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Metal Detecting for Native Copper
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Metal Detecting for Native Copper

CHRIS GHOLSON

 

My first true experience with the red metal occurred nearly fifteen years ago. I was out prospecting about an hour north of Phoenix, Arizona with my trustee Minelab XT17000; which at the time was one of the best VLF metal detectors on the market. This particular day I was working my way up a small, dry creek bed, scanning all the exposed bedrock cracks and crevices for gold nuggets. Very quickly I began noticing brightly colored green and blue staining on many of the rocks lying in the gravel. I waved my coil over a few of the larger samples and when I didn’t receive a signal, I simply tossed them back down and kept moving. As I hiked further up the creek I came upon a mellow, but repeatable target with my detector. The signal sounded exactly like a tiny gold nugget and I eagerly swept aside the soil expecting to see the distinctive glint of gold at any moment. Instead, what I discovered was a solid, rounded lump of something green. It gave off a clear high pitched signal on my detector and was fairly heavy, but I knew it wasn’t gold. I dropped it into my pocket, and once again kept moving. By the end of the day I had collected about a quarter pound handful of the weird green rocks, and much to my delight three shiny gold nuggets. A friend of mine owned a rock shop in the nearby town of Black Canyon City, so I decided to pop in and show off my freshly dug gold. When I poured out my finds on the counter I was shocked to see he was actually more interested in the green rocks. “Wow, these are some nice copper nuggets you’ve got.” “Copper…is that what those are?” I asked. “Sure, they are only green on the outside. Watch I’ll show you.” He grabbed a hammer from his toolbox and smacked one hard. Sure enough, the green coating crumbled away and exposed a lovely reddish color beneath. Half an hour later as I was on my way out the door he called out, “Be sure to let me know if you want to sell them!”

 

Although not as valuable as gold, native copper nuggets are a rarity in their own rite. The metal was cherished by our ancient ancestors, and is still prized today nearly 10,000 years later. Peruse any local rock shop or some of the various mineral dealer websites and you will see that a market for native copper does exist. Many samples sell for a few dollars; others command prices in the thousands. Fortunately for us electronic prospectors, copper is highly conductive and readily identified with a metal detector. Many locations have produced substantial amounts of the metal, but not all of them have yielded pieces of detectable size. In order to be successful, the modern copper hunter must know where to go and what clues to look for.

 

Native copper is one of the few metals to occur naturally as an un-compounded mineral. It has a reddish, or orange color on freshly exposed surfaces, but typically is weathered and coated with a green tarnish known as patina or verdigris. Among pure metals that occur at room temperature, copper has the second highest electrical and thermal conductivity after silver. It is also easily worked and remarkably ductile. Copper is so malleable it can be rolled down to one one-thousandth inch in thickness, and, by cold drawing, its length can be increased as much as 5,000 times! Its malleability and excellent conductivity make it an ideal metal for making electrical products. Other uses are in products such as pipe, tubing, plumbing fixtures, hardware, and machine tool products. Most copper is combined with other metals to form more than 1,000 different alloys.  

 

Native copper was an important ore of copper in ancient times and was used by pre-historic peoples. Neolithic humans about 10,000 years ago first used native copper as a substitute for stone. It is likely that gold and meteoritic iron were the only metals used by humans before copper. Some estimates of copper's discovery place this event around 9000 BC in the Middle East. Evidence of this comes from a copper pendant which was found in what is now northern Iraq that dates all the way back to 8700 BC. The Egyptians and the Sumerians were among the first to practice metallurgy, first reducing ores with fire and charcoal around 4000 BC. In Europe, Otzi the Iceman, a well-preserved human male dated to 3200 BC, was found with an axe that had a copper head which was 99.7% pure. High levels of arsenic in his hair suggest he was involved in copper smelting. In the Roman era, copper was principally mined on the island of Cyprus, hence the origin of the name Cyprium, "Metal of Cyprus", which was later shortened to Cuprum. Native Americans living in the Great Lakes region are also known to have crafted axes, chisels and spearheads from the metal.

 

Like gold, copper can take the shape of rounded nuggets, flat sheets, wires, and can also be found in specimen form (i.e. still attached to host rock). The size of these copper treasures varies widely, ranging from microscopic grains to huge masses weighing many thousands of pounds. In fact, I know of one detectorist in Michigan that in 2007 recovered a single nugget weighing 3,500 pounds! While copper occurs in many regions around the globe, some have proven more lucrative for detectorists than others. Electronic prospectors wishing to hunt copper abroad should consider the following countries: Chile, Canada, Russia, Zambia, Poland, China, Mexico, Indonesia, Germany, Kazakhstan, and Peru.

