0361-0128/07/3676/739-5 739 Introduction The Jinding Zn-Pb deposit in western Yunnan, China (Fig. 1), with a reserve of approximately 220 million tons (Mt) of ore grading 6.1 percent Zn and 1.3 percnet Pb (Third Geological Team, 1984), is one of the largest Zn-Pb deposits in the world. Hosted in coarse siliciclastic strata of Early Cretaceous and Paleocene ages and having no direct relationship with magmatism, the deposit is generally con- sidered as one formed from basinal fluids and has been compared to Mississippi Valley-type, sandstone-type, and sedimentary exhalative-type (SEDEX) deposits (Qin and Zhu, 1991; Li, 1998; Kyle and Li, 2002). Two contrasting genetic models have been proposed for the deposit (i.e., syngenetic or SEDEX-type by Wang et al., 1992, and epige- netic by Qin and Zhu, 1991, Li, 1998, Kyle and Li, 2002, and Xue et al., 2007). Regardless of the genetic model, it was generally agreed that the ore-forming fluids ascended along a major subvertical fault, which exerted a first-order control on the mineralization. However, little attention has been paid to the hydrodynamic nature of the hydrothermal system. Most studies assumed that the basinal fluid flow was in a hydrostatic regime (e.g., Sun and Xu, 1989; Qin and Zhu, 1991; Xu and Li, 2003), whereas we have previously SCIENTIFIC COMMUNICATIONS SAND INJECTION AND LIQUEFACTION STRUCTURES IN THE JINDING Zn-Pb DEPOSIT, YUNNAN, CHINA: INDICATORS OF AN OVERPRESSURED FLUID SYSTEM AND IMPLICATIONS FOR MINERALIZATION GUOXIANG CHI, † Department of Geology, University of Regina, 3737 Wascana Parkway, Regina, Saskatchewan, Canada S4S 0A2 CHUNJI XUE, Faculty of Earth Sciences and Resources, China University of Geosciences, Beijing 100083, China JIANQING LAI, Department of Geology, University of Regina, Canada, and School of Geoscience and Environmental Engineering, Central South University, Changsha, Hunan, China 410083 AND HAIRUO QING Department of Geology, University of Regina, 3737 Wascana Parkway, Regina, Saskatchewan, Canada S4S 0A2 Abstract The Jinding deposit is a large Zn-Pb deposit hosted in coarse siliciclastic strata of Early Cretaceous and Paleocene ages in the Lanping-Simao basin, western Yunnan, China. The deposit, characterized by fine- grained sphalerite and galena disseminated in sandstones of the Cretaceous Jingxing Formation (K1j) and sand- stones and limestone breccias of the Paleocene Yunlong Formation (E1y), was generally considered as one formed from basinal fluids passively controlled by sedimentary lithofacies and structures. This paper reports sand injection and liquefaction structures occurring as millimeter- to centimeter-wide mineralized sand veins and irregular bodies of light-colored sandstones cutting red-colored sedimentary rocks, and relates them to episodic release of overpressured fluids. The proposed model for the flow of ore-forming fluids differs from previous models in that the fluid flow did not passively follow preexisting pore space and was actively creating new porosity and permeability in the conduits. This implies that the development and distribution of fluid over- pressures in the basin may have exerted a control on mineralization, in addition to lithofacies and structures, and the sand injection and liquefaction structures as described in this paper may be used as indicators of favorable conditions for mineralization. † Corresponding author: e-mail, guoxiang.chi@uregina.ca ©2007 Society of Economic Geologists, Inc. Economic Geology, v. 102, pp. 739–743 Beijing N siliciclastics siliciclastics siliciclastics siliciclastics J J-K diorite -K E T E syenite E T Thrusts 2-3 3 limestone volcanics & sediments 2 1 1 2-3 Kunming map area Lanping-Simao Basin China Jinding N Lancangjiang Fault Pijiang Fault Jinshajiang Fault 5 km Qiaohou Fault 99 30'E o 26 40' o 26 20' o FIG. 1. Geologic map of part of the Lanping basin showing the location of the Jinding Zn-Pb deposit in western Yunnan, China (after Kyle and Li, 2002).