Ground-Based Hyperspectral Imaging at Various Scales



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Detailed mineral mapping at millimeter to centimeter scales can be useful for geological investigations, including sedimentologic and petrologic analysis, resource exploration, and other applications. This work presents case studies of close-range ground-based hyperspectral imaging from centimeter to sub-millimeter scales using sensors operating in the visible near infrared and short wave infrared spectral ranges. In a sedimentological study, ground-based hyperspectral imaging was combined with terrestrial laser scanning to produce mineralogical maps of Late Albian rudist buildups of the Edwards formation in Williamson County, Texas. The Edwards Formation consists of shallow water deposits of reef and associated interreef facies. Hyperspectral data were registered to a laser point cloud-generated mesh with sub-pixel accuracy and were used to map compositional variation by distinguishing spectral properties unique to each material. Calcitic flat-topped toucasid-rich bioherm facies were distinguished from overlying porous sucrosic dolostones, and peloid wackestones and packstones of back-reef facies. Ground truth was established by petrographic study of samples from the area. This research integrated high-resolution datasets to analyze geometric and compositional properties of this carbonate formation at a finer scale than traditional methods and modeled the geometry and composition of rudist buildups. Three case studies of economic deposits in active and abandoned mines are presented. Vertical exposures in a Carlin-style sediment-hosted gold deposit, an active Cu-Au-Mo mine, and an active asphalt quarry were studied to produce images that delineate mineral alteration at centimeter scale, to demonstrate a method of outcrop characterization that increases understanding of petrogenesis for mining applications. In the Carlin-style gold deposit, clay, iron oxide, carbonate, and jarosite minerals were mapped. In the copper porphyry deposit, different phases of alteration, some of which correspond to greater occurrence of ore deposits, were classified. A limestone quarry that contains bitumen deposits used for road paving aggregate was also imaged. Sub-millimeter scale laboratory imaging spectroscopy was applied to evaluate a sample suite of diagenetically altered limestones, sulfide-rich quartz veins, and eclogite. These samples were selected due to the availability of geochemical or petrographic data for mineralogical abundances to be compared to hyperspectral imaging results. Different classification techniques were evaluated for accuracy against ground truth data.



Hyperspectral imaging, Mineral mapping, Outcrop studies


Portions of this document appear in: Krupnik, Diana, Shuhab Khan, Unal Okyay, Preston Hartzell, and Hua-Wei Zhou. "Study of Upper Albian rudist buildups in the Edwards Formation using ground-based hyperspectral imaging and terrestrial laser scanning." Sedimentary geology 345 (2016): 154-167. And in: Krupnik, Diana, and Shuhab Khan. "Close-range, ground-based hyperspectral imaging for mining applications at various scales: Review and case studies." Earth-Science Reviews (2019): 102952.