stripes
Occurrence number:
174-00-034
Country:
United States
Region:
Montana
Location:
Longitude: -109.67, Latitude: 47.17
Carbonatite:
No
The North Moccasin Mountains were formed by doming concentric to a single large laccolithic intrusion, while the South Moccasin Mountains were uplifted by a cluster of stocks, laccoliths and sills. The principal igneous rock type in the north, and comprising about half of the southern igneous suite, is a porphyritic syenite with phenocrysts of sanidine, andesine, hornblende, aegirine-augite, quartz, biotite and magnetite with a little sphene, apatite and zircon. Quartz monzonites and other types of syenite are present but are not peralkaline.
Economic:
Gold was formerly mined in the area. There is scattered gold mineralization and a possible potential for exploitation of Mo and Cu in breccia pipes.
Age:
K-Ar determinations on sanidine gave 64.1 ±1.5 and 65.8 ±1.6 Ma and four fission-track determinations on sphene, zircon and apatite 62.1 ±6.6 to 70.9 ±9.0 Ma (Lindsey, 1982).
References:
LINDSEY, D.A. 1982. Geologic map and discussion of selected mineral resources of the North and South Moccasin Mountains, Fergus County, Montana. United States Geological Survey, Map I-1362
Map:
Fig. 1_135 North (left) and South Moccasin Mountains (after Lindsey, 1982, Map I-1362).
Location: