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阿尔泰柯鲁木特-吉得克矿集区 Li-Be-Nb-Ta 成矿作用
王春龙
学位类型博士
导师秦克章 ; 周可法
2017-05-01
学位授予单位中国科学院大学
学位授予地点新疆乌鲁木齐
学位专业理学博士
关键词阿尔泰地区 柯鲁木特-吉得克伟晶岩区 富 Li 伟晶岩 矿物学 铌钽矿物u-pb 年代学 母体花岗岩 伟晶岩含矿性评价 Chinese Altai Kelumute-jideke Pegmatite Field Li-enriched Pegmatite Mineralogy Columbite-group Mineral U-pb Geochronology Parental Granite EvaluatIng Of Rare-metal MIneralization In Pegmatite
摘要柯鲁木特-吉得克伟晶岩区是阿尔泰地区重要的稀有金属矿集区,且发育区域上少见的以吉得克花岗岩为中心的稀有金属伟晶岩区域分带。近年来库卡拉盖矿区外围卡鲁安地区以及群库尔矿区深部稀有金属勘查工作取得重大进展,使得该伟晶岩区成为区域上稀有金属伟晶岩研究的热点地区。本论文选取该伟晶岩区规模最大的两个稀有金属矿床——柯鲁木特与库卡拉盖 Li-Be-Nb-Ta 矿床为重点研究对象,在系统的野外地质调查基础之上,对这两个矿区中的代表性稀有金属伟晶岩开展了岩相学、矿物学、熔-流体和年代学研究,以揭示稀有金属伟晶岩的成因机制及演化过程。同时对该伟晶岩区的吉得克花岗岩进行了岩石学、矿物学、岩石地球化学和年代学方面的系统研究,来揭示花岗岩与稀有金属伟晶岩之间的成因联系,建立区域成岩-成矿模式。在对该伟晶岩区深入研究的基础之上,试图总结阿尔泰地区发育大规模稀有金属矿化伟晶岩的成矿地质特征,同时提出若干条稀有金属含矿性评价判别标志,用以指导区域稀有金属勘查工作。柯鲁木特与库卡拉盖矿区的稀有金属伟晶岩脉尽管在赋存围岩、控矿构造以及内部分带特征上存在明显差异,但野外观察表明这些伟晶岩脉均主要由石英-锂辉石-钠长石带组成,该带在各伟晶岩脉中的体积分数通常>70%,同时同一伟晶岩脉内部各带之间不发育演化程度的显著差异。此外两个矿区均以 Li 矿化为主,因而这些稀有金属伟晶岩脉均属于内部分带相对不发育的富 Li 伟晶岩。矿物组合表明其属于钠长石-锂辉石型伟晶岩。柯鲁木特与库卡拉盖矿区主要稀有金属伟晶岩脉中的微斜长石、云母、铌钽矿物、锆石等贯通性矿物的主微量元素特征表明,这些伟晶岩脉各内部相带均达到了较高的演化程度,此外两个矿区主要稀有金属伟晶岩的演化程度相近。各伟晶岩脉原生相带中云母及铌钽矿物相对均一的内部结构,则表明其主体形成于相对平衡条件下的结晶作用。在柯鲁木特 112 脉中的锆石及铌钽矿物中观察到稀土元素四分组效应以及微量元素 non-CHARAC 比值等“极端”分异行为,可能反映了形成该伟晶岩初始熔体高度演化的本质特征。综上这些内部分带相对不发育的富 Li 伟晶岩,形成于演化程度较高的初始熔体在近平衡条件下的结晶作用。对石英、绿柱石、锂辉石与钠长石中熔-流包裹体与熔融包裹体的成分分析表明,各类包裹体的气相成分包括 H2O、CO2 以及 N2,固相成分中观察到较多的石英及类似矿物,升温过程中多表现为气相先于结晶相消失,表明形成这些稀有金属伟晶岩的熔体具富 Si、相对富 H2O 的特征。显微测温结果显示两个矿区各稀有金属伟晶岩脉中各类包裹体的完全均一温度范围分别为 710–850 ℃与 600–750 ℃,反映了形成伟晶岩熔体的温度。首次对研究区内的稀有金属伟晶岩开展 LA-ICP-MS 铌钽矿物 U-Pb 年代学研究。由于运用铌钽矿物进行 U-Pb 定年能够规避锆石由于高 Th、U 含量发育蜕晶化作用而导致的问题,同时本文获得的铌钽矿物年龄谐和度较高且误差较小,因而认为其代表了两个矿区稀有金属伟晶岩脉的形成时代。柯鲁木特矿区 112 与 116 脉各相带获得的年龄范围为 204.5–207.9 Ma,库卡拉盖矿区 650、807 及 806 脉则为 202.4–206.8 Ma。这些年龄结果表明两个矿区主要稀有金属伟晶岩脉的形成及演化集中于晚印支期,由于分布范围基本一致,表明其为同期构造-岩浆事件的产物。此外铌钽矿物年龄结果表明,最为集中的一组锆石 U-Pb 年龄(194.2–205.5 Ma)可能记录了从伟晶岩结晶到蜕晶化作用持续的时间。各伟晶岩脉中的锆石表现出类似的 Hf 同位素组成特征,包括呈较低的正值或负值的 εHf(t)值(-0.44–+2.29),以及集中分布于中元古代的 TDMC模式年龄(1098–1270 Ma),表明这些稀有金属伟晶岩的成岩源区以古老壳源物质为主。野外地质观察认识到吉得克花岗岩以成分和结构的显著不均一为特征,包括中-粗粒二云母花岗岩、二云母钾长花岗岩与细粒二云母花岗岩三个岩相。主量元素特征显示各岩相成分主要为过铝质的 S 型淡色花岗岩,与全球范围内研究程度较高的稀有金属伟晶岩的母体花岗岩特征一致。微量元素特征以及白云母、微斜长石的矿物学特征显示各岩相均达到了较高的分异演化程度,因而具备了进一步演化形成稀有金属伟晶岩的潜力。各岩相的锆石 U-Pb 年龄介于 203.4–207.8 Ma,该区间与稀有金属伟晶岩的铌钽矿物及锆石 U-Pb 年龄范围也基本一致。综上证实了吉得克花岗岩高度分异演化的特征,结合其与周围稀有金属伟晶岩之间的时空关系,提出该岩体为柯鲁木特-吉得克伟晶岩区的母体花岗岩。据此建立了区域成岩-成矿模型,来解释伟晶岩特征性区域分带的成因。通过总结阿尔泰地区以及全球范围内大型-超大型稀有金属伟晶岩的控矿因素及地质特征,结合近年来阿尔泰地区稀有金属勘查工作的进展,分析阐述了阿尔泰地区有利于稀有金属伟晶岩形成的主要因素,以及一些可用于稀有金属勘查工作并已证实有效的找矿标志,并对前人已有的含矿性评价指标进行量化。上述工作使本研究除具理论意义之外,也兼具勘查应用。
其他摘要The Kelumute-Jideke pegmatite field is one of the most important rare-metal ore deposit clusters in the Chinese Altai, within which the uncommon regional zonation of rare-metal pegmatites around the Jideke granite has been observed. Great advances in rare-metal exploration have been achieved in the Kukalagai and Qunkuer ore districts in recent years, which made this pegmatite field became the regional focus for the study of rare-metal pegmatites. Based on field observation, an integrated study including petrography, mineralogy, melt-fluid inclusion and geochronology, is carried out on representative pegmatite dykes in the Kelumute and