Abstract:

Heqing manganese deposit is located in the southwestern margin of Yangtze platform in Yunnan Province, China. Carbon and oxygen isotopes indicate that Songgui Formation which is the main ore bearing stratum experienced one transgression and another long-term regression. The paleotemperature derived from oxygen isotopes are higher due to the exchange of oxygen isotope between biological (algae) metabolites and seawater, changes in paleoclimate and sea depth. The paleosalinity show normal marine sediments and there are good correlation between the paleosalinity and the value of δ¹³C. δ¹⁸O values from cores are higher mainly owing to the variation of paleosalinity, which are good correlation with δ¹³C value. With the sea level falling, the possibility of buried organic was decreased, which led to negative values of δ¹³C. Through a comprehensive analysis of carbon and oxygen isotopes, it is concluded that the depositional environment was at least a semi-enclosed shallow or near continental basin. With uplifting of Yangze platform continuously and climate changing from humid, hot into arid gradually, the manganese ores were formed accompanied by falls in sea level.

Key words: manganese deposit, Songgui Formation, carbon and oxygen isotope, Heqing, Yunnan