火成岩的晶体群与成因矿物学展望

岩浆系统物理过程的研究进展导致了岩浆系统成熟度的概念,因而认识到火成岩中的晶体并非全部由寄主熔体晶出。本文将火成岩中的矿物晶体按其加入岩浆系统的方式划分为3种晶体群:固体晶体群、熔体晶体群和流体晶体群。固体晶体群系指呈固态加入岩浆的晶体群,包括残留晶亚群和捕虏晶亚群;熔体晶体群系指从熔体中晶出的晶体群,包括从不同深度水平岩浆房中晶出的晶体亚群(岩浆房晶体亚群)、岩浆上升途中晶出的晶体亚群(通道晶体亚群)、在岩浆系统中长期循环的晶体亚群(循环晶亚群)和岩浆侵位后晶出的晶体亚群(基质晶亚群)。流体晶体群系指从流体相晶出的晶体群,包括从超临界流体晶出的晶体亚群(超临界晶体亚群)、从气体晶出的晶体亚群(凝聚晶体亚群)和从热液晶出的晶体亚群(热液晶体亚群)。这种划分方案为火成岩成因矿物学研究打开了新的窗口,阐明不同晶体群的标型特征和形成条件是成因矿物学研究的重要任务。理论上,残留晶与原生岩浆保持热力学平衡,捕虏晶一般与岩浆不平衡,熔体晶体群在岩浆系统演化的特定阶段上与岩浆保持热力学平衡,而流体晶体群则一般不与岩浆平衡,但超临界晶体亚群可部分与岩浆平衡。各种晶体群在火成岩中的保存程度与岩浆系统的存续时间尺度和晶体吸收速率紧密相关。在快速上升和固结的岩浆系统中,所有的晶体群都有可能得到保存。相反,在缓慢上升和固结的岩浆系统中,有可能仅保留有基质晶亚群。因此,晶体群的数量和颗粒大小可以用来定性评价岩浆系统存活的时间尺度,定量化结构分析将成为成因矿物学的重要研究内容。     

赣杭构造带龙游地区早白垩世基性岩矿物化学、岩石地球化学特征及其地质意义

通过龙游晚中生代基性岩岩相学观察、全岩主量、微量元素和Sr-Nd同位素及矿物电子探针分析,对岩石成因、岩浆演化和构造环境进行探讨。龙游基性岩岩性为橄榄辉长岩,Sr-Nd同位素显示为幔源特征;主量、微量元素特征显示其经历了以橄榄石、辉石为主的分离结晶作用,且未发生明显的地壳物质混染。橄榄石颗粒具核-边结构,富Mg贫Fe的核部Fo值为90.1～91.8,指示原始岩浆是软流圈地幔,富Fe贫Mg的边部显示橄榄石Fo值为77.4～85.3,且核-边两部分的Fo值相差较大,显示原始橄榄石形成之后受到地幔熔体/流体的交代作用。辉石斑晶大多属于透辉石,在部分斑晶的边部发育少量霓辉石。透辉石斑晶普遍具有核-幔-边结构,从核部到边部的SiO_2含量降低,TiO_2、Al_2O_3含量升高,结晶温度升高,显示原始辉石形成之后受到温度更高的地幔熔体/流体的交代作用。研究认为,古太平洋板块后撤造成岩石圈地幔拉伸作用并形成赣杭构造带深部断裂后,部分软流圈物质受到地幔流体/熔体的交代作用,并沿这些深部断裂向上侵位,经历了以橄榄石和辉石矿物为主的分离结晶作用和微弱的地壳物质混染,最终形成龙游橄榄辉长岩。     

河南省嵩县庙岭金矿床地质特征与成矿时代

河南嵩县庙岭金矿位于华北陆块南缘外方山地区,矿床赋存于中元古界长城系熊耳群火山岩中断裂构造带内,属破碎蚀变岩型金矿.成矿热液蚀变矿物钾长石Ar-Ar法定年的年龄为(121.6±1.2) Ma,矿床形成与区域上旱白垩世构造-岩浆-流体活动有关,为岩浆期后热液活动的产物.     

