Fluid Inclusion Characteristics And Discussion On Genesis Of The Dapai Iron Polymetallic Ore Deposits In Southwestern Fujian Province

Dapai iron polymetallic deposit,locates in the southwestern Fujian late Paleozoic depression,is a typical Makeng type iron deposit,which is commonly found in the southwestern Fujian.The ore bodies in Dapai deposit are mainly hosted in the middle and upper part of carboniferous-lower Permian carbonate formation.Late Mesozoic granite rock is also related to the spaces where the ore bodies locate.The skarn type deposit Fe-Cu-Pb mineralization of Dapai iron deposit,together with carbonatization and silicified alteration,was controlled by a series of shallow thrust nappe and interlaminar slip structure.Skarn mineralization process can be divided into following parts:early stage and late stage of skarn,quartz sulfide stage,and late stage of carbonate.The lack of fluid inclusions research of the Dapai deposits limits the study on the evolution of the ore forming process,fluid information of which can also be used to offer a reasonable explanation for the vertical distribution of the lead-zinc bodies over the magnetite bodies.In this article,several representative mineral fluid inclusions in different ore-forming stages are selected for experiments.The components of these fluid inclusions are mainly H₂O,shown by Laser Raman composition analysis.Homogenization temperatures of early stage of skarn vary from 205.1°C to 405°C with NaCleqv contents of 0.36 to 27.4%.Homogenization temperatures of late stage of skarn vary from164.2°C to 389.2°C with NaCleqv contents of 0.36 to16.5%.Homogenization temperatures of quartz sulfide stage vary from163.4°C to249.9°C with NaCleqv contents of 0.18 to 2.77%.Homogenization temperatures of the last stage vary from 150°C to 203.9°C with NaCleqv contents of 0.18 to 3.35%.The density is from 0.49 g.cm^-33 to 1.32 g.cm^-3.Generally,the fluid inclusions exhibit high temperature,high salinity,and medium-high density,which accords with the ore-forming progress of skarn deposit.In skarn stage,fluid temperature is high and stable.Both high and low salinity inclusions are found during this temperature.Mineral compositions and ore deposit geochemical features reveal that boiling happened during this stage,resulting to the different fluid solubility and-magnetite precipitation.In the quartz-sulfide stage,atmospheric precipitation mixed to the original ore forming fluid,which rapidly reduced the fluid temperature and changed other properties of the fluid.The migration direction of Pb and Zn elements were also changed during this event and cause mineralization of these metal elements in different locations,magnetite body at the bottom and lead-zinc body at the top.