Diabase And Mineraliztion Of Makeng Iron Ore Deposit,fujian Province

Makeng iron deposit is located in Longyan city Fujian province being the large magnetite deposit in the Yongmei depression metallogenic belt in south-western Fujian,having the largest iron reserves in southern China. To decipher the genesis of the deposit will bring much impact to the other deposits distributing along the belt which share the similar characteristics with Makeng deposit. Much work has been done while the genesis of Makeng deposit remains controvertial.On the bases of collecting and summarying previous data with large field work and underground observation, this paper argue that iron is been held between the P1jq(lower Permian Jingshe formation-Qixia formation) limestone and C1l(lower Carboniferous) sandstone. Ore body is obviously and strictly controlled by local structure presenting the stratiform and lamellar-alike features. Lithology profile from diabase to marble has been spotted in mining area including diabase�'skarnized diabase�'garnet diopside skarn�'garnet diopside ore rock�'marble from one side to another. Partial band of more complicate skarn minerals like tremolite、actinolite、vesuvianite、rhodonite etc can be seen with undeveloped zonation. Magnetite are found to coexist with garnet and diopside and sharply contact with bleached marble with fluid escape structures being found on the marble side. Above-mentioned two features has been defined Makeng deposit as traditional skarn type. Molybdenite poorly disseminate or fill as veins in diabase or Lindi formation sandstone as to be thought as later production compared to magnetite. Recent Sm-Nd isochron age of garnet shows that metallogenic time is around 160 Ma, in which case Dayang-Juzhou granite that have been recognized as the major related pluton have zircon U-Pb age around 120-155 Ma. Despite of the lack of 160 Ma diabase being found, iron-rich fluid and mafic magma come from deep mantle while molybdenite is concentrated in crust from the perspective of metallogenic specialization. Hence the diabase will be the mother rock for Makeng iron deposit displaying the skarn alteration zoning features at the same time. Dayang-Juzhou granite are more likely to contribute molybdenite to deposit in later phase and bring later alteration to whole system like second phase skarn mineral veins and silisification of Lindi formation sandstone.Under tunnel observation and research on fluid inclusions, magnetite are straightly contact with diabase but no granite because of the Lindi sandstone in between. This paper postulates that Paleo Pacific plate subduction lead to the tectonic setting turning to active continental margin. As subduction goes deeper, basaltic ocean crust will release volatiles up to overlying mantle wedge resulting in melting process which generate the primary magma of Makeng diabase. Magma goes up because of the pressure difference till it reaches the crust-mantle boundrary heating lower crustal materials into granitic magma. With further surface rupture, mafic magma fill in the fracture in mining area as veins of diabase along with mantle-derived iron-rich fluid which is high in temperature and salinity. When fluid emplace near the marble, skarn alteration wll be triggered as well as the iron precipitation. As the napping structure developes, 140 Ma granite emplace in its very spot, with the different magma conduit, granite can not get through Lindi formation sandstone to get touched with ore body.