Oxygen, Sulfur And Lead Isotopic Compositions And Significance For Ore Genesis Of Dapai Iron-lead-zinc Polymetallic Deposit In Southwestern Fujian Province

The Dapai iron and lead-zinc polymetallic ore deposits of southwestern Fujian is located in southern of the southwestern Fujian depression zone in late Palaeozoic. The southwestern Fujian is located in the southwestern of southwestern China, which experienced the complex evolution process, especially strong tectonic-magmatic activity in Mesozoic which accompanying with a large number of Late Mesozoic granitic magmatism. The Makeng type iron deposits are widely distributed in southwestern Fujian, which genesis has attracted the attention of geological colleagues. To explore the genesis of the Makeng type iron deposits, it is necessary to investigate the sources of metallogenic material by isotope method and analyze further genesis significance of Makeng type iron ore in the southwestern Fujian. The Dapai iron and lead-zinc polymetallic ore deposit is newly discovered in the southwestern Fujian, which has the characteristics of the Makeng type iron deposits. Summarizing the field work, the Dapai deposit ore body is mainly hosted in the carbonate formation, which main ore-controlling structure are a series of shallow thrust nappe structure and decollement zone. The medium-fine grained porphyaceous adamellite is highly related to the ore-forming where nearby contacting with the carbonate rock often accompanying with skanization, carbonatization and silicification alteration. Ore-forming mainly goes through four stages including skarnized stage, magnetite stage, quartz-sulfide stage and late carbonate stage. Magnetite stage and quartz-sulfide stage are main metallogenic stage. The deposit possesses typical features of strata bound skarn deposit.In this paper, based on the analysis of ore-forming geological conditions about Dapai iron-lead-zinc polymetallic deposit in southwestern Fujian, author choose magnetite, garnet to test oxygen isotopic compositions and pyrite, sphalerite and galena to test sulfur and lead isotopic compositions. Studies have shown that the δ18O values from garnet vary 3.4~6‰ indicating the possibility that the oxygen isotopic compositions of garnet skarn inherited those of the concealed granite body. The oxygen isotope data from magnetite have been used for calculating the δ18O values in the ore-forming fluid at magnetite stage. They are 9.23~11.34‰ at assumed temperature of 500℃ or 8.58~10.69‰ at assumed temperature of 600℃ respectively, which shows the 180 was mixed into the ore-forming fluid. The δ34S from ore sulfides has a small range of variation-2.6~1.5‰, the distribution of values is around the zero,(0±3‰) a characteristic that implies a magmatic sulfur. The 206Pb/204 Pb, 207Pb/204 Pb and 208Pb/204 Pb ratios of sulfide ores range within 18.486~18.537, 15.665~15.712 and 38.823~38.979 respectively. The lead isotopic ratios vary in a small range. A comprehensive analysis of the lead isotopic data indicated that the metallogenic materials of this deposit are closely related to magmatism, mainly derived from the lower crust but show crust-mantle mixing. Combining Makeng type iron polymetallic deposits of southwestern Fujian and chronology discussion of mesozoic granites in southwestern Fujian, it is deduced that the formation of Dapai iron-lead-zinc polymetallic deposits has connection with intrusion and metasomatic of mesozoic granites(~130Ma).