Monday, October 6, 2008

Gold Ore Prospecting Tips

Placer mining is, of course, all about recovering "free" gold deposited by erosion and hydraulic action in streambeds and drywashes. At the same time, that very same placer gold we are focused on recovering probably originated in a vein or ore body elsewhere. In the old days, savvy prospectors often followed what they termed "float" (loose gold ore) directly to the source of nearby placer gold.

Prospecting for Gold Ore a Lost Art?

In many respects prospecting for gold ore has become a lost art, especially where it concerns small-scale or recreational miners. You may disagree and you have every right to do so. But the fact remains that during the heyday of Western mining, most prospectors and gold miners had a good sense of the geology of gold and a practiced "eye" for spotting potential bonanzas through a sequence of fundamental knowledge, experience, and visual clues. Today this is not always the case.

What the Old Timers Looked For

What did the old timers look for when they searched for signs of gold mineralization, or ore bodies and float? A number of things, including the following, which still remain valuable tips for modern-day prospectors and miners:

1) Sudden changes in country rock* or vegetation: sudden or dramatic changes in country rock or vegetation quite often signified geological change and potential gold mineralization. Changes in country rock are probably easily understandable, but why vegetation? Because the old timers knew that certain types of plants or trees would not grow in highly mineralized zones while others would proliferate. This was an important sign to them in their quest for precious metals.

(* the most prevalent or common host rock in a given area)

2) Abrupt changes in color in the earth and country rock: the old timers also knew that abrupt changes in the color of the earth beneath their feet and in the country rock surrounding them often heralded mineralized zones. When passing through such areas or zones they would closely examine any and all physical clues around them.

3) Decomposed rock eroding out from a ledge or vein: many residual placers or lode veins were readily identified by this characteristic. The old timers often referred to these areas as "blow outs" and took great pains to examine and sample them thoroughly.

4) "Rotten" looking quartz or quartzitic material that crumbles or crushes easily: often called "blossom rock" (if containing visible gold) by the old timers, this material was visually examined and then crushed, panned, or assayed.

5) Heavily iron-stained, pyritic, or multi-colored rock or quartz material: despite their lack of formal education, the old timers knew that rock or white quartz that showed physical signs of oxidation (reds, oranges, yellows, blues, blacks, etc.) or that contained iron pyrite ("Fool's Gold") was a good indicator that precious metals might be nearby. They called this type of material "peacock rock" and understood its significance in determining areas of potential gold mineralization.

6) Evidence of other metals or minerals such as platinum, copper, silver, mica, garnets, or other semi-precious stones: the old timers intuitively understood the chemical and physical relationships among various minerals and metals. Even if gold was not readily apparent to them, the presence of these other metals or minerals indicated the likelihood of gold, even as a "byproduct."

There is much more to what the old timers knew and practiced, and I'll cover some of that information in another post. In the meantime, remember these tips from yesteryear the next time you are out and about.

Who knows? They may point you right to the gold.

(c)  Jim Rocha (J.R.)  2008


  1. Thank you for your kind comment. Jim (J.R.)