New isotopic evidence bearing on bonanza (Au-Ag) epithermal ore-forming processes

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• 作者：James A. Saunders ; Ryan Mathur ; George D. Kamenov ; Toru Shimizu…
• 关键词：Epithermal ores ; Copper isotopes ; Sulfur isotopes ; Lead isotopes ; Magmatic source ; Nanoparticles
• 刊名：Mineralium Deposita
• 出版年：2016
• 出版时间：January 2016
• 年：2016
• 卷：51
• 期：1
• 页码：1-11
• 全文大小：1,173 KB
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• 作者单位：James A. Saunders (1)
  Ryan Mathur (2)
  George D. Kamenov (3)
  Toru Shimizu (4)
  Matthew E. Brueseke (5)
  
  1. Department of Geosciences, 210 Petrie Hall, Auburn University, Auburn, AL, 36849, USA
  2. Department of Geology, Juniata College, 1700 Moore Street, Huntingdon, PA, 16652, USA
  3. Department of Geological Sciences, University of Florida, 241 Williamson Hall, P.O. Box 112120, Gainesville, FL, 32611, USA
  4. Magma-hydrothermal deposits Research Group, Geological Survey of Japan, AIST, 1-1-1 Higashi, Tsukuba, 305-8567, Japan
  5. Department of Geology, Kansas State University, Manhattan, KS, 66506, USA
  
• 刊物类别：Earth and Environmental Science
• 刊物主题：Earth sciences
  Geology
  Mineral Resources
  Mineralogy
  
• 出版者：Springer Berlin / Heidelberg
• ISSN：1432-1866

文摘

New Cu, S, and Pb isotope data provide evidence for a magmatic source of metal(loid)s and sulfur in epithermal Au-Ag deposits even though their ore-forming solutions are composed primarily of heated meteoric (ground) waters. The apparent isotopic discrepancy between ore metals and ore-forming solutions, and even between the ore and associated gangue minerals, indicates two different sources of epithermal ore-forming constituents: (1) a shallow geothermal system that not only provides the bulk of water for the ore-forming solutions but also major chemical constituents leached from host rocks (silica, aluminum, potassium, sodium, calcium) to make gangue minerals and (2) metals and metalloids (As, Te, Sb, etc.) and sulfur (±Se) derived from deeper magma bodies. Isotopic data are consistent with either vapor-phase transport of metal(loids) and sulfur and their subsequent absorption by shallow geothermal waters or formation of metallic (Au, Ag, Cu phases) nanoparticles at depth from magmatic fluids prior to encountering the geothermal system. The latter is most consistent with ore textures that indicate physical transport and aggregation of nanoparticles were significant ore-forming processes. The recognition that epithermal Au-Ag ores form in tectonic settings that produce magmas capable of releasing metal-rich fluids necessary to form these deposits can refine exploration strategies that previously often have focused on locating fossil geothermal systems.