Evolution of fluids associated with metasedimentary sequences from Chaves (North Portugal)

In order to identify and characterise fluids associated with metamorphic rocks from the Chaves region (North Portugal), fluid inclusions were studied in quartz veinlets, concordant with the main foliation, in graphitic-rich and nongraphitic-rich lithologies from areas with distinct metamorphic grade. The study indicates multiple fluid circulation events with a variety of compositions, broadly within the C–H–O–N–salt system. Primary fluid inclusions in quartz contain low salinity aqueous–carbonic, H₂O–CH₄–N₂–NaCl fluids that were trapped near the peak of regional metamorphism, which occurred during or immediately after D2. The calculated P–T conditions for the western area of Chaves (CW) is P=300–350 MPa and T500 °C, and for the eastern area (CE), P=200–250 MPa and T=400–450 °C. A first generation of secondary fluid inclusions is restricted to discrete cracks at the grain boundaries of quartz and consists of low salinity aqueous–carbonic, H₂O–CO₂–CH₄–N₂–NaCl fluids. P–T conditions from the fluid inclusions indicate that they were trapped during a thermal event, probably related with the emplacement of the two-mica granites.

A second generation of secondary inclusions occurs in intergranular fractures and is characterised by two types of aqueous inclusions. One type is a low salinity, H₂O–NaCl fluid and the second consists of a high salinity, H₂O–NaCl–CaCl₂ fluid. These fluid inclusions are not related to the metamorphic process and have been trapped after D3 at relatively low P (hydrostatic)–T conditions (P<100 MPa and T<300 °C).

Both the early H₂O–CH₄–N₂–NaCl fluids in quartz from the graphitic-rich lithologies and the later H₂O–CO₂–CH₄–N₂–NaCl carbonic fluid in quartz from graphitic-rich and nongraphitic-rich lithologies seem to have a common origin and evolution. They have low salinity, probably resulting from connate waters that were diluted by the water released from mineral dehydration during metamorphism. Their main component is water, but the early H₂O–CH₄–N₂–NaCl fluids are enriched in CH₄ due to interaction with the C-rich host rocks.

From the early H₂O–CH₄–N₂–NaCl to the later aqueous–carbonic H₂O–CO₂–CH₄–N₂–NaCl fluids, there is an enrichment in CO₂ that is more significant for the fluids associated with nongraphitic-rich lithologies.

The aqueous–carbonic fluids, enriched in H₂O and CH₄, are primarily associated with graphitic-rich lithologies. However, the aqueous–carbonic CO₂-rich fluids were found in both graphitic and nongraphitic-rich units from both the CW and CE studied areas, which are of medium and low metamorphic grade, respectively.     

On the origin of oriented rutile needles in garnet from UHP eclogites

Although oriented rutile needles in garnet have been reported from several ultrahigh‐pressure (UHP) rocks and considered to be important UHP indicators, their crystallographic features including growth habit and lattice correspondences with garnet host have never been properly characterized. This paper presents a detailed analytical electron microscopic (AEM) study on evenly distributed oriented rutile needles in garnet of two eclogitic rocks from Sulu. Some garnet in one UHP diamondiferous quartzofeldspathic rock from the Saxonian Erzgebirge, and in one high‐pressure (HP) felsic granulite from Bohemia also contain a few unevenly distributed oriented rutile needles. They have also been studied for the purpose of comparison. Despite different distribution patterns, AEM revealed that all rutile needles are oriented along the 〈111〉 directions of garnet with their lateral sides surrounded by the {110} planes of garnet, and that the growth directions of most needles are close to the normal of the {101} planes of rutile. No other specific crystallographic orientation relationships between rutile and garnet host were observed, and there is no pyroxene associated with rutile, as necessitated by the precipitation reaction of rutile in garnet as previously proposed. A simple solid‐state precipitation scenario for the formation of the rutile needles in garnet in these two eclogitic rocks is not justified. Three alternative mechanisms are considered for the formation of oriented rutile needles: (i) the rutile needles may be inherited from precursor minerals; (ii) the rutile needles may be formed by a dissolution–reprecipitation mechanism; and (iii) the rutile needles may be formed by cleaving and healing of garnet with rutile deposition. None of these mechanisms can fully explain the observations, although the first one is less likely and the third one is preferred. This study presents an example where the presence of oriented/aligned inclusions in minerals does not necessarily imply a precipitation origin.     

