Reconnaissance geology, geophysics, and geochemistry of the southeastern part of the Lewis and Clark Range, Montana [report]

1968 unpublished
Weak lead-zinc mineralization was general in a narrow northwest-trending belt about 30 miles long in the southeastern part of the Lewis and Clark Range, Mont. Reconnaissance geological and geochemical studies identify the belt and indicate the stratigraphic and structural control of the mineralization; geophysical data permit inferences of the location of buried plutons that may have been the source of the metals. The mineralization appears to be spatially related to the South Fork thrust zone.
more » ... h Fork thrust zone. This zone, containing Precambrian and Paleozoic rocks, is part of the easternmost major thrust block in this range. In this zone, anomalous quantities of lead and zinc occur in the Spokane Formation and Helena Dolomite of Precambrian age, the Flathead Sandstone of Cambrian age, and the Jefferson and Three Forks Formations of Devonian age. Most of the mineralization is in the nearest permeable and porous carbonate or calcareous sandstone bed to the westernmost thrust fault of the South Fork thrust zone. Magnetic and gravity data were used in denning the area for geological and geochemical studies of the many major magnetic anomalies that indicate buried plutons. One large positive anomaly, in particular, that lies just west of the center of the belt may have a genetic relationship to the lead and zinc mineralization. This mass is interpreted to be a quartz monzonite pluton lying just below the westwarddipping South Fork thrust at a calculated depth of about 10,500 feet beneath the surface.
doi:10.3133/b1252e fatcat:wybh5vxvlrggdcn6papfmddjxi