(Carbonaceous phyllite gold ore being removed in Alaska. Note the outcrop in the upper right of the photo.)
I want to spend just a bit more time in this post on carbonates and gold veins, and to that end I'll be adding some comments and information on the subject from Tom V., a Bedrock Dreams reader and supporter. I think you'll find what Tom has to say quite interesting.
Here's what Tom has to add to our discussion of carbonates and vein gold:
"Some years back I accidentally stumbled across an ore body on a relative's wooded farm. It was a layer of greenish-white rock in a two-foot thick layer going up a steep hillside that bottomed out at a creek in the bottom of a small valley (or ravine?) maybe 150-feet wide. I thought the ore might have some copper (Cu) in it, so maybe it might be copper carbonate?"
(Free-milling gold in a specimen of copper-carbonate feldspar.)
"I sent samples out for assaying but the assay report said 0.03 ounces per ton of GOLD and a smidgeon of silver, NO copper. I also made the mistake of taste-testing the rock...that was the last time I ever taste test a possible metallic type rock. It had a STRONG metallic taste which set off a nasty panic attack. Glad I had some tranquilizers handy!"
"30 Pounds of Galena"
"My relative has no interest in the vein material I had assayed and, to be honest, having to mine 30 tons of rock to get an ounce of gold doesn't sound too appealing to me."
"I wonder if it might be worthwhile metal detecting the hillside for a concentration of gold or other metal concentration? Keeping my footing on a 60-degree slope will be a challenge, however. I've detected/recovered 30 pounds of galena on my relative's property from metal detecting. (Note: Galena is a common lead ore that frequently contains small amounts of silver and more rarely, gold. J.R.) An assay on a galena crystal showed 0.12 ounce per ton for Au and a smidgeon for silver (Ag). Historical records indicate the galena was about 60% lead. I sure wasn't expecting that Au in the galena."
(Big chunk of galena ore containing large amounts of silver.)
"I am now wondering if all the waste rock...especially the rock around old smelters might be worth reprocessing for the gold? The old timers were just after the lead as far as I know. The one downside is that the state of Wisconsin has made mine owners liable to infinity due to sulfuric acid pollution of streams from refining/leaching sulfide ores. That kinda removes one's incentive....unless it's done on a hobby (small-scale) basis perhaps."
"I know where an old smelter is in Dodgeville, Wisconsin, but no slag piles remain in place beside it. I wonder where they went? The old smelter is a cone-shaped kiln structure about 25-feet high with a six-inch hole at the bottom. I assume the lead came out there. How did these things work? Old topographic maps show names like furnace, etc."
(Ruins of an old smelting furnace in Wisconsin.)
"Anyway, in two more months I hope to get back to Indiana and get that landowner permission I should've got last fall for two gold placer creeks."
Pretty Big "If's"
First off, I want to commend Tom for taking the time and money to get his field samples assayed. Fire, chemical, or spectrographic assays are the only tried, true, and trusted methods for determining exactly what a given piece of ore (or rock) contains from a precious metals standpoint. His galena assay revealed a gold value of 0.12 troy ounces of gold per ton of material. This comes out to about 3.73 grams of gold per ton, a value many large companies like Goldfield or Newmont Mining might consider viable from a profit standpoint. That is, if hundreds of other samples taken averaged 0.12 troy ounces per ton or higher in gold and if the ore body was extensive enough to warrant a large-scale, open pit mining operation. Let's add another "if." Is that galena ore refractory? If so and the gold is difficult to extract or chemically leach, then all bets might be off from a profit standpoint. And here's the final "if." Can you or Newmont or Goldfield get the required environmental permits to mine or are you gonna have to fight the New Green Church every single step of the way? Those are some pretty big "if's" brothers and sisters, but that's the nature of making a go at mining vein gold these days.
Want Gold and Lots of It?
As placer gold miners we're often blind to the true nature of hard-rock mining...it's costs, it's equipment requirements, it's permitting process, and the sheer hard work it takes to make a go of working vein material on a small-scale, in particular. Hard-rock or lode mining is a whole new ballgame when it comes to prospecting, processing, and gold recovery and there's no doubt that it's a much more dangerous proposition than running a highbanker next to some high-mountain stream. But if you want gold and lots of it, you're best bet is always the source of that placer gold you're panning in that creek or river. Finding it and getting it are the real issues, however. Hopefully, this series of posts will make that task slightly easier for you.
(Hard-rock mining invariably requires more capital than any other form of gold mining.)
As far as metal detecting goes, I say why not Tom? If you have a good gold machine with effective ground canceling abilities and know all its ins and outs, then go for it. A detector is simply another prospecting tool and in this case you need all the tools you can afford at your disposal. Ditto for all of you out there. You should always remain open-minded when it comes to how you search for gold and how you go about getting it out of the ground.
Hang tough all. There's more to come soon.
(c) Jim Rocha (J.R.) 2016
Questions? E-mail me at firstname.lastname@example.org