Recognizing the evolution of the stratabound polymetallic massive sulfide deposits in Tongling mineralization cluster, East China through colloform pyrite
Recognizing the evolution of the stratabound polymetallic massive sulfide deposits in Tongling mineralization cluster, East China through colloform pyrite
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从胶状黄铁矿认识华东铜陵矿化群层控多金属块状硫化物矿床演化
DOI：
10.1016/j.oregeorev.2022.104915
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发表时间：
2022
影响因子：
3.3
通讯作者：
Jiancheng Xie
中科院分区：
文献类型：
--
作者：
Liang Xu;Qiaoqin Xie;Yuefei Zhou;Jiayu Wang;Tianhu Chen;Xiaochun Xu;Jiancheng Xie
层控铜金硫化物矿床广泛分布于中国东部的长江中下游成矿带中。这些矿床严格沿石炭系地层分布，但与白垩纪闪长岩密切相关。沉积和岩浆证据的同时存在，使得这些层控块状硫化物矿床的成因成为一个悬而未决的问题。胶状黄铁矿(Py-c)广泛分布于层控硫化物矿床中，其成因一直存在争议，制约了层控硫化物矿床成矿模式的建立。本研究采用光学显微镜、粉末X射线衍射仪(XRD)、场发射扫描电子显微镜(FE-SEM)、微区激光拉曼光谱和气相色谱-质谱仪(GC-MS)对Py-C的矿物组成、形貌、微观结构和有机成分进行了系统的研究。结果表明，Py-c有三种织构：橄榄状织构、同心条带织构和泥晶织构(无其他特征织构)。同心带状织构呈浅带和暗带交替出现，分别由细小和粗大的Py-c晶组成。所有Py-c矿石的物相组成相似，主相为黄铁矿，次要相为菱铁矿、白云石和石英，微量相为粘土矿物(如伊利石)和有机质。黄铁矿晶体的大小为50 nm~1.4mμm，大部分为正面体和亚面体，其中正面体晶体呈立方体和球状。立方晶体表面光滑，无条纹。Py-c矿石中含有碎屑石英和自生石英。碎屑石英颗粒呈高度圆形。PY-C结晶器压痕广泛存在于颗粒表面。碎屑石英周围的Py-C没有重结晶。自生的石英颗粒是正面体和亚面体，覆盖的尺寸范围从数百纳米到几微米，并聚集形成晶簇。此外，还发现少量有机质与Py-c共存。正构烷烃分析结果表明，Py-c中的有机质主要由微生物和陆生高等植物组成，表明以陆地有机质为电子供体的微生物有可能形成Py-c。这些系统的分析表明，铜陵层控硫化物矿床中的Py-c是在半封闭的海盆中通过生物地球化学中介的沉积作用形成的。在燕山期(侏罗纪-白垩纪)，Py-c通过重结晶作用转变为巨晶黄铁矿(Py-m)，或通过热变质作用和矿物-流体反应转变为磁黄铁矿和黄铜矿。铜陵成矿群具有高孔隙度、高化学活度和有机质等特点，对燕山期岩浆热液中铜、金的沉淀起到了关键作用，并对层控硫化物矿体的形成起了制约作用。
Stratabound Cu-Au sulfide deposits are widely distributed in the Middle -Lower Yangtze River Mineralization Belt, eastern China. These deposits are strictly distributed along the Carboniferous stratum, but occur in close proximity to the Cretaceous diorite rocks. The simultaneous presence of sedimentary and magmatic evidence leads the genesis of these stratabound massive sulfide deposits to be an open question. Colloform pyrite (Py-c) is widely distributed in stratabound sulfide deposits and its genesis remains controversial which contrarily limits the establishment of a metallogenic model for the stratabound sulfide deposits. In this study, the mineral composition, morphology, microstructure, and organic composition of Py-c were systematically studied using optical microscopy, powder X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), micro-area laser Raman spectroscopy, and gas chromatography-mass spectrometry (GC–MS). Results reveal three types of textures of Py-c: oolitic, concentric-banded, and micritic (no other characteristic texture). The concentric-banded texture shows alternating light and dark bands which are composed of fine and coarse Py-c grains, respectively. All the Py-c ores are similar in phase composition, where the main phase is pyrite, the minor phases are siderite, dolomite, and quartz, and the trace phases are clay minerals (e.g., illite) and organic matter. The size of pyrite crystals varies from 50 nm to 1.4 μm. Most of the pyrite crystals are euhedral and subhedral, where the euhedral crystals show cubic and spheroidic shapes. The surfaces of cubic crystals are smooth and stripless. Detrital and authigenic quartz are found in Py-c ores. Detrital quartz grains are highly round. Py-c mold impressions are widespread on the grain surface. Py-c around the detrital quartz did not recrystallize. Authigenic quartz grains are euhedral and subhedral, cover a size range of hundreds of nanometers to several micrometers, and aggregate to form crystal clusters. In addition, small amounts of organic matters are found co-existing with Py-c. Results ofn-alkanes analysis show that organic matters in Py-c consist mainly of microorganisms and terrestrial higher plants, indicating a possibility of forming Py-c by microorganisms which used terrestrial organic matters as electron donors. These systematic analyses indicate that Py-c in Tongling stratabound sulfide deposits was formed through biogeochemical-mediated sedimentation processes in a semi-enclosed sea basin. In Yanshanian period (Jurassic-Cretaceous), Py-c was transformed to macrocrystalline pyrite (Py-m) through recrystallization or to pyrrhotite and chalcopyrite through thermal metamorphism and mineral-fluid reaction. Py-c ores, which have high porosity, high chemical activity, and organic matter, could have played key roles in precipitating Cu and Au from Yanshanian magma-derived hydrothermal fluids and constrained the formation of stratabound sulfide orebodies in the Tongling mineralization cluster.