【作者】 洪为；

【导师】 张作衡；

【作者基本信息】 中国地质科学院 ， 矿物学、岩石学、矿床学， 2012， 硕士

【摘要】 西天山是中亚造山带的重要组成部分,经历了复杂的增生造山过程。西天山成矿带是我国重要的铁-铜-金多金属成矿带。自2004年以来,西天山阿吾拉勒成矿带的矿产勘查取得突破性进展,相继勘查或发现了数个大中型的铁矿床。查岗诺尔大型磁铁矿床位于西天山北缘阿吾拉勒东段,赋矿围岩系石炭系大哈拉军山组火山岩,可能是早石炭世末期准噶尔洋向南俯冲于伊犁板块之下的大陆边缘岛弧的产物。该矿床主要由Fe Ⅰ和Fe Ⅱ两个矿体组成,其中主矿体Fe Ⅰ底盘夹一个透镜状大理岩,主要为层状、似层状、透镜状,受NW、NWW、NE断裂及环形断裂构造控制,矿化发生在围岩中的各种层间裂隙或断裂中。围岩蚀变主要呈现为石榴石化、阳起石化,绿帘石化以及绿泥石化等。本文在野外地质调研和室内矿相学研究的基础上,利用电子探针、电感耦合等离子体质谱、同位素质谱和显微测温等技术手段,开展了矿物学、微量元素地球化学、稳定同位素、流体包裹体和Sm-Nd年代学等研究,并将查岗诺尔铁矿与其它典型矿床进行类比研究,分析成矿物质来源,探讨矿床成因,构建成矿模式,为深入总结阿吾拉勒成矿带中铁矿床的成矿机制和成矿规律提供依据。取得的主要认识有：(1)矿体赋存于大哈拉军山组中-上部的火山碎屑岩和火山熔岩中,发育石榴石、透辉石、方柱石、阳起石、绿帘石、绿泥石、钾长石等脉石矿物,矿石矿物主要为磁铁矿,伴有少量的赤铁矿、黄铁矿和黄铜矿。矿石构造主要为角砾状、斑点状、斑杂状、豹纹状、块状、浸染状、条带状等,矿石结构以它形-半自形粒状结构、交代结构、填隙结构、包含结构、共生边结构等较为常见。(2)矿床的蚀变分带具有热液矿床的特点。根据矿石组构和矿物共生特征,可以划分为岩浆期和热液期(包括矽卡岩亚期和石英-硫化物亚期)两个成矿期,进一步可以细分为磁铁矿-透辉石阶段、绿泥石-黄铁矿阶段、磁铁矿-石榴石-阳起石阶段、青磐岩化阶段、硫化物阶段和石英-碳酸盐化阶段6个成矿阶段。(3)利用电子探针对石榴石和辉石的端元组分的研究表明,矿床发育以钙铁榴石-钙铝榴石和透辉石-钙铁辉石为组合的钙质矽卡岩,与国内外的典型矽卡岩型铁矿的石榴石和辉石的端元组分具有相似性。在磁铁矿和赤铁矿的Ca+Al+Mn vs Ti+V图解中,多数的样品落入矽卡岩型铁矿的区域；磁铁矿的TiO2-Al2O3-MgO图解中,多数的样品落入沉积变质-接触交代磁铁矿趋势区。(4)岩浆期的磁铁矿∑REE很低,稀土配分模式大致呈轻、重稀土较富集而中稀土亏损的U型,富Ti、V、Cr,表明铁质可能来自安山质岩浆的结晶分异作用；矽卡岩亚成矿期的磁铁矿∑REE极低,略微富集LREE,其它稀土元素亏损强烈,贫Ti、V,略富集Ni、Co和Cu。矽卡岩亚期的含矿和无矿矽卡岩中的石榴石的稀土配分模式类似,∑REE含量相对较高,呈HREE富集、LREE亏损、弱正Eu异常的分布型式,显示了交代成因石榴石的特征,暗示与其共生的磁铁矿也是通过热液流体与围岩地层的交代反应生成的,铁质来自围岩。(5)磁铁矿氧同位素显示,从岩浆期到矽卡岩期,δ18O具有降低的趋势,反映了围岩蚀变等热液活动对成矿流体的改变。岩浆成矿期和矽卡岩期硫同位素主要显示岩浆来源,但岩浆期可能有少量围岩地层硫或海水硫的混入。成矿晚期阶段的方解石δ13CPDB-δ18OSMOW呈正相关,指示可能存在不同类型NaCl浓度混合或流体-围岩之间的水岩反应,大理岩为成矿作用提供了部分的成矿物质。(6)成矿晚期方解石中的流体主要为NaCl-H2O体系,包裹体主要为气液两相包裹体。流体包裹体均一温度-盐度的相关性表明,在随着成矿作用的逐渐进行,晚期流体的盐度逐渐降低,可能经历了等温混合作用以及不同温度、盐度的流体的混合过程。(7)与磁铁矿关系密切的石榴石Sm-Nd等时线年龄为316.8±6.7Ma,指示了高温热液蚀变的时间,表明主要的磁铁矿体形成时代为早石炭世晚期,成矿作用及其高温热液蚀变不是矿区二叠纪岩体侵入携带的岩浆热液与大理岩发生的矽卡岩化所导致的,可能是大哈拉军山组火山岩喷发后的岩浆期后热液与下伏大理岩发生的接触交代反应所引起的。(8)结合矿床地质特征、矿石组构特征、稳定同位素和典型矿物的稀土微量分布型式,并将查岗诺尔铁矿的地质地球化学特征与典型的矽卡岩型铁矿和火山岩型(包括岩浆型)铁矿进行对比,认为查岗诺尔铁矿可能是岩浆型和矽卡岩型(主要)的复合叠加矿床,矽卡岩化对铁成矿有重要的贡献。更多还原

【Abstract】 As one of the important components of the Central Asian Orogenic Belt, Western Tianshan Mountains experienced complex accretionary orogenic process, and Western Tianshan metallogenic belt is also one of the famous Fe-Cu-Au poly-metallic regions. From2004on, great progress has been achieved in iron exploration in the Awulale metallogenic belt of Western Tianshan Mountains due to the discovery of several medium to large-size Fe deposits. Located in the eastern Awulale metallogenic belt, north side of Western Tianshan Mountain, the large-scale Chagangnuoer iron de-posit is hosted in the volcanic rock termed by Carboniferous Dahalajunshan Formation, which may be the product on the continental arc created by the subduction of the Junggar Ocean southward beneath the Yili plate in the late Early Carboniferous. This iron ore consists of two predominate ore bodies named as Fe I and Fe II, with one lentoid marble as footwall rock beneath the main ore bodies Fe I which exhibit as lamellar, stratoid and lenticular, controlled by NW, NWW, NEE strike faults and circular faults. Mineralizations take