四川米易青皮村镁铁质侵入体的固结过程

含矿与无矿侵入体的区分是阐明岩浆型矿床成因的基础,也是深部找矿预测的依据。本文选择四川米易青皮村岩体为例,通过岩相学及矿物成分剖面和定量化结构分析,试图阐明无矿岩浆侵入体的固结过程,并与攀枝花含矿岩体对比,进一步揭示含矿与无矿侵入体形成过程的区别。岩相学分析表明,青皮村岩体中粒辉长岩的造岩矿物可以划分为四个世代：①粗粒斜长石→②中粒斜长石+单斜辉石→③黑云母+铁钛氧化物→④伟晶状斜长石,展示了封闭系统的固结过程。加上粗晶辉长岩脉的矿物组合钠长石+单斜辉石+角闪石+磷灰石,可以将青皮村岩体的组成矿物划分为5个世代,进而划分成四个晶体群：通道晶体群、岩浆房晶体群、基质晶体群和流体晶体群。晶体成分剖面分析表明,通道晶和岩浆房晶显示正环带,具有封闭系统降温结晶的特点,其中通道晶的生长伴随着减压作用;基质晶初始为正环带,末期显示反环带,反映了残余流体的聚集与逃逸;而流体晶体群的产出则反映了超临界流体的相分离和排气作用。定量化结构分析揭示了岩浆固结晚期的粗化过程,是封闭岩浆系统固结过程的重要证据,与岩相学和晶体成分剖面分析结果一致。此外,青皮村岩体中Fe Ti氧化物含量甚低,其体积分数仅为4%,暗示它们不可能聚集成矿。与攀枝花岩体相比,青皮村岩体固结过程中缺失先存晶体的溶蚀结构,后者被认为是高温含矿流体输入的结果。据此,本文提出,外来含矿流体(透岩浆流体)输入与否决定了镁铁质岩浆侵入体的产矿能力;进而认为,是流体输入导致了岩浆分异,而不是岩浆分异产生了含矿流体。     

长白山地区新生代火山岩及其幔源包体的矿物化学及矿物包裹体研究

长白山地区新生代火山岩主要为玄武岩类、粗面岩类和碱性流纹岩类。其中奶头山期碱性玄武岩中含有幔源的尖晶石二辉橄榄岩包体和辉石岩包体。幔源包体及不同期次火山岩的主要矿物是橄榄石、单斜辉石、斜方辉石、尖晶石、斜长石、碱性长石。不同寄主岩石中的矿物组成及其化学成分具有一定的变化，反映了岩浆分异演化的特征；矿物及火山熔岩中的包裹体成分及玻璃熔体结构的激光拉曼光谱分析结果表明，地下深处的岩浆含有较多的挥发分，岩浆上升过程中发生了强烈的出溶作用；岩浆由起源经分异演化上升到地壳浅部直至喷发，幔源的挥发分减少，而浅成或壳源的挥发分增多，特别是在岩浆喷发过程中，地下水或大气成分起了重要作用     

长白山地区新生代火山岩及其幔源包体的矿物化学及矿物包裹体研究

长白山地区新生代火山岩主要为玄武岩类、粗面岩类和碱性流纹岩类。其中奶头山期碱性玄武岩中含有幔源的尖晶石二辉橄榄岩包体和辉石岩包体。幔源包体及不同期次火山岩的主要矿物是橄榄石、单斜辉石、斜方辉石、尖晶石、斜长石、碱性长石。不同寄主岩石中的矿物组成及其化学成分具有一定的变化，反映了岩浆分异演化的特征；矿物及火山熔岩中的包裹体成分及玻璃熔体结构的激光拉曼光谱分析结果表明，地下深处的岩浆含有较多的挥发分，岩浆上升过程中发生了强烈的出溶作用；岩浆由起源经分异演化上升到地壳浅部直至喷发，幔源的挥发分减少，而浅成或壳源的挥发分增多，特别是在岩浆喷发过程中，地下水或大气成分起了重要作用。     

河南嵩县庙岭金矿地质特征与钾长石40Ar/39Ar定年

河南嵩县庙岭金矿位于华北陆块南缘熊耳山—外方山地区。矿床赋存于中元古界熊耳群火山岩中近南北向断裂带内,矿体呈似层状、透镜状产出,矿石具浸染状、细网脉状构造和微细粒它形粒状晶粒结构、交代结构,围岩热液蚀变有硅化、钾长石化、绢云母化、黄铁矿化等,矿化具有多阶段的特点,属破碎带蚀变岩型金矿。成矿热液蚀变矿物钾长石Ar-Ar法测年的结果：坪年龄为121.6Ma±1.2Ma,等时线年龄为117.0Ma±1.6Ma,表明矿床形成于早白垩世,与熊耳山地区祁雨沟、瑶沟等金矿床形成于同一时期,属与早白垩世构造-岩浆-流体活动有关的产物。     

