福建龙岩马坑铁矿床成因的探讨

THE ORIGIN OF MAKENG IRON DEPOSIT, FUJIAN

马坑铁矿是福建最大的铁矿床。近年来中国地质科学院矿床所、南京地矿所、长春地质学院、南京大学、福州大学、南京地质学校等单位对该矿床分别进行了工作，对其成因则有接触交代成矿说、复合叠生层状矿床说、陆源沉积热液叠加改造成矿说与海相火山沉积热液改造成矿说。

The Makeng iron deposit occurs in the Shanggu-Yongmei depression in southwestern Fujian. The ore body occurs in the limestone of the Makeng anticline.Recognized from the bottom upward are quartz-magnetite, actinolite-magnetite and diopside-magnetite ores, reflecting the compositional variation of the original sedimen-tary formation from siliceous-ferruginous to siliceous-calcareous-ferruginous. Various relict textures and structures of sedimentary origin are observed in the ores, such as relict oolitic texture, dusty poikilitic texture, nebulitic texture, relict pea texture, relict colloidal texture and bedded streaky structure. The main ore body and other small ones are conformable with the wall rocks. All the above facts provide evidence of sedi-mentary origin for the iron deposit.Fe mineralization is related to volcanism. The iron ore deposit and volcanic rocks are similar in age from Lower Carboniferous to Lower Permian.Geochemically, δO18(SMOW) value is 2.16%, A1203, K20, Na20 and P203 are very low, Ti, Ge, Zn and Pb, are relatively high, Si02/Al203 > 5, and Ni/Co < 3. This kind of element association is characteristic of that of volcano-sedimentary depo-sits.After sedimentation, the iron ores Underwent strong deuteric alteration and local molybdenization in response to the intrusion of diabase and the Luzhou-Dayang granite.It is concluded that the Maksng iron deposit is related to marine volcanism and it was formed through precipitation and underwent strong deuteric alteration. In other words, the Makeng iron deposit must be a marine volcano-sedimentary-hydrothermal re-formed ore deposit.