首钢秘鲁铁矿马尔科纳矿区9-10号矿体地质特征及成矿模式

Geological characteristics and metallogenic model of iron ore body No.9&10 in Marcona Mine Shougang Hierro Peru

秘鲁马尔科纳铁矿位于南美安第斯山金属成矿带中。9-10号矿体赋存在志留-泥盆系马尔科纳组角岩中,MINA9、MINA10两个矿体实为同一矿体,只是被后期安山玢岩脉切割分成为两段。矿体呈层状、似层状产出,走向上连续,由一个主矿体组成,地表出露主矿体长1 450m,平均宽度100m。西部矿体走向近EW,倾向NW,倾角较缓;东部矿体走向NEE,倾角中等,围岩为角岩。矿体沿走向厚度稳定,9号矿体沿倾向矿体变薄,10号矿体沿倾向矿体增厚;由于后期氧化作用,铁矿体具有明显的垂直分带特点,由上到下分为氧化带、过渡带和原生带。综合矿物学和Ar同位素地质年代学研究结果,铁矿床主要形成于侏罗纪—早白垩世,成矿分为7个成矿阶段,中-晚侏罗世(171~156 Ma)的磁铁矿阶段、磁铁矿-硫化物阶段和多金属硫化物阶段是马尔科纳铁矿的主要成矿期;早白垩世(110~101 Ma)出现脉状铁-铜-硫化物叠加矿化阶段。马尔科纳铁矿的成矿模式:板块的碰撞-俯冲,造成强烈的幔源岩浆活动,形成大规模火山喷发和高钾钙碱性岩的侵位,火山(岩浆)期后的含矿流体沿NEE向断裂侵位,磁铁矿聚集矿化,形成马尔科纳铁矿的主矿体;主成矿期后又弱的叠加矿化,与中基性岩脉和断裂一起改造、破坏了先期阶段的矿体。

Marcona iron deposit is located at the Andes Mountain ore belt.Ore body 9&10occur in hornstone of Silurian-Devonian Marcona formation.In fact the two ore bodies are of the same ore body that is cut into the two by late porphyrite dyke.The ore bodies are in layer or layeroid and extend continuously1450 mlong and 100 m wide at surface.The ore body strike EW and dip NW at gentle angle in the west and strike NEE and dip at medium angle in the east.The wall rock is hornstone.Thickness is stable in strike but ore body 9gets thinning along dip and ore body 10 thickening.Due to late oxidation the ore body is vertically zoned from top to bottom as oxidation zone,transitional zone and primary zone.Combination of mineralogy and Ar isotope chronology shows that the iron deposit was formed during Jurassic Period-Early Cretaceous Epoch.Mineralization can be divided into 7stages of which Middle-Late Jurassic Epoch(171~156 Ma)is magnetite stage,magnetite-sulfide stage and multi-metal sulfide stage are the main stage,in Early Cretaceous Epoch(110~101Ma)occurred overprinting stage of Fe-Cu sulfides.Metallogenic model is built in the paper.Plate collision-subduction caused strong activity of the mantlesourced magma and large scale volcanic eruption and emplacement of high potassium calci-alkali intrusive rock and the post-magma ore fluid emplaced along NEE fault and magnetite accumulated to form the main ore bodies.After the main ore stages overprinted weak mineralization which modified and intermediatebasic dykes destroyed the pre-existing ore bodies.