摘要
式可布台铁矿位于西天山阿吾拉勒成矿带西端,是该成矿带内典型的沉积型铁矿床,目前该矿床在成因方面存在喷流沉积和化学沉积(类似条带状铁建造)两种认识。前人多聚焦于矿床地质和地球化学特征的探讨,对矿石和矿物组成及沉积-成岩(成矿)过程的分析较为薄弱。为此,本文选取式可布台铁矿中不同类型矿石开展详细的岩相学和矿物学研究,力图为揭示铁矿形成过程提供关键信息。岩相学分析表明,式可布台铁矿主要由赤铁矿、铁碧玉(石英)、黄铁矿、重晶石以及少量菱铁矿组成。赤铁矿根据形态特征可划分为板柱状、鳞片状(叶片状)、粒状和微粒状四种结构,其中微粒状极细粒赤铁矿为原生矿物,推测可能由Fe(Ⅲ)氢氧化物在成岩早期脱水形成;粗粒状赤铁矿是在成岩晚期或浅变质过程中由早期微粒状赤铁矿重结晶形成。菱铁矿结晶程度一般较差,其内部常见细粒石英和赤铁矿包裹体,与有机质共存,指示其可能是由Fe(Ⅲ)氢氧化物在成岩阶段通过异化铁还原作用(DIR)形成。黄铁矿主要为粗粒结构,其Co/Ni比值位于热液成因区(平均为3.44),表明黄铁矿属于热液成因型黄铁矿。重晶石多为他形-半自形结构,粒径较细,表明重晶石也应为海底热液沉淀物。依据矿体特征、矿石组构、矿物类型以及矿物颗粒间相互关系及矿物成因,可将成矿过程划分为两期:沉积期和成岩期。在沉积期以原始沉积物为主,包括Fe(Ⅲ)氢氧化物、无定形二氧化硅、无定形Si-Fe(Ⅲ)氢氧化物凝胶等松散沉积物以及重晶石和黄铁矿等结晶矿物。在成岩期,早期沉积物脱水形成赤铁矿、石英和铁碧玉,部分Fe(Ⅲ)氢氧化物与有机质反应形成菱铁矿。式可布台铁矿矿物组合以赤铁矿为主,含典型矿物铁碧玉、黄铁矿和重晶石,而缺少硅酸盐矿物,与现代海底含金属沉积物和古生代铁碧玉矿床相似,
The Shikebutai iron deposit is located in the western end of the Awulale metallogenic belt in the West Tianshan Mountains.It is a typical sedimentary iron deposit in this metallogenic belt.At present,there are two opinions about its genesis,namely,the exhalative deposition and the chemical deposition(similar to banded iron formation).Previous studies mostly focused on the geological and geochemical characteristics of the deposit,but analysis of its ores and mineral composition and sedimentation-diagenesis(metallogenic)process is relatively weak.Therefore,this paper selected different types of ores in the Shikebutai iron deposit to carry out detailed petrographic and mineralogical studies,in an attempt to provide key information for revealing the genesis of the deposit during the formation of the iron deposit.Petrographic analysis shows that the Shikebutai iron deposit is mainly composed of hematite,jasper(quartz),pyrite,barite and a small amount of siderite.According to the morphological characteristics,hematite can be divided into four structures:plate columnar,scale(phylloid),granular structure and particulate structures.Among them,the particulate extremely fine hematite is a primary mineral,which is speculated to be formed by dehydration of ferric hydroxide in the early diagenetic stage;while the coarse-grained hematite is formed by early particulate hematite recrystallization in the late diagenesis or weak metamorphism.The siderite is generally poor of crystallinity,often with fine quartz and hematite inclusions and coexisting with organic matter,indicating that it may be formed by ferric hydroxide through dissimilatory iron reduction(DIR)in diagenetic stage.The pyrite is mainly coarse-grained,with a Co/Ni ratio located in the hydrothermal genetic area(averaged at 3.44),indicating that it belongs to hydrothermal pyrite.Most of the barites are anhedral to subhedral structure with relatively fine particle sizes,indicating that they should also be submarine hydrothermal sediments.According to the characteristics
作者
张新
董志国
彭自栋
张连昌
张帮禄
王长乐
ZHANG Xin;DONG ZhiGuo;PENG ZiDong;ZHANG LianChang;ZHANG BangLu;WANG ChangLe(Key Laboratory of Mineral Resources,Institute of Geology and Geophysics,Chinese Academy of Sciences,Beijing 100029,China;College of Earth and Planetary Sciences,University of Chinese Academy of Sciences,Beijing 100049,China;Development and Research Center,China Geological Survey,Beijing 100037,China;China University of Geosciences,Beijing 100083,China)
出处
《岩石学报》
SCIE
EI
CAS
CSCD
北大核心
2022年第10期3125-3142,共18页
Acta Petrologica Sinica
基金
国家自然科学基金原创探索计划项目(42150104)
中国科学院基础前沿科学研究计划从0到1原始创新项目(ZDBS-LY-DQC037)和中国科学院青年创新促进会联合资助。
关键词
赤铁矿
菱铁矿
矿物成因
沉积-成岩过程
式可布台铁矿
西天山
Hematite
Siderite
Mineral genesis
Sedimentary-diagenetic processes
Shikebutai iron deposit
West Tianshan Mountains