应用电感耦合等离子体质谱技术研究牦牛坪矿床霓长岩化蚀变矿物微量元素特征

近年来全岩电感耦合等离子体质谱（ICP-MS）和原位激光剥蚀电感耦合等离子体质谱（LA-ICP-MS）微量元素地球化学测试在地球科学领域的应用越来越广泛。霓长岩化是碳酸岩型稀土矿常见的蚀变类型,但其中的蚀变矿物微量元素特征与稀土矿化关系并不清楚。本文对川西牦牛坪矿床两期霓长岩化脉（无矿脉和含矿脉）中的霓辉石、钠铁闪石同时开展ICP-MS和LA-ICP-MS微量元素测试。结果表明：同期次的霓长岩化脉中,霓辉石、钠铁闪石全岩ΣREE含量远高于单矿物原位ΣREE含量,背散射图像显示霓辉石、钠铁闪石矿物中叠加了一些氟碳铈矿、重晶石微矿物。不同期次霓长岩化脉中霓辉石原位微量对比,含矿脉中的霓辉石具有更高的La/Nd值（0.19~0.23）、LREE/HREE值（6.58~7.79）、Ce/Nd值（0.95~1.11）、La_N/Yb_N值（2.07~2.33）。对比全岩微量组成,含矿脉中高含量的La、Ce、LREE、ΣREE,强烈的轻重稀土分异,可能代表了高稀土通量的霓长岩化流体。霓长岩化脉的出现以及脉体中霓辉石、钠铁闪石这些全岩微量、原位微量地球化学指标,可为碳酸岩型稀土矿床找矿勘查提供参考。     

内蒙古迪彦钦阿木斑岩钼矿床成矿流体的出溶、演化及对成矿的制约

迪彦钦阿木钼矿床位于内蒙古东乌旗地区,矿区侵入岩不发育,主要为细粒正长岩和基性岩脉,矿体主要发育在侏罗纪火山岩中,少量发育在细粒正长岩中,主要矿化类型为细网脉状、脉状、浸染状,具有斑岩型矿化特征。矿区的细粒正长岩中可见含矿石英-钾长石囊团或由之构成中心相的热液脉体,是岩浆-流体转化过程的直接证据。本文在详细岩相学观察的基础上,对石英-钾长石囊团中主要组成矿物开展了阴极发光图像分析,对石英、萤石中流体包裹体开展了显微测温实验,并借助SEM/EDS、显微激光拉曼探针、LA-ICP-MS等手段对包裹体成分进行了系统分析,基于以上实验结果对岩浆流体的出溶过程、出溶流体特征及矿质沉淀机制进行了探讨。研究结果表明,矿区钼成矿与细粒正长岩岩浆出溶流体有关;富F和挥发分造成成矿岩浆具有低的固相线温度和较低的黏度,因此成矿岩浆可以沿断裂快速上侵到地壳浅部;岩浆上侵过程中的减压沸腾可能是流体出溶的主要机制;早期出溶流体为富F和富CO₂的中高温(227~457℃)、中低盐度[w(NaCl_eq)=0.3%～8.6%]流体,由于快速减压造成流体沸腾形成低盐度富CO₂的气相和高盐度液相,沸腾引起的CO₂逃逸可能是矿质沉淀的主要原因。     

宁芜盆地娘娘山组钾质火山岩的岩相学和矿物学特征及其地质意义

宁芜盆地娘娘山组钾质火山岩为盆地内中生代最晚期火山喷发形成的火山岩,其矿物成分中钾长石主要为透长石;辉石均为透辉石;黑云母为镁质黑云母,黑云母结晶温度为650℃～750℃,氧逸度(logfo2)约为-12～-10。这些矿物的化学特征与庐枞钾质火山岩中矿物的化学特征非常接近,综合其全岩地球化学、同位素年龄数据,表明娘娘山组钾质火山岩形成于造山后的构造环境。对黑云母的成分分析表明其岩浆来源较深,应为幔源岩浆分异演化的产物,并推测与地壳发生了较弱的同化混染作用,同时娘娘山组钾质火山岩的岩相学和矿物化学特征揭示了其岩浆演化的过程。     

