November 2009

Economic Geology

Porphyry deposits (Part 2)

By R.J. Cathro

 

Bingham Canyon, circa 1900, showing the future site of the porphyry mine at the junction of Bingham Creek (to the left) and Carr Fork (to the right). The Wall property is on the lower slopes of the hill in the centre of the picture. The Highland Boy Mine is out of sight up Carr Fork. (from Parsons, 1933 without attribution; believed to be a USGS photo)


The Utah mine is … the biggest thing that men have made. By the end of 1931 there had been moved at Utah 222,000,000 cu. yd. of material, including ore and the waste rock that overlay it. This figure will be increased at an average rate of nearly 20,000,000 yd. per year. Excavations for the Panama Canal are estimated at 232,000,000 cu. yd., but the Canal is 50 miles long ….  


~ Parsons, 1933, p. 45

This chapter is derived mainly from a 1997 paper by Ken Krahulec of the Utah Geological Survey. In addition to being the most comprehensive and thorough compilation of the history of the Bingham Canyon camp, it provides invaluable information about the people who played key roles in the discovery and early development of the porphyry deposit. Krahulec also provided photographs, other references and editing help. Some additional background information was also obtained from Parsons (1933) and Rickard (1932).

Ira Gershwin wrote the lyrics of the song They All Laughed for the 1937 movie “Shall We Dance,” and the music was composed by his brother George. The Gershwins were sophisticated New Yorkers who probably knew next to nothing about mining. If they had, Ira would probably have added a couple of clever lines about the Bingham Canyon porphyry copper mine into the song. The mine’s history would certainly fit with the theme of the song — the tenacity of those who succeed while faced with intense skepticism. 

In many ways, Bingham Canyon, located 50 kilometres south of Salt Lake City, was a typical mining camp in the western United States between the 1850s and 1890s, a period when new discoveries were made almost daily and financing was readily available. Bingham was discovered and initially developed by adventurers flocking to, or returning from, the California Gold Rush or the silver discovery at Comstock, Nevada. The early focus was on placer gold and on silver and gold veins. Base metals weren’t exploited until the railways arrived in the 1870s. Commercial production of copper did not begin for almost 40 years after the camp was discovered, even though as early as 1870 it was recognized that copper was the predominant metal in the camp; the name Bingham is now synonymous with the metal.

Bingham Creek flows northeasterly and drains an area of rugged terrain near the northern end of the Oquirrh Mountains, where peaks reach elevations of almost 3,250 metres. Argentiferous galena was found by loggers in 1857 but the first claims weren’t staked until 1863 when Civil War soldiers, many of whom had learned something of gold mining in California, were stationed nearby. The camp passed through several early development phases, starting with an estimated 100,000 ounces of placer gold that were recovered near the mouth of the canyon, and then expanding into stamp milling of gold-quartz veins farther upstream, starting in 1882.

After unsuccessful attempts to treat lead sulphides, silver was successfully smelted from lead carbonate ores from the interval between the mouth of the canyon and Carr Fork, a distance of about eight kilometres. Carr Fork enters Bingham Creek from the west and is the principal tributary. The best veins averaged over 1,500 g/t (50 oz/ton) Ag and nearly 35% Pb, but the oxidized ores, which only extended down to the water table at a depth of 10 to 15 metres, were soon exhausted. The underlying sulphides proved untreatable because the galena-sphalerite-chalcopyrite mixture was refractive and produced dirty concentrates.

By 1874, Bingham Canyon had 53 mines and a population of 800 that was crammed into a one-street town centred at the wider junction of Bingham Creek and Carr Fork and extended down the torturously narrow canyon. The Engineering and Mining Journal referred to Bingham in 1912 as “a sewer five miles long.” Fortunately, copper sulphate in the creek water not only killed the bacteria but eliminated offensive odours. In 1885, D.B. Huntley noted that the water in Bingham Creek between Carr Fork and Copper Centre Gulch, the next tributary above Carr Fork, contained copper in solution, and that native copper had been deposited in the organic-rich parts of the creek bed and in iron-cemented gravels (ferricrete). Although most prospectors failed to notice its significance, this was a clear indication that a large copper sulphide system was being oxidized and leached upstream.

Enos A. Wall may have been the first person to recognize that the disseminated ”low-grade” copper mineralization in Bingham Canyon might have economic potential. A successful inventor (of a roll crusher for grinding mills), businessman and entrepreneur from Indiana whose mining career had taken him to Colorado, Montana and Idaho, he arrived in Utah in 1887 and became involved in the Mercur gold camp, about 30 kilometres southwest of Bingham. When he visited Bingham, he was impressed at once by a zone of disseminated chalcocite and bornite that was exposed in monzonite for a distance of 100 metres in the wall of Bingham Creek just above Carr Fork. It was also exposed for a length of 30 metres in the abandoned Soldier Tunnel. Sampling revealed that the average grade was at least 2.4% Cu. Wall was able to re-stake two claims that covered the showing because the original claims covering this area had lapsed due to disinterest.

While Wall couldn’t afford to develop the property on his own, he did manage to enlarge the property to 72 hectares (179 acres) by 1887 and to explore it with 1,065 metres of drifts and crosscuts in several adits by 1896. That work was partly financed by the 1894 sale of the Brickyard gold mine at Mercur to Captain Joseph R. De Lamar, a Dutch-born mine operator and a genuine sea captain, who owned the Golden Gate Mine at Mercur, one of the largest and most successful cyanide mills in the United States. At this time, selective mining of the better copper veins in Bingham Canyon had proven unprofitable and interest in that metal was very low. In fact, the ”low-grade” mineralized monzonite was derisively referred to as “wall-rock.” Wall had submitted his property to many of the important people involved in copper mining in the West, including Benjamin Guggenheim of American Smelting and Refining, Marcus Daly of Anaconda and William Clark of United Verde, but they all turned him down.

Wall was finally able to interest De Lamar in his copper property in 1895, when the copper price was low, and again in 1898 when it was higher. De Lamar sent his general manager Hartwig A. Cohen, his mining engineer, Robert C. Gemmell, and his metallurgical and construction superintendent, Daniel C. Jackling to make a careful evaluation. It involved the collection of 566 channel samples underground and a 69-tonne mill test in a small stamp mill. They calculated an indicated reserve of 13.6 million tonnes averaging 2.22% Cu and 0.6 g/t (0.018 oz/ton) Au, which Cohen concluded would be unprofitable because it was covered by a 15 metre-thick leached cap.

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