投稿时间：2020-03-17
修订日期：2020-05-11
网络发布日期：2020-10-31
中文摘要:查岗诺尔铁矿是新疆西天山阿吾拉勒铁矿带内的重要大型铁矿床之一。矿体赋存在下石炭统大哈拉军山组安山质火山岩中，与普遍发育的石榴子石化、阳起石化和绿帘石化时空关系密切。石榴子石和绿帘石分属不同热液成矿阶段，它们均发育丰富的环带结构，具体表现为明显地颜色、干涉色、背散射图像及成分（FeO、Al2O3、SiO2、MnO、TiO2）等差异性。石榴子石具有2个世代、3个类型。早世代石榴子石（Grt1和Grt2）产于块状石榴子石-磁铁矿蚀变岩，呈褐黄色，粒度较细，发育核-边结构，呈非均质性，显示异常干涉色，其核部（Grt1-c）均匀相对富钙铝榴石（Gro51-53And41-43Spr4-8），而边部（Grt1-r）发育振荡成分环带，总体相对富钙铁榴石（Gro18-35And60-77Spr4-6）；Grt2核部（Grt2-c）呈均质性，为钙铁榴石（And99-100Spr0-1），边部显异常干涉色，发育振荡成分环带，为钙铝铁榴石（Gro34-54And38-61Spr6-9）。晚世代的石榴子石（Grt3）以细脉状或角砾胶结物形式分布，呈红褐色，自形粗粒结构，显非均质性，发育振荡成分环带，端员组分总体以钙铁榴石为主，次为钙铝榴石（Gro27-43And50-68Spr3-8）。石榴子石结构和元素含量变化表明，早期石榴子石形成于弱氧化-氧化、中性-碱性流体体系，其中向边部生长过程，由于新注入流体以及周期性压力汇聚和释放，体系的氧逸度、pH值呈振荡变化；晚期石榴子石形成于弱氧化、弱碱性、动荡的开放流体环境。绿帘石发育3个世代（Ep1、Ep2和Ep3）。Ep1发育核-边结构，核部（Ep1-c）均匀无环带，XFe值（XFe=Fe3+/（Al+Fe3+），原子比值）为0.19~0.21，w（MnO）为0.05%~0.18%，w（TiO2）为0.10%~0.12%，生长边（Ep1-r）多发育振荡环带，XFe值为0.26~0.29，w（MnO）为0.01%~0.14%，w（TiO2）为0.19%~0.26%。Ep2沿Ep1-r边缘生长，不均匀且经历了溶解-再沉淀过程，XFe值为0.15~0.20，w（MnO）为0.42%~1.19%，w（TiO2）为0.02%~0.07%。Ep3呈柱状或不规则粒状交代Ep2、贴近或穿切Ep1-r生长，较均匀、无环带结构，XFe值为0.28~0.37，w（MnO）为0.12%~0.77%，w（TiO2）为0.02%~0.10%。绿帘石成分变化表明，从Ep1-c到Ep1-r，到Ep2，再到Ep3，流体体系氧逸度经历了先增加，后降低，再升高的变化过程。同时，流体成分也在变化，先从相对贫Ti和Mn向相对富Ti贫Mn演化，而后又变为富Mn贫Ti。因此，在热液磁铁矿矿化阶段，查岗诺尔铁矿的成矿热液的物理-化学环境是不断变化的。研究显示，石榴子石和绿帘石结构和成分研究可以刻画热液成矿系统的流体演化历史。
Abstract:The Chagangnuoer iron deposit is one of the large-size iron deposits within the Awulale metallogenic belt，West Tianshan，Xinjiang. It is hosted in the andesitic volcanic rocks of the Lower Carboniferous Dahalajunshan Formation. Spatially and temporally，iron orebodies are associated with the well-developed hydrothermal garnet，actinolite，and epidote. The garnet and epidote are the main minerals in different hydrothermal stages. Both of them have zoned texture，shown by the color，grain-size，optical characteristics，BSE image，and chemical composition. There are two generations of garnet, consisting of three different types. The early generation garnet（Grt1 and Grt2） commonly occurs in massive garnet-magnetite rocks，and is characterized by brown-yellow color，relatively smaller size，and obvious core to rim zonation. Grt1 shows anomalous optical characteristics under crossed nicols; the core（Grt1-c）is relatively rich in the grossular（Gro51-53And41-43Spr4-8），while the rim（Grt1-r）with oscillatory zoning is richer in andradite（Gro18-35And60-77Spr4-6）. Grt2 is characterized by inverse core to rim zonation. The core（Grt2-c）is isotropic andradite（And99-100Spr0-1）. However，the rim（Grt2-r）shows anomalous optical cha-racteristics under crossed nicols，and is of anisotropic andradite-grossular series（Gro34-54And38-61Spr6-9）with oscillatory chemical zonation. The late generation garnet，named Grt3, generally occurs as veinlets or cements of the magnetite breccia. The Grt3 is different from the Grt1 and Grt3 by its reddish brown color，lager grain size，and oscillatory zoning. The end members of garnet are mainly andradite， followed by grossular（Gro27-43And50-68Spr3-8）. The garnet texture and chemical composition variations indicate that, during the early garnet deposition, the fluids were weakly oxidized to oxidized，and intermediate to alkaline. During the process of the rims formation，the oxygen fugacity and pH values changed regularly，due to the addition of Fe-richer fluids or related periodic fluctuations of pressure build-up and release. In the late garnet stage，there were weakly oxidized and mildly alkaline fluids in a relatively open system. Three generations of epidote were recognized，named Ep1，Ep2，and Ep3. Ep1 is typically composed of a core（XFe=0.19~0.21）and an overgrowth rim （XFe=0.26~0.29），which mostly shows oscillatory zoning and has highest TiO2 content （0.19%~0.26%）. Ep1 has the lowest MnO content （0.01%~0.18%）. Ep2（XFe=0.15~0.20）is heterogeneous and has undergone dissolution-reprecipitation process. It is characterized by lowest TiO2 content （0.02%~0.07%）but highest MnO content（0.42%~1.19%）. Ep3 （XFe=0.28~0.37）is homogeneous and has replaced the Ep2. Its MnO content is 0.12%~0.77%，and TiO2 content is 0.02%~0.10%. The chemical variation from Ep1-c to Ep3 indicates that, in the late stage of the iron mine-ralization, the oxygen fugacity of fluid increased firstly，then reduced，and finally increased again. At the same time，the fluid composition also changed，from poorness in Ti and Mn to richness in Ti，and then richness in Mn. Therefore，during the hydrothermal iron mineralization stages in the Chagangnuoer deposit，the physical-chemical condition evolution was complex. This research indicates that, in addition to the garnet，the epidote can be a potential tracer for fluid evolution in the hydrothermal ore deposit based on detailed texture and chemical study.
keywords:geology garnet epidote oscillatory zoning physical-chemical condition Chagangnuoer iron deposit western Tianshan
文章编号：
中图分类号：
文献标志码：
基金项目:本文得到国家重点研发计划项目（编号：2018YFC0604004）资助
引用文本：
冯浩轩,申萍,李昌昊,武阳,石福品,李文广.2020.新疆西天山查岗诺尔铁矿床环带石榴子石和绿帘石的发现及意义[J].矿床地质,39(5):805~824FENG HaoXuan,SHEN Ping,LI ChangHao,WU Yang,SHI FuPin,LI WenGuang.2020.Discovery of zoned garnet and epidote in Chagangnuoer iron deposit, western Tianshan Mountains, Xinjiang, and its significance[J].Mineral Deposits39(5):805~824
图/表
