OTR Field Trip – August 27, 2011

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Title: Mineral Belt Trail Bicycle Trip: Geology and Mining History of the Leadville District

Leader: Fred Mark

Publication:  The Outcrop, August 2011, p. 17

Overview

The Leadville Mining District produced world class quantities of zinc, lead, silver as well as gold and copper over its 140 year history. It is notable for its complex structure and diverse mineralogy and large supergene as well as hypogene mineral deposits. As understanding of structure, mineralogy, geology, and metallurgy grew during the first 100 years previously unrecognized occurrences were discovered and brought into production adding new wealth and extending the life of the district. The human story of the district is equally rich. Many of the significant sites of the discovery and mines are crossed by the Mineral Belt Trail. A bicycle trip on the trail will provide an opportunity to get an “up close” view and discuss many of these sites and learn about the historic characters associated with them.

Short (very) Geologic History

The story of the district began in Paleozoic time when carbonate rocks were deposited that would later host mineralization. Fast forward to Laramide compression when the District and the region were subject to folding, faulting, and igneous intrusion. During Eocene there was more igneous intrusion and deposition of the hypogene mineral suite. This was followed by later uplift and erosion and development of the Rio Grande Rift, and finally the development of the supergene mineral suite, placer deposits, and glaciation.

Discoveries

The first discovery was placer gold in California gulch in 1860. This set off the first rush and was the beginning of the Tabor story. Next came the discovery of lode gold in 1868 and the development of mines such as the 5 20 and the Printer Boy. Recognition and production of high grade supergene lead carbonate at the The Rock Mine in 1874 resulted in prospecting, discovery, and large scale production of lead carbonates by 1877. The spring of 1878 saw the discovery of high-grade bonanza supergene silver on Fryer Hill, and by 1880, the district was the largest silver producing district in the world, with production of 10 million ounces. As supergene lead and silver ore was mined out, production of hypogene minerals became more important, with zinc production surpassing silver in 1902 and lead in 1903. Recognition of supergene zinc mineralization in 1909 lead to flush production amounting to 10% of total U.S. metallic zinc production in 1912. Major discoveries were made on the east side of the district as late as the 1960s and large scale underground mining continued there to 1999 but that activity cannot be seen from the Mineral Belt Trail and will be a topic of a future trip.

The Mineral Belt Trail

The Mineral Belt Trail is a premier bicycle/hiking trail during the summer and cross country/snowshoe trail in the winter. The views of the Sawatch and Collegiate ranges and the upper Arkansas Valley are breath-taking. The trail is paved, 11.2 miles in length, and has a vertical rise of 600 feet, mostly following old railroad grades. Leadville is at an elevation of 10,200 feet, so people with heart or respiratory conditions must use caution.

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