西秦岭温泉斑岩钼矿床岩浆-热液演化

西秦岭北缘广泛出露印支期中酸性侵入岩和相关的斑岩-矽卡岩矿床。温泉矿床位于该矿带东段,是其内已探明规模最大的斑岩钼矿床。温泉矿床发育多阶段热液脉体,黄铁矿作为其中的贯通性金属硫化物,其化学组成蕴含着岩浆-热液演化及金属沉淀过程等诸多信息,对于斑岩系统模型的厘定具有重要意义。温泉矿床热液脉体时序为:钾长石-黑云母-石英脉(A脉)、石英-黄铜矿脉、石英-辉钼矿脉(B脉)和石英-绢云母-黄铁矿脉(D脉)。A脉是斑岩系统岩浆-热液演化的最早期脉体,主要矿物组合为钾长石+黑云母+石英+黄铁矿±磁铁矿±磷灰石±黄铜矿,代表了引起早期基性岩浆矿物被蚀变为黑云母的流体通道;B脉与钾长石化蚀变关系密切,围岩中斜长石斑晶大量被蚀变为钾长石;石英-辉钼矿脉切割所有早期黑云母化-钾化蚀变阶段的石英-硫化物网脉,并形成于所有斑岩侵位之后,少量黄铁矿和黄铜矿共生于辉钼矿裂隙及边部;D脉是斑岩系统岩浆-热液成矿作用的最晚期事件,其主要被黄铁矿和石英及少量黄铜矿填充,发育晚期的绢英岩化和泥化蚀变,长石多发生破坏性蚀变。四个阶段石英网脉中黄铁矿电子探针分析显示,A脉的黄铁矿中Cu、Mo和Au含量均较低,有少量的金属硫化物(黄铁矿+黄铜矿)沉淀,但通常不能形成规模矿体;石英-黄铜矿脉的黄铁矿中Cu含量明显较高,且多与高品位Cu矿体的空间产出位置相一致,可能是斑岩系统伴随钾化蚀变作用主要的铜沉淀阶段;B脉的黄铁矿中Mo含量明显较高,与高品位钼矿体空间产出关系密切,可能代表了斑岩系统钼成矿作用的主要阶段;D脉的黄铁矿中Au含量明显升高,可能代表了金在斑岩系统岩浆-热液成矿作用的最晚期事件中的沉淀。     

Variations in Chemical Composition of Clay Minerals and Magnetic Susceptibility of Hydrothermally Altered Rocks in the Hishikari Epithermal Gold Deposit, SW Kyushu, Japan

Hydrothermal alteration, involving chiefly chlorite and illite, is extensively distributed within host rocks of the Pleistocene Hishikari Lower Andesites (HLA) and the Cretaceous Shimanto Supergroup (SSG) in the underground mining area of the Hishikari epithermal gold deposit, Kagoshima, Japan. Approximately 60% of the mineable auriferous quartz‐adularia veins in the Honko vein system occur in sedimentary rocks of the SSG, whereas all the veins of the Yamada vein system occur in volcanic rocks of the HLA. Variations in the abundance and chemical composition of hydrothermal minerals and magnetic susceptibility of the hydrothermally altered rocks of the HLA and SSG were analyzed. In volcanic rocks of the HLA, hydrothermal minerals such as quartz, chlorite, adularia, illite, and pyrite replaced primary minerals. The amount of hydrothermal minerals in the volcanic rocks including chlorite, adularia, illite, and pyrite as well as the altered and/or replaced pyroxenes and plagioclase phenocrysts increases toward the veins in the Honko vein system. The vein‐centered variation in mineral assemblage is pronounced within up to 25 m from the veins in the peripheral area of the Honko vein system, whereas it is not as apparent in the Yamada vein system. The hydrothermal minerals in sandstone of the SSG occur mainly as seams less than a few millimeters thick and are sporadically observed in halos along the veins and/or the seams. The alteration halos in sandstone of the SSG are restricted to within 1 m of the veins. In the peripheral area of the Honko vein system, chlorite in volcanic rocks is characterized by increasing in Al in its tetrahedral layer and the Fe/Fe + Mg ratio toward the veins, while illite in volcanic rocks has relatively low K and a restricted range of Fe/Fe + Mg ratios. Temperature estimates derived from chlorite geothermometry rise toward the veins within the volcanic rocks. The magnetic susceptibility of tuff breccia of the HLA varies from 21 to less than 0.01 × 10^?3 SI within a span of 40 m from the veins and has significant variation relative to that of andesite (27–0.06 × 10^?3 SI). The variation peripheral to the Honko vein system correlates with an increase in the abundance of hematite pseudomorphs after magnetite, the percentage of adularia and chlorite with high Fe/Fe + Mg ratios, and the degree of plagioclase alteration with decreasing distance to the veins. In contrast, sedimentary rocks of the SSG maintain a consistent magnetic susceptibility across the alteration zone, within a narrow range from 0.3 to 0.2 × 10^?3 SI. Magnetic susceptibility of volcanic rocks of the HLA, especially tuff breccia, could serve as an effective exploration tool for identifying altered volcanic rocks.     

