Late-stage Precambrian granites in the St. Francois Mountains are among the most uraniferous in North America. The St. Francois province has potential for uranium mineralization of economic importance, especially in the later differentiates.

Structural lineaments and circular features displayed on images produced by electronic data processing of Landsat multispectral scanner data may be related to late-stage intrusives with uranium potential. Strong north-south lineaments and associated circular and arcuate features may correspond to major weaknesses in the earth’s crust along which fracturing, faulting, and volcanism have occurred. The strike of the lineaments transects the older dominant northwest-southeast and northeast-southwest structural grain of the region. This, and the remarkable preservation of Precambrian structures of volcanic origin, indicate that the lineaments may be related to late-stage, uranium- and thorium-rich intrusives. The Ironton lineament, a major north-south lineament, is closely related spatially to Precambrian iron and manganese deposits.

Field work along the Ironton lineament suggests that it is related to a late period of Precambrian volcanism and that structural deformation along the lineament continued into early Paleozoic time. Areas of faulting, shearing, and hydrothermal alteration affecting both Precambrian and Paleozoic rocks have been located. A circular feature along the lineament has been found to be centered by a manganese deposit of possible hydrothermal origin.

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