A Unique Prospecting Method - April 2003 Issue

A Unique Prospecting Method

by Dr. Ralph Pray

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In 1948, I lived alone in the Cerrillos Mountains south of Santa Fe, New Mexico, at the Tom Payne Mine. When lead and zinc metal prices suddenly took a nosedive, our ore and concentrate shipments from the Payne to the ASARCO smelter in El Paso barely paid the rail freight. I went broke—couldn’t even get a haircut. My isolated cabin wasn’t far from New Mexico’s famous old turquoise diggings. Although it was a waste of time fooling around in the ancient Indian mines, I tried prospecting outcrops in the area. Nothing.

The Pueblo Indians living along the Rio Grande south of Santa Fe had chipped turquoise from the Chalchihuitl Mine for over a thousand years, until perhaps 1700. A newcomer could hardly be expected to discover a vein of sky-blue stone beneath the Indians’ abandoned sites, not unless the new guy tried something different and got very lucky.

My First Anthill

There were anthills near old workings. Ants are known to bring grains of rock up to the surface. So, I got down on my hands and knees to look for blue specks in nearby anthills. Within thirty minutes I spotted tiny blue grains in one deserted, cone-shaped mound about eight-inches high. I dug a pit down through the mound. A thin vein of solid turquoise opened up a few feet down. That was the Tedi Mine, named later for my girlfriend in town. It wasn’t the best blue stone, not at that shallow depth, but it got better as I went deeper. I staked the claim with my 38 Smith & Wesson.

I traded the easily-polished portion of my freshly-mined turquoise for Navajo rugs with enterprising Indians on the Santo Domingo reservation. The Pueblo necklace-makers soaked the rounded pale-blue chips in urine to deepen the color. Weak ammonia can react on copper in turquoise to turn it bright blue. Poorly-informed tourists bought this jewelry to wear around the neck, next to their skin. My high-grade stone was the only new Cerrillos turquoise Santa Fe’s shops had seen in over forty years. Lapidarists and silversmiths came on board my little Cerrillos Turquoise Company. Bob Castner, State Auditor of New Mexico, set the first cabochon of turquoise from the Tedi Mine in his Elks Lodge ring. I’m still wearing an enchanted stone I pried from beneath that anthill fifty-five years ago. Sky-blue Tedi turquoise, with its dark brown matrix, brought premium prices. I got a haircut.

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This unique prospecting method is very different from the list of everyday approaches aimed at looking for a mineral occurrence. The normal search in the field involves outcrop sampling, float examination, the search of old workings, and tracing known faults. Where valuable minerals lie completely covered by overburden, there is little chance of discovery using only these standard visual practices. A unique method is needed.

Other Anthills

W.F. West, manager of the Leopard Mine, Zimbabwe, following assay results of 0.1 ounce per ton gold in ant heaps built up on overburden Kalahari sand, proposed an anthill prospecting theory in 1965. The hills were over blind fissures containing payable ore bodies being mined at the time. The insects in West’s area mined passages down to water, carrying the debris back up to the surface. The water table was at 180 feet. These termites had built mounds reaching heights of four feet. Kalahari sand covers much of south-central and southern Africa, effectively concealing outcrops. Thus the work of the termite field assistants was of great value in mineral exploration. This is not an isolated happening.

The Vila Manica copper deposit in Mozambique is covered by sand to a depth of 45 feet in places. Insect mounds above the ore vein in intrusive serpentine were found (1973) to contain anomalous concentrations of nickel and copper. The name of the insect field assistant is Macrotermitidae.

A.J. Johnson, editor of Chamber of Mines Journal (Zimbabwe), had this to say in a 1982 personal letter to Professor Robert R. Brooks at Massey University in New Zealand: “Just before the past conflict brought prospecting to a close, a gold mine did come into operation based on information supplied by anthills.” That mine is still in operation and is suitably named “Termite Mine.”

My Last Anthill

A small hardrock gold show on the Blair Brothers Ranch, near Mitchell Caverns State Park in San Bernardino County, California, had one anthill near the vein and a number of them scattered nearby. These were not your regular pick and shovel underground workers. These ants seemed to have drills, jaw crushers and no close friends. A bite was painful. In a flurry of optimism, while exploration-drilling the property, we sampled a dozen anthills for fire assay. There were wells down to water several hundred feet nearby, but I’m sure the ants needed to go only ten or twenty feet to find enough year-round moisture to suit their needs. Forty years after my anthill success in New Mexico, this one was a bust. The anthill fire assay results were all the same—nil.

Why Ants Prospect

No ant goes underground looking for rich ore. They’re too busy. They couldn’t care less about minerals, other than the ease of burrowing through them. Water is the target and the quickest way to it is down cracked fault planes, through soft slickensides and along talc-coated vein walls. They chew their way into the easy stuff and carry it to the surface. Ants and termites operate above the water table, in the oxidized zone, where rock alteration has led to softening. They don’t actually fracture quartz with their clasping jaws. Natural freeze-thaw cycles, earthquakes, and other invasive events crack vein material over geological eons, permitting the ant to pick up broken pieces from the mother rock.

For the modern human prospector, what could be simpler than the examination of recent anthills in old mining districts? One has to simply scoop up the fine-grained sample and pan it for heavies. If anything is left after taking out the magnetics, further attention may be warranted.

There’s a name for this anthill business. It’s new, nothing any mining school ever heard of in the old days. The study of insects and animals as they react with their mineral environment is called geozoology.

Sources

“Biological Methods of Prospecting for Minerals,” R. R. Brooks, Wiley-Interscience, 1983, pp 102-105.

“Geology of the Cerrillos Area, Santa Fe County, New Mexico,” Bulletin 48, New Mexico Bureau of Mines & Mineral Resources, 1957.

“Archeology and History of Santa Fe County,” Special Publication No. 8, New Mexico Geological Society, 1979, pp 13-16.

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Dr. Ralph E. Pray is the owner/operator of the Mineral Research Laboratory in Monrovia, California. He welcomes your questions or comments; (626) 357-6511.