Monday, July 27, 2015

Mining Tips From an Old Timer (Part 9)

(A "small"-scale gold miner with her batea in South America.)

Here's the ninth installment in this series of mining tips from yours truly. Take what works for you and apply it to your own small-scale gold prospecting and mining efforts.You never know what added benefits may come from it down the road a piece.

25. A portable sluice box should always accompany you when you're working wet placer ground.

No matter how experienced you are as a prospector or miner, or how adept you are at running a suction dredge, highbanker, or gold trommel in wet placer environments, you should still have a portable sluice box with you at all times. Next to a gold pan, the sluice box is the single most versatile and efficient piece of gold-getting gear that ever came down the pike. Bar none, and that's a fact. Want proof? Just take a walk back through time and see what an important tool the sluice box was in gold rushes throughout the world, including the most significant one ever...the California Gold Rush. The sluice's extended version, the "long tom," undoubtedly recovered more gold than any thousand modern-day suction dredges, highbankers, or trommels. Don't get me wrong here. I love suction dredges, highbankers, and trommels as much as the next miner and have used the first two extensively in my small-scale mining career. They are motorized improvements on basic gold-getting concepts that go wayyyyyyyyyyyyy back in time and as such they deserve both praise and merit. But each one of these modern mining implements requires either one or more SLUICE BOXES as its gold recovery core component. There it is.

(Here's one of those portable, fold-up jobs.)

Without a doubt modern, motorized pieces of mining equipment can process a lot more gold-bearing material more efficiently than the standard, "shovel 'er in" sluice box fed by a solitary miner. But in my view versatility is a much overlooked mining equipment attribute these days. That's where the venerable old sluice box steps into the gap. It's versatile, pure and simple. Especially nowadays where you can purchase extremely lightweight boxes, some of which can even be folded up and stored in a backpack. The sluice box:
  • Can be used as is for processing samples more quickly and efficiently than panning them.
  • Is easily employed as a primary means of processing gold-bearing material (where enough water is available).
  • Provides a back-up means for running gold-bearing material if motorized equipment fails or can't be repaired on-scene.
 (What happens when that motorized gear goes "kaput" and can't be repaired on-scene?)
  • Can function like a rocker box in situations where low (or slow moving) water conditions exist.
  • Remains cheap, lightweight, durable, easily transportable, and requires no gasoline or significant mechanical aptitude to operate or repair. 
  • Is easy to set up and operate.
Those are some pretty decent attributes, don't you think? So it's probably not a good idea on your part as a small-scale miner to thumb your nose at the sluice box, whatever the simplicity of its design and operation. As I've said before, I've had my Keene Engineering portable box for 35 years now and it'll be accompanying me again this week when I make yet another prospecting foray here in Northern New Mexico. Don't own a portable sluice box? Then make one or buy one.

26. Get down to the heart of the matter.

I've probably already danced around the bedrock issue in this series of tips and I know for a fact I've discussed it elsewhere in Bedrock Dreams since it's a topic of conversation worth repeating. Whether true or "false" in its composition, bedrock is always the heart of the matter when it comes to getting the gold. Yes, you've heard me many times speak about thinking outside the box when it comes to prospecting for gold and in numerous instances this approach WILL serve you well. That said, however, you should always understand that deposition physics are based on hard and fast rules that have been proven out over time, scientifically and through first-hand experience. Yes, it's true that Ma Nature enjoys a good joke like anyone else and loves throwing curve balls at times when it comes to where placer gold turns up. But over and above the atypical variances, placer gold will seek its lowest point over time. This is true in both wet and dry placers, with the former being quicker and more consistent in terms of bedrock deposition over time and the latter taking longer and being less consistent in overall deposition over the same period of time.

 (My friend and occasional mining pard Kane Fisher searching true bedrock for dry placer gold.)

