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March-April 2012

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Through the 'Scope: Microminerals of the Tonopah-Belmont Mine Big Horn Mountains, Maricopa County, Arizona

The Tonopah-Belmont mine is home to one of Arizona's more unusual mineral assemblages and ranks high on most micromineral collectors' locality lists. It has been producing fine specimens of unusual and rare lead minerals for many years and is the type locality for the copper-zinc species bechererite.

The mine is located in the Big Horn Mountains about 75 miles west of Phoenix (fig. 1). Although four-wheel-drive is not required to reach the mine, a high-clearance vehicle is a must. The roads steadily diminish in quality the closer one gets to the mine; the last several miles are over roads that are not maintained and include dry wash crossings and short, steep sections. In 2002 the mine was sealed with bat gates by the state of Arizona through the Abandoned Mine Safety Fund to prevent entry by people while allowing colonies of bats to continue to use the mine for shelter. Today, the old mine dumps, surface workings, and outcrops are still accessible and continue to provide the collector with fine micromineral specimens (figs. 2 and 3). As usual, the more patience and persistence the collector has, the better the results will be. Most collectors avoid the summer months when temperatures are often above 100°F. The property does not appear to be posted against trespassing, and we are unaware of any restrictions on surface collecting.

Ron Gibbs, a mining engineer, is an active field collector and the author of several articles on western mineral localities.

Mark Ascher, an engineer, is an enthusiastic field collector of microminerals and an associate in the University of Arizona Mineralogy Lab.

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