In situ LA-(MC)-ICP-MS trace element and Nd isotopic compositions and genesis of polygenetic titanite from the Baogutu reduced porphyry Cu deposit,Western Junggar,NW China |
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| Institution: | 1. Key Laboratory of Mineral Resources, Institute of Geology and Geophysics, Chinese Academy of Sciences, P.O. Box 9825, Beijing 100029, China;2. John de Laeter Center for Isotope Research, Department of Applied Geology, Curtin University, Perth, WA 6845, Australia;3. University of Chinese Academy of Sciences, Beijing 100049, China;1. Key Laboratory of Mineral Resources, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029, China;2. College of Earth Science, University of Chinese Academy of Sciences, Beijing 100049, China;3. State Key Laboratory of Lithospheric Evolution, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029, China;1. School of Earth and Environmental Sciences, Queens College, City University of New York, 6530 Kissena Blvd., Flushing, NY 11367, USA;2. Department of Earth & Planetary Sciences, American Museum of Natural History, New York, NY 10024, USA;3. Department of Geosciences, Pennsylvania State University, 332 Deike Bldg., University Park, PA 16802, USA;1. Instituto de Astronomia, Geofísica e Ciências Atmosféricas, Universidade de São Paulo, Rua do Matão, 1226, CEP 05508-090 São Paulo, SP, Brazil;2. Instituto de Geociências, Universidade de São Paulo, Rua do Lago, 562, CEP 05508-080 São Paulo, SP, Brazil;3. Department of Geology, The University of Kansas, 1420 Naismith Drive, Slawson Hall, Lawrence, KS 66045, USA |
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| Abstract: | Titanite (sphene, CaTiSiO5) is sensitive to changes in temperature, oxygen and water fugacity, and fluid composition. In order to understand formation processes and the nature of hydrothermal fluids, various types of titanite from Cu ores at the Baogutu reduced porphyry Cu deposit were chosen for detailed study. Magmatic titanite is associated with biotite, plagioclase and K-feldspar, whereas hydrothermal titanite occurs with K-feldspar, chlorite, actinolite and calcite. The formation of hydrothermal titanite was related to hydration of igneous minerals under high fH2O, whereas the widespread replacement of ilmenite by titanite (without magnetite) indicates a relatively low oxygen fugacity. Magmatic titanite has low Al, high Fe, Y, Sn, Zr, Nb and REE contents, relative to hydrothermal titanite. On the basis of the Zr-in-titanite and Al-in-chlorite geothermometers, formation temperatures for magmatic and hydrothermal titanite are estimated to be 687–739 °C and 250–670 °C, respectively. The gradual decrease in REE, Y and Sn contents from magmatic to late hydrothermal titanite was probably caused by precipitation of REE-bearing minerals. Magmatic and hydrothermal titanites have similar chondrite-normalized REE patterns with negative Eu anomalies and relatively flat HREE. Randomly selected titanites have Nd isotopic compositions similar to the host rocks. Thus, both magmatic and hydrothermal titanite are believed to have been predominantly derived from a mantle source. |
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