Core Drilling & Testing
Core drilling is not usually something that amateurs will be able to get into since it is a bit more complicated and the equipment that needs to be used for it is quite costly. Nonetheless, if the amateur does have a deposit core drilled the main idea is to get to bedrock if the placer is an old waterway, or to drill through to the of no value area if it is an alluvial placer. The sample drill holes should be spaced around like in the case of the first samples however this does not necessarily need to take place in the same exact spot. They should continue to be drilled until bedrock has been reached, the depth has been noted and the sample has been obtained from that specific area.
The greatest concern and danger of test drilling placers, especially when it is done by hand, is that the drill will sometimes run into a big boulder that will give an indication of bedrock when it actually in fact isn’t. If various holes are drilled sometimes the boulder will show itself by making the drill stop way before its normal depth.
Every once in awhile the prospector should let the drill penetrate the indicated bedrock to see if the original stream bed used to have a false bedrock. There have been a good number of rich deposits that have been found this way.
The reality is that most amateurs do not get to the point of trenching or core drilling however most of them will be able to see an ore body or an outcrop that seems promising and they will most likely be interested in getting it sampled. Doing this can turn into something that takes a great deal of work but these problems can be taken care of.
The fist thing a prospector needs to do is examine the deposit and see how much of the vein or outcrop needs to be sampled. Keep in mind that in most occasions, the amateur prospector will only be interested in the vein. It is not common for an amateur to open an adit and be worried about removing a lot of country rock. In most cases the average amateur will simply take care of cleaning out a vein to a shallow depth and in the cases in where the vein is narrow, the sample can be high graded from the vein itself. Doing this type of high grading is fine, however if the deposit does need a good amount of mining done on it a good amount of the country rock needs to be mixed with the sample to get an idea of how much the general mineralization percentage is. If the vein is very big, it would be a good idea to obtain various samples along the face of it given that color is often not an indication of some kinds of mineralization.
When samples from rock are taken these samples will usually vary depending on the nature of the rock itself. If you see that the material of the vein shatters or breaks very easily, you can usually get samples by simply using a rock hammer. When you notice that the rock starts to get more resistant to this kind of method, you can use a little drill, chisels and pry bars to obtain the samples. If nothing else works, you can drill a little hole in the rock and then shatter the rock by blasting it.