Geochemistry and Fluid Inclusions Analysis of Vein Quartz in the Multiple Hydrothermal Systems of Mankayan Mineral District,Philippines

Several high‐sulfidation epithermal gold orebodies in the Mankayan Mineral District were formed in an environment that has been already affected by earlier porphyry‐type mineralization. This study reports the geologic and geochemical characteristics of the Carmen and Florence epithermal orebodies, which are located in the south of the Lepanto main enargite–gold orebody. The gold‐bearing epithermal quartz veins in the Carmen and Florence areas are of two types: (i) the enargite‐rich veins and (ii) the quartz–pyrite–gold (QPG) veins. The two types of veins are mainly hosted by the Cretaceous Lepanto Metavolcanics basement rocks, with minor veins cutting the Pleistocene Imbanguila Dacite Pyroclastics. The mineral assemblages and homogenization temperatures of fluid inclusions indicate that the Carmen and Florence orebodies were deposited by fluids varying from high to very high sulfidation state. The enargite and QPG epithermal veins of Carmen and Florence cut porphyry‐type quartz veinlet stockworks and veins that host polyphase hypersaline fluid inclusions that did not homogenize at or below 400°C. These high‐temperature quartz exhibits distinctly different mineral chemistry from the quartz of the QPG and enargite‐rich epithermal veins. In particular, the Ti content of quartz of the porphyry‐type veinlet stockwork is elevated (>100 ppm), whereas the Ti concentration of the epithermal vein quartz crystals are below detection limits. The Fe concentration of quartz is high in epithermal vein quartz (>300 ppm), whereas nearly undetected in the porphyry‐type stockwork veinlet quartz. Multiple generations of quartz with different mineral chemistry, fluid inclusions morphology, temperature, salinity and bulk gas compositions, and stable isotopic ratios indicate the variable hydrothermal conditions throughout the mineralization history of the Mankayan District. The temperature, pH, sulfidation state, oxidation state, and fluid composition vary among the orebodies in Carmen and Florence areas. Furthermore, the characteristics of earlier alteration affected the apparent characteristics of subsequent mineralization.     

Pyroxenes of the Khibiny alkaline pluton, Kola Peninsula

Seven pyroxene varieties were identified in nepheline syenites and foidolites of the Khibiny pluton: enstatite, ferrosilite, diopside, hedenbergite, augite, aegirine-augite, and aegirine. Enstatite and augite are typical of alkaline and ultramafic rocks of dike series. Ferrosilite was found in country quartzitic hornfels. Diopside is a rock-forming mineral in alkaline and ultramafic rocks, alkali gabbroids, hornfels in xenoliths of volcanic and sedimentary rocks and foyaite, melteigite-urtite that assimilate them, and certain hydrothermal pegmatite veins. Hedenbergite was noted in hornfels from xenoliths of volcanic and sedimentary rocks and in a hydrothermal pegmatite vein at Mount Eveslogchorr. Aegirine-augite is the predominant pyroxene in all types of nepheline syenites, phonolites and tinguaites, foidolites, alkaline and ultramafic rocks of dike series, fenitized wall rocks surrounding the pluton, and xenoliths of Devonian volcanic and sedimentary rocks. Aegirine is an abundant primary or, more often, secondary mineral in nepheline syenites, foidolites, and hydrothermal pegmatite veins. It occurs as separate crystals, outer zones of diopside and aegirine-augite crystals, and homoaxial pseudomorphs after Na-Ca amphiboles. Microprobe analyses of 265 pyroxenes samples allowed us to distinguish ten principal trends of isomorphic replacement and corresponding typomorphic features of pyroxenes. Compositional variations in clinopyroxenes along the sampled 35-km profile from the margin of the Khibiny pluton to its center confirm the symmetric zoning of the foyaite pluton relative to semicircular faults of the Minor Arc and the Main (Central) Ring marked by Devonian volcanic and sedimentary rocks, foidolites, and related metasomatic rocks (rischorrite, albitite, and aegirinite). Changes in the composition of pyroxenes are explained mainly by the redistribution of elements between coexisting minerals of foyaites in the process of their intense differentiation under the effect of foidolite melts that have intruded into the circular fault zones.     

