Gold mining itself is fraught with financial risk and grave uncertainty. The risk begins with finding a gold mine in the first place. Only about one in a thousand prospects ever becomes a mine. And all gold mines are certainly not profitable.
There are a lot of differences between the operations of successful mining companies and ones that become financial failures, but one of the consistent key differences between them is their sampling programs. No mineral deposit is uniformly rich. If the property is a good one, some spots may be rich, some will be lower grade but still rich enough to be profitable, but many will be too low-grade to work profitably.
Most modern gold mines are originally found with surface geochemistry. Stream sediment sampling is especially productive in reconnaissance exploration. If successful, more detailed sampling is performed. Then, if warranted, comes claim staking or other types of land acquisition.
Designing A Sampling Program
Probably the first thing one needs to determine is what the goal of your sampling program is. Using poorly planned sampling methods is guaranteed to give you poor results. When beginning a sampling project, it’s important to plan what you are doing in advance. What are you trying to determine? Are you exploring for new deposits or trying to characterize the average grade of a known vein or other deposit?
Sampling of placers is difficult, as placer deposits are typically stratified with increased concentration of values in layers, especially on bedrock. Often the paying layer of bedrock may extend one or more feet into bedrock because of crevices. Good placer sampling requires larger-sized bulk samples and accurate collection of materials from the bedrock or other paying strata such as false bedrock or flood layers.
Effective hardrock orebody sampling requires some understanding of the structure of the ore deposit. Sometimes this can be difficult when considering a new deposit to determine in what direction the deposit goes. Some deposits have sharp contacts with the country rock, and some just slowly grade from ore into waste.
Grab samples are samples of rock material from a small area, often just a few pieces or even a single piece of rock “grabbed” from a face, dump or outcrop. These are the most common types of samples collected when surveying an area or beginning exploration for hardrock deposits in the field. The sample usually consists of material that is taken to be representative of a specific type of rock or mineralization. It is more associated with exploration programs.
Pan sampling was utilized by the old timers to test veins and other deposits by collecting a sample, crushing it to fine sand, and carefully panning the results to see what heavy minerals, such as gold, remain. With experience, the old timers learned to correlate the amount of color they saw in a pan full of crushed vein material with the approximate ounces per ton reading one would get from a normal fire assay. A very large percentage of the hardrock gold mines across the world were originally discovered using some variation of this method.
Geochemical sampling involves collecting and analyzing things like soils, stream sediments and rocks, and testing for certain chemical elements that are associated with valuable mineral deposits. These methods are extremely efficient exploration tools and a few well-located sediment samples can be used to test vast areas for potential mineral deposits. The presence of these trace elements can be nearly impossible to recognize in a hand specimen, but lab analysis by methods such as Atomic Absorption (AA) can reveal elevated levels that are only in the parts per million range. Many well-known ore deposits were discovered using these methods.
So What Does This Mean For The Individual Prospector?
What does all this mean to the small operator or weekend prospector? The miner needs to know the difference between exploring and mining, and that exploring always comes first. Explore and prospect around to find the best part of your claim. Few small operators spend enough time prospecting and sampling, they want to move too quickly to getting the gold! The best paystreaks are not always exactly where you expect to find them. Don’t start out mining; start out prospecting, then go to sampling, and finally on to mining.
Of note is that sixty percent of current mines were discovered by independent prospectors or “penny” stock companies. It is up to the individual to educate himself on the subject, but “weekend prospecting” is still very much with us. It is a wonder that more people do not pursue this, since it fits in with today’s outdoor lifestyle, and is potentially much more rewarding than hiking or birdwatching.