新疆尼勒克县圆头山后碰撞花岗斑岩的同位素年代学及地球化学特征

圆头山黑云母花岗斑岩位于尼勒克县城南,岩体普遍发育的铜矿化,以中部碎裂带中矿化最强。岩石具有典型的斑状结构,斑晶由碱性长石和黑云母组成,基质以长石、云母和石英为主,并含有少量的硫化物。圆头山黑云母花岗斑岩的轻重稀土分馏明显,并且明显富集大离子亲石元素(LILE) (除Sr外)和Pb,同时亏损高场强元素(HFSE)和Nb、Ta、P、Ti,显示出弧火山岩的地球化学特征。圆头山黑云母花岗形成年龄为269±3Ma,其源区以具有弧火山岩特征的下地壳为主,同时含有少量的幔源物质,而且在岩体的侵位过程中有高(⁸⁷Sr/⁸⁶Sr)_i (0.706054~0.709228)和高Pb含量(5.05×10^-6~32.5×10^-6)的陆壳物质混染。在下地壳物质熔融过程中,位于下地壳底部的富水和成矿元素的MASH带物质也被圈入,使原始岩浆富水和成矿物质。圆头山黑云母花岗斑形成于碰撞后阶段,岩石的形成主要受岩石圈地幔拆沉作用的控制,而岩石圈地幔的拆沉可能与中亚造山带的垮塌或塔里木地幔柱活动有关。     

易门赵普新沟白钨矿矿床地质及控制因素

新沟白钨矿属典型的接触交代(矽卡岩)变质矿床。晋宁晚期的岩浆活动强烈,黑云二长花岗岩是矿区主要成矿岩体。钨矿体赋存在花岗岩体两侧与昆阳群大龙口组灰岩接触带矽卡岩中,地层、岩石、构造对矽卡岩及矿体都有控制作用。     

Low-rhenium molybdenite by metamorphism in northern Sweden: Recognition, genesis, and global implications

Re–Os dating of molybdenite is an accurate means to date intrusions and intrusion-related ore deposits using the model age or isochron approach. But, molybdenite has a new niche in the greenschist- to granulite-facies metamorphic environment. Re–Os ages for metamorphic molybdenite may be used to construct regional metamorphic histories. Age significance and accuracy are established by analyzing multiple molybdenite separates extracted from single, petrographically-characterized molybdenite occurrences. In this study, twelve geologically distinct molybdenite-bearing samples from two small Mo districts in northern Sweden trace a 150 m.y. Paleoproterozoic Svecofennian metamorphic history from 1900 to 1750 Ma. These data reveal a little-known, widespread and protracted, Late Svecofennian anatexis in northern Sweden.The Kåtaberget Mo–(Cu, F) deposit is located in the Moskosel granite batholith north of the economically-renown Skellefte district. Four different molybdenite samples from outcrop at Kåtaberget indicate an intrusion age of 1895 ± 6 Ma with the formation of later pegmatite–aplite at 1875 ± 6 Ma. The Allebuoda (Björntjärn) and Munka Mo–(W) deposits in the Rappen district are represented by three outcrop and five drill core samples of molybdenite-bearing aplite–pegmatite–granite. These two deposits were previously described as intrusion-related Climax-type Mo mineralization. Re–Os ages for molybdenites from these deposits range from 1865 to 1750 Ma and, significantly, Re concentrations are markedly low, extending to the sub-ppm level. Age agreement within the deposits is conspicuously lacking, whereas, with one exception, age agreement within any single sample (geologic occurrence), as established by analysis of additional molybdenite separates, is very good. These data, together with fundamental geologic observations discussed in this paper, suggest that Mo–(W) mineralization in northern Sweden is not intrusion-related, but the local product of episodic melting of Archean–Paleoproterozoic supracrustal gneisses related to the Svecofennian orogeny. Petrographic traverses across the boundary between widespread, foliation-parallel units of aplitic to pegmatitic pink granite and hosting biotite gneiss directly capture the process of ore formation. Dehydration breakdown of zircon-rich biotite aligned with the foliation in the gneiss is accompanied by formation of new pristine, post-deformational biotite plus sulfides, oxides, hydrothermal zircon and fluorite, all associated with microcline-dominant leucosomes.This process has profound implication for the traditional leucogranite, intrusion-related genesis attributed to the broad classification of Mo–W–Sn–base and precious metal mineralization (e.g., South Mountain Batholith, Nova Scotia; Okiep, Namaqualand, South Africa; Mactung, Yukon; Pogo–Liese, Tintina, Alaska; Carajás and Goiás–Rio Tocantins, Brazil; New England Batholith, NSW, Australia; Bergslagen, Sweden; Nevoria, Western Australia; Alpeinerscharte, Austria; Erzgebirge, Germany; Sardinia–Corsica Batholith). In addition to biotite, metallogenic contributions (e.g., Mo, W, Sn, U, Bi, Cu, Pb, Zn, Fe, Ni, Co, Au, Ag, Te, As, Sb, REE) in various combinations may also be controlled by breakdown of amphibole. In effect, the trace element composition of dehydrating or recrystallizing components in a gneissic rock essentially defines the local and district metallogenic suite. In the absence of focusing structures (e.g., shear zones, sheeted vein development), this process will generally form small and disconnected subeconomic deposits with erratic and unpredictable grades. Low Re content in associated molybdenite is a key indicator for a subeconomic origin by local melting of biotite gneiss (Mo–W) or muscovite schist (Sn–W).     

