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- Genre: Masters Thesis
- Member of: Theses and Dissertations
- Resource Type: Text
Description
Growth of the Phoenix metropolitan area led to exposures of the internal bedrock structure of surrounding semi-arid mountain ranges as housing platforms or road cuts. Such exposures in the Sonoran and Mojave deserts reveal the presence of sedimentary calcium carbonate infilling the pre-existing fracture matrix of the bedrock. Field surveys of bedrock fractures filled with carbonate (BFFC) reveal an average of 0.079 +/- 0.024 mT C/m2 stored in the upper 2 m of analyzed bedrock exposures. Back-scattered electron microscopy images indicate the presence of carbonate at the micron scale, not included in this estimation. Analysis of the spatial extent of bedrock landforms in arid and semi-arid regions worldwide suggests that ~1485 GtC could potentially be stored in the upper 2 m horizon of BFFCs. Radiocarbon dating obtained at one of the sites indicates it is likely that some of the carbonate was flushed into the bedrock system during glacial wet pulses, and is stored on Pleistocene timescales or longer. Strontium isotope analysis at the same site suggest the potential for a substantial cation contribution from weathering of the local bedrock, indicating the potential exists for sequestration of atmospheric carbon in BFFCs. Rates of carbon release from BFFCs are tied to rates of erosion of bedrock ranges in desert climates.
ContributorsHarrison, Emma (Author) / Dorn, Ronald (Thesis advisor) / Reynolds, Stephen (Committee member) / Schmeeckle, Mark (Committee member) / Arizona State University (Publisher)
Created2013
Description
The Kinsley Mountain gold deposit of northeastern Nevada, located ~70 km south of Wendover, Nevada, contains seven sediment-hosted, disseminated-gold deposits, in Cambrian limestones and shales. Mining ceased in 1999, with 138,000 ounces of gold mined at an average grade between 1.5-2.0 g/t. Resource estimates vary between 15,000 and 150,000 ounces of gold remaining in several mineralized pods. Although exploration programs have been completed within the study area, the structural history and timing of precious-metal mineralization are still poorly understood. This study aims to better understand the relation between stratigraphy, structural setting, and style of gold mineralization. In order to accomplish these goals, geological mapping at a scale of 1:5,000 was conducted over the property as well as analysis of soil and rock chip samples for multi-element geochemistry. Using cross-cutting relationships, the structural history of Kinsley Mountain has been determined. The deformation can broadly be categorized as an early stage of compressional tectonics including folding, attenuation of the stratigraphy, and thrust faulting. This early stage was followed by a series of extensional deformation events, the youngest of which is an ongoing process. The structural history determined from this study fits well into a regional context and when viewed in conjunction with the mineralization event, can be used to bracket the timing of gold mineralization. The northwest oriented structure responsible for concentrating decalcification, silicification, and mineralization has two generations of cave fill breccias that both pre- and post-date the gold event. The statistical analysis of multi-element geochemistry for rock chip and soil samples has determined that Au is most strongly associated with Te, while weaker correlations exist between Au and Ag, As, Hg, Mo, Sb, Tl, and W. This suite of elements is associated with an intrusion driven system and is atypical of Carlin-type gold systems. From these elemental associations the gold mineralization event is thought to be controlled by the emplacement of a felsic intrusion. The responsible intrusion may be an exposed quartz monzonite to the south of the study area, as suggested by possible zonation of Cu, Pb, and Zn, which decrease in concentration with increasing distance from the outcropping stock. Alternatively, an unexposed intrusion at depth cannot be ruled out as the driver of the mineralizing system.
ContributorsMacFarlane, Bryan (Author) / Reynolds, Stephen (Thesis advisor) / Hervig, Richard (Committee member) / Burt, Donald (Committee member) / Arizona State University (Publisher)
Created2012
Description
This combined research provides in-depth insights into both the tectonic evolution of the Bradshaw Mountain region in Arizona and the effective use of Structure-from-Motion (SfM) photogrammetry in remote geological education. The first study focuses on deciphering paleostress fields in the Bradshaw Mountains region, which helps unravel Earth's past tectonic activities and lithospheric evolution. By examining fractures in plutonic stocks, ranging in age from 73 to 64 million years, crucial insights into the area's tectonic history were obtained. Fracture properties such as size, frequency, orientation, and location were diligently recorded. Further examination in a regional context revealed a complex stress regime during the Laramide orogeny, underpinned by diverse fracture and aplite dike orientations. The findings hint at potential influences of stress reversal during Laramide pluton emplacement and crystallization on regional principal stress, which deviated from previous regional tectonic studies. Factors like crustal dilation, local uplift, tensile stress cycle, and topographic stress could explain the lack of predicted mineralized orientations. The implications of these findings are vital for reconstructing Laramide tectonic and magmatic activities in the region, although further research is required to fully understand the causative mechanisms.
The second study centers on the use of SfM photogrammetry in geological education, with a focus on remote learning environments. This involves creating 3D models of hand samples and outcrops with exceptional resolution for detail recognition. Detailed guidance on hardware and software specifications, image capture conditions, file management, and 3D model creation using Metashape is provided. The study emphasizes the dual-masking technique for optimum texture quality and the role of SketchFab in the analysis and viewing of the final product. This integration of SfM photogrammetry into geological education supplements traditional hands-on learning and enhances students' grasp of geological concepts. The technique provides an immersive, interactive experience, especially beneficial for students unable to physically access geological samples, and fosters critical thinking through a hands-on digital interface.
ContributorsHurst, Joseph Gregory (Author) / Reynolds, Stephen (Thesis advisor) / Semken, Steven (Committee member) / Johnson, Julia (Committee member) / Arizona State University (Publisher)
Created2023