Two fluid systems in the Lanping basin, Yunnan, China — Their interaction and implications for mineralization Chunji Xue a, ⁎ , Guoxiang Chi b , Yuchuan Chen c , Denghong Wang c , Hairuo Qing b a State Key Lab. of Geological Processes and Mineral Resources, China University of Geosciences, Xueyuan Raod, Beijing 100083, China b Department of Geology, University of Regina, 3737 Wascana Parkway, Regina, Saskatchewan, Canada S4S 0A2 c Institute of Mineral Resources, Chinese Academy of Geological Sciences, Beijing, 100037, China Received 7 September 2005; accepted 23 November 2005 Available online 20 March 2006 Abstract The Lanping basin in SW China is a Late Triassic to Eocene basin filled with terrestrial sediments. The basin is located between the Tibet–Yunnan and Yangtze plates, controlled by deep-seated faults, and contains a number of metallic deposits, including the world-class Jinding Zn–Pb deposit. Based on fluid inclusion and noble gases, Pb, and S isotope data, we proposes that there were two fluid systems operating in the basin: one was derived from the mantle, characterized by high CO 2 content and relatively low salinities, and the other was from within the basin, having relatively high salinities and low temperature. The former was probably a major carrier of metals, whereas the latter provided reduced sulfur through reduction of sulfates. The formation of major base metal deposits requires geologic conditions that favor interaction of the two fluid systems, which lead to precipitation of sulfides in a localized volume. © 2006 Elsevier B.V. All rights reserved. Keywords: Lanping basin; Jinding; Mantle fluids; Mixing 1. Introduction The Lanping basin in western Yunnan, SW China (Fig. 1) has drawn much attention because of its tectonic location between the Tibet–Yunnan and Yangtze plates and because it hosts several important mineral deposits (Xue et al., 2004). These include the world's largest sandstone-hosted Zn–Pb deposit (Jinding) and several Cu ± Ag ± Co deposits (Baiyangping, Baiyangchang and Jinman) (Fig. 1). The genesis of the Jinding deposit has been a subject of lively debate since the 1980s. Some authors think that the hydrothermal fluids, metals and sulfur were derived from the basin (Kyle and Li, 2002), whereas others propose that mantle sources for some components were important (Xue et al., 2000). This paper documents evidence for the mantle and crust fluid systems in the Lanping basin, and proposes that mixing of the two fluid systems is the key process in forming mineral deposits in the basin. 2. Geologic setting The Lanping basin is the northern part of the Lanping–Simao basin (Fig. 1), which developed on the Changdu–Simao microplate between the Yangtze plate to the east and the Tibet–Yunnan plate to the west. The basin is filled with Late Triassic to Eocene sedi- ments dominated by terrestrial siliciclastic deposits with several evaporitic intervals. Regional faults that trend Journal of Geochemical Exploration 89 (2006) 436 – 439 www.elsevier.com/locate/jgeoexp ⁎ Corresponding author. E-mail address: chunjix@chd.edu.cn (C. Xue). 0375-6742/$ - see front matter © 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.gexplo.2005.11.027