The degree of oxidation of iron in synthetic iron-magnesian biotites

Summary Chemical analytical and pyrolytical methods have been used to study the Fe⁺²/Fe⁺³ ratios and dehydroxylation reactions in synthetic biotites. It has been found for the biotites with Fe/(Fe + Mg) of 20 to 70 mole % that the oxidation degree decreases from 26 to 16% with increasing iron. Based on the measured amounts of water and hydrogen released during pyrolysis it is inferred that the deprotonization is a dominant reaction at low temperatures (T 600°C), accompanied by dehydration as the temperature increases. Depending on the composition, a complete dehydroxylation takes place at T 900 °C, and the measured amount of water corresponds to the iron oxidation degree in the starting samples. The results of this study have important implications with respect to determination of the formation conditions of biotite-bearing rocks, and also for improvement of the techniques for determination of different valence of iron and water.

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Le degré d'oxidation du fer en biotites synthétiques contenants le fer et le magnésium

Résumé Des méthodes chimiques et pyrolitiques ont été utilisées pour l'étude des rapports Fe⁺²/Fe⁺³ et de la réaction de la déhydroxilation en biotites synthétiques. On a trouvé pour les biotites avec Fe/(Fe + Mg) de 20-70 mole % que le degré d'oxidation décroît à partir de 26 jusqu'à 16% pendent que le contenu du fer s'accroît. Sur la base de la quantité d'eau et hydrogène liberée pendant la pyrolyse, on infère que la déprotonisation est une réaction dominante à températures basses (T = 600°C), mais quand la température s'accroît, la déprotonisation est accopagnée de la déhydratation. Dépendant de la composition il y a une déhydroxilation complète à T = 900°C, et la quantité de l'eau mesurée correspond au degré d'oxidation du fer dans les specimens initials. Les résultats de cette étude infuencent la détermination des conditions de formation des roches contenantes biotite et aussi l'amélioration des techniques de la détermination du fer de valences différentes et de l'eau.

