Gold Indicators and Indications (Conclusion)
In this post I'll be tying things up with what Aussie miner Jack has to say about this topic. At various points I'll intrude with a few definitions, explanations, and so on by placing my perspective in italics. But essentially this is Jack's show...as it's been all along.
(The term "reef" is Aussie for vein, lode, or outcrop. J.R.)
Here are a few things to think about:
How many reefs are out there that were never worked by the old timers? Perhaps they never had the time to try them out. (Although most of the old timers knew their stuff about lode indicators/indications, the overall level of prospecting expertise varied from individual to individual. So it's likely throughout the world that some vein material was overlooked. However, I think the more likely reason for certain lode indications being left "untouched" is economics. It takes a lot of money and equipment to fully develop a potential hard-rock mine and if the precious metal showing was considered "borderline" or economically unfeasible at the time, then it was very likely bypassed when a troy ounce of gold was worth only $18.00, $22.00, or $35.00 [USD]. Smaller or less rich "reefs" like this can, however, present good opportunities for the modern small-scale guy or gal. J.R.)
(Gold-bearing reef at the Charters Towers Mine in Australia.)
Have you ever worked an unknown reef and found that it is shredding gold? If not, then it may helpful to research data from this list:
Unworked iron-enriched quartz. (Quartz with heavy iron sulfide enrichment or mineralization. J.R. )
Unworked iron-enriched brecciated quartz. (Quartz that's cemented together with larger or more coarsely grained pieces of angular rock. J.R.)
Unworked quartz and ironstone. (Ironstone is a sedimentary rock that is highly ferrous in nature. In Australia ironstone and quartz are often associated with various gold fields, both lode and placer. However, ironstone can be found in numerous localities throughout the world. J.R.)
Unworked quartz and molybdenite. (Molybdenite is a mineral of molybdenum disulfide. It has a grey or bluish-grey color and is similar in appearance and feel to graphite. J.R.)
(Molybdenite in a quartz stringer.)
All of these reef types would be worth a closer look. I think about them all the time and we (my "pard" and I) spend a fair amount of our time prospecting for them. I've found a few reefs, leads, and precipitate enrichments in my time and a couple of them payed very well. The most interesting are the precipitate enrichment type reefs. (Jack provides a description of precipitate enrichment in the following section. J.R.) They are very hard to locate if you can't read and follow the signs (indicators/indications). It's well worth the effort in trying to find any of these reef types.
What's a simple description of the methods you employ to find these sorts of reefs? No, I'm not after your trade secrets here! I do it using sing both electronic and manual loaming Mate. (Basically, loaming is the panning of loose surface samples in a systematic and recorded manner. The electronic aspect is, of course, the use of metal detectors or other electronic detection or sampling gear. J.R.) The hardest part in all this is picking the best or most likely areas to concentrate your efforts on. In my experience, the "5000" (I'm assuming Jack is referring to the Minelab GPX 5000 detector here. J.R.) revolutionized my approach regarding this type of prospecting as it picks up even the smallest fly shit-sized pieces gold!
(Minelab GPX 5000.)
This is a geological process where mobile water-soluble gold (usually in the form of sulfides) contacts an alkaline mineral which neutralizes it. This frees the gold from the sulfides and renders it insoluble in water where it then can be deposited. In some instances precipitate enrichment can form large, beautiful crystals and in other cases it can be very rich (many, many troy ounces) inside a concentrated area of one square meter or less. The precipitate enrichment process most commonly occurs in alkaline types of clay like kaolin/kaolinite and calcium-rich clays near limestone. These may not be directly associated with reefs, but the sulfides may have come from a nearby ore body, reef, or directly from sedimentary rocks. These types of deposits are a lot rarer than regular reef deposits.
(I want to thank Jack for providing the heart of this series of posts and for his willingness to share his experience and mining acumen. Good on ya, Mate! And well done.)
(c) Jim Rocha 2018
Questions? E-mail me at firstname.lastname@example.org