We are upgrading the repository! A content freeze is in effect until November 22nd, 2024 - no new submissions will be accepted; however, all content already published will remain publicly available. Please reach out to repository@u.library.arizona.edu with your questions, or if you are a UA affiliate who needs to make content available soon. Note that any new user accounts created after September 22, 2024 will need to be recreated by the user in November after our migration is completed.
Geochemistry, mineralogy, and genesis of the Copperstone gold deposit, La Paz County, Arizona.
Author
Salem, Hanaa Mahmoud.Issue Date
1993Committee Chair
Guilbert, John M.
Metadata
Show full item recordPublisher
The University of Arizona.Rights
Copyright © 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.Abstract
Copperstone is a mid-Tertiary "detachment gold" deposit that is herein classified as a new subtype of epithermal deposit. Copperstone is similar to many active geothermal systems in terms of host lithology, temperature, and related siliceous alteration mineralogy, except in the hypogene oxide assemblages, the high salinity, and the lack of sulfides and the pathfinder toxic elements. The host rock is mainly Jurassic quartz latite porphyry and Tertiary sedimentary breccias. Early stages of alteration were K-metasomatic and propylitic, and alteration that accompanied gold mineralization was mainly chloritization and silicification. Mineralization is structurally controlled and is restricted along the Copperstone Listric Fault with minor mineralization along high-angle NE and NW faults, as with many other deposits in west-central Arizona. The gold stage of mineralization was superimposed on previously K-metasomatized rocks. Hypogene mineralization can be divided into 3 paragenetic stages: early amethyst-quartz-Fe-rich-chlorite-specularite-hematite-Au° of stage C; late-stage fine-grained euhedral quartz-adularia-chrysocolla ± malachite ± magnetite ± chalcopyrite-pink fluorite-barite-ankerite-calcite-Au° of stage D; and barren quartz-pale green fluorite-barite-calcite-hematite of stage E. Gold occurs as free particles or is encapsulated in amethyst and late fine-grained euhedral quartz. The time of mineralization is Miocene or younger and the depth of mineralization was 1 Km. Gold mineralization was related to boiling such that a hot spring system did operate at Copperstone. Copperstone is a hydrothermal system created during the last stages of detachment faulting, with mineralization controlled by boiling, and "second boiling" was the principal trigger of Copperstone gold deposition in an environment of falling temperatures and pressures on chloride-rich brine fluids. Variation in δ³⁴S indicates that two different fluids are involved in this system, and that a deeper, "lighter" hydrothermal fluid mixed with a "heavier" basin brine. δ¹⁸O values from carbonates confirm the extent of isotopic exchange with an aqueous reservoir and indicates that oxidation accompanied gold deposition.Type
textDissertation-Reproduction (electronic)
Degree Name
Ph.D.Degree Level
doctoralDegree Program
GeosciencesGraduate College