     

腾冲铜厂山矽卡岩型铅锌矿床

腾冲西北部滇滩—燕洞一带，燕山晚期花岗岩活动强烈，矽卡岩型矿床发育，形成众多铁、铜、铅、锌矽卡岩型矿床，是腾冲西北部重要成矿区，本文介绍的腾冲铜厂山矽卡岩型铅锌矿即是其中之一。矿床形成与燕山晚期黑云二长花岗岩关系密切，矿体位于上二叠统碳酸盐岩外接触带矽卡岩中。地层、岩石、构造对矽卡岩及矿体都有控制作用。最后提出矿床成因见解。     

赞皇变质窍隆黑云母^40Ar／^39Ar年代学研究及其对构造热事件的约束

太行山南段赞皇变质杂岩中黑云母给出了1827～1793Ma的~(40)Ar/~(39)Ar坪年龄,代表了变质基底在经历高温热扰动后冷却到300℃时的热事件年龄。结合华北克拉通变质岩的其他年代学资料,认为1800Ma士华北克拉通内经历了一次广泛而强烈的构造热伸展事件,致使克拉通基底岩石快速抬升到中上地壳,其冷却速率>6℃/Ma,隆升速率>200m/Ma。赞皇变质杂岩内苍岩寺、岗西-榆底-黑水河东和坡底-郝庄韧性剪切带内糜棱岩中黑云母分别给出了1689Ma、1633Ma和1645Ma的~(40)Ar/~(39)Ar坪年龄,代表了剪切带变形的主变形时代,这一年龄也为约束长城系的底界年龄提供了新的信息。结合已有的热年代学资料,推断华北克拉通内部赞皇变质地区中元古代的冷却速率约0.4℃/Ma,隆升速率为15m/Ma。由此也表明,自中元古代以来华北克拉通内部未受到后期构造热事件的强烈扰动,赞皇变质杂岩并非中生代变质核杂岩,而是早元古代变质穹隆。     

U–Pb and Ar–Ar geochronology of the Fujiawu porphyry Cu–Mo deposit,Dexing district,Southeast China: Implications for magmatism,hydrothermal alteration,and mineralization

The Fujiawu porphyry Cu–Mo deposit is one of several porphyry Cu–Mo deposits in the Dexing district, Jiangxi Province, Southeast China. New zircon SHRIMP U–Pb data yield a weighted mean ²⁰⁶Pb/²³⁸U age of 172.0 ± 2.1 and 168.5 ± 1.4 Ma from weakly altered granodiorite porphyry and quartz diorite porphyry, respectively. Two hydrothermal biotites from granodiorite porphyry give an Ar–Ar step-heating plateau age of 169.9 ± 1.8 and 168.7 ± 1.8 Ma. Hydrothermal apatite exsolved from altered biotite yields an isotope dilution thermal ionization mass spectrometry isochron age of 164.4 ± 0.9 Ma. The apatite age is similar to the ages obtained from hydrothermal rutile (165.0 ± 1.1 and 164.8 ± 1.6 Ma) and indicates that the magmatism and hydrothermal activity in the Fujiawu deposit occurred in the Middle Jurassic. Hydrothermal fluid circulation related to multiple stages of magma emplacement resulted in Cu–Mo mineralization in the Fujiawu porphyry deposit. The zircon SHRIMP U–Pb ages and the published molybdenite Re–Os age (170.9 ± 1.5 Ma) represent the timing of magma crystallization and Mo mineralization, whereas the rutile and apatite U–Pb ages reflect the timing of Cu mineralization following quartz diorite emplacement. The data suggest slow cooling after emplacement of the quartz diorite porphyry.     

Zircon U–Pb and biotite 40Ar/39Ar geochronology from the Anzan emerald deposit in Zambia

