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Alteration Geochemistry, Fluid Inclusion, and Stable Isotope Study of The

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Alteration Geochemistry, Fluid Inclusion, and Stable Isotope Study of The AN ABSTRACT OF THE THESIS OF Richard H. Fifarek for the degree ofDoctor 0f Philosophy in Geology presentedon May 8, 1985. Title: Alteration Geochemistry,Fluid Inclusion, and Stable Isotope Study of the Red Ledge VolcanogenicMassive Sulfide Deposit, Idaho Redacted for privacy Abstract approved: Cyrus W. Field The Red Ledge Zn-Cu-Ag deposit is hostedby island arc volcanic and sedimentary rocks correlativewith the Lower Permian Hunsaker Creek Formation of the Seven DevilsGroup. Mineralization is gene- tically related to a dacite-rhyodacite domalcomplex, and consists of a stockwork feeder system and an overlying strata-boundcap of stacked stringer and massive sulfidelenses (3-4 couplets). Footwall alteration assemblages grade outwardfrom silicified vein selvages through zones of sericite and sericite-chioriteto a propylitic halo. Altered host rocks have been variablyenriched in Si02, Fe203, MgO, 18o K2O, and and consistently depleted in FeO, CaO, and Na20. l8o Average values of felsic rocks in the propylitic,phyllic and silicified alterationzones are 9.6, 10.6, and 12.2 permil, respec- tively. Homogenization temperatures of primary-appearingvapor- liquid inclusions in vein mineralsaverage 274 °C. Calculated values of the feeder vein fluidsvary from 00/00during early amethyst deposition, to 4-5.5 0/00during intermediate quartz-sulfide deposition, and finally to 0-1 during late barite-carbonate deposition. This paragenetic trend is consistent withisotopic exchange between convecting seawaterand volcanic rocks at reasonable temperatures and integrated water to rock ratioswith respect to the water (w/r): early fluids at 250 °C and moderate w/r, interme- diate fluids at 400-450 °C and loww/r (deep in the volcanic pile), and late fluids at 250-290 °C andmoderate w/r. Average values of sulfides and barite decrease upwardfrom vein (-2.8 & 15.2 0/00 0/ resp.), through stringer (-5.1& 14.5 resp.), to massive (-5.1 & 12.7 0/00) mineralization. These isotopic shifts are consistent with the progressive addition of Permianseawater (0 °C, cS34S = 10.5 0/00) to the rising intermediate fluids (275 °C, t34S= 12-230/00) Small additions (10% seawater)resulted in equilibrium cooling to 240 °C and a sympathetic decreasein sulfide and barite S34S values. Additional mixing resulted in rionequilibriumcooling and a further decrease in barite values. The isotopic variablilty of vein carbonates (3C = -10.8 to -0.8 0/00& l8o= 9.1 to 20.10/00)and vein sulfates (634S= 13.6-19.00/00& l8o= 7.8-10.5 °/oo) suggest that seawater also mixed with latefluids up to +1000 feet below the seafloor. Hydrothermal carbon was leached from thecountry rocks, whereas hydrothermal sulfur, bothin the Red Ledge and analagous deposits of the western Cordillera,was largely derived from seawater via an intermediate step involvingthe inorganic reduction of sea- water sulfate. © 1985 RICHARD H. FIFAREK All Rights Reserved Alteration Geochemistry Fluid Inclusions and Stable Isotope Study of the Red Ledge Volcanogenic Massive Sulfide Deposits Idaho by Richard H. Fifarek A THESIS submitted to Oregon State University in partial fulfillment of the requirements for the degree of Doctor of Philosophy Completed May 8, 1985 Commencement June 1985 APPROVED: Redacted for privacy ssor ot (eoroy in c1(arge of fajor Redacted for privacy of Departmeny,äf Geology Redacted for privacy Dean of GraduatSchoo Date thesis is presented May 8, 1985 Typed by researcher for Richard H. Fifarek ACKNOWLEDGEMENTS Financial support for this investigationwas provided by grants from the ASARCO Foundationand Texasguif, Inc. and through temporary employment with the Branch of CentralMineral Resources, U. S. Geological Survey. Major and minor element analyseswere furnished by the Branch of Marine Geology,U. S. Geological Survey. For arranging this monetary support, I wouldlike to thank Cyrus W. Field of Oregon State University,Richard B. Taylor, Charles H. Thorman, and Tracy L. Valuer ofthe U. S. G. S., and Allan P. Juhas formerly of Texasguif, Inc. Michael L. Cummings of Portland State Univeritykindly allowed the use of a petrographic microscope. Sample material and unpublished geologicdata on the Red Ledge deposit were provided by Texasguif, Inc.and Roney C. Long. Most of the samples and data on othervolcanogenic massive sulfide deposits in the western Cordillerawere released to the author by Conoco, Inc. Two samples from the Lynx Minewere supplied by Arthur E. SoregaroU of Westmin Resources Ltd., andone sample from the Keating District and unpublished geologic dataon the Blue Jacket were contributed by Ronald Willden of J. L. CarrollMineral Exploration. The generous assistance of these companies andindividuals