Alkaline Rocks and Carbonatites of the World

Setup during HiTech AlkCarb: an online database of alkaline rock and carbonatite occurrences

South Park

stripes

Occurrence number: 
174-00-081
Country: 
United States
Region: 
Colorado
Location: 
Longitude: -105.78, Latitude: 39.08
Carbonatite: 
No

In the central part of the South Park basin in central Colorado lamprophyric intrusions outcrop as a dyke and a sill-like body about 1.6 km long. Eleven other intrusions of similar type and up to 16 m thick were encountered in a nearby oil well. In the sill a chilled border facies grades into a zone, up to 24 m thick, of a mafic rock of biotite phenocrysts in a groundmass of labradorite, alkali feldspar, olivine, aegirine-augite, analcime and other zeolites. This passes into a central felsic zone 17 m thick of analcime syenite of alkali feldspar, a little albite, biotite, aegirine-augite, 23% analcime, and a little thomsonite and natrolite. Modes, chemical analyses and discussion of the petrogenesis of these multiple intrusions will be found in Jahns (1938) and Stark et al. (1949).

References: 

JAHNS, R.H. 1938. Analcite-bearing intrusives from South Park, Colorado. American Journal of Science, 36: 8-26.
STARK, J.T., JOHNSON, J.H., BEHRE, C.H., POWERS, W.E., HOWLAND, A.L., GOULD, D.B. and others. 1949. Geology and origin of South Park, Colorado. Memoir, Geological Society of America, 33: 1-188

Scratchpads developed and conceived by (alphabetical): Ed Baker, Katherine Bouton Alice Heaton Dimitris Koureas, Laurence Livermore, Dave Roberts, Simon Rycroft, Ben Scott, Vince Smith