The line profile can be downloaded in .csv format to provide a spreadsheet of slope and aspect. The small subscription fee includes downloading topo images of your work area with survey markers, sample markers, and vectors you layout and save as your sampling continues.

Fun Stuff!

- Geowizard

[Geowizard]

Penetrometer;

Another thought... I have been involved in exploration for GOLD as well as mining for a long time. One of the methods used in soil sampling is a penetrometer. It's basically a pipe, sometimes with a liner that is driven, usually by a machine into the ground. With it, you can get a vertical profile of the strata and can accurately sample the different layers of soil and sediments. The sample is pressed out of the pipe or tube and looks like a core sample.

Over a long period of time - millions of years, different forces can act on the surface that drive sediments in different directions. Watersheds can change because winds, snow, rain accumulate in miniscule amounts that progressively change the landscape enough to affect the direction of colluvial flows.

Thinking both on a large scale and a small scale, collecting sample data and piecing it all together is like solving a puzzle without a picture to go by!

Super fun stuff!

- Geowizard

[Geowizard]

Auger;

Augers are an option for soil sampling. The trade-off is that you get a scrambled sample depending how much you advance the auger before pulling a sample. The sample will be scrambled to a degree anyway regardless of how often you pull a sample because it is impossible to avoid dragging the wall of the hole both going in and coming out. There is a loss of accuracy in the process. If only a "gross" estimate is needed and changes over ten or more feet are all that is relevant, then an auger gets a good albeit rough sample with depth.

- Geowizard

[Geowizard]

Haul samples or haul water?

PickaxeCA brought up the question on another thread. It's an important consideration. In my experience, I have found that the compromise is a mid-point indoors shelter where the environment is stable. Even just a canvas wall tent where things can be setup in an orderly manner with an inflow and outflow of samples. With a reliable, stable flow of water for washing samples without wind, rain, bugs and other forces affecting the process.

Water if not immediately available can be from a 275 gallon IBC plastic tote on a 4 foot stand. They have a large lid on the top and can be filled from another tank on a pickup or truck with a water pump. Pre-owned totes are inexpensive.

A couple of tubs and a sluice with a 12V recirculating pump, maybe a table and a chair, you're all set!

- Geowizard

[chickenminer]

Slatco, can't say I know any placer miners that use soil sampling for prospecting a placer deposit. But it seems a reasonable first step to take on new ground. You said the ground you are looking at " has not had much placer work done", but it did have some? Any idea of the depth to bedrock?
Mining in the Yukon would be a whole different experience than in BC !

[Slatco]

Thanks Geo and Chicken. At this point I am doing more internet prospecting than anything else and the info avail from YukonGeo is mostly related to hardrock geophysical. The purpose of my question was to see if there was a potential placer link with the soil sampling.

[PickaxeCA]

It depends if you have access to equipment that can drill down deep enough for you to get information about the deeper layers. The big time operations in the Yukon all drill when seeking new placer ground. In the absence of drilling it's all about machine dug test pits, or for smaller operations, large hand dug pits. or trenches.

The surface values you would obtain through soil sampling on a grid for placer certainly cannot hurt, but you would be missing out on 90%+ of the information you would need (3-12 feet+ below surface).

FYI - I use soil sampling for hard rock prospecting all the time. It enables me to very quickly test an area to determine if there is free mill gold present, and if that gold is rough, angular and low travel (implying it's from a vein in the immediate vicinity).

I personally like to pan soil samples on site, and I hike in 1-2 gallons of water with me, and pan in a small dish tub. With careful panning I can catch gold that is barely visible to the naked eye under my 10X jeweller's loupe.

[Geowizard]

Introducing Shawn Ryan;

Shawn Ryan used a tulip planter to discover GOLD in the Yukon!

Watch this:

The second gold rush - a prospector's perspective: Shawn Ryan at TEDxWhitehorse

https://www.youtube.com/watch?v=9bIIskBJVvg

I have posted many times before about Shawn Ryan and his early years. Using a Tulip planter, he discovered the over Two Billion Dollar (CAD) White Gold Deposit.

He has made millions and acheived international recognition at PDAC (Prospectors and Developers Association of Canada).

https://www.pdac.ca/

PDAC Convention 2011 - Shawn Ryan - Bill Dennis Award.wmv

https://www.youtube.com/watch?v=3T9semq0AhM

Shawn Ryan brought together a suite of GOLD prospecting technologies.

Groundtruth today:

https://groundtruth.ca/

Stick around. There's more!

- Geowizard

[PickaxeCA]

In a podcast interview with Shawn Ryan he mentions digging deeper than everyone else for soil samples.

Plus, as Geowizard mentioned, he uses a tulip planter for taking samples.

The guy takes a very high number of soil samples to find hard rock deposits. He uses soils because there is only 2-3% outcrop in the Yukon, on average (according to him).

It's probably worth emulating some of his techniques (at a much smaller scale).