Metamorphic fluid superimposition of the Changba–Lijiagou Pb–Zn deposit, West Qinling Orogen, central China
Published:April 17, 2019
Pei Ni, Tian-Gang Wang, Guo-Guang Wang, Wen-Sheng Li, Jun-Yi Pan, 2019. "Metamorphic fluid superimposition of the Changba–Lijiagou Pb–Zn deposit, West Qinling Orogen, central China", Metamorphic Geology: Microscale to Mountain Belts, Silvio Ferrero, Pierre Lanari, Philippe Goncalves, Eugene G. Grosch
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Several large to giant Pb–Zn deposits in the West Qinling Orogen in central China are argued to be of SEDEX (sedimentary exhalative) type or of epigenetic hydrothermal type. Additionally, the nature of the mineralizing fluids is poorly known. Our observations suggest that early stage primary marine sedimentary mineralization is characterized by laminated or disseminated fine-grained massive sulphide ores, and late stage metamorphic superimposition is represented by coarser equigranular annealed textures and the disruption of thinly laminated structures. Three coexisting types of fluid inclusions were recognized: H2O–NaCl (type I); H2O–NaCl–CH4–CO2 (type II); and CH4–CO2 (type III). The coexisting type I and II inclusions show similar homogenization temperature values but different salinities, indicating that fluid immiscibility occurred. Formation pressures calculated using type III inclusions are high (72.5–174.5 MPa). The lead isotopes of the sulphides and calcites show a narrow range. The primary sedimentary ore textures plus the similar lead isotopes between the ores and the wall rocks suggest a SEDEX origin, but the annealed recrystallization textures, the immiscible carbonic fluid inclusion assemblages and higher formation pressures suggest a strong late-stage metamorphic superimposition on the original SEDEX-type ores.
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Metamorphic Geology: Microscale to Mountain Belts
CONTAINS OPEN ACCESS
In Earth evolution, mountain belts are the loci of crustal growth, reworking and recycling. These crustal-scale processes are unravelled through microscale investigations of textures and mineral assemblages of metamorphic rocks. Multiple episodes of metamorphism, re-equilibration and deformation, however, generally produce a complex and tightly interwoven pattern of microstructures and assemblages. Over the last two decades, the combination of advanced computing and technological capabilities with new concepts has provided a vast array of novel petrological tools and high-resolution/high-sensitivity techniques for microanalysis and imaging. Such novel approaches are proving fundamental to untangling the enigma represented by metamorphism with an unprecedented level of detail and confidence. As a result, the first decade and a half of this century has already seen the tumultuous development of new research avenues in metamorphic petrology. This book aims to provide a timely overview of the state of the art of this field, of newly developed petrological techniques, future advancements and significant new case studies.