Friday, March 8, 2013

Gold Sampling: a 3-Phase Plan of Attack (Part 6)

 (Hand-dug sample or test trench complete with sample bags.)

In this series of posts I'm endeavoring to not only bring your attention to the importance of gold sampling, but provide you with information on various sampling approaches, methods, and techniques. So if you're interested in learning more, read on.

PHASE II. SAMPLING (continued)

Trenching: Old-time hard rock and placer miners used trenching frequently in the heydays of Western mining. Unlike some sampling approaches, trenching doesn't require heavy equipment but can be accomplished with pick and shovel if you're willing to bust your ass a bit. Obviously, in commercial or large-scale gold mining sampling operations, the hand tool approach goes bye-bye and the excavators, backhoes, and bulldozers step in.

Gold Concentrates
Gold Concentrators

Trenching (like other sampling approaches) is used to gather information or data about the potential gold values within a given location or area. Typically, a fairly narrow and initially shallow trench is dug, most often perpendicular to the stream flow. Then, samples are taken from set distances and depths based on real or estimated cubic yardage.

Determining What's What

Hard-rock miners could often locate vein material this way or offshoots of primary veins or hidden "blowouts" just under the surface. Placer miners could determine if any paystreaks or pockets existed and, of course, get an idea of how many colors they could expect to recover in overburden gravels and successive layers deeper down. In certain instances, another trench (or trenches) would be excavated upstream or downstream to determine the extent of an existing paystreak.

Like some other sampling approaches, trenching is best suited for areas like dry placers, benches, or areas where ancient gold-bearing gravels sit high and dry well away from modern stream courses. You can well imagine the results if you tried trenching into a running stream or area containing water close to the surface. It can be done to some extent (especially using heavy equipment like an excavator) but your gold value data is going to end up pretty much skewed because of potential gold loss and rocks and gravel sliding right back into your would-be trench. Trenching is really not suited for these sorts of circumstances.

I've Been There Too...

I know that the majority of you good folks out there are not gold mining for a living and that your field time is precious to you. If you're looking at this mining thing more from a family fun or recreational standpoint, your time and effort is better served through a bit of hand sampling (I'll talk about that later...). Above all, no matter what scale of mining you're doing, you should remain passionate about it and truly enjoy what you're doing. However, if you decide to pick up the scale or pace of your gold recovery efforts down the road, sampling will serve you well in the end.

 (Ahh...the joys of a hand-dug test trench.)

Listen, I know it's no fun humping a pick and shovel like some Third World coolie in order to sample while everyone else around you is running equipment and getting some gold. I also know how strong a temptation it can be to just abandon the deliberate, logical approach and start shoveling whatever's at hand through your sluice box or into your trommel or highbanker. Hell...I've been there too, you know?

But what will ultimately separate the real miners from the "wannabes" is a solid knowledge of the basic principles and applications of gold sampling and the patience and ability to apply those principles effectively and efficiently.

Best of luck to one and all.

If you liked this post, you may want to read: "The Geology and Dynamics of Beach Gold Placers (Part 1)" 

(c)  Jim Rocha (J.R.)  2013

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

4 comments:

  1. Hello JR, here in Idaho, I've found many test pits that measure about 6-10 feet wide by 15-20 feet long and 10 feet deep.I've always wondered what was the tip off that this might be a good spot? Your picture makes me wonder too, it looks like a good hay field, not a gold mine. Then there is the Forest Nazis, they say it is illegal to dig pits on federal lands. I say throw them in and fill it up! Too bad we can't do that anymore!

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  2. Don't let the terrain fool you...that one trench is in a gold-bearing area. When the Cripple Creek strike was found in CO, the area of those rich veins didn't look anything like typical gold country. Fooled a lot of folks until they started digging...turned out one of the richest strikes in CO. Best, J.R.

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  3. J.R., I'll be contacting the Forest Service Monday to see what hoops I have to jump through to use a small backhoe on my claims. I hope to be trenching soon on those claims I told you about. I'll get back to you asap.
    Best wishes!
    Rattlesnake Jim

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    1. Good luck with those people Jim. Keep me posted, OK? Best, J.R.

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