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Monday, May 7, 2012

How to sample a lode gold deposit


_Pieces of drill cores
Photo by Constantino Figini 


Once you have discovered a promising outcrop of lode gold the next step is to sample the deposit.  This can be done in several different ways, but sometimes the old tried and true methods are the best.  The simplest way is to chisel a channel right across the outcrop of ore in which you are interested.  This is a lot of hard work but is well worth the effort.  The chiseling is done with a one inch (25 mm) stone chisel and a four pound hammer (2 kg), a short handled striking hammer works best for this.  The chips are saved in a cloth sample bag for later assaying.

Another situation you may come across is several outcrops of potential ore around your site that is in this case too much to sample the outcrops singly in a first sampling program on the site.  In this case you can go around the site and simply chip off a small sample from each outcrop, then have it assayed.  This isn’t the best method for sampling channeling is, but at least it will give some idea of what you have discovered.  Be sure you keep the samples random, and don’t favor what looks like hi-grade ore because this will skew the results of your sampling.

If you want to be sure about the accuracy of your samples send them to three different assayers then average the readings so you will come up with an average reading instead of a single assay.  This has been found to be more accurate.

After the preliminary sampling has been done, and your site has been proved to hold gold it is time to go onto more sampling to find out how much gold your site really holds, and if it is large enough to develop a mine.  It can take a lot of money to develop a hard rock gold mine, sometimes more then a billion dollars.  You should also keep in mind that only about one in a hundred gold discoveries are eventually developed into a paying gold mine.  They call it lode gold because it takes a load of money to develop it into a mine.

Drilling the orebody is the accepted method of proving the size of a gold deposit that is commercially viable.  This is done using a diamond core drill that gives you a solid core sample to examine.  Core drilling rigs come in several sizes with the smallest ones a drilling rig that can be back-packed.  There are several companies that make these drills that are capable of going at least 15 meters into solid rock.  Even larger rigs are available capable of drilling more then 1,200 feet into bedrock.

A back-pack rig is within the scope of something a prospector can carry into the bush with him, but larger rigs are best handled by specialized drilling companies.  The samples these take are cylinders or stone bearing the ore.  The first thing that happens when a core is retrieved is to split it in half lengthwise so the prospector retains half of the core with the remainder being shipped off to an assayer.  A series of core drill cores are used to delimit the actual size of an orebody by moving the drill rig further to the initial hole until the last hole bored is beyond the last hole bearing payable ore.  Many of these drilling programs encompass drilling kilometers of core drill holes.

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