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Wednesday, July 23 2014

Wouldn't it be nice if we all had access to geologists, drilling crews, and huge rock crushers to sample hardrock deposits? Well, if that's not in your budget but you still need to determine if an outcropping or vein might be promising before you stake a claim, a portable Cobra Crusher and a few grab samples can work nicely. A grab sample is just that -- randomly chosen rock samples you need to crush and test for gold or other precious metals.Cobra portable Rock Crusher

Although grab samples can seem counter productive because of the randomness, they can still provide you with a basic, overall understanding of the area and the possibility of higher grade ores in the vicinity. When looking for a grab sample, choose mineralized portions of the vein, pieces of mine dumps near a portal or shaft, or chunks of mineralized float that have broken away from the vein. Mineralized quartz on a mine dump near a mine portal or shaft makes for good grab samples. Often the operators of small mines had to sort and ship only the best of the ore. That means high grade materials can be left behind in mine dumps.

What's especially great about the Cobra Crusher is that it's portable and light weight. You don't have to collect and then lug around heavy rocks and wait until you get back home or to your camp to know if they are worth anything. You can crush a few small rocks right in the field, then pan out the powder to see if its gold bearing. Having a small light-weight crusher with you in the field saves guess work. You'll know for sure right there and then if the site you've discovered is worth further consideration.

If you don't have water to pan the powder on the spot, crush the rock and store the powder in a plastic bag. Label the bag with GPS coordinates so you know EXACTLY where you got it. Then, after you've panned it later, if you find it contains a good bit of gold, you will know exactly where to return for further testing. It's also helpful to snap a photo of the place where you collected the rock. Matching the GPS coordinates with your photo ensures you'll be able to get back to that exact spot at a later date.

In addition to collecting rocks, you might want to take some chip samples from a wide vein. Use a rock hammer to break off small pieces and then run them through the Cobra Crusher. Again, pour the powder into a well labeled bag if you can't pan in the field and can wait until a later time to get the results.

When preparing for a sampling expedition, use the information on your local Bureau of Land Management website or in their office. In these files, geologists might have made notes about the specific mines in the area, and/or there will be details about the ore grade, tonnage and past production -- all good indicators so you don't waste your time. Mine maps can often be found in these files as well. You might be able to locate old stopes or mapped veins. This information can tell you where high grade ores were found in the past, which is where you might want to explore today.

Posted by: Denise AT 02:15 pm   |  Permalink   |  0 Comments  |  Email
Saturday, February 15 2014

Among the many improvements made to mining technology during the Industrial Revolution, perhaps the most important involved drilling and blasting. In the early days, black powder, a relatively low-power explosive was the only blasting agent available. To use it, holes had to be pounded into rock by hand. Working in teams of two, one miner would hold a pointed steel chisel while the other hit it with a sledge hammer. Each hole had to be hand drilled to six or eight inches in depth. Needless to say, this was slow, tedious, and tiring work. During a 10-hour shift, a team could typically drill, load, and fire black powder charges in only eight or 10 holes. Depending on the size of the mine tunnel, that single blast could bring down three quarters to two and a half tons of rock.

Dynamite, an explosive five times more powerful than black powder, was invented in 1866 by Swedish chemist, Alfred Bernhard Nobel (the Nobel Prizes awarded today were named after him). Nobel held 350 different patents; dynamite is his most famous claim to fame. By the mid 1870s, dynamite had largely replaced black powder in the mines.

widow maker drillAround the same time period, pneumatic machine drills were first developed. Compressed air to power the drills was piped underground from large steam-powered compressors located at the surface. Machine drills could accommodate five to six foot drill steels that were capable of drilling three to four foot holes into sold rock in a matter of minutes. This new drill increased the tonnage of rock that could be blasted by two-man teams of miners to between four and 10 tons per shift. But, the new technology was not without hazards— namely the disease of silicosis. Machine drilling created clouds of razor sharp microscopic silica dust that miners breathed into their lungs. It took only a few years of operating this drill for a miner to develop this incurable disease. 

Unfortunately, thousands of hard rock miners died before J. George Leyner of Denver, Colorado invented a better machine drill that all but eliminated deadly silicosis. The improved drill forced water into the drill hole and created a harmless mud out of the drill shavings. The mud acted as a very efficient wet grinding compound while also cooling the drill bit, and the flow of water flushed out the drill hole. Leyner patented his mechanism in 1897. This type of drill hasn’t changed much over the years, and is still used in modern-day hard rock mines.

Posted by: Denise AT 07:24 pm   |  Permalink   |  0 Comments  |  Email
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