St Peters dome district (Oligocene)

Region West, Rocky Mountains
Mineral systems
Deposit types
Critical minerals
Other minerals

Information leading to the delineation of this focus area

Basis for focus area Historical fluorite producer. Outline of study area drawn to enclose MRDS records with fluorite. A general interpretations is that some of the fluorite deposits are Oligocene (~ Cripple Creek age) and superimposed on Pike Peak granite that contains zones of fluorite, Be and/or zircon deposits. Alkalic porphyry potentially related to nearby Cripple Creek Au-Te deposit, hence the low sulfidation classification. Steven (1949) noted small amounts of Cu, Pb, and Zn sulfides, as well as reports of Ag and Au production (host ore, unknown). He suggests a similar paragenetic sequence to the Cripple Creek deposit, although it is not apparent that this hypothesis was ever tested further.
Identified resources Identified resources of fluorite; historical production of fluorite, minor gold and silver.
Production Approximately 16,100 tons of fluorite produced from the district in the 1940s (regardless of mineral system or deposit age).
Status Past mining.
Estimated resources 145,000 tons of approximately 35% CaF2 Indicated + Inferred resources. Other references indicate greater than 65,000 tons containing a minimum of 35% CaF2 (Brady, 1975).
Geologic maps Keller and others (2004), scale 1:24,000.
Geophysical data Inadequate Rank 5 aeromagnetic and Rank 3 aeroradiometric coverage.
Favorable rocks and structures Lamprophyre dikes (and associated fractures).
Deposits Cheyenne/St Peters Dome district (MRDS dep_id: 10013843), Duffields deposit, Timberline/Cather Springs.
Evidence from mineral occurrences MRDS.
Geochemical evidence Minor sphalerite associated with sulfide stage of mineralization (Steven, 1949).
Geophysical evidence A regional magnetic low with subtle circular patterns indicating more magnetic material corresponds to the Pikes Peak intrusion. The focus area is at the edge of the low. The patterns may be variations in petrology of the granite or younger intrusions. The possible association is intriguing, but needs follow up.
Evidence from other sources Unknown.
Comments Fluorite deposits are spatially associated with alkalic porphyries comparable to those from nearby Cripple Creek district (Steven, 1949; Wallace, 2010). However, the host Pikes Peak granite also contains cryolite and could potentially be a magmatic source for fluorite. Pikes Peak is an "A-type" granite, thus a Climax-type mineral system might be more suitable, depending on the actual age of fluorite mineralization. Possible occurrence of Bi, Ga, Ge, In and Te are inferred from the mineral system/deposit type table (Hofstra and Kreiner, 2020) .
Cover thickness and description Good exposure.
Authors Joshua M. Rosera, V.J.S. (Tien) Grauch, Michael K. O'Keeffe.
New data needs Geological mapping. Fluorite geochronology (for example, U/Pb laser ablation ages) can distinguish age of deposits (Proterozoic Climax-type fluorspar, or Oligocene alkalic porphyry similar to Cripple Creek?).
Geologic mapping and modeling needs Several quadrangles mapped at 1:24,000 scale including the Colorado Springs, Manitou Springs, and Cheyenne Mountain. Mount Big Chief quadrangle needs to be mapped at 1:24,000 scale. Pueblo West 1:250,000 scale map covers this area.
Geophysical survey and modeling needs New high resolution aeromagnetic and radiometric surveys would help delineate variations in petrology of the Pikes Peak granite. The magnetic data could help image petrologic variations or younger intrusions within the Pikes Peak granite where they are not exposed.
Digital elevation data needs Lidar is adequate.