Pb isotopic features of the Lala IOCG ore deposit on the southwestern margin of the YangtzeBlock and their significance

Pb isotope data available concerning the ore sulfides and host rocks from the Lala IOCG ore deposit on the southwestern margin of the Yangtze Block are data of radiogenic anomalous Pb. Generalized global growth curves and multistage evolution models are not applicable to interpret their features. In this study, the data were reinterpreted according to the Pb isotopic evolution principle. Two independent Pb growth curves were built for the biotite schist and albite granulite based on the corrected Pb isotope composition of host rocks, which provide a new reference for the evolution of Pb isotope in the Proterozoic rocks on the southwestern margin of the Yangtze Block. All the Pb isotope compositions of ore sulfides plotted on or between the two curves form two distinctive linear clusters. The lower cluster yielded an age of 1605Ma，which represents the chalcopyrite and pyrite mineralization during the volcanic eruption-sedimentation stage, whereas the upper cluster yielded an age of 1119Ma, which represents the metamorphic mineralization stage. The age of the upper cluster and that of the lower cluster are consistent with the molybdnite Re-Os isochron age and zircon U-Pb age of volcanic rocks respectively, which suggests that the method of Pb isotopic dating is feasible and reliable. Biotite schist and albite granulite are metal fundamental reservoirs of the Lala IOCG ore deposit. The metal materials of ore sulfides are characterized by a mixed source.