CALCITE Sm-Nd ISOCHRON AGE OF THE ERGADIJI LEAD-ZINC DEPOSIT IN WESTERN SICHUAN PROVINCE: Geological Implication

The Ergadiji medium-sized lead-zinc deposit is located on the junction of Sichuan, Yunnan, and Guizhou provinces, southwestern margin of Yangtze block. The orebody is mainly occurred in stratoid and lenticular forms in the dolomite of Sinian Dengying Formation, with the carbonaceous sand shale of Lower Cambrian Qiongzhusi Formation as the roof. The main metallic minerals are sphalerite and galena with the Zn grade of 5.30% and Pb grade of 3.25% averagely. The nonmetallic minerals are mainly calcite and quartz. The ores are in idiomorphic crystal, metasomatism-erosion and solid solution separation textures and veinlet-disseminated, massive and brecciated structures. The Pb-Zn mineralization of the deposit is closely related to silicification, bituminization and calcilization. Through the study on the Sm-Nd isotope system of 8 calcite samples associated with Pb-Zn ores in the metallogenic period, the results show ¹⁴⁷Nd/¹⁴⁴Nd is 0.058489-0.663246, ¹⁴³Nd/¹⁴⁴Nd 0.511852-0.512626, and the Sm-Nd isochron age of 203±6 Ma (MSWD=1.2), also representing the ore-forming age of the deposit. The Ergadiji Pb-Zn deposit is of typical Mississippi Valley type (MVT), with its mineralization closely related to the orogeny after the closure of Paleo-Tethys Ocean, rather than the magma activity of Mount Emei basalt.