Chemical compositions of tourmaline in the Yindongzi-Tongmugou Pb-Zn deposits,Qinling, China: Implications for hydrothermal ore-forming processes |
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| Authors: | S -Y Jiang M R Palmer Y -H Li C -J Xue |
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| Institution: | (1) Department of Geology, University of Bristol, BS8 1RJ Bristol, UK;(2) Institute of Mineral Deposits, 100037 Beijing, China;(3) Xi'an College of Geology, 710054 Xi'an, China |
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| Abstract: | A microprobe study has been carried out on the chemical composition of tourmaline from the Yindongzi and Tongmugou stratabound Pb-Zn ore deposits, eastern Qinling, China. Tourmaline was analysed from a variety of rock types representative of its various occurrences associated with the ore bodies. All the tourmalines studied here belong to the schorl-dravite series. Most are of hydrothermal origin with Mg > Fe and Na > Ca. Some detrital cores of tourmaline have been recognized from their geometry and chemistry, with Fe > Mg. The chemical trends from core to rim in zoned grains suggest a multi-stage model for the growth of tourmaline and genesis of the ore bodies. The first stage was represented by a more Mg-rich hydrothermal fluid in the submarine hydrothermal system, producing Mg-rich tourmalines by selective replacement of clay-rich sediments close to the sediment-water interface. The second stage was dominated by Fe-rich hydrothermal fluid and resulted in overgrowth of Fe-rich tourmaline rims. This stage also led to the nucleation and growth of new tourmaline crystals and was responsible for the formation of the main massive sulphide orebodies. Finally, a further period of hydrothermal activity or a metamorphic event led to the formation of an additional rim of Mg-rich tourmaline. |
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