The Forgotten Potential of Elluvial Gold (Part 1)
(Elluvial gold typically contains matrix material.)
Like most of you out there, I'm a placer gold miner first and foremost. I've done my small share of hard rock or lode prospecting as well, but I've spent the bulk of my small-scale mining career sluicing, dredging, or dry washing the streams and washes of the western and southwestern United States with occasional forays into Old Mexico. All this said, how many of you have ever prospected or mined for elluvial gold or recognize its potential in terms of gold recovery possibilities? Have your interest now do I? Good. Read on then.
First off, for those of you not yet clear on the subject let me define the difference between alluvial and elluvial gold (please note that these are my personal, miner's definitions, not something pulled from a geology text book):
Alluvial gold: The gold commonly found in low-lying areas such as rivers, streams, creeks, gulches, dry washes, and some beaches (including off-shore deposits like those found in Nome, Alaska). This is what we commonly refer to as placer gold and is what the bulk of the information and tips here in Bedrock Dreams is concerned with. Alluvial gold can run the gamut from large, coarse pieces with matrix material still attached to it, to nuggets, smaller "chunkers," flakes, and fine or "flour" gold. Most wet placer gold will be worn or smoothed by the combined action of water, sands, gravel, and rock depending how far that stream-borne gold has traveled. In dry or desert placers, recovered gold can exhibit similar types of wear or smoothing, especially if that gold was part of an an ancient river. However, most desert or dry placer gold is rough, coarse, and/or spiky with a higher concentration of non-gold alloys (iron, silver, or copper). This is the rule of thumb, anyway.
(Placer gold from wet areas typically shows signs of wear or "smoothing.")
Elluvial gold: This is the main topic of this post (and any subsequent posts) so if you're new to this small-scale gold prospecting and mining thing you'd be well served to pay close attention, not only to the definition of elluvial gold but to the recovery possibilities it can hold for all of us, regardless of experience level. Elluvial gold is recently eroded gold, typically derived from veins, lodes, outcrops, or what the old timers called "blow outs." In a sense, elluvial gold is in the process of eventually becoming placer gold but is caught up in a stage of downward transition from its source to those streams, gulches, and dry washes I already mentioned in my explanation of alluvial gold. Most elluvial gold is very coarse and nearly always contains host rock matrix material attached to it. Notice I said "nearly always." Some elluvial gold will show up minus any matrix material attached to it but it will still be coarse and not water-worn. Gravity is the primary mover of elluvial gold downhill, but other natural forces such as heavy rains or snows, mudslides, or hillside collapses often contribute to its movement. Just like its cousin, placer gold, elluvial gold can be found in large pockets or paystreaks or scattered about over a wide area like seed in a high wind on the flanks of a hill or mountainside. Now here's one final point I want to make in defining elluvial gold: it is NOT what I've termed "high point" gold since high water levels or stream flooding have little, if anything, to do with its movement or deposition. Got that? Good.
I Believe the Possibility Exists
After the lessons learned by would-be Argonauts in the Appalachian Region gold strikes of the American southeast and then the California Gold Rush, most old timers who prospected the West and Southwest were after bigger game than generic placer gold, unless those placers were extremely rich in nature. That bigger game I just spoke of was the source of all that placer gold...those lodes, veins, outcrops, or blow outs I also mentioned earlier. The typical routine followed by prospectors and miners in both wet and dry placer areas was to find color in a stream or wash, trace its path upstream until no color was found, and then begin searching again up and away from the low-lying areas on both sides (if hills or heights existed on both sides) or a single side where a solitary hill or mountain existed. If feeder streams or washes existed, they might also follow these up as long as color was found and then repeat the earlier process of searching. In certain instances the old timers found "float" higher up. Float was actual ore or country rock that was highly mineralized or contained visible gold. Now here's where things may get a bit confusing so let me explain. Strictly speaking, float was (and is) not elluvial gold. Sometimes elluvial gold existed side-by-side with rich float, sometimes it was there by its lonesome, and in other instances it was absent altogether. You see, Ma Nature just loves playing funny little tricks on gold prospectors and miners.
(Gold ore or "float.")
Again, what those crafty old timers were really after was the lode deposit that spawned that float or that elluvial gold. They wanted to hit the "big one" and many of them did just that by following the simple procedure outlined in the previous section. With gold at $18.00 (USD), $22.00, or even $35.00 a troy ounce, they had little interest in recovering random pieces of float or, more importantly, elluvial gold scattered down a hillside and often buried from their sight. Ahhhh...now you're starting to get the picture about the hidden potential of elluvial gold aren't you? I knew my faith in you was well founded. Now you see that the possibility exists in scattered (or even numerous) locations here in the U.S. (or elsewhere in the world for that matter) that overlooked, un-worked, or perhaps under-worked elluvial gold deposits are still in place, sitting there waiting to be discovered or even re-discovered by an astute prospector or small-scale miner. You see, the main emphasis on both ends of the spectrum historically was on placer gold or lode deposits, not on elluvial gold per se. It would be very difficult to prove my theory, of course, but I've been around the mining block a while now (35+ years) and I've found one good elluvial deposit myself. You can take it or leave it from there. Your call.
In my next post I'll be addressing elluvial deposits directly and will gladly throw a few tips your way... provided you're interested in all this, of course (and I think you are!).
Best of luck.
(c) Jim Rocha (J.R.) 2015
Questions? E-mail me at firstname.lastname@example.org