Advanced Prospecting & Detecting for Hardrock Gold

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Waldemar Lindgren (see References), in early literature, defined a vein as "a tabular mineral mass occupying or closely associated with a set of fractures formed by deposition from solutions by filling fissures and pores in the wall rock, or by replacement of the wall rock, or by both filling and replacement. The term "true fissure vein," as popularly used, is intended to imply persistence in depth." Much of the: western Cordilleran gold deposits are associated with Tertiary volcanic centers, with Nevada being the premier gold-producing state. The term "cordillera" (see A. J. Eardley in References), as used within this booklet, refers to the broad area west of the Great Plains—from the Pacific Ocean to the eastern front ranges of the Rocky Mountains—belonging to orogenetic belts of different ages, together with their associated plateaus and intermontane basins. Up to about 1960, most western gold mining was centered on high-grade vein-type deposits mined by expensive underground mining methods. However, starting in the mid 1960's, gold, and also silver, has been recovered by bulk mining, open pit, heap leach sodium cyanide methods using activated carbon. This process was first developed in the early 1950's under the supervision of J.B. Zadra, then the quiet and unassuming chief of the Nevada Bureau of Mines at the University of Nevada in Reno. Now with modern equipment, many old-time mine workings and their dumps, once considered "worked out," are being completely engulfed and consumed by this technology. Modern high-frequency metal detectors have made it worthwhile to investigate existing, or surviving, old gold mine dumps—too small and unimportant to justify heap leaching—and the surrounding area, for overlooked surfacial veins and possible small paystreaks and pockets of detectable eluvial gold.