Kukalagai Li-Be-Nb-Ta deposits, to reveal the genesis and internal evolution of these rare-metal pegmatites. Meanwhile, a systematic study of petrology, mineralogy, petro-geochemistry and geochronology has been carried out on the Jideke granite, to reveal the genetic link between granite and rare-metal pegmatites, and create a regional petrol-metallogenic model for this pegmatite field. Based on detailed studies of this pegmatite field, in combination with summarizing metallogenic features of large rare-metal pegmatites in the Chinese Altai, we try to present several indicators for the evaluation of rare-metal mineralization in pegmatite.Despite the obvious differences in wallrocks, ore-controlling structures and internal zonation of rare-metal pegmatites in the Kelumute and Kukalagai ore districts, field evidence reveals that these pegmatites are dominated with the quartz-spodumene-albite zone, which covered over 70 vol.% of these dykes. Besides, there is little variation in the degree of fractionation between different internal zones of the same pegmatite.Considering that these two deposits are featured by large scales of lithium mineralization, rare-metal pegmatites in the two ore districts are typical zonless Li-enriched pegmatites.Moreover, mineral assemblages indicate these that these pegmatites belong to the highly fractionated albite-spodumene subtype pegmatite.Major and trace element features of microcline, micas, columbite-tantalite and zircon from representative pegmatites in the Kelumute and Kukalagai ore districts, indicate high and similar fractionation degrees for these rare-metal pegmatites. Despite the different occurrences of the same mineral in these two ore districts, trace element compositions reveal little variation in the fractionation degree of these pegmatites. Relatively homogeneous internal structure of columbite-tantalite and micas from primary zones of these pegmatites, indicate a nearly equilibrium crystallization during the primary magmatic stage. In addition, extreme fractionation behaviors including the lanthanide tetrad effect and non-CHARAC behaviors are observed in zircon and columbite-tantalite from the Kelumute No.112 pegmatite, and are ascribed to an intrinsic feature of highly evolved pegmatitic melts. Consequently, neraly equilibrium crystallization in highly evolved initial pegmatitic melts, formed these relatively zoneless Li-enriched pegmatites. The LA-Raman analysis of melt-fluid and melt inclusions in quartz, beryl, spodumene and albite from representative rare-metal pegmatites in the two deposits, reveals that vapor phases in different types of inclusions are mainly H2O, CO2 and N2, while crystallized phases are dominantly quartz or other silica-rich minerals. Besides, vapor phases are commonly homogenized before crystallized phases during heating, indicates that these pegmatites were formed by silica-enriched and H2O relatively enriched melts. The microthermotery data for melt-fluid and melt inclusions in the Kelumute ore district range from 600 to 750 ℃, and 710 to 850 ℃ in the Kukalagai ore district, reveals the temperature of these pegmatitic melts.For the first time, LA-ICP-MS