Don't Forget Those Gravel Bars (Part 2)
In Part 1 of this series of posts I provided you with some general information regarding gravel bars. In this particular post I'll give you some basic information on how to go about working them:
Sample a gravel bar's upper end first. It's no great secret that in most instances the upper end of an auriferous gravel bar will contain the best gold values overall. Why? Simply because it is the upstream end of a given gravel bar that forms first, with the subsequent mass or area of the bar forming from that initial deposition of flood-borne sand, gravel, rock, and gold. So, your initial sampling efforts should be focused in that upper area.
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Make sure you sample thoroughly. This is true whether you're working a gravel bar, bedrock, bench gravels, or anywhere else for that matter. Take a number of lateral (side-to-side) samples as well as samples to depth (vertical) to determine where the best gold values are. Note here that in most gravel bars these gold values tend to be laid down in shallow paystreaks that can be restricted to just one area (e.g., the upper end) or scattered throughout the entire length and breadth of the gravel bar.
Be prepared to work. Even in areas with a great deal of running water some gravel bars can be tightly consolidated and hard to process. In these instances the rock and gravel become "cemented" tightly together and you'll have to engage in a bit of real, old-time pick and shovel work to loosen them enough to run. Like just about everything else to do with gold mining, working gravel bars is not for the infirm, the lazy, or the timid.
Watch for layers with heavy black sands and metallic trash. If you run across one of these while working a gravel bar, then you're probably in business my friend. Although gravel bars can produce decent gold values without you ever uncovering a layer like this, if you do uncover one, so much the better. From my own experience layers such as these mean you're in the money.
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Sometimes as you dig down into a gravel bar you'll uncover a paystreak like this and will begin to find lots of heavy (and sometimes coarse) black sands, bits and pieces of lead, and old rusty metal pieces including old square-headed nails. Along with this trash you'll also find lots of fine gold, small-to-medium-to-large flakes, and even a wayward nugget or two if you're onto a really good bar. (Anyone who has worked gravel bars in the Northern Motherlode region of California knows what I am talking about here.)
You're best bet for working a gravel bar is a sluice box or highbanker. This not rocket science of course. Since you're going to be working rock and gravel that is above the waterline for the most part, a suction dredge is not going to do you much good (unless you care to sample the upper end of the bar below the existing waterline). I've used both a sluice box and a highbanker to great effect on gravel bars that were good producers, so it's pretty much a judgement call on your part. If you want to work extra hard you can screen or "classify" your material first but shoveling directly on or into the box or highbanker works too.
Moving material is the key to success. Again, this is just as true when working gravel bars as it is in most aspects of placer gold mining. The more gold-bearing material you move or process, the more gold you can expect to recover. A very simple and elegant equation, isn't it?
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So there you have it my friend. Don't forget those gravel bars the next time you're out and about.
And good luck while you're at it.
If you liked this post, you may want to read: "Don't Forget Those Gravel Bars (Part 1)"
(c) J.R. 2009
Questions? E-mail me at firstname.lastname@example.org