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" Environments of gold telluride mineralization in the Mahd adh Dhahab District, Arabian Shield "
A. M. Afifi
W. C. Kelly
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Latin Dissertation
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English
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| Record Number
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1112648
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TLpq303850030
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| Main Entry
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A. M. Afifi
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W. C. Kelly
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| Title & Author
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Environments of gold telluride mineralization in the Mahd adh Dhahab District, Arabian Shield\ A. M. AfifiW. C. Kelly
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| College
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University of Michigan
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| Date
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1990
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| student score
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1990
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| Degree
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Ph.D.
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| Page No
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299
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| Abstract
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The Mahd mine is a well preserved Late Proterozoic epithermal vein deposit of the chlorite-adularia type. The veins and wall rocks wee investigated by integrated geologic, petrologic, fluid inclusion, and COHS isotopic studies. The veins are hosted by bimodal basaltic and dacitic rhyolitic volcanic rocks that have been metamorphosed to spilitic and keratophyric compositions. The hydrothermal event followed folding and burial metamorphism of the volcanic wall rocks to the pumpellyite facies (250-350C, 1-3 kbar, XCO2 < 0.05), whereas post-vein metamorphism did not exceed the zeolite facies. Fluid inclusion and S-O isotopic thermometry indicate vein filling at 270-160C, and probably <0.5 kbar. The hydrothermal fluid was dilute (<5 wt.% NaCl) and its H-O isotopic composition (usd\delta\spusdO = 2 to 2 per mil, usd\deltausdD = 15 to 40 per mil) was probably derived from meteoric waters by exchange with the metavolcanic rocks. Magmatic fluid contributions are indicated by: (1) the usd\delta\sp{34}usdS values of sulfides (2 to 6 per mil); (2) the introduction of reduced H2Te- and Bi-rich fluids; and (3) potassic hydrothermal assemblages (sericite + pyrite or adularia + chlorite). The isotopic variations in the late barite (usd\delta\sp{34}usdS = 12 to 28 per mil; usd\delta\spusdO = 5 to 13 per mil) and calcite (usd\delta\spusdC = 7 to 5 per mil, usd\delta\spusdO = 8 to 13 per mil) reflect complex cooling and mixing mechanism at the wane of hydrothermal activity. The sulfidation and oxidation of chlorite in the hydrothermal system was evaluated using Al-conservative reactions involving chlorite, muscovite, pyrite, hematite, and K-feldspar. The evolution from sericite + pyrite to microcline + chlorite assemblages reflects progressive reaction of H2S- and K-rich hydrothermal fluid with the metavolcanic wall rocks and buffering of fS2 and fO2 by the pyritization of chlorite. Boiling is the most likely cause for ore deposition and for periodic oxidizing conditions that precipitated hematite. Thermodynamic data for tellurides were compiled and used to evaluate the fTe2, fS2, and fO2 conditions of telluride deposition in general. The Precambrian mineralization at the Mahd mine displays many of the characteristics of magma-driven meteoric dominated epithermal systems. Its preservation has clear implications to exploration in sub-greenschist facies terranes regardless of their age.
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Earth sciences
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Geology
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Geology
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Mineralogy
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