火山岩磁化率特征及其影响因素:以准东石炭系巴塔玛依内山组为例

以准噶尔盆地东部石炭系巴塔玛依内山组火山岩为例,通过测量分析不同岩性类型火山岩磁化率,确定研究区主要类型火山岩的磁化率特征,总结磁化率的影响因素。结果表明,研究区内基性火山岩的平均磁化率为11.705×10~(-3)SI,中性火山岩的平均磁化率为6.325×10~(-3)SI,酸性火山岩的平均磁化率为0.345×10~(-3)SI,磁化率可以有效区分这三种具有不同磁性矿物组合的岩石类型。研究区火山岩受成岩作用改造强烈,其磁化率受矿物组成、成岩方式、结构构造及岩石蚀变等因素的综合影响。进一步研究发现,钙质、硅质等逆磁性矿物不同程度地交代辉石和角闪石等强磁性矿物斑晶,且作为填隙物的主要成分充填于岩石孔缝中,是致使研究区中基性火山岩整体磁化率明显偏低的主要原因。     

内蒙古乌奴格吐山大型铜钼矿床成矿流体来源及演化: 流体包裹体及氢氧同位素地球化学证据

内蒙古乌奴格吐山大型铜钼矿床位于得尔布干成矿带西南段。矿体产于燕山早期二长花岗斑岩、流纹斑岩等构成的火山通道相与外围黑云母花岗岩接触带内外。矿床从中心向外发育典型的热液蚀变分带: 钾化带、绢英岩化带和伊利石—水白云母化带。根据矿物组合不同,将热液成矿期分为早、中、晚3 个阶段,其矿物组合分别为石英+钾长石+黄铁矿±辉钼矿、石英+绢云母+ 黄铜矿± 辉钼矿+黄铁矿、石英+碳酸盐矿物+黄铁矿±闪锌矿。流体包裹体研究表明,乌山斑岩铜钼矿床发育L 型富液相包裹体、V 型富气相包裹体、S 型含子矿物多相包裹体以及PG 型纯气相包裹体。激光拉曼探针分析表明,石英斑晶和早阶段石英内水溶液包裹体除H2O 外,多数含CO2,少数还含有 CH4,C4H6 等,含子矿物多相包裹体中子矿物主要有赤铁矿和黄铜矿; 中阶段石英内只有少量V 型包裹体含CO2,多数只有H2O,S 型包裹体中子矿物有黄铜矿和黄铁矿,不再含有赤铁矿; 而晚阶段石英内包裹体只含H2O。成矿流体由H2O--CO2 --NaCl 体系逐渐演化为H2O--NaCl 体系。成矿早、中、晚3 个阶段均一温度分别集中在340℃ ～ 460℃,240℃ ～ 360℃和120℃ ～ 240℃; 盐度变化范围分别为 5. 32 ～ 53. 26 wt% NaCl. eqv,1. 65 ～ 41. 58 wt% NaCl. eqv 和0. 66 ～ 14. 05 wt% NaCl. eqv。初始流体是直接从浅部结晶冷凝的岩浆熔体中出熔的高温、高盐度和高氧逸度的成矿流体。富气相包裹体、富液相包裹体和含矿物的多相包裹体普遍共生,流体的沸腾可能是早期金属硫化物大量沉淀的重要机制。结合氢、氧同位素研究,认为中--晚阶段天水的混入导致的流体混合及降温作用在成矿过程中也发挥了重要作用。     

Fluid Inclusion and Stable Isotope Studies at Don Sixto,a Precious Metal Low Sulfidation Deposit in Mendoza Province,Argentina

