Thursday, June 28, 2012

Gold Processing and Extraction

Visible gold in goethite and quartz, Mary Ellen Mine
If you decide to mine lode gold, you can keep it simple and dig for specimen-grade gold samples from veins and breccias. Although such samples with visible gold are rare and more valuable than the price of gold, if you have the right vein or ore shoot, they are worth pursuing. When ever you see gossans or tawny to brown limonite and goethite in quartz - look for visible gold! Gossans are something prospectors need to learn to recognize.

If you decide to mine your lode using open pit or underground methods - you will need deep pockets to pay for mining as well as permitting. In this case, it may be easier to start looking for a company that has the expertise and deep pockets.

Detrital gold is by for the best type of gold to search for as a prospector as it has already been mined by Mother Nature, and now it is up to you to figure out how to concentrate it. To extract placer (detrital) gold from a creek using a gold pan (not recommended as it will wear out your back), sluice, trommel, dredge or some other concentrating equipment, you will likely need permits from the State or Feds. The government is totally out of touch when it comes to permitting, as in most cases they will try to permit you to death. Some states may even require a permit to operate a gold pan on public property even though this would be as absurd as requiring a permit to operate a fork in a restaurant; however, Democrats were actually talking about this when I left Wyoming. One of the easiest ways to find out rules and regulations for prospecting in your state is to join a local prospecting club. The ICMJ Prospecting and Mining Journal has a number of useful resources you may want to check on.  Many gold prospecting clubs are associated with the Gold Prospectors Association of America: and there are independent groups such as the Wyoming Prospectors Association. When I was in Wyoming, there was a faculty member in the University of Wyoming Geology Department who thought gold panners were polluting Douglas Creek. Obviously, she never tried to operate a gold pan herself, otherwise she would not have made such ridiculous statements.  If you find the right creek, and have a backhoe and trommel, some people can make a nice living.
Gold Panning in the Medicine Bow Mountains. This lady was one of
several who attended one of my field trips to the Medicine Bow Mountains
in the historical Centennial Ridge district. I showed the attendees how to
pan for gold and then let them try their luck in the Middle Fork of the
Little Laramie River. No one found gold at what was known as the
Mother Lode prospect, but some found nice specimens of pyrite (fool's gold)
and several found almandine and pyrope garnet! Pyrope garnet is a
tracer mineral used to find diamond deposits! So, somewhere upstream
(or up-slope) there is an eroding diamond pipe leaking pyrope garnets into
the creek. In addition, many people discovered why it takes a strong back
to pan for gold.
Years ago, I met two prospectors from Lander Wyoming who were working Smith Gulch at South Pass while I was mapping the greenstone belt and old mining districts, and they were recovering about 20 ounces of gold per week (Hausel, 1991). At 1600/ounce, that's only about 32,000 per week. Not bad for two guys.

Often we get used to seeing gold pans filled with gold - this does not really happen in real life; so when we see gold filled pans, remember, the gold was found with some other equipment and placed in the pan for a photo opt.

To assist you in your prospecting, I have several publications that are available for free download on my website.

Panning is an easy process - it just takes a little confidence and a couple of pans full of sand and mud, and soon you will be an expert. Gold has a very high specific gravity (15 to 19.3) which means you are going to have to make a serious effort to wash gold out of your pan. So put a little effort into your panning. If you are ending up with a tablespoon or two of what are known as black sands (mostly magnetite with a few other minerals such as ilmenite, zircon, etc), those have specific gravities of around 4 to 5. Thus gold is going to be 3 to 4 times heavier than those black sands.

Stamp mill at Goldfields, Arizona
While panning for diamonds in California, we recovered a gemstone known as benitoite near Poker Flat and chromian diopside from serpentinites in northern California (Hausel, 1996). In Wyoming, we recovered many gem-quality garnets, some diamonds, and numerous sapphires and rubies from our pan concentrates and found dozens of localities where gold had not been reported before (one was the Laramie City landfill!) (Hausel and others, 1994). In several samples collected in the Laramie Mountains near Vedauwoo, we recovered fluorite (easy to recognize in black sands as it is purple in this area and crushes easily) and many samples with chromian diopside and pyrope garnet in the vicinity of Eagle Rock. This suggests there are undiscovered diamond pipes! While searching for evidence of diamond pipes, we found a distinct, but very small, structurally-controlled vegetation anomaly (41o17'39.96"N; 105o22'46.95"W) along the edge of Eagle Rock. This same area has several beaver ponds to the northwest, any of which could be hiding a diamond pipe.