Unless it's already exposed (or partly so), getting down to stream or wash bedrock is no easy feat. Overburden is the culprit here, that layer (or those successive layers) of waste or pseudo-waste rock, dirt, and gravel that can blanket gold-rich bedrock like a dark shroud. Very few small-scale miners I know (including myself) have the time or desire to hand-dig their way through 10, or 20, or 30 feet or more of nearly sterile overburden to get at bedrock gold. Nope, no thank you. I'll pass on that one. Now you know why many of the old timers formed "companies" or larger groups of miners in order to have the manpower to damn up or divert existing streams and then clear out the boulders, rocks, and accumulated dirt and gravels to reach bedrock. You see, that's where the best (largest) and the most gold was. This fact still remains true today...overall.

27. True Bedrock and "Gold Robber"

As I've told you before, there are both natural or true bedrocks and there are what are termed "false" bedrocks. True bedrock is the underlying rock structure (sometimes called the "country rock") of the gold locale you're working and can be composed of granite, serpentine, schist, gneiss, greenstone, andesite, diorite, and so on. True bedrocks are impervious to the passage of gold. They provide the final barrier for the downward settling or mixing of placer gold. True bedrock cracks, crevices, or depressions are often packed with gold ranging from fines (flour gold) on up to large nuggets and everything in between. Typically, however, placer gold resting on true bedrock or within its cracks and crevices is coarse and large. Pockets, paystreaks, and other rich concentrations of gold are common on true bedrock that's never been worked or worked only sporadically or partially. Much of the same is true for "false" bedrocks which are typically composed of clays or tightly packed conglomerates. Clay was known by the old timers as "gold robber" since its gluey like consistency underwater bound placer gold particles to itself. Clay layers, although not as impervious as solid rock (true bedrock) are very effective at stopping the passage of placer gold downward, especially when those clay layers are thicker than just a few inches. Placer gold moving ever downward in a stream or wash will hit a clay (in the desert, caliche) layer and dig itself a resting spot into the very upper part of that layer until lucky you comes along and frees it from its clayey prison. I have EXTENSIVE experience working false bedrocks and clay layers, and I can tell you this. They can present as fine a gold-recovery opportunity as some stretches of true bedrock, minus the cracks, crevices, and deep depressions that are typical of true country rock.

 (Conglomerate and clay layer mixture in Australian dry placer area.)

Here's one more thing. Since clay layers aren't solid in the sense of true bedrocks, the possibility exists that multiple "false" bedrocks can exist below an existing stream or wash. Sometimes you'll stumble upon this fact inadvertently or by accident, but oftentimes there are visible clues around that'll lead you to this conclusion. What are those clues? Benches, terraces, or feeder streams. Anyway, the thing to remember in this eventuality is that each and every one of those false bedrocks (clay layer or conglomerate) can present another high-magnitude gold recovery opportunity if you have the stamina, guts, and gear to dig your way through successive layers because they're typically separated by rock and gravel of all sizes and are a bitch to get to in many instances. If you're really lucky, you'll find yourself a false bedrock composed of clay lying just below a very shallow (6-10 inches) coating of overburden, as I've done numerous times in northern California wet placers and believe it or not, dry placers in southern/southeastern California. That should get your mind to wandering a bit!

There's always more to come so hang in there and thanks for your support of Bedrock Dreams in all respects.

(c) Jim Rocha (J.R.) 2015

Questions? E-mail me at jr872vt90@yahoo.com

1 comment:

  1. Hello JR, what I like best about a sluice box is that there is no noise. A little gurgling water maybe, but no engine. Part of the reason for me to do this is relaxation. It's pleasant standing in a creek on a hot day in the mountains, and finding some gold that nobody except you has ever seen, is a plus. I like the lonely, quiet places best. My sluice is a homemade one I made from an old road sign. It works just as well as a friend's Keene sluice and cost next to nothing. Like tying fishing flies, reloading bullets or anything else you make yourself, it adds to the pleasure of it when it works. Anybody can go out and buy something, it means more when you make it yourself. A friend wants to go this weekend, but it's not looking like I'll get to do it.......soon I hope.

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