This open-file report for Archuleta, Hinsdale, La Plata, Mineral, and San Juan Counties includes an introduction to the geology and mineral resources of the counties along with an index map of tract locations, maps of metallic mineral prospects, industrial mineral prospects, coal resources, and 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-01-20D
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
From the Introduction:
Archuleta, Hinsdale, La Plata, Mineral, and San Juan Counties occupy a large part of southwestern Colorado. This evaluation of the mineral and mineral fuel resource potential was conducted for the nearly 62,000 acres of state mineral lands within these five counties. 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 77 individual tracts that range from approximately 40 acres to 13,877 acres.
Major tectonic features in these counties include the San Juan volcanic field, the Needle Mountains, and the San Juan Basin. The San Juan basin is a major energy resource of coal, coalbed methane, and conventional oil and gas. La Plata County was the largest gas-producing county in Colorado in 1999. Coalbed methane is also a major resource for the both La Plata and Archuleta Counties, as is coal. There has never been oil or gas production in Mineral, Hinsdale, and San Juan Counties.
Several historically important and highly productive precious- and base-metal mining districts are located in the area covered in this report. By far the most significant of these districts are located in the San Juan Mountains in San Juan, Mineral, and Hinsdale Counties. Archuleta County is not known to have economically significant metal resources.
Several varieties of industrial minerals and construction materials are present in these counties. The most economically important industrial minerals in this region are sand and gravel. Others have included bentonite and fuller’s earth clay, zeolite, fluorspar, clay, and sandstone, as discussed in the report.