Persistent Link:
http://hdl.handle.net/10150/289837
Title:
Origin and redistribution of metals in sedimentary rocks
Author:
Chernoff, Carlotta
Issue Date:
2002
Publisher:
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:
Integrated analysis of whole-rock and mineral geochemical data from black shale and metamorphosed black shale demonstrates the importance of sulfides as trace-element hosts and reveals the influence of depositional environment on whole-rock and mineral chemistries. Detailed analysis of Fe-sulfide contents provides evidence of considerable elemental redistribution during diagenesis and metamorphism, indicating that such sulfides plausibly serve as a source of metals and other elements to epigenetic fluids. Spatial and temporal analysis of the distribution of Phanerozoic black shale, phosphorite, and ironstone suggests a related geologic origin coupled to marine upwelling. Organic-rich sedimentary rocks from diverse geologic settings in China, Canada, US Great Basin, and US Mid-Continent were studied along with regionally metamorphosed black shale (Maine) and contact metamorphosed carbonaceous argillite (Nevada). Assessment of whole-rock geochemistry in these samples was supplemented with analysis of a large geochemical database compiled from published sources. Both the studied sample suite and literature database reveal systematic elemental enrichments and depletions that can be related to depositional environment. Regionally metamorphosed black shale demonstrates trace-element loss with metamorphism (Au, As, and Sb), an observation that fits well with models proposing black-shale-derived mineralizing fluids. Compositional and textural features of sedimentary and metamorphic sulfides were investigated utilizing petrographic and in situ analysis methods. Concentrations of As, Se, Ni, Co, Cu, Zn, V, Cr, and Mo in sulfides were acquired by electron microprobe. Au, Pt, and sulfur isotope contents were measured in Fe-sulfide by SIMS. Fe-sulfide data demonstrate a complex history of pyrite growth due to diagenetic, metamorphic and hydrothermal processes. Sulfur isotopes reflect bacterially mediated growth of framboidal pyrite and redistribution of this sulfur with advanced diagenesis and metamorphism. Early framboidal pyrites are enriched in many trace metals. Later diagenetic and metamorphic pyrites are typically lower in trace metal content and demonstrate recrystallization to coarser crystals. Comparison of trace elements in framboidal and coarse overgrowth pyrites shows systematic elemental changes (losses: Au, Pt, Ni, Cu, Zn, V and Cr; gains: Se; variable: As and Mo). This pattern is found in many black shales, regardless of bulk chemistry or depositional environment. Metamorphic replacement of pyrite by pyrrhotite results in similar losses from the sulfide fraction of the rock. Mass balance of the whole-rock trace inventory indicates that Fe-sulfide is an important host for As, Se, Ni, Co, and Au. These mass balance results, combined with evidence of trace element redistribution during diagenesis and metamorphism, point to a possible sourcing of metals, sulfur and other elements from black shale.
Type:
text; Dissertation-Reproduction (electronic)
Keywords:
Geology.
Degree Name:
Ph.D.
Degree Level:
doctoral
Degree Program:
Graduate College; Geosciences
Degree Grantor:
University of Arizona
Advisor:
Barton, Mark D.

Full metadata record

DC FieldValue Language
dc.language.isoen_USen_US
dc.titleOrigin and redistribution of metals in sedimentary rocksen_US
dc.creatorChernoff, Carlottaen_US
dc.contributor.authorChernoff, Carlottaen_US
dc.date.issued2002en_US
dc.publisherThe University of Arizona.en_US
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_US
dc.description.abstractIntegrated analysis of whole-rock and mineral geochemical data from black shale and metamorphosed black shale demonstrates the importance of sulfides as trace-element hosts and reveals the influence of depositional environment on whole-rock and mineral chemistries. Detailed analysis of Fe-sulfide contents provides evidence of considerable elemental redistribution during diagenesis and metamorphism, indicating that such sulfides plausibly serve as a source of metals and other elements to epigenetic fluids. Spatial and temporal analysis of the distribution of Phanerozoic black shale, phosphorite, and ironstone suggests a related geologic origin coupled to marine upwelling. Organic-rich sedimentary rocks from diverse geologic settings in China, Canada, US Great Basin, and US Mid-Continent were studied along with regionally metamorphosed black shale (Maine) and contact metamorphosed carbonaceous argillite (Nevada). Assessment of whole-rock geochemistry in these samples was supplemented with analysis of a large geochemical database compiled from published sources. Both the studied sample suite and literature database reveal systematic elemental enrichments and depletions that can be related to depositional environment. Regionally metamorphosed black shale demonstrates trace-element loss with metamorphism (Au, As, and Sb), an observation that fits well with models proposing black-shale-derived mineralizing fluids. Compositional and textural features of sedimentary and metamorphic sulfides were investigated utilizing petrographic and in situ analysis methods. Concentrations of As, Se, Ni, Co, Cu, Zn, V, Cr, and Mo in sulfides were acquired by electron microprobe. Au, Pt, and sulfur isotope contents were measured in Fe-sulfide by SIMS. Fe-sulfide data demonstrate a complex history of pyrite growth due to diagenetic, metamorphic and hydrothermal processes. Sulfur isotopes reflect bacterially mediated growth of framboidal pyrite and redistribution of this sulfur with advanced diagenesis and metamorphism. Early framboidal pyrites are enriched in many trace metals. Later diagenetic and metamorphic pyrites are typically lower in trace metal content and demonstrate recrystallization to coarser crystals. Comparison of trace elements in framboidal and coarse overgrowth pyrites shows systematic elemental changes (losses: Au, Pt, Ni, Cu, Zn, V and Cr; gains: Se; variable: As and Mo). This pattern is found in many black shales, regardless of bulk chemistry or depositional environment. Metamorphic replacement of pyrite by pyrrhotite results in similar losses from the sulfide fraction of the rock. Mass balance of the whole-rock trace inventory indicates that Fe-sulfide is an important host for As, Se, Ni, Co, and Au. These mass balance results, combined with evidence of trace element redistribution during diagenesis and metamorphism, point to a possible sourcing of metals, sulfur and other elements from black shale.en_US
dc.typetexten_US
dc.typeDissertation-Reproduction (electronic)en_US
dc.subjectGeology.en_US
thesis.degree.namePh.D.en_US
thesis.degree.leveldoctoralen_US
thesis.degree.disciplineGraduate Collegeen_US
thesis.degree.disciplineGeosciencesen_US
thesis.degree.grantorUniversity of Arizonaen_US
dc.contributor.advisorBarton, Mark D.en_US
dc.identifier.proquest3061012en_US
dc.identifier.bibrecord.b43042594en_US
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