山东省昌邑市南任铁矿地质特征及成因初探

南任铁矿床位于莱州-安丘铁成矿带西北部,对其矿床成因认识存在较多争议。矿区内地层广布,构造、岩浆岩不发育。铁矿体呈透镜状产于滹沱纪粉子山群小宋组的底部层位,无穿插或交代围岩现象;围岩蚀变以蛇纹石化、绿泥石化为主,愈近矿体矿化蚀变愈强。矿石矿物以磁铁矿为主,少量黄铁矿、黄铜矿;脉石矿物主要为蛇纹石、绿泥石。矿石的结构构造主要为浸染状构造,半自形—他形粒状结构。岩矿石稀土元素含量表明磁铁矿主要为火山深成岩浆结晶分异形成,部分与火山沉积作用有关;磁铁矿化学成分特征也反映了这一点,综合认为其成因可能属海相火山岩型之火山岩浆-热液和火山沉积复合类型。在此基础上,总结了莱州-安丘铁成矿带上不同成因铁矿床的分布规律,为今后该地区铁矿勘查指明了方向。

Analysis on Geological Characteristics and the Origin of Nanren Iron Deposit in Changyi City of Shandong Province

Nanren iron deposit locates in northwest of Laizhou-Anqiu iron belt. There are many controversies in understanding its origin. Strata developed well in this area, while geological structures and magmatic rocks are not developed. Iron ore bodies occurred in the lower part of Xiaosong formation of Fenzishan group in Hutuo system with the enticular type. It has no penetrations or adjacent rock metasomatism. Alteration types of country rocks are mainly serpentinization and chloritization. The rate of mineralization and alteration will be more intense when approaching to the ore body. Ore minerals are magnetite and tiny amounts of pyrite and chalcopyrite. Gangue minerals are serpentine and chlorite basically. Ores are disseminated and hypautomorphic xenomorphic granular structures. The content of rare earth indicates that magnetite mainly came from magmatic crystallization and differentiation and partly related to volcano sedimentary. Chemical composition of magnetite have also identify the conclusion. It is regarded that the origin of Nanren iron deposit probably is marine volcanic complex deposit including magmahydrothermal deposit and volcano sedimentary deposit. The distribution rules of iron deposits in iron metallogenic belt have been summarized. It will provide some references for surveying iron deposit in the belt in the future.