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dc.contributor.advisorMonecke, Thomas
dc.contributor.authorQuigley, Ashley Kaye
dc.contributor.committeememberHitzman, Murray Walter
dc.contributor.committeememberKelly, Nigel
dc.contributor.committeememberAnderson, Eric D.
dc.date.accessioned2016-05-24T22:45:54Z
dc.date.available2016-05-24T22:45:54Z
dc.date.issued2016
dc.descriptionIncludes bibliographical references.
dc.description2016 Spring.
dc.description.abstractThe Paleoproterozoic (ca. 1875 Ma) Penokean volcanic belt represents one of the world’s most significant orogens hosting volcanogenic massive sulfide (VMS) deposits. Sporadic exploration from 1970-1995 has identified a large number of VMS deposits and prospects throughout the belt, including the world-class Crandon deposit that comprises an estimated 61 million tonnes of polymetallic massive sulfide ore. Despite successful exploration and the significant economic potential in the Penokean volcanic belt, only limited academic research has been conducted focusing on constraining the tectonic, structural, and volcanic setting of the VMS deposits. Many key aspects of the regional geology are not well understood, which is in part due to extensive glacial cover of the Paleoproterozoic bedrocks. As part of the present study, aeromagnetic and gravity data were used to study the geological make-up of the Penokean volcanic belt. The data were integrated with existing mapping to constrain the bedrock geology under the glacial cover. Interpretation of the geophysical data showed that several distinct geological domains could be distinguished. Whole-rock major and trace element geochemical data were used to identify magmatic affinities of volcanic rocks within the geophysically defined domains. The results of the geochemical analyses reveal subtle differences between the geophysical domains. The majority of the volcanic rocks sampled have a tholeiitic affinity with fewer calc alkaline and transitional rocks. The geochemical evidence suggests that volcanism was arc-related, with the massive sulfide deposits being presumably formed in zones of intra-arc or back-arc extension. High-precision chemical abrasion ID-TIMS U-Pb dating was performed on zircon grains separated from felsic volcanic samples collected from the host rock successions of some of the major VMS deposits and prospects within the Penokean volcanic belt. Results of the geochronological investigations showed that four of the deposits, namely Bend, Horseshoe, Lynne, and Pelican River, were all formed at about 1874 Ma. This suggests that several of the deposits of the Penokean volcanic belt formed during a major, but short-lived, period of rapid extension. The Back Forty massive sulfide deposit, located at the east end of the Penokean volcanic belt, is hosted by rhyolite that yielded an apparent age of about 1833 Ma. This is approximately 50 million years younger than the host rock successions of the other deposits of the belt. There are two possible explanations for this apparent age. The first explanation is that this represents a crystallization age and the host rocks to the Back Forty are part of a distinctly younger volcanic succession. Alternatively, a thermal event at 1833 Ma may have reset the U-Pb isotopic system. A crystallization age at around 1833 Ma is potentially consistent with an age recorded for a felsic volcanic rock from the Mountain area to the southwest. The rhyolite sampled from the host rock successions of the Lynne and Back Forty deposits were found to contain rare Archean-aged zircon grains. These zircon grains yielded U-Pb ages of approximately 2700 Ma and are presumably inherited from an Archean basement. The existence of inherited ages supports the model that volcanism of the Pembine-Wausau terrane occurred, at least in part, on older Archean basement.
dc.format.mediumborn digital
dc.format.mediummasters theses
dc.identifierT 8031
dc.identifier.urihttp://hdl.handle.net/11124/170152
dc.languageEnglish
dc.publisherColorado School of Mines. Arthur Lakes Library
dc.relation.ispartof2016 - Mines Theses & Dissertations
dc.rightsCopyright of the original work is retained by the author.
dc.subjectmassive
dc.subjectPaleoproterozoic
dc.subjectPenokean
dc.subjectsulfide
dc.subjectU-Pb
dc.subjectVMS
dc.titleSetting of volcanogenic massive sulfide deposits in the Penokean volcanic belt, Great Lakes region, USA
dc.typeText
thesis.degree.disciplineGeology and Geological Engineering
thesis.degree.grantorColorado School of Mines
thesis.degree.levelMasters
thesis.degree.nameMaster of Science (M.S.)


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