Nature and origin of early and late cherts in the Leadville Limestone, Colorado

Bulletin of the Geological Society of America
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Abstract

Two generations of chert have been observed in the Mississippian Leadville Limestone of west-central Colorado: (1) an early chert inferred to have precipitated from hypersaline marine waters of high pH after those waters seeped into carbonate muds prior to final burial and lithification of the carbonate; and (2) a late chert that appears to have precipitated from ground waters as amorphous silica after initial lithification but prior to or during karst erosion of the formation in Late Mississippian (?) and Early Pennsylvanian time. A third type of microcrystalline quartz, hydrothermal jasperoid, is associated with ore deposits of Laramide age in the Leadville, but it is not discussed here.

Conditions in west-central Colorado at the time that the early cherts formed in the Leadville were probably similar to those associated with the formation of early diagenetic chert in modern sediments, and the early chert in the Leadville is believed to have formed in a manner similar to the modern early cherts.

The silica of the late chert appears to have come from Paleozoic sandstones below the Leadville. It was carried by slightly acid artesian waters into the formation, probably in concentrations of less than 60 ppm SiO2 Super-saturation of amorphous silica occurred within the Leadville and probably was obtained by evaporative concentration at the water-air interface during dry seasons. Dissolution of the limestone by the slightly acid waters may account for the removal of the calcite that is replaced by chert.

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Publication type Article
Publication Subtype Journal Article
Title Nature and origin of early and late cherts in the Leadville Limestone, Colorado
Series title Bulletin of the Geological Society of America
DOI 10.1130/0016-7606(1970)81[3033:NAOOEA]2.0.CO;2
Volume 81
Issue 10
Year Published 1970
Language English
Publisher Geological Society of America
Description 16 p.
First page 3033
Last page 3048
Country United States
State Colorado
City Leadville
Other Geospatial Sawatch Range, White River
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