Gold Sampling: a 3-Phase Plan of Attack (Part 7)
(Pumping water from a hand-dug test pit.)
We're gradually getting to the end of the gold sampling phase of this series of posts and I thank you all for your patience here. In this post I'll tie things up on actual sampling approaches, clearing the way next time for a discussion of sample analysis.
PHASE II: SAMPLING (continued)
Test Pits: Next to actual gold panning, digging test pits ("holes in the ground") is probably the oldest and simplest means of gathering samples from gold placers. I've literally seen hundreds upon hundreds of test pits in my day in nearly any gold context you could imagine. Most of these were of the hand-dug variety and typically the result of hard work done by old timers. I've also seen numerous test pits that were dug by mechanical means, although these never impressed me as much as those opened up with blood, sweat, and probably a few tears as well.
Gold Panning Kits
Test pitting is very direct. You simply dig down through layers of (hopefully) gold-bearing gravel and pull or process samples from various depths and/or layers to get a reasonable idea of the gold values present. Like most other approaches, digging test pits is best suited to dry ground gold locales. That said, a case could be made that suction dredge test holes in streams and rivers are essentially another form of test pitting and I agree with this premise.
One thing to bear in mind about test pits is illustrated by the photo at the beginning of this post. If actual stream water is nearby or the water table is close to the surface you run the risk of having water backfill your holes. This can prove problematic for any number of reasons, including your ability to take representative samples from that hole. Pumps can alleviate this problem and are a must if you're in a good gold area and looking to make money commercially (or make money period.)
I'll digress a bit here and discuss "coyote holes" for a minute or two. Any of you who've been around this small-scale mining thing for a while now have undoubtedly heard this term used at one time or another. I'm going to stick my neck out here and tell you that in the greatest majority of cases, "coyote holes" are NOT test pits but small-scale mining diggings.
A "true coyote" hole is usually dug laterally into a tightly packed or cemented gravel bank or bench and then expanded around and overhead using a pick, shovel, and lots of elbow grease. Unlike most test pits, "coyote holes" are not wider at the mouth and narrower down, but typically have an entrance barely big enough for a grown person to crawl through. Once you're inside, they open up into "rooms" or tunnels where gold-bearing gravels can be hacked away at, removed, and processed.
(Yours truly checking out a "coyote hole" in an old New Mexico mining district.)
"Coyote holes" scare the crap out of me and I NEVER enter them because in most instances (like those I found in a gold location only 14 miles from my home) they are not shored with timbers. The old timers who dug these things were usually (but not always) Chinese miners or others who were NOT allowed onto the best gold ground in an area for prejudicial reasons. It must have taken a great deal of faith and desperation for these fringe miners to work gravel walls and overheads that could collapse onto them if gravity refused to do its thing or Ma Nature turned fickle. Anyway, I'm just providing you with a bit of mining trivia here...
I've said it before and I'll say it again: "A gold pan is not a piece of mining equipment but a sampling and concentrate processing tool." In the broadest sense, any time you pull out your gold pan and try to tease a bit of color from various spots at a given gold location you are, in essence, sampling. Panning is the single most common approach to sampling but if done in a willy nilly or "Chicken Little" fashion it becomes somewhat of an exercise in futility. Just like all the gold sampling approaches I've mentioned in this series of posts, you should approach test pitting or panning in a logical, systematic way to get the most accurate information about existent gold values.
You can "poo-poo" this statement of mine and go on about your business the way you see fit...after all, that's your prerogative. All I'm saying is that if you take the time to approach your "business" in a planned and productive manner, you'll end up with a much clearer view of the gold values around you and inevitably, more gold over the long haul. Make sense?
The Systematic "Thing"
As I move forward here, the whole idea behind sampling is to gather samples for analysis. It doesn't matter all that much (well, it does but I won't go there for now) if you process your placer samples on site, but it surely does if you're a hard-rock miner where fire and chemical assays can tell you whether you've hit a dead end in "Bust City" or are instead staring down a potential fortune.
This is where the systematic thing raises its head again. It's not only about how and where you gather your samples, but how you ID and tag or mark them. I know some of you hate this buzz word of the computer generation, but "it's all about the data."
More next time.
If you liked this post, you may want to read: "Sinking a Placer Test Shaft: 'Greywolf's' Method"
(c) Jim Rocha (J.R.) 2013
Questions? E-mail me at email@example.com