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Halogen-rich scapolite-biotite rocks from the Tongmugou Pb-Zn deposit, Qinling, northwestern China: implications for the ore-forming processes

Published online by Cambridge University Press:  05 July 2018

Shao-Yong Jiang ,
M. R. Palmer ,
Chun-Ji Xue  and
Yan-He Li
Shao-Yong Jiang
Affiliation:
Department of Geology, University of Bristol, Bristol, BS8 1 RJ, U.K.
M. R. Palmer
Affiliation:
Department of Geology, University of Bristol, Bristol, BS8 1 RJ, U.K.
Chun-Ji Xue
Affiliation:
Xi’an College of Geology, Xi’an, 710054, China
Yan-He Li
Affiliation:
Institute of Mineral Deposits, Beijing, 100037, China
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Abstract

Coexisting scapolite, biotite and hornblende in scapolite-biotite rocks from the Tongmugou Pb-Zn deposit, Qinling, northwestern China are characterized by high levels of chlorine. Scapolite composition varies from EqAn27 to EqAn47 with 47–80 wt.% Cl. The scapolite composition is a sensitive indicator of the NaCl activity in coexisting hydrothermal fluid. Biotite contains 0.3–1.2 wt. % Cl and also has high F contents (0.2–0.7 wt.%). The hornblende is a Cl-rich hastingsite with Cl>3.5 wt.% and high (Na2O + K2O) contents (3.2–3.9 wt. %), high Xk [= K/(K + Na)] values (0.45–0.55) and high XFc [= Fe/(Fe + Mg)] values (0.76–0.79). The chlorine within these minerals is thought to be derived from evolved seawater. The scapolite-biotite rocks are products of Cl-rich alteration of volcanoclastic sedimentary rocks during submarine hydrothermal processes. Multiple-stage hydrothermal activity culminated with the circulation of a high-NaCl fluid that was also responsible for the formation of the massive sulphide deposits.

Keywords

halogensscapolite-biotite rockhydrothermal fluidsChinaPb-Zn deposits
Type
Petrology and Geochemistry
Information
Mineralogical Magazine , Volume 58 , Issue 393 , December 1994 , pp. 543 - 552
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 1994

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