is gratefully acknowledged. I would like to sincerely thankRobert 0. Rye for the opportu- nity to utilize the isotopic andfluid inclusion facilities at the Branch of Isotope Geology, U. S. C.S. (Denver, Co.) and for his guidance during the initial phaseof this study. Moreover, I would like to express my gratitudeto Joseph F. Whelan, Mark A. Huebner, and Michael Wasserman for theirpatience and amiability during many training sessions in various laboratorytechniques. Generous and warm hospitality were extended to the author and hisfamily while in Denver by Robert 0. Rye, Joseph F.Whelan, Gary P. Landis, and Roberta H. Dixon and their respectivefamilies. The concepts expressed in thisinvestigation greatly benefited fromdiscussions with Cyrus W. Field,Robert 0. Rye and Ronald G. Senechal (Oregon State Wiiversity). Editorial comments from Cyrus W. Field and Ronald G. Senechalwere most welcome. Finally, I am deeply grateful forthe encouragement and support provided by my wife,Katheryn, and by myfamily throughout graduate school. Table of Contents Page Introduction.................................................. 1 Regional Geologic Setting..................................... Li. Blue Mountains Province................................... 7 Hells Canyon Inlier...................................... 10 Geology of the Red Ledge Deposit............................... 14 Stratigraphic Units...................................... 15 Intrusions............................................... 20 GeologicEnvironment..................................... 22 Hydrothermal Alteration....................................... 24 Petrography.............................................. 26 Major Element Chemistry.................................. 31 Minor and Trace Element Chemistry........................ 42 Protolith Compositions ........................................ 44 Mineralization................................................ 48 Geology and Mineralogy.................................... 48 Mineral Paragenesis...................................... 55 Metal Grades and Variations.............................. 61 Metamorphism.................................................. 64 FluidInclusions.............................................. 66 Petrography.............................................. 66 Thermometric Properties.................................. 69 Hydrogen Isotopic Composition of Inclusion Fluids ........ 72 Discussion of Results.................................... 73 Stable Isotope Geochemistry . 76 Analytical Procedures..................................... 76 Sulfides and Sulfates ..................................... 79 Simple Equilibrium Cooling........................... 86 Mixing of Seawater and HydrothermalFluids........... 91 Isotopic Equilibria .................................. 100 Sulfides and Sulfates from SimilarDeposits.......... 108 Source of Hydrothermal Sulfur........................ 122 Carbonates ................................................ 125 Models of Isotopic Variations........................ 130 Source of Hydrothermal Carbon........................ 136 Silicates and Whole Rocks ................................. 137 Hydrothermal Fluids.................................. 142 Whole Rocks .......................................... 147 Origin of Fluid and RockCompositions................ 152 Genetic Model .................................................. 165 Conclusions.................................................... 171 References Cited ................................................ 175 List of Tables Table Page 1. Mineralogy, Alteration Assemblages and Textures 32 of Analyzed HostRocks, Red Ledge Deposit, Idaho. 2. Major, Minor andTrace Element Composition of Host 33 Rocks, Red LedgeDeposit, Idaho. 3. Average ChemicalComposition of Selected Volcanic 36 Rocks. 4. Petrography and HomogenizationTemperatures of 68 Fluid Inclusions in Vein Minerals. 5. Hydrogen Isotopic Composition ofInclusion Fluids 73 in Vein Quartz. 6. Isotopic Composition of Sulfidesand Sulfates. 80 7. End Member Fluids and EquationsUtilized in Model 92 Calculations of Seawater-Hydrothermal FluidMixing. 8. Sulfur Isotopic Temperatures. 102 9. Sulfur Isotopic Data for SelectedVolcanogenic 113 Massive Sulfide Deposits in theWestern Cordillera. 10. Isotopic Composition of Carbonates,Red Ledge 126 Deposit, Idaho, and Hells Canyon,Oregon-Idaho. 11. Oxygen Isotopic Composition ofQuartz. 138 12. Oxygen and Hydrogen IsotopicComposition of Phyllo- 142 silicates. 13. Isotopic Composition of the HydrothermalFluids 143 Responsible for the Red Ledge Mineralizationand Alteration. 14. Oxygen Isotopic Composition ofSamples of Whole Rock 148 and Phenocryst Phases. 15. Parameters Utilized in Calculatingthe Isotopic 155 Evolution of Convecting Seawater. List of Figures Figure Page 1. Location of the Red Ledge deposit. 2. Geology of
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