A predictive exploration model for MVT Pb-Zn mineralization in Central Texas : insights from the Southeast Missouri Lead District




Williams, Nathan D.

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Minor Pb-Zn occurrences on the flanks of the Llano Uplift in Central Texas have many geologic similarities to the world-class Mississippi Valley Type (MVT) deposits of Southeast Missouri. In both areas, metallic sulfides are hosted in dolomitized Cambrian carbonates, commonly in areas where local basement highs forced depositional pinch-outs of the basal sandstones. In Southeast Missouri, mineralization has been attributed to basinal fluid migration associated with late Paleozoic Ouachita deformation and appears to be spatially related to regional faults that may have served as fluid conduits. In Central Texas, there is also evidence that mineralization is associated with basinal fluids tied to Ouachita deformation and abundant regional faults serve as plausible fluid pathways. Moreover, Southeast Missouri and Central Texas are distinctly rich in Pb, an atypical characteristic for MVT deposits that are usually Zn dominant. These similarities suggest that an understanding of spatial associations between sites of known mineralization and regional geology, geochemistry, and geophysics in Southeast Missouri will be a useful guide in future exploration efforts in Central Texas.

The weights-of-evidence approach is used to evaluate regional geology, geochemistry, and geophysical datasets and produce posterior probability maps for MVT deposits in Southeast Missouri. Host rock characteristics, stream sediment geochemistry, and proximity to basement highs are some of the most useful data for predicting these deposits. Model parameters derived from Southeast Missouri are applied to the Llano Uplift region of Central Texas. Although available data sets for Central Texas are less detailed than Southeast Missouri, the Central Texas models generally agree with areas known to contain MVT mineralization. A higher resolution basement structure map for Central Texas would be useful for more detailed analysis. Central Texas model results are compared with semi-quantitative geochemical data from insoluble residues from wells throughout the Llano region and indicate that the model may be useful in explaining the measured Pb concentrations in these wells. Several new permissive areas to the south and southwest of the Precambrian core of the Llano Uplift are identified that may warrant additional follow up investigation. This work illustrates the potential utility of mineral potential modeling to prioritize areas for exploration for undiscovered MVT mineralization in Central Texas.


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