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Philip M. Bethke 56 1900, and Burbank (1932) adds twenty-one producers through 1930, the end of significant mining in the district. Through 1970, the Bonanza district produced just over $11.5 million in gold, silver, copper, lead, and zinc (Marsh and Queen 1974). Mineralization in the Bonanza district was of the adularia-sericite, or low-sulfidation , type, as at Creede. However, there are significant differences between the districts. The ores at Bonanza contained gold and silver telluride minerals, unknown at Creede, and the Bonanza Veins filled relatively short structures in a network of variously oriented faults in the subsided block of the caldera, as opposed to the horizontally continuous fault systems of the Creede Mining District. The mines at Bonanza exploited quartz-pyrite veins that contained sphalerite, galena, chalcopyrite , bornite, tennantite, and gold and silver telluride minerals as the principal ore components. Wall-rock alteration associated with mineralization consisted of seritization (a general term that encompasses the formation of fine-grained muscovite, or sericite, and clay minerals such as illite). An earlier period of acid-sulfate alteration, similar to that at Summitville, affected the district’s volcanic rocks—particularly a volcanic dome at Porphyry Peak—but apparently had no related mineralization. Of the many mines in the Bonanza district, the Rawley Mine was by far the mostimportant.Orewasoriginallydiscoveredin1880onthenorthslopeofRawley Gulch, approximately 2 miles (3.2 km) northeast of the town of Bonanza, where the mine exploited a north-south-trending vein. A small mill was constructed in 1902, and a small amount of concentrate was shipped in that year and again in 1905. Until 1910, most work was devoted to development and the locations of ore bodies . In 1911–1912, a 6,000-foot-long (1.8 km) tunnel was driven perpendicular to the vein, approximately 1,200 feet (366 m) below the uppermost workings, to more economicallydraintheworkingsandtransportthebrokenoretothemillinSquirrel Gulch. A new mill was completed in Squirrel Gulch in 1923, and a 7.5-mile-long (12 km) aerial tramway was constructed from the mill to the town of Shirley on the Denver and Rio Grande Railway, directly north of the mill. The years 1923 through 1930, when the mine was shut down, were the mine’s most productive. In total, the Rawley Mine produced 480,644 tons of ore between 1902 and 1930. The nextmost -productive mines in the district were the Cocomongo and Bonanza Mines (operated as one), located on Kerber Creek about 1.25 miles (2 km) north of town. Together, these mines produced about 160,000 tons of ore between 1902 and 1927, when operations ceased. The Empress Josephine Mine, located in 1881 in Copper Gulch, three-quarters of a mile (1.2 km) northeast of Bonanza, produced some high-grade ores that contained a variety of telluride minerals including the gold telluride mineral Empressite, first described from that mine and named after it. The Empress Josephine was the largest producer in the district in the early years, but the ore body turned out to be small, and total production was apparently limited to 5,000 tons of ore. Some mining activity continued at Bonanza until 1970, but it is not clear that there was any production from the district after 1930. M i n e r a l i z at i o n i n t h e e a s t e r n s a n J u a n M o u n ta i n s 57 Acid mine drainage from waste piles and workings adversely affected Kerber Creek and some of its tributaries, particularly Squirrel Creek. The greatest damage resulted from waters draining waste at the Rawley tunnel and mill site. In 1991, ASARCO, the main recent operator in the district, and other private parties historically involved in mining operations in the district formed the Bonanza Group to undertake a voluntary cleanup of lands contaminated by their operations, in cooperation with local governments, the Colorado Department of Public Health and Environment (CDPHE), the US Forest Service (USFS), and the EPA. The USFS was responsible for managing activities on public lands and the CDPHE for work on private lands, as well as oversight for construction on both public and private lands. Remediation efforts included moving the waste pile from the Rawley mill site to a more secure on-site repository, plugging the Rawley tunnel, and reclaiming riverbanks in the Kerber Creek Watershed. As a result of these efforts, the metal content and acidity of the waters of Kerber Creek were significantly...

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