Tectonic Evolution And Metallogenic System In Lanping Basin,Yunnan Province, China

Located in the central part of Sanjiang Tethys Orogenic Belt,Lanping Basin developed into a classic orogenic basin.It experienced a complex evolution history,resulting from tectonic evolution of Meso–Neo Tethys Orogenic Belt and India-Eurasia collision.Lanping Basin is also a significant metallogenic region.However,there are multi science issues need to be solved,including the controversial tectonic evolution of Lanping Basin and the imperfect metallogenic systems.In this study,we discuss the affiliation of Simao Terrane,the sediments provenance and the basin nature by the clastic rock geochemistry and geochronology,and then summarize the basin tectonic evolution.On this basis,this study illuminates the metallogenic systems and the composite mineralization by dissecting the classic deposits in Lanping Basin.The clastic rocks exhibit geochemical features with right-leaning light rare earth elements,flat heavy rare earth elements patterns,negative Eu anomaly,low ratios including La/Sc?mean4.35?,Sc/Th?mean 0.79?,Cr/Th?mean 5.01?and Co/Th?mean 0.76?.The detrital zircons peak ages concentrate on the three ranges of 2516–2304 Ma,1893–1855 Ma and 244–185 Ma.These features suggest that the sediments mainly derived from Yangtze Block and Simao Terrane.Simao Terrane shows similar detrital zircons ages distribution and Hf isotopic features with Yangtze Block during Neoarchean,Paleoproterozoic and Paleozoic,but different from Tengchong-Baoshan Terrane,which indicates that the former belongs to Cathaysian old land,and the latter is part of Gondwanaland.Whole-rock geochemistry and sedimentology evidence indicate that Lanping basin developed under the passive continental margin setting during Late Triassic–Paleocene,including Early-Middle Triassic foreland basin,Late Triassic–Early Jurassic rift basin,Middle Jurassic–Late Cretaceous depressed basin,Paleocene–Eocene foreland basin and the strike-slip pull-apart basin stage from Oligocene.The isotopic features with?⁶⁵Cu?-0.35–0.21‰?,?¹³C?-5.3–-4.1‰?,?¹⁸O?11.9–15.5‰?and?³⁴S?-2.0–-4.0‰?of Jinman-Liancheng Cu-Mo deposit suggest that the ore-forming material mainly came from the sedimentary rocks in basin.The H-O isotope composition(?D ranging from-95.2‰to 109.7‰,?¹⁸O ranging from 6.2‰to 8.0‰)and fluid inclusions features?160–300?,8–20%NaCleqv?indicate that the ore-forming fluids mainly are metamorphic water,mixed with hot brine and meteoric.The deposit exhibits feature of meso-low temperature hydrothermal vein type deposit.The Zn(?⁶⁶Zn ranging from 0 to 0.35‰)and in-situ S(?³⁴S ranging from-22.0‰to-13.0‰and-1.0‰to 2.0‰)characteristics from Jinding Pb-Zn deposit suggest that the material mainly derived from Cenozoic sandstone,gypsolyte and ancient oil-gas reservoirs.And the high Co/Ni ratio?0.5–10?suggests that the ore-forming fluid are mainly composed of basin hot brine,and Jinding deposit is one of Mississippi Valley Type?MVT?deposits.The deposits at the south part of Lanping Basin?Bijiashan Sb,Zhacun Au and other mineralized spots?are characteristic by low temperature,low salinity fluids,material from limestone and magmatite,which are similar to epithermal deposits.Combing with the mineralizing process and basin tectonic evolution,this study summarizes three metallogenic systems including Paleocene–Early Eocene meso-low temperature hydrothermal vein type Cu-Mo-Pb-Zn-Ag,Oligocene MVT Pb-Zn and Eocene epithermal metallogenic system.Furthermore,two types of composite mineralization are presented.