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dc.contributor.authorRauschkolb, Michael Howard
dc.creatorRauschkolb, Michael Howarden
dc.date.accessioned2015-06-18T11:09:48Zen
dc.date.available2015-06-18T11:09:48Zen
dc.date.issued1983en
dc.identifier.urihttp://hdl.handle.net/10150/557950en
dc.description.abstractThe Northwest orebody, located in Pima County, Arizona, is a large tonnage skarn containing copper, silver, and molybdenum mineralization. The orebody is separated from the main orebodies of the Twin Buttes mine by the Twin Buttes fault. Sulfide mineralization and silicate alteration are systematically zoned along a westerly trend away from the fault and from a central intrusive complex. Original host rock chemistry was the major control on the silicate and sulfide mineralogy of the skarns. The highest grade ore occurs in a garnet-diopside alteration zone within beds of altered limestone and dolomite. Lower grade ores formed in cal-silicated siltstones, quartzites, and granitic rocks. The skarns exhibit a complex history of sequential veining and replacement. The alteration can be subdivided into an early thermal event, followed by three stages of hydrothermal alteration. The first stage of hydrothermal alteration is characterized by the formation of anhydrous Ca-Mg-Fe-Al silicates, predominantly garnet and diopside. Stage II is a period of sulfide mineralization. The copper sulfides were deposited when copper in the hydrothermal solutions reacted with Fe⁺⁺⁺₋ rich garnet to form chalcopyrite. Mineralization continued during Stage III as increasingly pyritic sulfide mineralization was deposited with hydrous silicate minerals, predominantly epidote and actinolite. Several points of evidence show that the mineralization in the Northwest orebody is related to the intrusive activity at the center of the Twin Buttes mine area and not to either the pre-mineral Ruby Star Granodiorite or to a buried intrusive at depth.
dc.language.isoen_USen
dc.publisherThe University of Arizona.en
dc.rightsCopyright © is held by the author. Digital access to this material is made possible by the University Libraries, University of Arizona. Further transmission, reproduction or presentation (such as public display or performance) of protected items is prohibited except with permission of the author.en
dc.subjectGeology -- Arizona -- Pima County.en
dc.subjectGeology -- Arizona -- Twin Buttes Mine.en
dc.titleThe geology of the Northwest orebody, Twin Buttes Mine, Pima County, Arizonaen
dc.typetexten
dc.typeThesis-Reproduction (electronic)en
dc.identifier.oclc10874952en
dc.identifier.oclc10874940en
thesis.degree.grantorUniversity of Arizonaen
thesis.degree.levelmastersen
thesis.degree.disciplineGeosciencesen
thesis.degree.disciplineGraduate Collegeen
thesis.degree.nameM.S.en
dc.description.noteThis item was digitized from a paper original and/or a microfilm copy. If you need higher-resolution images for any content in this item, please contact us at repository@u.library.arizona.edu.en
dc.identifier.bibrecord.b1457522xen
dc.identifier.bibrecord.b14575218en
dc.identifier.callnumberE9791 1983 152en
refterms.dateFOA2018-05-25T20:10:02Z
html.description.abstractThe Northwest orebody, located in Pima County, Arizona, is a large tonnage skarn containing copper, silver, and molybdenum mineralization. The orebody is separated from the main orebodies of the Twin Buttes mine by the Twin Buttes fault. Sulfide mineralization and silicate alteration are systematically zoned along a westerly trend away from the fault and from a central intrusive complex. Original host rock chemistry was the major control on the silicate and sulfide mineralogy of the skarns. The highest grade ore occurs in a garnet-diopside alteration zone within beds of altered limestone and dolomite. Lower grade ores formed in cal-silicated siltstones, quartzites, and granitic rocks. The skarns exhibit a complex history of sequential veining and replacement. The alteration can be subdivided into an early thermal event, followed by three stages of hydrothermal alteration. The first stage of hydrothermal alteration is characterized by the formation of anhydrous Ca-Mg-Fe-Al silicates, predominantly garnet and diopside. Stage II is a period of sulfide mineralization. The copper sulfides were deposited when copper in the hydrothermal solutions reacted with Fe⁺⁺⁺₋ rich garnet to form chalcopyrite. Mineralization continued during Stage III as increasingly pyritic sulfide mineralization was deposited with hydrous silicate minerals, predominantly epidote and actinolite. Several points of evidence show that the mineralization in the Northwest orebody is related to the intrusive activity at the center of the Twin Buttes mine area and not to either the pre-mineral Ruby Star Granodiorite or to a buried intrusive at depth.


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