CAJ | 학술논문

龙桥铁矿床是庐枞火山岩盆地中的一个大型的铁矿床,多年来对其矿床成因的认识存在较大的争论.文章在野外地质研究工作的基础上,通过对矿床中菱铁矿的岩矿分析鉴定和电子探针测试,确定了矿床纹层状矿石中的菱铁矿为沉积成因.通过对菱铁矿的产出特征分析,并结合龙桥铁矿床的部分地质地球化学研究成果,认为在该矿床形成过程中,早期沉积形成了纹层状的菱铁矿层,在燕山期的岩浆热事件中,部分沉积菱铁矿被交代形成了磁铁矿和具有残余骸晶结构等一系列矿石交代组构特征的矿物.纹层状矿石既具有沉积特征,也具有热液改造特征,证实了矿床的形成存在早期(三叠纪)的沉积成矿(菱铁矿)作用和晚期(燕山期)的热液成矿(磁铁矿)作用.菱铁矿的研究为进一步确定龙桥铁矿床的成因提供了新的佐证.
룡교철광상시려종화산암분지중적일개대형적철광상,다년래대기광상성인적인식존재교대적쟁론.문장재야외지질연구공작적기출상,통과대광상중릉철광적암광분석감정화전자탐침측시,학정료광상문층상광석중적릉철광위침적성인.통과대릉철광적산출특정분석,병결합룡교철광상적부분지질지구화학연구성과,인위재해광상형성과정중,조기침적형성료문층상적릉철광층,재연산기적암장열사건중,부분침적릉철광피교대형성료자철광화구유잔여해정결구등일계렬광석교대조구특정적광물.문층상광석기구유침적특정,야구유열액개조특정,증실료광상적형성존재조기(삼첩기)적침적성광(릉철광)작용화만기(연산기)적열액성광(자철광)작용.릉철광적연구위진일보학정룡교철광상적성인제공료신적좌증.
The Longqiao iron deposit is one of the most important large ore deposits in Luzong basin, one of the ore-concentrated area in the Middle and Lower Yangtze Valley metallogenic belt. The genesis of this ore deposit remains a problem of much controversy. Based on careful and detailed field investigation and mineral association research, this paper has reported some new achievements concerning siderite minerals in this deposit. There exist two types of siderites in the ores: one occurs in the lamellar ores, and the other assumes the veined form. Petrographic and electron probe analyses as well as C-O, H-O isotope geochemical characteristics of the siderites in the lamellar ore all show that siderites of this kind were formed earlier than magnetite and other minerals associated with magnetite, and that they occurred in a marine sedimentary environment. Some siderites were transformed into magnetite by later hydrothermal activities, resulting in the formation of residual and metasomatic textures in the ores. The lamellar iron ores are composed of sedimen-tary siderite and hydrothermal minerals such as magnetite, garnet, pyrite and phlogopite as a result of the water-rock interaction be-tween the hydrothermal fluids evolved from the Mesozoic magmatic intrusion and the siderite-beating Early Mesozoic (Middle Trias-sic) marine sedimentary rocks. Most of the magnetites in the ore deposit, espeeiaUy in the massive iron ores, were precipitated direct-ly from the magmatic water-dominated hydrothermal system. The metallogenic process of the Longqiao iron deposit can be divided in-to the early (Middle Triassic) sedimentary ore-forming stage characterized by the deposition of siderite-beating rocks and the late (Early Cretaceous or Yanshanian) hydrothermal ore-forming stage characterized by the formation of magnetites associated with other hydrothermal minerals.