columbite-tantalite U-Pb dating has been carried out in the studied area. By adopting columbite-tantalite U-Pb dating, this study avoids problems of zircon in pegmatites due to its high Th, U contents and widespread metamictization.Besides, our columbite-tantalite U-Pb ages are highly concordant and with small uncertainties, which are reliable and can represent formation ages of these pegmatites.Time ranges of 204.5–207.9 Ma and 202.4–206.8 Ma have been obtained for pegmatites in the Kelumute and Kukalagai ore districts, repectively, which indicate formation and evolution of these pegmatites are mainly during the Late Indosinian. Moreover, these columbite-tantalite U-Pb ages, indicate that the dominant range (194.2–205.5 Ma) of zircon U-Pb ages recoded the timing duration from emplacement of pegmatites to metamictization of zircon. Similar hafnium isotopic compositions of zircon from the two ore districts has been observed, which include low positive or negative εHf(t) values (-0.44–+2.29), and TDM C model ages that concentrated in the middle Mesoproterozoic (1098–1270 Ma). These features indicate that rock-forming materials were dominated by ancient continental materials.Field observation reveals the high heterogeneity in composition and textures of the Jideke granite, three different lithology including nearly equigranular two-mica granite,two-mica potassium feldspar granite and fine-grained two-mica granite have been identified. Major element features indicate peraluminous leucogranitic composition for different petrofacies of the granitic stock, which are consistent with typical parental granite of rare-metal pegmatites globally. Trace element features combined with mineralogy of muscovite and microcline indicate highly fractionated nature of the granite, which is capable of differentiating pegmatitic melts. Zircon U-Pb dating results reveal that the formation of different petrofacies were between 203.4–207.8 Ma, while this time range is nearly overlapping with the time span of rare-metal pegmatites. Consequently, these evidence sustains that the Jideke granite is the parental granite of the Kelumute-Jideke pegmatite field. Accordingly, we established the petrol-metallogenic model for the pegmatite field, and tried to discuss the origin of regional zonation for pegmatites.By summarizing the ore-controlling factors and geological features of major large and giant rare-metal pegmatites regionally and globally, combined with the experience of recent advances in rare-metal exploration in the Chinese Altai, we try to figure out the favourable factors for rare-metal mineralization in the Chinese Altai, and propose several indicators for further rare-metal prospecting and exploration. Besides, quantification of existing indicators has been conducted as well. Consequently, our work has both of scientific and economic significances.
学科领域地球探测与信息技术
语种中文
文献类型学位论文
条目标识符http://ir.xjlas.org/handle/365004/14791
专题研究系统_荒漠环境研究室
研究系统_空间对地观测与系统模拟研究室
作者单位中国科学院新疆生态与地理研究所
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王春龙. 阿尔泰柯鲁木特-吉得克矿集区 Li-Be-Nb-Ta 成矿作用[D]. 新疆乌鲁木齐. 中国科学院大学,2017.
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