This open file report for Larimer County includes an introduction to the geology and mineral resources of the county along with an index map of tract locations, as well as maps of oil and gas test wells with oil field locations, metallic mineral prospects, and industrial mineral prospects. The main body of the report is an evaluation of each individual tract, which includes text as well as corresponding topographic and geologic maps. Digital ZIP/PDF download. OF-01-21D
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:
Larimer County consists mostly of the Front Range, Laramie Range and Medicine Bow Mountains of northern Colorado. The county is located in northern-most Colorado along the border with Wyoming. This evaluation of the mineral and mineral fuel resource potential was conducted for the nearly 84,920 acres of state mineral lands within the county. 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 county was divided into 104 individual tracts that range from approximately 8 acres to 13,400 acres.
In 1998, Larimer County ranked 12th among Colorado’s counties in annual oil production and 25th in annual natural gas production from a total of 21 producing fields. The only coal area in Larimer County is the Wellington area in the very northeast part. There are no significant metallic mineral districts in Larimer County. The Manhattan (Red Feathers Lakes) and Masonville districts were the largest producers. Small amounts of gold and silver came from vein deposits in Precambrian rocks. Diamonds occur in in kimberlites in the county in several districts.
There are several important pegmatite occurrences in the Precambrian metamorphic rocks of Larimer County, especially in the Crystal Mountain district. They have been reported to contain beryl, feldspar, spodumene, mica, columbite-tantalite, and uranium minerals (Hanley and others, 1950). However, production has been minor.