Geochemical tracing of ore-forming material sources of Carlin-type gold deposits in the Yunnan-Guizhou-Guangxi triangle area - A case study of the application of the combined silicon isotopes geochemistry and siliceous cathodoluminescence analysis

This paper deals with characteristics of silicon isotope compositions and siliceous cathodoluminescence of host rocks, ores and hydrothermal silicified quartz of the Carlin-type ore deposits in the Yunnan-Guizhou-Guangxi triangle area. The study shows that primary silicified quartz is nonluminescent but quartz in host rocks and secondary silicified quartz are luminescent by the action of cathode rays. Correspondingly, silicon isotope compositions of host rocks, ores and hydrothermal quartz veins are clearly distinguished. In strata from the Middle Triassic to the "Dachang" host bed, delta(30)Si of the host rocks ranges from 0.0 parts per thousand-0.3 parts per thousand, while that of primary ore-forming silicified fluids from -0.1 parts per thousand to -0.4 parts per thousand; in the Upper Permian and Lower Carboniferous strata and Indosinian diabase host beds, delta(30)Si of the host rocks is from -0.1 parts per thousand to -0.2 parts per thousand and that of the primary silicified quartz veins from 0.3 parts per thousand-0.5 parts per thousand. This pattern demonstrates the following geochemical mineralization process: primary ore-forming siliceous fluids migrated upwards quickly along the main passages of deep-seated faults from mantle to crust and entered secondary faults where gold deposits were eventually formed as a result of permeation and replacement of the siliceous ore-forming fluids into different ore-bearing strata. This gives important evidence for the fact that ore-forming fluids of this type of gold deposits were mainly derived from upper mantle differentiation and shows good prospects for deep gold deposits and geochemical background for large and superlarge gold deposits.