The Dunmore lode is located near Ouray, Colorado in the northwest part of the San Juan Mountains. In structure as well as mineral assemblage it shows a connection between the chimneys and veins of the region. The lode averages about 100 feet wide for 1,200 feet along the Dunmore claim. The fissure zone is over two miles long and displacement along it has offset a folded pre-Cambrian complex 4,500 feet prior to the deposition of 2,400 feet of volcanic tuff. Fissures in the pre-Cambrian rocks controlled in part the intrusion of dikes and the formation of veins. Late Tertiary faulting extended the Dunmore fissure into the San Juan tuff, dropping the south side about 80 feet. Although most of the lode crops out in the pre-Cambrian rocks, it extends upward across the profound unconformity into the tuff. The complex lode contains sharply-marked fissure veins, sheared slate dragged into the fault zone, a sheared dike, breccia chimneys, and pebble dikes. An assemblage consisting of quartz, sericite, kaolin, and pyrite appears to be of early Tertiary age. The more productive part of the lode, however, is late Tertiary and consists of hematite chimney enclosing a copper shoot, and tungsten chimney, and compound base-metal fissure veins. These chimneys and veins are mostly localized along early Tertiary structures, but their mineral sequences correlate them with the social stage of late Tertiary deposition recognized by Burbank in the adjoining Red Mountain and other districts. The Dumore lode, however, is believed to have been deposited at greater depth and higher temperature and nearer to a source of supply than the lodes of these districts.
The ore possibilities are discussed in relation to the future development of the Dunmore mine, and recommendations are made for the development of various parts of the lode.
Earth and Planetary Sciences
Level of Degree
Department of Earth and Planetary Sciences
First Committee Member (Chair)
Vincent Cooper Kelley
Second Committee Member
Stuart A. Northorp
Third Committee Member
Harold Daniel Larson
Dunmore Mine, Ore Deposits, Tertiary Period
Silver, Caswell. "Geology and Ore Deposits of the Dunmore Mine, Ouray County, Colorado." (1946). https://digitalrepository.unm.edu/eps_etds/213