Massive sulfide deposits of the Wadi Bidah Mineral District, Saudi Arabia: Geologic control of mineralization; remote sensing and mineral exploration; geochemical exploration and petrogenesis

The Wadi Bidah Mineral District located in the Neoproterozoic (900–550 Ma) Arabian Shield of southwestern Saudi Arabia contains small, well-exposed, stratabound, volcanogenic massive sulfide deposits and associated zones of hydrothermal alteration. This dissertation combines new field data, orbital remote sensing data, and geochemical data to determine geologic controls on sulfide mineralization, how remote sensing data can be used for mineral exploration in arid environments, and how geochemical data, in particular the rare earth elements (REE), can be used as vectors in geochemical exploration. Field and remote sensing data were used to map lithologic units and mineral deposits, analyze and define regional structural trends, and establish geologic controls on sulfide mineralization. The sulfide deposits of the WBMD are found within a group of felsic volcaniclastics, which also hosts a marble unit. Based on the distribution of the sulfide deposits relative to the marble unit, all sulfide deposits appear to be stratabound. Structural control of mineralization appears to be limited to post-mineralization folding and shearing. Remote sensing data are used to create color composite images with combinations of bands and band ratios. Images are used to find, map and evaluate massive sulfide deposits. These deposits have a surface expression in the form of iron-rich caps (gossans) and zones of hydrothermal alteration, all having distinct spectral signatures. Optimum combinations of ASTER and Landsat ETM+ bands used for differentiating gossans and alteration zones from the host rock are 6-2-1 and 8-7-5 and optimum combinations of band ratios are 4/2-4/5-5/6 and 5/7-4/5-4/8, respectively. Geochemical analyses focus on the REE, because the presence of a large positive Eu anomaly (Eu/Eu* = 30.5) in the massive pyrite and corresponding positive Eu anomalies in gossans (average Eu/Eu* = 14.6) indicate that the REE are relatively immobile during supergene weathering and metamorphism. Hydrothermally altered schists in close proximity to the deposits also possess large positive Eu anomalies (average Eu/Eu* = 12.9), in contrast to the unaltered country rock (average Eu/Eu* = 1.08). Use of REE signatures of deposits, alteration zones, and country rocks provides a vector to mineralization, and has direct applications in the exploration for volcanogenic massive sulfide deposits.