Part 2 Exploration for platinum-group elements

Sulfide-bearing samples, collected by Art Howland and J.W. Peoples during the early 1930s, were analyzed for PGE’s by INCO, and the results reported by Howland and others (1936). In one of the samples from layered gabbro of the Banded series, they reported the presence of Sperrylite and a mineral they called stibiopalladinite. They compared this part of the complex to the Merensky Reef of the Bushveld Complex. These important observations did little to encourage the PGE exploration until the early 1960s, when at least two independent groups began to examine the PGE potential of the Stillwater Complex. Page and Jackson (1967) found platinum-group minerals in samples of chromite that had been collected over the previous years. During the summers of 1967, 1978 and 1969, they submitted many rocks from the complex for PGE analysis. However, except for samples from the lower chromitites the results were not encouraging.

In 1961, H. K. Conn of the Johns-Manville Corporation attended the Commonwealth Mining Congress in South Africa and visited the Rustenburg platinum mines on one of his tours. This visit sparked his imagination that there might be a zone similar to the Merensky Reef in the Stillwater Complex because he was already familiar with the complex and the work of Howland and others. (1936) regarding PGEs in the complex. Nothing was done until 1967, when E.L. Mann and S. G. Ellingwood visited the Stillwater Complex and initiated a modest program of soil sampling and reconnaissance mapping. Results were generally disappointing, and Johns-Manville might well have walked away from the area after the first summer, were it not for one set of samples displaying weak Pt, Pd, Cu, and Ni values. Field exploration continued each year, with only minimal encouragement until 1973, when Johnson-Manville geologists discovered the major Stillwater PGE zone, commonly referred to now as the J-M Reef.

After trenching and drilling confirmed the lateral continuity and character of the the mineralization, claim staking accelerated. By the summer of 1975, the Johns-Manville Corporation held claims over all but about 1.5 miles of the 28-mile strike length of the J-M Reef.

Other areas distinct from the J-M Reef were also found to have satisfactory recoveries. In 1974, the Janet 50 zone and on outcrops on the West Fork of the Stillwater River were found with PGEs. On August 22, 1974, 3,600 feet of strike length ore grade material was delineated on the West Fork, and on December 15, an exploration adit was begun. The exploration successfully define the tabular nature of the deposit, but water flow from an intersected fault zone forced the rift to be cemented. By 1977, exploration had confirmed the presence of a zone 3.4 miles long by 6.9 feet wide, which averaged 22.3 g of platinum and palladium per ton, in a ratio of 1/3.5. Metallurgic tests provided recoveries of 85 percent of the platinum and palladium, and 69 percent of the nickel and 75 percent of the copper from test samples.

Exploration continued, and in 1979 the Chevron Resources Company joined the Johns-Manville Corporation to form the joint-venture company Stillwater PGM Resources. By autumn 1982, extensive additional exploration and testing again confirmed the broadly tabular continuity of the ore package with encouraging ore grades. Furthermore, a test stope showed that shrinkage stoping would be an acceptable mining method.

During this aggressive exploration period by Johns-Manville, The Anaconda Minerals Company was in 1977 recovering from its losses in Chile, and reviewed the company’s land ownership in the Stillwater complex. Regional mapping led to their discovery of the PGE bearing reef on the GAY claim group, and much drilling and testing was initiated. In spring 1982, the Anaconda Minerals Company and Stillwater PGM Resources began negotiations to form a joint venture on a land package centered on Anaconda’s claims on the J-M Reef on the Stillwater River Valley. Stillwater PGM Resources agreed to add flanking claims to those held by Anaconda, thus extending the land package to a 6-mile strike length.

Agreement was reached to form the Stillwater Mining Company, a Chevron-Manville-Anaconda partnership, with Chevron Resources Company as the managing partner. A program to prove reserves and determine grade was initiated. Detailed field mapping was continued, augmented by a surface drilling program.

continued
<<prev | 1 | 2

Learn about the many uses of Palladium