A Possible Gold Strike??

[Micropedes1]

I have been running analysis on ore samples indicated via geophysical interpretation and gathered during the summer. I have one in particular that really stands out and was totally unexpected.

What I thought just HAD to be a gold/silver signal from my analysis turned out to be a broad band of graphite, no visible gold. My VLF detector just loved the deposit but went wild at a few points. Lots of digging ensued, but no results. I filled a zip-lock and moved on. Disappointed.

Analysis time. This stuff does not behave like the refractory ore that I am accustomed to. But preliminary analysis indicates precious metals; mostly silver, but some gold. Sphalerite and pyrite. And concentrated at the boundary layer between the host rock and graphite intrusive.

More samples from the location are warranted. But preliminary estimates using my sampes indicate 10 grams/ton of electrum. I need discussion on recovery methods for this type of ore as it is beyond my experience.

[Jim_Alaska]

Glen, I have no clue on recovery such as you describe. But if it may help I do have a resource for lab analysis that is top notch and run by a friend of mine. My friend is a top level chemist and her lab does work world-wide.

[Micropedes1]

Any help would be much appreciated.

I used a gravity column to concentrate heavies. Then an aqua regia extraction on the recovered heavies before running thru my AA unit. My problem is that the ore is complex, with gold incorporated into other sulfide minerals. And the graphite remaining after passing thru the gravity column still tests positive for gold. So....my 10 g/ton estimate is off by a considerable amount.

And it is my understanding that the graphite prevents a simple cyanide leach. I am at a loss on how to proceed with a profitable recovery sequence. I am thinking gravity, froth, and roast before chemical leach. But I may be way off. And this much processing could prevent recovery from being economically viable. Might there be an easier way?

[Micropedes1]

There is considerable amount of graphite. Enough to make marketing that commodity the principle recovery ore. Could probably use that to pay for the precious metal recovery. The combined seams extend for over 150 feet, only recently exposed by landslide

[Jim_Alaska]

Glen, I'll send a link to this thread to my friend and see what she says based on what you describe.

[Geowizard]

Glen,

A very interesting deposit!

In any sulfide deposit, samples are roasted to remove the sulfur.

Now, it's all oxides!

Carbon is a spectator... It is inert and of no concern with respect to GOLD.

Start with a known dry weight i.e. 100 grams.

You are on track to assay the GOLD contained in your samples. You already know AR will take the GOLD into solution. With GOLD in solution, filter the Carbon and any remaining sediments, the GOLD will remain in the solution that passes the filter. AR has to be cooked down to almost dryness and re-hydrated.

Cook it down twice and re-hydrate. Make up the volume of solution with DI water to 100 ml. Calibrate the AA spectrometer with a fresh store bought standard. For example, Sigma Millipore. I cut the GOLD standard solution of 1000 ppm by a dilution factor of 10 to 100 ppm. Parts per million (ppm) = grams per metric tonne. With a calibration curve that is set to run from 100 ppm through zero, you are within the calibration limits.

Note: I presently work in an Assay office at a mine in Arizona cap'ed at a quarter Billion dollars. I operate AA spectrometers at the mine every day as I have for decades.

With respect to silver and lead, remove them up front, under heat with dilute Nitric. Rinse the remaining solids which will still contain GOLD. Then proceed as mentioned above.

Good luck!

Geowizard