The Kafubu Emerald Area in Zambia is an important producer of gemstone-quality emeralds. The country rocks include carbonatization altered rock and emerald-hosting biotite chlorite schist from the Anzan emerald deposit in the Kafubu area, Zambia. The technique of LA-MC-ICP-MS is used to perform chronology measurements of the country rock and emerald-hosting rock which belong to Muva Supergroup, yielding zircon U-Pb concordia ages of 1966 ± 12 Ma in carbonatization altered rock and 1853 ± 58 Ma and 1344 ± 30 Ma in biotite chlorite schist. Meanwhile, dating of biotite chlorite schist using the biotite ⁴⁰Ar–³⁹Ar method has obtained the plateau age of t = 578.3 ± 2.6 Ma, isochron age of 577.5 ± 3.0 Ma and reverse isochron age of 577.4 ± 3.0 Ma. Thus, we have redefined the age of Muva Supergroup in the Copperbelt Province in Zambia to be older than or equal to 1966 ± 12 Ma, and found that the ore bodies in the Anzan emerald deposit underwent three phases of metamorphism at 1853 ± 58 Ma, 1344 Ma ± 30 and 578.3 ± 2.6 Ma and finally accomplished the emerald mineralization. The age of the Anzan emerald deposit is earlier than the Kagem (452.1 ± 16 Ma) and the Kamakanga emerald deposits (447 ± 8.6 Ma).     

内蒙古呼和浩特北二道凹岩群黑云角闪片岩SHRIMP锆石U-Pb定年

二道凹岩群是20世纪70年代初1∶200000区域地质调查时在呼和浩特市北二道凹地区命名的,其岩石组合为变质砾岩、各种片岩、大理岩等。依据最新1∶250000区调成果,自下而上分了三个岩组,即红山口岩组、哈拉更沟岩组、东梁岩组。为进一步研究二道凹岩群的地质时代,本文对东梁岩组的黑云角闪片岩中锆石进行了高精度SHRIMP U-Pb测年研究,其时代为1890±8 Ma,认为该年龄值系黑云角闪片岩原岩的形成时代,即代表了二道凹岩群上部中基性火山岩的形成年龄,结合已有的年龄数据,进一步佐证了二道凹岩群形成于古元古代(1800~2400Ma)。     

江西大湖塘钨矿田平苗矿区含矿花岗岩矿物学特征及对成矿的指示意义

赣西北大湖塘钨矿田位于江南造山带东段,是世界级超大型W-Cu-Mo多金属矿田,矿化类型以细脉浸染型矿化为主,成矿作用与燕山期高分异花岗岩密切相关。本文通过对平苗矿区与成矿关系密切的燕山期花岗岩中黑云母和斜长石等矿物进行系统的原位主量元素和微量元素分析,探究岩浆的氧逸度、岩浆系统的深部动力学特征和详细结晶过程,并对成矿作用的指示意义进行探讨。研究表明,似斑状二云母花岗岩从岩浆结晶早期到晚期,一直保持较低的氧逸度（NNO-QFM）,可能与岩浆源区中更多的富泥质沉积岩有关,这种富钨的泥质岩源区和还原性岩浆环境更有利于钨矿的形成。燕山期花岗岩中斜长石的钙长石（An）和CaO含量均远低于晋宁期黑云母花岗闪长岩,很难为白钨矿化提供足够的钙,而黑云母花岗闪长岩由于体积巨大、钙含量高,很可能为区内大规模的白钨矿化贡献了大量的钙元素。斜长石原位分析显示,An和Al₂O₃含量之间存在显著的正相关性,而与FeO含量之间无明显的正相关性,FeO随着An含量的增加基本保持稳定,斜长石中Sr和Ba含量之间也无显著的负相关性,表明该区岩浆房为化学成分相对封闭的岩浆系统,岩浆演化过程中只有热量混合和/或减压作用,没有发生明显的镁铁质岩浆注入与混合。因此,钨、铜、硫等成矿元素应主要来自岩浆源区双桥山群的富泥质变质沉积岩和变质玄武岩的贡献,而非由外来基性岩浆的补给提供。该区岩浆岩形成于华南板块由挤压向伸展的转换期,挤压环境有利于在地壳浅部形成长期稳定的、规模较大的高分异岩浆房,促进成矿元素高度富集和大规模岩浆热液的形成,导致该区发生大规模的钨铜矿化。