place along fissures and fractures in the wall rocks. Wall rock alterations chiefly exhibit garnetization, actinolitization, chloritization, epidotization and so on. On the basis of field geological survey and indoor ore microscopy, using by these tec-hnical means of electron microprobe, inductively coupled plasma mass spectrometry, isotope mass spectrometry and mircothermometry, doing some studies included mineralogy, trace element geoch-emistry, stable isotope, fluid inclusion and Sm-Nd geochronology etc., and compared geological ch-aracteristics of the Chagangnuoer iron deposit with those of other typical iron deposits, to search ore-forming source, to explore ore genesis, and to build metallogenic model, in order to further summarize mineralization mechanism and metallogenic regularity of iron ores in the Awulale Belt, this thesis has proposed several points as follows.(1) This iron deposit is hosted in the upper-middle sections of andesite and andesitic volcanic-lastics of Carboniferous Dahalajunshan Formation. Ore minerals are mainly consisted of magnetite, and subordinately pyrite and chalcopyrite while the gangue minerals are composed of garnet, actin-olite, chlorite, epidote, tremolite, and calcite et al. Ore structures mainly occur as brecciated,spotted and mottled,"leopard pattern", massive, disseminated and banded, whereas ore textures dominantly display as anhedral, allotrio-hypidiomorphic, metasomatic, filling and intersertal.(2) The alteration zonation is similar with typical hydrothermal deposits. According to ore fab-ric and mineral paragenesis, this deposit can be divided into two ore-forming stages, which are magmatic stage and hydrothermal stage (included prograde sub-stage and quarts-sulfide sub-stage), and could be further subdivided into magnetite-diopside phase, chlorite-pyrite phase and magnetite-garnet-actinolite phase, propylitic phrase, sulfide phase and quartz-carbonate phase.(3)Electron microprobe analyses show that componential characteristics of garnet and pyroxene are quite similar with those in calcic skarn from the major large iron deposits, and probably are resulted from skarnization. In the Ca+Al+Mn vs Ti+V discriminant diagram showing spot analyses of magnetite and hematite, almost of data from the Chagangnuoer ore are fall into the district of skarn type of iron deposit. In addition, in the ternary plots of TiO2-Al2O3-MgO of magnetite, many data from the Chagangnuoer ore are seated in the sedimentary metamorphogenic and contact meatasomatic trending region while less amount of those dropping into magmatic mafic-ultramafic trending region. (4) In the magmatic stage, REE in magnetite is very low, rich in LREE and HREE but depl-eted in MREE with a U type pattern. This kind of magnetites has a higher Ti, V, Cr, indicating that Fe might come from the crystallization differentiation of andesitic magma. On the other hand, in the prograde sub-stage, magnetites have a lower REE content, a bit rich in LREE but other REE strongly