陕西省勉略宁矿集区铜厂铜-铁矿床地质特征及其成因探讨

Geological characteristics and genesis of the Tongchang copper-iron deposit in the Mian-Lue-Ning ore-cluster region,Shaanxi Province

铜厂铜-铁矿床是勉略宁矿集区具有代表性的矿床之一,主要由上部的铜厂铜矿床和下部的杨家坝铁矿床(铜厂铁矿床)组成。根据磁铁矿和硫化物的相对含量,铜厂铜-铁矿床的矿石可分为磁铁矿矿石、含硫化物磁铁矿矿石和硫化物矿石三类。系统的岩相学和矿相学研究表明,其矿石矿物主要为磁铁矿、黄铜矿、黄铁矿和磁黄铁矿;矿石结构包括自形-半自形-他形粒状结构、交代残余结构和包含结构,矿石构造包括块状、浸染状、脉状和条带状构造。铜厂铜-铁矿床的围岩蚀变种类较多,且具有一定的分带性,上部铜矿体围岩蚀变以硅化、碳酸盐化和黑云母化为主,以石英、方解石和黑云母为主的蚀变矿物组合显示钾化特征;下部铁矿体围岩蚀变有钠长石化、蛇纹石化、滑石化、透闪石化、碳酸盐化、绿泥石化等,以钠长石、蛇纹石、滑石、透闪石、方解石、白云石、菱铁矿、绿泥石、黑云母和磷灰石等为主的蚀变矿物组合显示钠化特征。铜厂铜-铁矿床中磁铁矿的TiO_(2)含量小于1.72%,Al_(2)O_(3)含量小于1.81%,均显示热液磁铁矿的特征,结合铜矿石脉穿插铜厂闪长岩及二者突变接触的地质特征,说明铜厂铜-铁矿床的形成与热液活动密切相关。同时,铜厂铜-铁矿床形成于早古生代加里东期,勉略宁矿集区在该时期处于大陆裂谷的扩张环境中,与铁氧化物-铜-金(Iron Oxide-Copper-Gold,简称IOCG)矿床的形成环境类似。通过与典型IOCG矿床地质特征、矿化蚀变特征、矿物组合特征、矿物地球化学特征及大地构造背景的系统对比,初步提出铜厂铜-铁矿床应属于IOCG矿床。

The Tongchang copper-iron deposit is an ideal representative deposit from the Mian-Lue-Ning ore-cluster region. The ores from the Tongchang copper-iron deposit can be divided into three types: magnetite ores, sulfide-bearing magnetite ores and sulfide ores. Systematic petrography and ore mineralogy research shows that the ore minerals are mainly composed of magnetite, chalcopyrite, pyrite and pyrrhotite;the ores have euhedral-subhedral-anhedral crystalline grained texture, metasomatic relict texture and poikilitic texture, and have massive, disseminated, vein and banded structures. The wall-rock alteration of the upper copper orebodies is characterized by silicification, carbonation and biotitization, and the altered mineral assemblages are mainly composed of quartz, calcite and biotite, showing the characteristics of potassic alteration. Moreover, the wall-rock alteration of the lower iron orebodies is characterized by serpentinization, talcification, tremolitization, carbonation and chloritization. The altered mineral assemblages are mainly composed of serpentine, talc, tremolite, calcite, dolomite, siderite, chlorite, biotite and a small amount of apatite, showing the characteristics of sodic alteration. The contents of TiO2 and Al2O3 in magnetite are lower than 1.72% and 1.81%, respectively, showing the characteristics of hydrothermal magnetite. Combined with the field geological phenomena of the copper ore veins intersecting the Tongchang diorite and the sharp contacts between them, the evidence indicates that the formation of the Tongchang copper-iron deposit is closely related to hydrothermal activity. Moreover, the Tongchang copper-iron deposit was formed in the Caledonian period of the Early Paleozoic, when the Mian-Lue-Ning area was in an expansion environment, similar to the formation environment of the iron oxide-copper-gold(IOCG) deposit. By comparing the geological characteristics, mineralization and alteration features, mineral assemblages, mineral geochemical characteristics and the geotectonic background of the typical IOCG deposit, it is tentatively proposed that the Tongchang copper-iron deposit should belonged to the IOCG deposit.