Some Mining, Prospecting, and Detecting Observations/Suggestions/Tips (Part 1)
(Gold mining operation in Barahona Province, D.R.)
Eduardo Herbert, mi amigo and fellow gold miner and suction dredger from the Dominican Republic (D.R.), has contacted me with some mining and metal detector questions. I've answered Ed personally via e-mail briefly, but I think the nature of his questions and my responses to them could provide valuable information to many of you out there.
The Crux of this Post
As you know if you've looked at some of his gold recoveries from previous posts (here, for example), you'll see right away that Ed is onto something good dredging in "Hispanola." As a matter of fact, Ed's done remarkably well by any small-scale miner's standards and should be commended for his dredging efforts in the Sierras of the D.R. With that introduction, let's get to the heart of the matter.
(Part of the D.R. Sierras.)
Most of the placer gold Ed has recovered in the Sierras of the D.R. is reasonably water-worn and very bright and shiny, as is most placer gold in general. However, some of Ed's recent gold finds from the river he's working have been coarser and very porous in texture. Other pieces he's dredged on bedrock are heavily oxidized, something Ed mentioned to me as well. A friend of Ed's has suggested that the coarser, porous pieces of gold are indicators that gold has entered the stream flow fairly recently and that a vein or veins of gold may be nearby and might be found with a good metal detector. These issues are the crux of this post and I'll provide my observations, suggestions, and tips in the following:
Coarser versus Water-Worn Gold
In general when talking about wet placers, the smoother, shinier, and more water-worn a piece of placer gold is, the longer it's been in a stream and the farther it has traveled. Ditto for smaller pieces of gold, including flakes and fines. Granted, there are numerous exceptions to every rule but this is a pretty good guide to go by when it comes to placer mining. So it goes in the opposite direction also.
The coarser and larger in size the gold in a stream, the greater the likelihood that same placer gold has entered a stream more recently. What's recent? I'll let the geologists answer that question since, to my knowledge, there's no real measure for determininge the exact time a piece of gold has been in a stream. Anyway, when that placer gold is really chunky, rough, or contains decent amounts of matrix material still attached to it then you can pretty well assume it's a very recent entry into the stream course. Remember, we're talking about wet, not dry, placers here. In Ed's situation, his friend may be on to something here. The presence of a distinctly different (coarser, more porous) type of placer gold in the same stream with predominantly smoother, more water-worn gold suggests the coarser gold is a relative newcomer to that stream. So an assumption that a vein, blowout, or ledge that's eroding out in elluvial form and then ending up as placer gold is reasonable in this case. The trick, of course, for Ed and his friend is first locating the elluvial gold that is moving into that river from nearby hillsides or terraces or is being brought into the stream underwater through an entry and erosion point.
(Water-worn placer nugget. Notice the smooth surface, luster, and lack of porousness.)
(Coarser placer gold. Note the rough textured surfaces, lack of luster due to oxidation, and porosity in some pieces. [Ed had a question about oxidation in some of his recoveries and I'll address that issue in the next post.])
1) The very first thing I'd do in this case is exactly what the old timers would have done back in the day. I'd start sampling with a gold pan carefully and thoroughly to see where the the first indications of that coarser, more porous gold start showing up. Although it's more costly and time consuming (not to mention the pain-in-the-ass factor) from a set up and reset standpoint, Ed could also use his dredge to do this but I think the panning idea is the quickest. You could start downstream where you know NO coarse gold has been recovered and work your way up, sampling in low deposition areas or behind obstructions (or on bedrock if you're underwater or it's accessible above) until you come across the shift from water-worn to coarse gold. Once you've located the coarse stuff, keep sampling until the coarser gold (newer entry into the stream) stops completely. Somewhere in that zone where the coarse stuff is found is an entry point or multiple entry points. Next you'll have to sample both sides of the stream in low-lying areas or any similar terrain feature that could channel the gold down into the existing stream course. As you do this you'll want to keep your eyes open for "float" (gold ore) that may be scattered about or the presence of elluvial gold. Once you've done that and the elluvial or gold ore increases, you're on your way to the source, only part of which (vein, lode, reef, blow out) may be above or even just below the surface. That's the way it was done in the old days. Now maybe this sounds like a painstaking job and the process could be expedited, but it's pretty much the way I myself would approach it (with some other prospecting "tools" at my disposal). Of course, if you had plenty of money, personnel, resources, and fancier equipment to throw into this search like the big boys in mining do, things could happen fast and a lot easier I suspect. But Ed's like you and I...a solitary miner maybe with a pard or two and downscale gear in relation to the big boys. Whatever the case, you have to be systematic in prospecting for the coarser gold that's showing up in that river in the Sierras of the D.R. The one bugaboo that Ed might experience in my old-timer's approach (or most prospecting approaches, for that matter) is heavy growth there in the Sierras. Prolific foliage can be severely limiting to eyeball prospecting, including spotting float, blow outs, etc. Ed may be up against this overgrowth issue, but I don't really know for certain.
(Old timer checking his pan for color.)
2) A good gold detector could be of great help in prospecting Ed's location, but there are some caveats to be considered here: You have to have the right machine for the job. A cheap piece-o-crap isn't going to be of much help in this regard unless the gold is in big pieces and laying free of metallic trash and heavy mineralized clutter. Ed's a smart guy though. He's got himself a Minelab GPX 5000, one of the best (and priciest!) gold detectors on the market today. The problem though, is any machine is only as good as the knowledge and skill of its operator. This is especially true when it comes to gold prospecting or nugget shooting. Any newbie can buy a detector and pull some clad coins from a public park, but put that same greenhorn in a highly mineralized environment often loaded with various-sized pieces of metallic trash where you have to listen closely for and properly identify the faintest signals designating gold, and it's a totally different story brothers and sisters. Ed will be the first to admit that he doesn't know how to use the GPX 5000 to its fullest advantage, something that simply takes time and practice to get really good at. Yes, you can read the users manual and do some bench testing and both those things help. But aside from one-on-one instruction from an experienced instructor, your best bet for becoming proficient with any machine and learning all its idiosyncrasies and subtle nuances is to get out there, gut it out, and use the damn thing until you know how it operates backwards and forwards. There's just no easy path here, just as there's no easy path to success as a small-scale gold miner.
(The Minelab GPX 5000 is an excellent gold machine, but for prospecting or nugget hunting I'd want a larger search coil.)
In my next post I'll continue on in this vein (pun intended!) and try to sort out Ed's questions with more answers. Until then, take care of yourself and one another.
(c) Jim Rocha (J.R.) 2016
Questions? E-mail me at firstname.lastname@example.org