depleted. Compared with the magnetites in magmatic stage, these magnetites are po-or in Ti, V but a bit abundant in Ni, Co and Cu content. Garnets in barren and ore-bearing skarn distribute the same REE patterns, having a relatively high REE content, enriched in HRRE but depleted in LREE, and with a not pronounced positive Eu anomaly, which displays the feature of garnet with metasomatic origin in the calcic skarn. And this hints that the magnetites, which have a paragenesis relationship with ore-bearing garnets, should be also a product of hydrothermal fluid replacement with wall rocks, and most of the mineralizing materials (Fe) probably are derivate fr-om andesitic strata.(5) Oxygen isotopes of magnetite show that the818O values display a decreasing trend, which reflects that wall alteration may change the ore-forming fluid. Both the sulfur isotope components between magmatic stage and prograde stage mainly distribute the magmatic feature, yet certain mi-nor strata sulfur or oceanic sulfur might be mixed in the former. In the late ore-forming stage, the δ13CPDB-δ18Osmow ratios of calcite show a positive linear correlation, probably attributing to the mixture of different concentrations of NaCl fluid or the water-rock reaction between ore-forming fluid and wall rocks, and marble may contribute to partial mineralization materials.(6)In the late ore-forming stage, fluid inclusions in the calcite are chiefly gas-liquid two phase type, indicating that ore-forming fluids may belong to NaCl-H2O system. Plot showing homogeni-zation temperature versus salinity of fluid inclusions in calcite provides the information that the sa-linity of late ore-forming fluids decreased with the reaction of mineralization, and that this process might be related with the isothermal mixing and mixture of various fluids with different temperat-ures and salinities.(7) Garnet, which has a closely paragenesis relationship with magnetite, yields the Sm-Nd iso-chron age with316.8±6.7Ma, which represents the formation epoch of high hydrothermal alteration. This result indicates that magnetite intergrown with garnet formed at the late stage of Early Carb-oniferous. Therefore, the iron metallogeny and high hydrothermal alteration should result from the metasomatism between the post-magmatic hydrothermal derivated from eruption of Dahalajunshan Formation volcanics and the underlying marble, rather than the skarnization caused by the magmat-ic hydrothermal from Permian intrusion with marble in ore district.(8) In combination the ore deposit geology, ore fabric features with mineralogy of typical mi-nerals, stable isotopes, and rare element chemistry, compared with typical skarn iron deposits and volcanic iron deposits (included magmatic type), conclusions have been drawn that the Chagangnu-oer iron ore is one polygenetic deposit with the skarn type (predominated) superposition upon the magmatic type, and that skarnizations would play an quite important role on the deposition of this iron deposit..更多还原