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NP$Form 10,O e OM8 AA=vd No.1ov-wm (6!E) United States Department of the Interior National Park Service National Register of Historic Places Continuation Sheet Section number 8 Page 5 sulfurets. Coloradans labeled them "refractory" or "rebellious. " Sulfurets were resistant to processing by stamp milling because the mercury could not bond with the gold as long as the ore was locked within the sulfides. The gold recovery rate dropped from three-fourths of the assay value to less than one-fourth, sometimes with no yield at all. A "process mania" ensued in which the Gilpin miners were swamped by fortune hunting "alchemists" and pseudo-scientists promising miracle desulfurization methods.' The unprofitability of stamp milling coincided with the need for capital for heavy machinery needed to excavate even farther down into the earth's surface. Some miners sent the ores to the smelting firm of Vivian and Sons in Swansea, Wales, for processing. Many others turned from mining to speculation, persuading novice Easterners to invest in non-existent and worthless claims. The speculative mania, the naivete of speculators about the elaborate and costly technology required to uncover complex ores, Indian attacks on the Great Plains that cut off communication, and the postwar economic slump combined to bring a financial crash in the spring of 1864. Depression continued in the Gregory district for the next 3 1/2 years. In 1867, the economy dramatically reversed and began an upward climb. In that year, Colorado ores took first prize at the Paris Universal Exposition, and Gilpin County news editor Oranda J. Hollister published the Mines of Colorado. These events stimulated new investment in the mines both nationally and in Europe. The most significant development, however, was the introduction on the Rocky Mountain mining frontier of a European extraction process by Brown University Professor of Chemistry, Nathanial P. Hill. First approached by the fortune-seeking Territorial Secretary William Gilpin at the height of the mining depression to advise him on purchases in the San Luis Valley, Hill came to Colorado at the end of May 1863. Soon Hill was lured away from his consulting enterprises into mine speculation in Gilpin County. He purchased options in the Bobtail, Fairfield, and other lodes, but ultimately retained only two mines at Central City with which he organized the Sterling Gold Mining Company and the Hill Gold Mining Company. He returned East in 1865, as others had done, and began experiments and research in the Welsh smelting technique called the Swansea process. This method used the copper and iron sulfides in ores, in a mixture called a "copper matte, " to collect gold and silver until it could be separated or refined into its component metals. Hill went to Europe to learn the process and then established the Boston and Colorado Smelting Company at Black Hawk in 1867 with a group of Boston partners.' This was the most important event of the 1860s decade for the area economy.