The discovery of the Black Cloud, mine, in Leadville, Colorado, had its beginning in the purchase of two small mines by a Philadelphia lace merchant and was achieved through, the combined efforts of the engineering and geological staffs of two major mining companies, Newmont and ASARCO. The story behind tine discovery begins in iMladelphia early in 1881 with the 53-year-old owner of a prosperous lace and embroidery business. Meyer Guggenheim knew nothing of mines and had never traveled west of the Mississippi River. He had acquired a fortune of a million dollars from various businesses and was responsible for a maturing family of seven sons. For $5,000 he purchased a one-half interest in two lackluster lead-silver mines located in California Gulch near Leadville, Colorado. Mining began in Leadville with a gold strike in 1859 and had recently boomed with, the discovery of rich Pb-Ag carbonate ores. Production of gold, silver, and lead from the district torough the end of 1880 totaled more than $35.7 million, but little of this had come from Mayer Guggenheim's mines, the A.Y. and the Minnie. During the months following his purchase, Guggenheim invested nearly $70,000 in dewatering, sinking new shafts, and -underground development, until in August, when his faith in mining investments surely must have then near collapse, he received word of a rich strike at the A.Y. By 1888 the A.Y. and the Minnie were earning him about $750,000 a year. Prior to their exhaustion in 1902 and eventual sale, the two mines netted the Guggenheim family over $15 million. This second fortune enabled them to build one of the greatest mining empires the world has known. From this beginning evolved three corporations which proved to the major forces in the minerals industry of the Western Hemisphere during the Twentieth Century: The American Smelting and Refining Company (now ASARCO Incorporated), Guggenheim Brothers (discoverer of Chuquicamata, El Salvador, and other important deposits), and the Kennecott Copper Corporation.
Figures & Tables
The central Colorado mineral belt is endowed with an impressive wealth of mineral deposits, including the world-class deposits at Leadville, Gilman, and Climax, that formed in a variety of geologic environments. The geology of the area spans more than 1.8 Ga, commencing with the Early Proterozoic accretion of volcanic arc and back-arc complexes to the southern margin of the Archean craton. These rocks were complexly deformed and intruded by large Early and Middle Proterozoic batholiths. During Paleozoic and Mesozoic time, the Proterozoic basement complex was buried beneath several kilometers of marine and continental sediments, and it was partially exhumed during Pennsylvanian orogenic uplift. Subduction-related calc-alkalic magmatism and uplift affected the region during the Late Cretaceous-early Tertiary Laramide orogeny. Oligocene and younger extension generated the north-trending Rio Grande rift zone, which was accompanied by bimodal magmatic activity.
Most of the mineral deposits in the central Colorado mineral belt are associated with Oligocene calc-alkalic magmatism or to later bimodal activity. Deposits of demonstrably Laramide age are relatively small, and a few small carbonate-hosted deposits may have formed during the Mississippian.
The mountains of central Colorado contain some of the largest concentrations of mineral deposits, including those at Climax, Leadville, and fiilman, in the Rocky Mountain region. These ores are part of an elongate zone of hydrothermal deposits, known as the Col or ado mineral belt, that extends northeast from the San Juan Mountains to the Front Range north of Denver (Fig. 1). Although most of the deposits are the products of Cenozoic tectonic and hydrothermal processes, the geology of the central Colorado mineral belt represents more than 1.8 billion years of tectonism, plutonism, and mineralized region, world-class cratonic sedimentation. As with any heavily deposits such as those described in this volume are the culminations of numerous unrelated geologic events that occurred over hundreds of mi11ions of years.
The intent of this paper is to briefly summarize the geologic history of central Colorado and its relation to mineralization. In general, the region is underlain by a crystalline Proterozoic basement complex on which several kilometers of Phanerozoic sediments were deposited. Orogenic up 1ift occurred in the late Paleozoic and twice during the Cenozoic, and a major rifting event began in the middle Tertiary. Voluminous plutonic rocks were emplaced during several Late Cretaceous and Cenozoic magmatic events. Recurrent orogenic activity throughout the geologic history generated new structures and reactivited many preexisting faults.