Would resistivity for hard rock?

[Reverie]

Hi folks new to the site here, figured I’d pick a few Brains if I can so I’m heading towards a new season prospecting in NL. When the winters done dumping snow I’ll be headed to a large hill in a volcanic rock zone. Evidence of pb and cu in river runoff and anomalous amounts of gold as well which tells me I’m possibly in an area where a vms deposit could be and I’ve narrowed it down to a specific side of the hill due to silt samples etc. Wondering the viability of using a soil resisitivity meter to locate the exact spot and how accurate this method can be. Any and all info appreciated guys thank you

 

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[Jim in Idaho]

I got into the resistivity method last summer. I'm working on a possible copper deposit in Nevada. I built my own resistivity unit, which is fairly simple. There are several different ways to go about this. You can apply a DC voltage across two probes, and measure the voltage and current and calculate the resistance. In that case, you would be looking for an annomoly (drop) in the resistance below the average you've been seeing. The downside of that method is several different conditions can cause the drop....water, or increased soil moisture being a big one. Another method is to do a "resistivity" type of scan. You can find a lot of articles on the 'net about resistivity, so I won't go into it. The unit I made can do either type, and has the capability of selecting the applied voltage. I can choose either 12vDC, or 66v, or 105v. Usually I use the 105 because I'm working a very dry area, and it requires a lot of voltage to get a readable current. But, when the probes are closer together, I need the 12v to keep the current in an accurate range. Resistance/resistivity is a really interesting field of study and use.
Jim

 

[BlasterJ]

I got into the resistivity method last summer. I'm working on a possible copper deposit in Nevada. I built my own resistivity unit, which is fairly simple. There are several different ways to go about this. You can apply a DC voltage across two probes, and measure the voltage and current and calculate the resistance. In that case, you would be looking for an annomoly (drop) in the resistance below the average you've been seeing. The downside of that method is several different conditions can cause the drop....water, or increased soil moisture being a big one. Another method is to do a "resistivity" type of scan. You can find a lot of articles on the 'net about resistivity, so I won't go into it. The unit I made can do either type, and has the capability of selecting the applied voltage. I can choose either 12vDC, or 66v, or 105v. Usually I use the 105 because I'm working a very dry area, and it requires a lot of voltage to get a readable current. But, when the probes are closer together, I need the 12v to keep the current in an accurate range. Resistance/resistivity is a really interesting field of study and use.
Jim

I've seen video of some big units that have a lot of copper ground rods in a row. I wonder if they have a switching device to differentially measure the resistance between a bunch of pairs and compute an average?

 

[Jim in Idaho]

Mostly they have software that switches the resistance measured. That data is entered into a software that does an "inversion" and outputs a graphic of what lies beneath. The visualized depth is determined by the probe spacing...generally, the depth seen is 50% of the probe spacing. Here's a pic of what the output resembles:
This was from my pasture during my learning process. Blue is low resistivity, green is moderate. Red/orange is high and is probably basalt lava that underlies the pasture. green is likely gravel from the Snake River, as it ran through most of this country at one time or another. it's now about 50' lower than here and 3/4 mile away. The software I use is free, and only 2D. There is a 3D version, but it's costly.
Jim