西昆仑沃克金矿床地质特征、金的赋存状态及矿床成因探讨

沃克金矿床是西昆仑西段金铜矿带近期发现的一处具有大型远景的金矿床。金矿体主要产于近东西向展布的韧-脆性剪切带中,赋矿岩石为穿切于绢云千枚岩中的石英脉。主要矿化类型为毒砂矿化、黄铁矿化、黄铜矿化,热液蚀变为绢云母化、硬绿泥石化和碳酸盐化。在野外地质勘查与研究的基础上,笔者结合镜下显微观察,将成矿阶段划分为早（S1）、主（S2）和晚（S3）阶段,主阶段形成大量硫化物及方解石石英脉。载金硫化物主要为毒砂,次为黄铜矿、方铅矿。利用电子探针（EPMA）对载金硫化物进行分析,结合单元素面扫描成像,笔者认为金矿石主要以细粒金和中粒金形式存在。流体包裹体显示温度变化范围230~493℃,w （NaCl） _eq为1.56%~18.19%,成矿流体具有中高温、中低盐度的特征,表现为NaCl-H₂O-CO₂体系。石英δ¹⁸O值为8.6‰~14.0‰,流体的δD值在-83.7‰~-103.6‰,显示出变质水和大气降水的混合流体来源特征;硫同位素组成显示成矿物质源自中浅变质岩。笔者认为,沃克金矿床为与韧-脆性剪切带有关的中成造山型金矿床。     

NaCl-H2O-CO2体系人工合成流体包裹体实验研究

NaCl- H2O-CO2体系流体是热液成矿系统中最常见的流体之一,针对该体系相关特征的研究对理解热液矿床的成矿机制和过程、成矿流体特征等具有重要的理论和实际意义.本文利用愈合人工水晶裂隙的技术,开展100 MPa、800℃条件下NaCl-H2 O-CO2体系流体的人工合成包裹体实验,并对其物理化学性质进行了初步探讨.通过对合成的包裹体进行岩相学观察、显微测温以及喇曼光谱分析,结果表明,在实验温压条件下合成的包裹体捕获了既定组成的流体;人工合成NaCl- H2O-CO2体系流体包裹体与天然流体包裹体具有相似的特征,可以作为天然包裹体的参照物应用于流体包裹体及地质流体的研究,特别是在评价CO2在热液矿床成矿过程中的作用方面,NaCl-H2O-CO2体系人工合成包裹体具有广阔的应用前景.     

中国东部幔源气体同位素地球化学

中国东部地幔岩包体及其单矿物中发育有大量的流体包裹体，采用阶段加热真空热爆的 方法脱出幔源包裹体中的气体，测试了气体的碳、氧、氦、氮等同位素组成。ＣＯ２的σ１３℃普遍较低， 主峰值为（－１８～－２２）×１０－3 ，多数样品在高温下的 σ１３℃普遍小于低温下的对应值。氧同位素变 化也很大，从－３．４×１０－３至２５．５×１０－３（ＳＭＯＷ），并呈现多峰的特征。σ１８Ｏ与σ１Ｃ３具有很好的相 关性，可能受控于同种分馏机制。Ｃ、Ｏ同位素组成特征表明，中国东部大陆地幔具有很大的化学不 均一性，可能是由地幔碳的多样性、源区的不均一性或地幔交代作用所致。氧同位素的变化可能是 结晶作用、去气作用或地壳物质混染所至。４Ｈｅ含量变化范围为（０．２４～２５．００）×１０－８，３Ｈｅ／４Ｈｅ变 化范围为（０．４６～１２．８０）×１０－６，４０Ａｒ含量从０．９７×１０－６到３４．１８×１０－６，４０Ａｒ／３６Ａｒ变化范围为 ２５０．５８～１２０２。３Ｈｅ／４Ｈｅ的变化反映了亏损地幔和富集地幔的存在。不同地区４０Ａｒ／３６Ａｒ的巨大差 异显示了地幔脱气程度的不同，也说明在地幔演化中Ａｒ、Ｈｅ同位素地球化学行为的差异。     

