Paleoproterozoic magnesite and borate deposits from eastern Liaoning Province: with a discussion about synchrono-heteropic facies of sedimentary mineralization
HU GuYue;LI YanHe;FAN ChangFu;ZHAO Yue;HOU KeJun;WANG TianHui;MRL Key Laboratory of Metallogeny and Mineral Assessment, Institute of Mineral Resource, Chinese Academy of Geological Sciences;Civil and Environmental Engineering School, University of Science and Technology Beijing;
A large number of Paleoproterozoic magnesite and borate deposits hosted in the strata of volcanic-sedimentary sequence of Liaohe Group in eastern Liaoning province serve as significant sources of magnesium and boron in China. An integrated major and rare earth element, stable isotope( C and S) and LA-MC-ICP-MS zircon U-Pb dating study was carried out for these two types of nonmetallic ore deposits in combination with other data available. The results show that: 1 the values of δ34SV-CDTof marbles and ores in magnesite deposits range from 15. 6‰ to26. 5‰, while the values of δ34SV-CDTand δ11B of marbles and ores in borate deposits range from 11. 6‰ to24. 3‰, and from 8. 8‰ to 13. 9‰, respectively, suggesting a marine evaporation genesis. 2 the values of δ34SV-CDTof pyrites in magnesite and borate deposits range from 16. 0‰ to 20. 7‰ and from 12. 3‰ to 13. 2‰, respectively, implying a marine evaporate reductive genesis; 3 the values of δ13CV-PDBof magnesite range from 0. 6‰ to1. 3‰, while values of relatively fresh marbles in borate deposits range from- 1. 5‰ to 4. 6‰, which records marine evaporation related positive δ13CV-PDBexcursion of Lomagundi event; 4 the B content and PAAS-normalized REE patterns of magnesite and borate deposits are similar; and 5 the CL images and U-Pb results of zircons in leptynite and leptite located outside the magnesite and borate deposit are similar, with a peak magmatic peak age of2. 2 Ga. Therefore, the magnesite deposits and the borate deposits, which are located on the northern slope and in central depression, respectively, are synchrono-heteropic facies of evaporative mineralization formed in a rhythmic environment of evaporation and volcanic-sedimentation at about 2. 2 Ga.