One of the common associations with gold in detrital deposits is the association of gold with uranium and carbon. This holds true in the Witwatersrand and all the other gold deposits of a detrital nature. For many years the origin of the carbon was hotly debated with the most recent evidence holding that it is from primitive life forms that lived in the distant past in the Archean.
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| Algae exposed at the intertidal zone similar to the ancient algae that trapped gold. Even today this kind of mat could be a good place to search for gold. Photo by Leonardo de Jorge |
It has been posited that these algae formed great mats similar to stromatolites that acted as a trap for the gold particles and uranium minerals in the same manner that modern mats of algae work to snare gold particles in a modern environment. It is common practice to use an artificial mat of the same nature in a sluice box to entrap gold.
Although the deposits can be several thousand feet deep now, but at the time of depositation they were relatively shallow at the bottom of running water that was only a few tens of meters deep subsequent Earth processes have buried them to their present depth.
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| An angular uncomformity with a basel layer of conglomerate that would be a good place to look for gold. The best place is right at the uncomfority. Photo by Lamprus |
At the time many of these gold bearing deposits were at the bottom of a braided stream channel that by being deposited in this manner explains the stringers of gold found in such a deposit. These stringers of gold are common in detrital gold deposits. Sometimes there is a layer of carbon that is as thin as a pencil line that is so rich in gold and other minerals that they are mineable. In many detrital deposits the slim lines occur at a regular frequency to the extent that the entire deposit is mined so that I can undergo further ore dressing to free the gold so it can undergo even further treatment usually by being leached with a solution of cyanide.
Even today if you encounter a mat of algae in the bottom of the stream or river is a good place to search for gold that has been caught in the mat by the action of running water.