A GIS investigation of regional geologic controls on mercury deposits in the southwest region of Arkansas.

摘要

The mercury district of southwest Arkansas, located within Clark, Pike, and Howard counties, contains 77 mapped mercury deposits, primarily in the form of cinnabar, found within the sandstones and shales of the Stanley and Jackfork Formations. The geographic locations of the majority of the deposits tend to form an east-northeast alignment in map view. Utilization of Geographic Information Systems (GIS) tools provided insight to the regional controls on the spatial distribution of the mercury deposits by examining the proposed relationships between mercury deposits and regional faults or changes in lithology, both of which have been suggested (Clardy and Bush, 1976) to explain the narrow band of permissive host rock for the deposits. GIS was used to determine which mode of deposition (structural features or lithologic changes) better explains the linear depositional pattern of mercuric minerals within the region by examining which potential control mechanism is closer to the deposit locations. The goal was accomplished by mapping the regional thrust faults and changes in lithology at an appropriate scale. Lithologic units were mapped using decision tree learning methods and a methodology, developed by Belt and Paxton (2005), dependant on topographic attributes unique to each rock type. A composite map of the changes in lithology, regional thrust faulting, and the deposits themselves were used to determine which of the suggested relationships exerts more control on the placement of the deposits by being physically closer. Investigation revealed that the faulting is the most controlling feature, on average, and that a regional variation in controlling mechanism exists. Within regions dominated by sandstone, contacts are the more controlling feature. Within shale dominated regions, the faults are the prevailing control feature.