New Mexico Mineral Symposium — Abstracts

The Goodsprings (Potosi; Yellowpine) mining district is one of the larger districts in southern Nevada. Goodsprings is located at the southern end of the Spring Mountains, approximately 30 air mi southwest of Las Vegas. The district is relatively unknown to mineral collectors because there has been no activity there since World War II. Many fine specimens were found when the mines were operating, and the old mines and dumps still contain good specimens, especially for the micromineral collector.

The first orebody in the district was discovered by Mormon missionaries in 1856 although large-scale mining did not begin until the 1890's. Mining activity was at its peak from 1906 to 1917, with moderate activity in 1924-28 and in 1943-44. Lead, zinc, and copper minerals were the principal ores produced, along with some gold, silver, vanadium, cobalt, and platinum. Explora¬tion for uranium was carried out in the 1950's, and recent exploration has focused on the potential for gold.

The geology of the Goodsprings district is complex. The Spring Mountains in this area consist of approximately 13,000 ft of Paleozoic and Mesozoic sediments, which were folded and faulted during orogenic events in the Late Jurassic to Early Tertiary. Thrust faults And high-angle faults are common. Sills and dikes of granite porphyry and lamprophyre were emplaced, and dolomitization of some of the limestone occurred. The ore mineralization probably occurred in the Early Tertiary. The orebodies are found almost exclusively in the Monte Cristo limestone (Mississippian), with the Yellowpine member accounting for approximately 85% of the ore mined in the district. The orebodies are tabular where parallel to bedding and where they cut across the beds. The primary sulfide minerals, galena, sphalerite, and chalcopyrite, have been highly oxidized and, with the exception of galena, are rarely found in the ore.

More than 50 minerals have been found in the Goodsprings district. Best known to collectors are superb specimens of fluorescent and crystallized hydrozincite, textbook orthoclase crystals (including Baveno and Carlsbad twins) from the granite porphyry, and the rare cobalt oxide, heterogenite. Other minerals of interest to collectors include wulfenite, pyromorphite, vanadinite, cerussite, anglesite, plattnerite, malachite (including pseudomorphs after azurite), dioptase, dolomite, hemimorphite, and mottramite.