(Some obstructions sit above or to the side of current stream courses.)
In this post I'll be continuing my mini-saga on stream and wash obstructions and just how important they can be in placer gold deposition and recovery. So plop yourself down and set a spell. You may just learn something new.
No Great Significance
First off, let's get one item about obstructions out of the way right now. And that is, just how to work obstructions in running streams (wet placers). There are a number of variables here since obstructions 1) may be found above or away from the current stream course; 2) they may be found in very shallow water; or 3) they may exist in deeper water where they're consistently impacted by water flow. I know you've been told countless times that trying to dig into water with a shovel to extract river gravels is a fruitless pursuit only attempted by the greenest of greenhorns or stuttering idiots who don't know any better. Although there's a goodly amount of truth to this premise, it's my contention that you can dig into submerged stream gravels with reasonable effect as long as those gravels are shallow in depth and the water flowing over them is not too strong or fast. This may not be the ideal approach but I've seen it used to great effect on a number of occasions by one of my old-timer mentors. In fact, this was his primary mining method to recover substantial amounts of coarse gold and nuggets beneath obstructions on feeder streams in the northern part of the California Motherlode Region (I'll go into his approach in depth later). To take things a step further, some gold mining and prospecting shop owners are now selling a scoop/bucket-shaped shovel meant specifically for digging submerged material. So there's not only a basis for this sort of approach but an obvious need for a specially designed tool to make it happen. Also, at this juncture I also refer you to one of the more popular TV reality gold shows where large barge-borne excavators are used for digging underwater into the gold-laden gravels of the Bering Sea. Will some gold be lost as it slips out of that excavator bucket or that shovel you're wielding while digging underwater and then retrieving it? Sure. But that doesn't seem to be a major problem for those miners excavating the sea bed, nor should it be for you in certain instances if you're a careful and smart miner. Granted, the Bering Sea excavator dredges are basing their approach on the sheer volume of gold recovered and what 's lost of the edges of the excavator bucket is of no great significance in the long term. Nor should it be for you on a much smaller scale. That's my opinion anyway. Whether you agree with it or not is your call.
(Who cares if some gold slips out the side of the excavator bucket?)
If You're Serious...
The most obvious and efficient approach to working deeper water obstructions is, of course, the suction dredge or, alternately, a highbanker equipped with a small suction hose for shallow water obstructions. Once you've identified a likely looking obstruction it's simply a question of setting up your unit, firing it up, and then going to town. However, the use of suction dredges and even highbankers that are suction equipped is a big NO-NO in California, Oregon, and other parts of the American West, including Idaho (according to my pard "Muskrat"). Other types of hand-held suction devices (suction tubes, etc.) may have some value in a water/obstruction context as well, but in all honesty that value would probably be slight unless shallow or exposed bedrock was adjacent to or under the obstruction in question. If you're fortunate enough to be working obstructions left high and dry then all this motorized gear stuff won't probably be necessary, although a highbanker or powered sluice of some sort may prove valuable in terms of getting the gold. This would be especially true if your holes start to fill with water once you start digging down by hand. If your holes remain dry then what you need at the very least are basic hand tools and some grit and determination. One of the tools you should seriously consider whether you're working wet, shallow, or dry obstructions is a "come-along." Undoubtedly you all know what this is, but in case you don't a come along is a ratchet-driven lever winch operated by hand that usually employs a strap or chain. The strap or chain is looped around the obstruction in question and then the come along is ratcheted, putting tension on the strap or chain, and then finally forcing that big dog out of its current resting place so you can sample the delectable gold-bearing gravels that will, in many cases, be resting underneath it. If you're truly serious about working large obstructions, a come along is an absolute must. In truth, a come along should be in any small-scale gold miner's kit no matter what sort of specialty mining you're doing or what sort of approach you're taking. The only exception here is if you're involved in "skim" panning or sluicing where you really don't give a flying "f" about how much gold you recover or how big or coarse it is. There are folks like this, you know? Not making a value judgment here...just telling it like it is.
(A standard come along.)
Greatest Single Gold Recovery
OK, let's get back to the main idea. If you read my previous post on this topic, I mentioned that the placement or location of obstructions is not as important a factor as their overall mass and/or shape. I won't go into a lengthy exposition here on the hydrological/hydraulic aspects of what I just said because you're smart enough to get that part (or at least I'm pretty sure you are). What may be a bit more mystifying to you is my premise that obstructions can be just about anywhere in a stream or dry wash and can still trap gold. Granted, in running water areas your first and best bet is to search for larger obstructions sitting along inside bends, in low pressure areas, or on exposed or shallow bedrock (or false bedrock). Certain deposition factors like this should always be trusted but, at the same time, should never be adhered to in slavish fashion. Keep thy mind open, OK? Here's the reason why. Over the years I've made some startling placer gold recoveries underneath and behind obstructions located in areas of streams and washes that are usually considered off the beam from a depositional standpoint. In fact, the greatest single recovery of gold I've ever experienced from working obstructions came from behind a boulder in a straight-shot passage of a wash...no low pressure area, no bedrock, and no inside bend. The old-timer mentor I mentioned earlier made excellent, large obstruction gold recoveries from so-called "poor" deposition areas as well. So don't get locked into a one-size-fits-all or by-the-book mentality when it comes to obstructions. This is especially true of desert or dry placer areas.
There's more to come. Be safe and more importantly, be good to one another.
(c) Jim Rocha (J.R.) 2015
Questions? E-mail me at firstname.lastname@example.org