 

For those looking for somewhere a little closer to home, there are a number of excellent destinations right here in the United States. The greatest native copper ore deposits ever found anywhere in the world and mined profitably were those of the Keweenaw Peninsula of Michigan's Upper Peninsula. The deposits in this region are vast and occur in a belt about 110 miles long with an average width of around 10 miles. The first humans to visit this area found an abundance of copper float simply lying on the surface in plain view. Most of these large chunks of native metal had been smoothed and polished by glacial scouring during the Ice Age. When the ice melted it left pieces of copper, some weighing several tons, scattered across the ground like pumpkins in a cornfield! Other areas to consider in the US include: Wisconsin, Indiana, New Mexico, Montana, California, Nevada, and most definitely Arizona. The Grand Canyon state currently leads the nation in copper production, and there is no shortage of places for a person armed with a detector to try their luck. Some of the best mining districts in Arizona to go for native copper include: Bisbee, Superior, Clifton-Morenci, Globe, Bagdad, Safford, Jerome, and Ajo. These are the major producers; however there are numerous smaller, lesser-known districts that could pay off nicely for those that don’t mind getting off the beaten path.  

 

Looking for copper is a lot like looking for gold. Firstly, a person will need good quality equipment. I suggest using a metal detector with heightened sensitivity and ground canceling abilities, such as those designed for finding gold. My top machine picks for hunting copper are the Minelab GPX-4500, Fisher Gold Bug 2, Whites GMT, or the Tesoro Lobo ST. A person will also need plenty of time, a positive attitude, and must be willing to do some research. Old mining bulletins, geological maps, talking with other prospectors, and the Internet are a great place to start this research. Another powerful tool I have discovered is a software program called Hystware. This program allows users to search a database of over 250,000 mining sites in the United States right from their home computer. It is a valuable source of information and sells for $99.

 

Once a person has done their research and selected an area to hunt, they will need to actually walk the ground. There is a lot of land out there to cover, so a person must be able to identify the clues Mother Nature has left behind. The best method I have found when detecting for copper is to focus on areas where the rocks are stained bright green and blue. The greenish colored rocks are usually something called malachite, and the bluish colored rocks are typically azurite. Both are copper carbonates. These colors are highly visible and an excellent indicator of oxidized copper ores. If you see green and blue, slow down, you may be in an area capable of producing native copper. Other minerals frequently associated with native copper include: limonite, kaolin, chrysocolla, quartz, cuprite, and chalcedony.

 

Whenever I am exploring an area for native copper I almost always detect the creeks, washes, and gullies first. With a specific gravity of 8.9, copper is a fairly heavy element and will tend to concentrate in many of the same places as gold. Focus on the inside bends, on the backside of large boulders, and never neglect to scan any exposed bedrock. Copper is an excellent conductor and will give off a signal similar to gold or lead. I should also mention that some of my best gold nugget patches also contained native copper nuggets. These two elements are closely associated, so where you find one you typically find the other. If you find a copper nugget or two in any drainage or waterway, you should attempt to find the source by scanning adjacent mountainsides and canyons for the bright greens and blues. If you are lucky enough to discover a virgin copper patch on a hillside you may need a five-gallon bucket to haul away your finds! Aside from the creeks and gullies, quarries and mine dumps offer great potential. If you come across an abandoned mine dump showing signs of copper mineralization, it may be worthwhile to scan the waste rock with your metal detector. Many beautiful specimens of native copper have been found in this manner.

 

As mentioned above, many specimens of native copper are obscured by black or green surface coatings which hide the natural beauty. Black coatings are cupric oxide, while green coatings are generally combinations of copper sulfate and copper chloride. On ancient artifacts, the green coating is termed patina and is regarded as a very desirable indicator of authenticity. However, on mineral specimens, the coating is generally regarded as offensive and most collectors want it removed.

 

A number of techniques have been developed for cleaning copper. The methods presented here were submitted by Herb Sulsky. To clean your copper sample, first make a paste using flour, salt, and vinegar. Brush it on, let it sit a while, then rinse it off. The acetic acid in the vinegar causes the tarnish to slowly dissolve. Stubborn coatings may require more than one application. Another technique can be done in a sealable glass container by mixing one part caustic soda (sodium hydroxide) with three parts rochelle salt (sodium potassium tartrate). To this add twenty parts of distilled water and carefully stir until the chemicals are dissolved. Suspend the copper specimen in the solution with copper wire. Some folk remedies for cleaning copper include scrubbing with buttermilk, using an ammonia/soapsud mixture, catsup, olive oil, or baking soda with ammonia. Whatever method you use, be sure to thoroughly rinse the specimen after cleaning and remember to dispose of all solutions safely. And once cleaned, consider protecting the fresh copper surface with lacquer to prevent further tarnishing.

 

The total amount of copper on Earth is vast; around 1014 tons just in the top kilometer of crust alone. However, only a tiny fraction of these reserves are economically viable, given present day prices and technologies. And once again, like gold, only a small percentage of our planet’s copper exists in nugget form. Because of its rarity and natural beauty, native copper is prized by mineral dealers and private collectors around the world. And as global consumption increases and prices rise, it stands to reason that these nuggets will only continue to become more valuable. There are many treasures out there waiting to be found, and the savvy prospector should be on the prowl for all of them; be it gold, silver, platinum, or copper. So, the next time you are out swinging your metal detector, don’t leave behind that big green boulder that gave a loud beep - it just might be the copper find of a lifetime!

Minelab, Nuggetfinder coils, gold nugget prospecting with metal detectors.Where to find placer gold.
Metal Detecting for Native Copper

 

             
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