大厂锡矿的成矿流体

本文详细研究了矿带内流体包裹体特征,测定了不同类型包裹体在冷热状态下相的转变点温度,利用有关的NaCl-H_2O体系、CO_2-NaCl-H_2O体系相图获得了矿带内不同类型矿床成矿的温度、压力等物理、化学参数。通过包裹体成分和同位素研究,阐明了成矿流体的性质、来源及其演化特征,探讨了成矿流体的沸腾和不混溶作用以及它们对成矿所作的贡献。估测了矿化深度和盲矿体存在的可能性。     

云南兰坪北部铜多金属矿化区成矿流体流动与矿化分带——流体包裹体和稳定同位素依据

滇西兰坪盆地北部发育了一类受逆冲推覆构造控制的浅成热液Cu—Ag—Pb-Zn矿化，形成了白秧坪、富隆厂、吴底厂、麻栗坪及金满、科登涧等大-中型矿床和矿点，并存在矿化分带。文章利用这些矿化脉体的流体包裹体和热液方解石的碳氧同位素组成资料，研究成矿流体与矿化分带的关系。结果表明，成矿流体主要属于NaCl-H2O成分体系，盐度ω(NaCleq)为2％～11％，形成温度为170～300℃，形成于1．8～3．8km深度内，这些相似性说明这类矿化的发生具有相似的流体性质和沉淀机制。热液方解石在δ^13C-δ^18O图解中呈近水平线展布的型式，指示流体源自地壳浅部的地下水系统，与海相灰岩等围岩作用形成了溶解碳以[HCO3^]-为主的成矿流体，流体与岩石的相互作用可能是成矿流体沉淀的主要机理。从西到东，流体包裹体的盐度-温度由高到低变化与矿化分带和逆冲推覆构造的根带→中带→锋带相配套，显示重力驱动流动可能是主要的流体流动机制。成矿流体在不同构造部位流动的通畅及流体．岩石系统的封闭-开放程度等流体流动性质与矿化发生的强度和规模有关，兰坪北部逆冲推覆构造中带的流体通畅地流动及沉淀时处于相对开放状态，有利于该区形成较大规模的浅成热液多金属矿化。     

新疆小于赞金矿流体包裹体分析及与加曼特和阿希金矿的比较

新疆小于赞金矿床石英中存在富液相气液两相包裹体、富气相气液两相包裹体和纯液相包裹体。包裹体均一温度为108~237℃,主要集中在130~180℃。测得的冰点温度范围为-0.1~-6℃,对应的盐度为0.18~9.21 wt%Na Cleqv,密度范围在0.82~1.04 g/cm3,在分析的过程中所测得的数据包括均一温度、冰点温度以及密度都在较低值区域分布。通过阿希金矿、加曼特金矿进行了系统的比较分析,认为小于赞金矿可能属于中低温低盐度低密度热液型矿床。     

