Phase relationships in the system zirconia-thoria

Abstract

In China, sediment-hosted Pb―Zn deposits represent a significant type of base-metal deposits are major sources of Pb and Zn and significant sources of Ag and Ge. In this paper, we focus discussion on MVT (Mississippi Valley type), SEDEX (sedimentary exhalative) and Jinding-type deposits because they constitute the major subtypes of sediment-hosted Pb―Zn deposits in China. For these deposits, which occur in a wide variety of carbonate and siliciclastic rocks having no obvious genetic association with igneous activity, we present an overview and re-evaluation with regard to: (1) nature, diversity, and geological settings, (2) spatio-temporal distributions, (3) structural controls on mineralization, (4) metallogenic process, and (5) C, O, S and Pb isotope geochemistry. Several of these deposits with known reserves are concentrated in eight main metallogenic belts. Available data from these deposits in China show the highest combined Zn and Pb reserves exist in the Qinling Mountains metallogenic belt, followed by the northern margin of the North China Craton (NCC), the Sanjiang fold belt, the Upper Yangtze River belt, the South China fold system, the Tianshan–Beishan Mountains belt, the Lower Yangtze River belt, and the Qilian Mountains belt. In these belts, the sediment-hosted Pb―Zn deposits have formed in a variety of tectonic settings representing a range of processes that have occurred within two billion years of earth history, but large-scale mineralizations have occurred notably in the Proterozoic, Late Paleozoic and Cenozoic. The Proterozoic era was important for the formation of SEDEX Pb―Zn deposits such as those in the interior and along the edges of the NCC and Yangtze Craton. The Guanmenshan is the only known MVT deposit formed within an intra-continental basin in the Proterozoic era. The Late Paleozoic was a productive period for MVT Pb―Zn deposits in China; in particular, there were significant MVT mineralizations during Devonian to Permian as a result of the amalgamation of the NCC and the South China Craton. The Cenozoic was a significant metallogenic era in China. For example, in the Sanjiang area during the Cenozoic, the Lanping Basin has evolved from a passive margin to open ocean basin and then has experienced ocean basin closure followed by the India–Asia collision and related tectonic activities including thrusting, and formation of strike–slip extensional basins, in which the Jinding-type deposits developed.