This open-file report for Alamosa, Conejos, and Rio Grande counties includes an introduction to the geology and mineral resources of the county along with an index map of tract locations, maps of metallic mineral prospects, industrial mineral prospects, oil and gas test wells and oil field locations. The main body of the report is an evaluation of each individual tract, which includes text as well as a topographic map and a geologic map. Digital ZIP/PDF download. OF-00-06D
Four general categories of resources are included in this inventory:
- oil and gas
- metallic minerals
- industrial minerals and construction materials
Each individual tract evaluation includes:
- A bar graph which ranks each tract’s resource potential for each of the four mineral categories. An explanation of the categories may be found at the end of this introduction
- Tract identifier number, county name, and county location map
- Tract location on a 7-1/2-minute United States Geologic Survey topographic map
- Tract location on a United States Geologic Survey surface outcrop map
- Location as to section, township, and range and approximate acreage
- Overview of tract geology
- Specific assessment of the resource potential for the four resource categories
- References used in assessing tract potential
This evaluation of the mineral and mineral fuel resource potential was conducted for the nearly 19,000 acres of state mineral lands within Alamosa, Conejos, and Rio Grande counties in south-central Colorado. It was conducted as part of its long-term evaluation of approximately 4 million acres of state lands administered by the State Land Board. For evaluation purposes, the counties were divided into 92 individual tracts that range from approximately 160 acres to 46,600 acres.
The three counties occupy two major geomorphic provinces: the San Luis Valley, and the San Juan Mountains. Only ten wells, all dry holes, have been drilled in Alamosa County with almost no hydrocarbon shows indicated to date. The only production, now abandoned, existed in the one-well Del Norte field of Rio Grande County. A total of 1,855 barrels of oil was produced. Only a few of the tracts evaluated in the counties have any potential for metallic mineral resources. Most of the state land is located in the San Luis Valley, which has little to no potential for metal deposits. The tracts in the mountainous areas of the counties are mostly located away from the known metal districts. Gold and silver resources have been identified within State Land Board Tract 21-01 in Conejos County, which is located within the Platoro caldera complex, less than 1 mi. southwest of the largest gold and silver mining region, the Platoro district. Additionally, gold, silver, lead, and/or copper mineralization are identified near three other tracts. The King turquoise mine, possibly the most significant turquoise mine in Colorado, is located in eastern Conejos County, about 0.5 mi. southeast of one tract.