Mariposa County, California
by Robert B. Cook, Carl A. Francis, and Bryan Lees
One of the most difficult specimens for a mineral enthusiast to acquire is a significant crystallized gold. Although gold specimens are not uncommon in dealers’ stocks, nor are many of them particularly expensive relative to the value of their contained gold, specimens exhibiting sharp, well-developed crystals of even modest size are quite rare and today are produced from only a handful of localities. Mines of the California Mother Lode belt and its peripheral districts have produced many of the finest such specimens. Examples include the Eagle’s Nest, Diltz, Mockingbird, Artru, and Colorado Quartz mines, the latter three being contiguous and on the same geologic structure. Specimens from these occurrences commonly have bright luster and rich color, with well-developed crystals in unusual and attractive arrangements, often on white quartz matrix. Although the Mockingbird mine was the subject of an article in last year’s September/October issue (Cook and Gressman 2008), recent discoveries of the remarkable “El Fuego” and “Bristlecone” specimens at the nearby Colorado Quartz mine (Moore 2009) have prompted the present article, which describes the Colorado Quartz mine and its magnificent gold specimens.
Dr. Robert B. Cook, an executive editor of Rocks & Minerals, is a professor emeritus in the Department of Geology and Geography at Auburn University, Auburn, Alabama. Dr. Carl A. Francis, a consulting editor of Rocks & Minerals, is curator of the Mineralogical Museum at Harvard University. Bryan Lees is president of Collector’s Edge Minerals, Inc., in Golden, Colorado, a company that specializes in mining and marketing mineral specimens.