闽西南马坑式铁矿成矿结构面特征及找矿意义

METALLOGENIC STRUCTCTURAL PLANE CHARACTERISTICS AND ITS PROSPECTING IMPORTANCE FOR THE MAKENG TYPE IRON DEPOSITS IN SOUTHWESTERN FUJIAN PROVINCE

马坑式铁矿位于闽西南晚古生代坳陷盆地内,是福建省境内最主要的矽卡岩型铁-多金属矿床。矿体主要受岩性界面及构造结构面控制,尤以硅钙面控矿作用显著。马坑式铁矿主矿体定位于林地组(C_1l)石英砂岩与经畲—栖霞组(C_2j—P_2q)碳酸盐岩的岩性界面(硅钙面)。通过对马坑式铁矿硅钙面的基本特征进行分析,划分了五类主要的成矿结构面类型:林地组与经畲组—栖霞组、经畲组—栖霞组与文笔山组、经畲—栖霞组内部碎屑岩与灰岩、经畲组—栖霞组与花岗岩类以及推覆(滑脱)界面。研究认为马坑式铁矿主矿体受不同的物理化学岩性界面(硅钙面)控制,这种界面在构造活动及流体参与过程中容易形成扩容空间,构成成矿地球化学障,有利于成矿物质的沉淀富集。在以上认识基础上,建立了以硅钙面为主要成矿作用标志的马坑式铁矿成矿模式,认为运用硅钙面控矿理论指导闽西南地区找矿预测的具有重要的找矿指导意义。

Located in the Late Paleozoic depression of southwestern Fujian,the Makeng type iron deposits are the main skarn iron polymetallic deposits.The major ore bodies are generally controlled by lithologic boundaries and tectonic structural planes,especially the interface between silica and calcareous bed,and they are located above the quartz sandstone of the Lower Carboniferous Lindi formation(C 1 l)and below the carbonate rocks of the Upper Carboniferous Jingshe formation-Upper Permian Qixia formation(C 2 j-P 2 q).In order to reveal the genesis and mineralization mechanism of the Makeng type iron deposits,the Si/Ca surface ore-controlling theory was used to discuss the metallogenic structctural plane characteristics and its ore-controlling mechanism.Five types of metallogenic interfaces were divided according to their features in this research.We deemed that the main ore bodies of Makeng type iron deposits were controlled by the physical and chemical differences between these Ca/Si surfaces,and it is easy to form expansion space and geochemical barrier near the surfaces in the process of tectonic and fluidic activities.Based on the understanding above,the metallogenic model of the Makeng type iron deposits was built using the Si/Ca surface ore-controlling theory.This work is thought to be meaningful to conduct prospecting research of iron polymetallic deposits in southwestern Fujian Province.