Sedimentary Environments of Late Cretaceous Ore-bearing Sequences at the Guihua Copper Ore Field in the Northern Chuxiong Basin, Yunnan Province, SW China

Key words: 
• sedimentary facies /
• paleogeography /
• sedimentary source /
• Late Cretaceous /
• Guihua copper orefield /
• Chuxiong Basin

Abstract: The Late Mesozoic Chuxiong Basin is located at the intersection of the western margin of the Yangtze platform and the Sanjiang orogenic belt in Yunnan province, SW China. Abundant strata-bound copper deposits and occurrences within multiple Cretaceous sandstones or mudstones have attracted considerable interest since the late 1970s. A significant amount of care was previously paid to the ore genesis of the sandstone-hosted copper deposits, but sedimentary environments and sources of their host rocks were overlooked, which seriously affects our understanding of their tectonic setting and ore-forming mechanism. Systematic geological surveying, tunnels, and drillhole logging demonstrate that the Upper Cretaceous Matoushan and Jiangdihe Formations were deposited in a braided river channel and marginal bank subfacies environment with a relatively dry climate. Detrital fragments of sandstone, conglomerate composition, and paleocurrent data demonstrate that the Chuxiong Basin developed in a southward facing paleogeography with a mixed source consisting of northern source rocks and basement uplift during the Late Cretaceous. Vast basic volcanics, granitoids, clastic rocks, carbonates, and minor metamorphic rocks should be exposed at the northern source area. The Upper Cretaceous Jiangdihe Formation also experienced the uplift and collapse events caused by syn-sedimentary compressional tectonics, and the sandstone-and mudstone-hosted copper mineralization was coeval with the growing tectonic events during the syn-sedimentation processes of the Late Cretaceous Jiangdihe Formation. This is a vital controlling factor of the major copper transport and deposition of the Guihua ore field in the Chuxiong Basin.