Not too far from Eagle Rock, we identified other possible diamond pipes that remain a mystery. These included what I originally called the Bowling Pin Anomaly (41o11'15.39"N; 105o19'34.67"W), a circular depression with carbonate in soils that had a couple of bowling pins in the depression when I first visited it several years ago. The entire area has many such anomalies including the HJ17 depression (41o12'01.92"N; 105o19'10.46"W).  Further south (actually just south of the interstate) I also identified 42 highly suspicious cryptovolcanic structures of which anyone of them could be a kimberlite (diamond) pipe. All of these anomalies remain untested due to various access problems.

Arrastra gold concentrator. This was a very primitive grinder with large rocks
attached to a pivot at the center. A mule would walk around in circles pulling
a lever that would continue to drag the boulders over a trough where gold-
bearing quartz would be placed to be crushed.
Other minerals of interest that I found while panning included a lot of white material that was impossible to pan out. It was too heavy! So I stuck it under a black light and with short wave ultraviolet light, it exhibited strong blue fluorescence - it was scheelite (a tungsten ore)! This was recovered from samples (along with some gem-quality iolite) near the old strong mine along the 9th street road in the Laramie Mountains.

And what else did I find in my panned samples - at one location in extreme northwestern Colorado, I recovered 4 diamonds, 17 rubies and 24 pyrope garnets while dry panning. Wow, what a find!  Actually, this was the site of the historical 1872 diamond hoax fraud which occurred near what is now called Diamond Peak (Hausel and Stahl, 1995). This great diamond hoax was amazing as it was an outcrop that was salted in 1871 and 1872 and the prospectors scammed some US Senators (first time in history that scam artists scammed scam artists).

A primitive roller mill displayed at the Douglas Museum, Jerome, Arizona.
Eric Hausel stands adjacent to the mill.
Well, got to go, I hear my wife yelling at me. Until next time, happy prospecting from the GemHunter. You can also follow some of my thoughts on Facebook. And if you are interested in breaking rocks - and what rock hound isn't - you can follow me on my other Facebook pages at Arizona and International.

References Cited

Hausel, W.D., 1991, Economic geology of the South Pass granite-greenstone belt, Wind River Mountains, western Wyoming: Geological Survey of Wyoming Report of Investigations 44, 129 p.

Hausel, W.D., 1996, Pacific Coast diamonds-an unconventional source terrane in Coyner, A.R., and Fahey, P.L., eds., Geology and ore deposits of the American Cordillera, Geological Society of Nevada Symposium Proceedings, Reno/Sparks, Nevada, p. 925-934.
Hausel, W.D., and Stahl, S., 1995, The great diamond hoax of 1872: Wyoming Geological Association Resources of Southwestern Wyoming Guidebook, p. 13-27.
Hausel, W.D., Marlatt, G.G., Nielsen, E.L., and Gregory, R.W., 1994, Study of metals and precious stones in southern Wyoming: Geological Survey of Wyoming Open File Report 94-2, 61 p.

Gold from Douglas Creek Wyoming. Photo shows gold recovered with the black sands removed (the penny is just used for scale). To remove black sands, simply wait until your panned concentrates are dry. Get a large and strong magnet, cover it with a paper towel and slowly sweep over the concentrates - whamo - nearly all of the black sands will be removed. What you have left is a little gold, garnets, mica and if you look close, you may even find diamond indicator minerals such as pyrope garnet, chromian diopside, picroilmenite, chromite and/or diamond. Diamond has a specific gravity of 3.5 and will often end up in the black sand concentrates. Much of the lighter colored material will be removed during panning: most of which will be quartz with a little feldspar. Quartz has a specific gravity of only 2.7.

Mining on Douglas Creek using a long tom and a
dredge on a rotating platform with shovel.

Gold nuggets in gold pan. The nuggets from Julian
Creek were recovered using a sluice and long tom
and not recovered in the pan.

Gold mined from Smith Gulch at South Pass using a backhoe and trommel.

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