Date of Award
Master of Science (MS)
Over the last one hundred twenty-five years, massive amounts of gold and silver have been mined from igneous rocks near the town of Telluride, located in San Miguel County, Colorado. Interestingly, not all gold and silver ore occurs in the igneous bodies. A small mining operation located near the town of Sawpit, the Lizzie-G and Jo Dandy claim, has recovered high-grade ore from a limestone replacement body occurring in the Pony Express Member of the Wanakah Formation (Upper Callovian Jurassic). To date, regional stratigraphic and structural studies have not been applied to locate similar sedimentary ore deposits. This study develops area-specific criteria that will assist in locating prospect areas that are similar to the Lizzie-G and Jo Dandy. Geologic methods applied in this study include field and petrographic descriptions of Wanakah Formation strata and analysis of structural elements using filed description, joint and fracture measurements, and aerial photography. Faults and factures were subsequently analyzed following preparation of two lineament maps and numerous stereonets. Most importantly, stratigraphic and structural relationships were investigated in the area of the Lizzie-G and Jo Dandy mines, and two cross sections constructed. Studies indicate that a number of criteria are important in identifying prospect areas. Stratigraphic criteria include the thickness of the Pony Express Limestone, the proximity of igneous rocks to the limestone deposits; and the degree of chemical alteration in igneous rocks. Density of structural features is greatest at the Lizzie-G and Jo dandy mine site and suggest the necessity for a “Conduit” to assist migration of mineralized fluids. Because of mineral deposits mapped near sawpit, faults and fractures trending generally east-west appear to be key for location of ore deposits. Four target prospect areas have been identified along or near the trace of a large normal fault trending approximately N 80 W. This fault is the center of mineralization in the Lizzie-G workings.
Copyright 1995 Douglas N. Dreiling
Dreiling, Douglas N., "Exploration Criteria for Au and Ag-Ore Deposits in the Pony Express Member of the Jurassic Wanakah Formation, Northeastern San Miguel County, Colorado" (1995). Master's Theses. 2505.