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Abstract

Geochemical studies of Leadville Formation dolomites provide information about the solutions from which they formed. Seven dolomite types can be grouped into six geochemical types on the basis of trace element contents and oxygen isotopes. Medium and coarse crystalline dolomite are indistinguishable on the basis of either trace element or oxygen isotope contents. Low trace element abundances and slightly negative δ18OPDB values are snggestive of diagenesis in solutions containing a significant meteoric component.

Fine crystalline dolomite formed penecontemporaneously with deposition and contains heavier oxygen than either medium or coarse crystalline dolomite or undolomitized Leadville Limestone. The oxygen isotope data supports dolomitization of fine crystalline dolomite by evaporatively concentrated sea water followed by stabilization by meteoric water.

Two varieties of zebra spar dolomite precipitated into cavities formed during karst dissolution. Trace element abundances and 18O composition of earlier formed “cloudy zebra spar” are similar to those of medium and coarse crystalline dolomite and suggest that this dolomite formed as cement during karst solution erosion. Later formed “clear zebra spar” contains lighter oxygen and higher Fe and other trace elements, and fluid inclusions in it indicate precipitation above 130°C from evolved brines. This dolomite is interpreted to have formed from sedimeutary brine fluids after burial by Pennsylvanian sediments. Baroque dolomite occurring as cement in karst breccia bodies contains very light oxygen (δ18OPDB = —20%) and is high in Fe, Mn, and base metals. This dolomite is intimately associated with sphalerite and galena in some ore deposits and formed by recrystallization of detrital dolomite sand in karst breccias during ore deposition.

Paleomagnetic studies reveal a well-defined late Paleozoic remanence in most dolomite types spatially removed from Laramide-Tertiary igneous activity. The remanences are carried in magnetite of possible diagenetic origin. Preservation of these remanences suggests that these rocks have not undergone significant aquatic alteration since late Paleozoic time.

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