滇西兰坪盆地茅草坪脉状Cu矿床流体包裹体和稳定同位素地球化学研究

兰坪盆地西缘发育一条重要的脉状Cu矿带,矿床的成矿流体来源一直存在较大的争议。本次研究对该矿带南段新发现的茅草坪矿床进行流体包裹体和H-O-C-S同位素研究,结合前人发表的该矿带矿床的同位素数据,探讨矿床成矿流体特征和来源。茅草坪矿床早(A1脉)、晚(A2脉)两期含矿石英脉中的流体包裹体均为含CO2盐水包裹体,可细分为含石盐子晶、富液相(水溶液相)、富气相(CO2相)包裹体等不同类型。根据流体包裹体的共生特点,将其划分为3组包裹体组合:(1)第I组,出现在A1脉石英中,为富液相(I-W型)、富气相(I-C型)和含石盐子晶(I-S型)包裹体共生;(2)第Ⅱ组,同样出现在A1脉石英中,为富液相(Ⅱ-W型)和富气相(Ⅱ-C型)包裹体共生;(3)第Ⅲ组,出现在A2脉石英中,为富液相(Ⅲ-W型)和富气相(Ⅲ-C型)包裹体共生。测温结果显示:I-S型包裹体均一温度在293~370℃之间,流体盐度为30.06%~39.76%Na Cleqv;Ⅱ-W型包裹体均一温度在302~490℃之间,流体盐度为1.23%~18.63%Na Cleqv;Ⅲ-W型包裹体均一温度在263~400℃之间,流体盐度为1.20%~11.34%Na Cleqv。同一组内,包裹体气/液相比高度变化,表明包裹体捕获时的流体呈不均一态,此时包裹体均一温度中低值部分近似代表该组包裹体真实的捕获温度。因此,从I组到Ⅲ组,包裹体分别捕获于280~320℃(I组、Ⅱ组)和260~280℃(Ⅲ组),结合盐度数据,反应初始成矿流体发生沸腾作用,伴随石盐子晶析出,流体盐度下降,随后温度降低。茅草坪矿床成矿流体富CO2的特点与区域内其他脉状Cu矿床一致,但盐度明显偏高。矿床热液石英的δDV-SMOW值变化在-94.6‰~-56.2‰之间,计算的流体的δ18OV-SMOW值集中在+8.1‰~+9.6‰之间,与区域其他脉状Cu矿床相似,数据主要落在原生岩浆水区域的下方,表明流体来源于岩浆水,但经历了开放系统下的脱气作用,没有盆地流体或大气降水的贡献;热液碳酸盐方解石的δ13CV-PDF值为-8.3‰~-2.4‰,δ18OV-SMOW值为14.46‰~16.63‰,与区域其他脉状Cu矿床的C-O同位素组成相似,但C同位素组成明显低于区域脉状Pb-Zn矿床(碳主要来自盆地流体溶解的碳酸盐岩);黄铜矿的δ34SV-CDT值变化于-6.4‰~-3.9‰之间,处于区域其他脉状Cu矿床的S同位素组成范围内,但区别于区域砂岩型Cu矿床(硫来自硫酸盐的细菌还原作用)。因此,推测矿床的CO2和硫可能也来自脱气的岩浆。茅草坪脉状Cu矿床成矿流体的研究表明:兰坪盆地西缘脉状Cu矿床成矿流体可能来自富CO2、经历脱气的岩浆水,没有大气降水和盆地卤水的参与。     

大青山逆冲推覆构造形成演化过程的流体证据

大青山逆冲断层带内热液脉体十分发育,按其产状可划分为充填脉和边缘脉。根据形成时间主要划分为3期:早期石英脉、中期石英脉和晚期方解石脉。早期石英脉中流体包裹体类型较为复杂,见有气液两相、含CO2三相、纯CO2及少量单液相等4种类型原生包裹体,分析表明流体主要来源于地壳深部或上地幔。中期石英脉中主要发育气液两相包裹体和少量单液相包裹体,流体主要来源于大气降水,并且有少量岩浆热液混入。晚期方解石脉内仅含有气液两相包裹体及少量的单液相包体,流体主要来源于层间建造水。根据逆冲变形事件期次、时间,结合热液脉体形成深度数据,确定了大青山逆冲推覆体系变形演化历史:印支期逆冲推覆事件发生在地壳7～8 km深度,燕山中期逆冲推覆事件发生在3～6 km范围内,而燕山晚期逆冲推覆事件发生近地表2 km范围内。