This open-file report for Boulder, Jefferson, Clear Creek, and Gilpin 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, and coal resources. 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
From the Introduction:
This evaluation of the mineral and mineral fuel resource potential was conducted for the nearly 41,767 acres of state mineral lands within Boulder, Jefferson, Clear Creek, and Gilpin Counties along the Front Range of 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 69 individual tracts that range from approximately 40 acres to 3,869 acres.
Boulder County has several oil and gas fields within the high plains region including part of the giant Wattenberg field. Historically, Jefferson County had a small oil and gas field, but that was abandoned in 1962.
Coal mining in Boulder County began in 1863 and continued until 1958, and in Jefferson County began in the 1860’s and continued until 1952. Over 140 and 50 coal mines existed in the Laramie Formation in the southeastern part of Boulder and Jefferson counties, respectively.
Boulder County is the northeastern terminus of the Colorado mineral belt and as such is blessed with numerous mining districts. The most prominent is the Boulder County tungsten district. Additionally, several precious metal (with base metal and fluorspar) districts occur in Boulder County. Clear Creek County is home to the Central City and Idaho Springs districts. Gilpin County is home to the Central City and Idaho Springs districts. In both counties, gold and silver are the primary minerals; however, substantial amounts of lead, zinc, and uranium have been produced. In Jefferson County, uranium has been the primary ore. Other metallic mineral deposits in Jefferson County include small copper and other base metal and precious metal occurrences in Precambrian rocks.