The Don Sixto mining area in Mendoza province, central‐western Argentina, contains an epithermal low sulfidation Au–Ag deposit. It is a small deposit (～4 km²), with a gold resource of 36 t. In Don Sixto, ore minerals are disseminated in the hydrothermal quartz veins and hydrothermally altered volcanic‐pyroclastic rock units of Permian–Triassic age. On the basis of the texture, ore mineral paragenesis and cross cutting relationship of gangue minerals, seven stages of mineralization were recognized and described. The first six stages are characterized by quartz veins with minor amounts of base metal minerals and the last stage is represented by fluorite veins with minimal quantities of base metal minerals; the precious metal mineralization is mainly related to the fourth stage. The hydrothermal veins exhibit mainly massive, crustiform and comb infilling textures; the presence of bladed quartz replacement textures and quartz veins with adularia crystals are indicative of boiling processes in the system. Fluid inclusion and complementary stable isotope studies were performed in quartz, fluorite, and pyrite samples from the vein systems. The microthermometric data were obtained from primary, biphasic (liquid‐vapor) fluid inclusion assemblages in quartz and fluorite. The maximum values for salinity and homogenization temperature (T_h) came from the stage IV where quartz with petrographic evidence of boiling has average values of 4.96 wt% NaCl_equiv. and 286.9°C respectively. The lower values are related to the last stage of mineralization, where the fluid inclusions in fluorite have average salinities of 1.05 wt% NaCl_equiv. and average homogenization temperatures of 173.1°C. The oxygen and sulfur isotopic fractionation was analyzed in quartz and pyrite. The calculated isotopic fractionation for oxygen in the hydrothermal fluid is in the range of δ¹⁸O_H2O = ?6.92 up to ?3.08‰, which indicates dominance of a meteoric source for the water, while sulfur reaches δ³⁴S_H2S = 1.09‰, which could be reflecting a possible magmatic, or even a mixed source.     

Progress on Formation Mechanism of the Fibrous Veins in Mudstone and Its Implications to Hydrocarbon Migration

The fibrous mineral veins are widespread in mudstones. According to the different microscopic morphology of the minerals, the fibres can be divided into stretched crystals, elongate-blocky crystals and the very fibrous crystals. Veins can also be classified according to the growth direction of these crystals into stretched veins, syntaxial veins and antitaxial veins. The resulting texture in the vein depends on the morphology of the fracture surface, the width of the fracture and the growth habit of the vein forming mineral. The crack-seal mechanism can only interpret the formation of the stretched crystal veins and the elongate-blocky crystal veins, and the antitaxial well-developped fibrous veins form without fracturing and the growth competition is inhibited during the rock deformation, which implies that the nutrient transport is by diffusional flow transport. Horizontal crack is the primary condition of the formation of the antitaxial bedding-parallel fibrous calcite veins in muddy hydrocarbon source rocks. The formation of the horizontal crack which caused by the abnormal high pressure can enhance the hydrocarbon generation efficiency and has a great effect on the rate and direction of hydrocarbon migration in the local. The presence of the veins indicates the hydrocarbon fluid can migrate laterally along the layers. The antitaxial bedding-parallel fibrous calcite veins in muddy hydrocarbon source rocks can be the sign of the generation and migration of hydrocarbon under the abnormal high pressure condition in petroleum-bearing basins.     

西藏雄村斑岩型铜金矿红柱石成因矿物学特征

雄村斑岩铜金矿中广泛分布有红柱石,红柱石主要呈三种产出状态:①石英-钾长石-白云母/绢云母-红柱石组合;②红柱石-石英-绢云母/白云母组合;③石英-红柱石-硫化物脉.矿物组合关系、红柱石结构和成分等特征均表明红柱石属热液成因.早期钾硅酸盐化带中的石英-钾长石-白云母/绢云母-红柱石组合形成于高温(大于550℃)、低+K...     

中国云南哀牢山含海蓝宝石伟晶岩的起源和成岩模拟实验研究

The Ailaoshan aquamarine-bearing pegmatites are associated with Proterozoic metamorphic rocks in the southern portion of the Ailaoshan fault-folded complex.The gem-bearing pegmatite mineralization zones of the region occur in areas generally consistent with the regional tectonic trend.The pegmatites are found in metamorphic rocks,migmatites and in the inner/outer contact zones of gneissoid granites. The Rb-Sr isochron drawn for the pegmatites is 26～31 Ma,(i.e.in Himalayan).The homogenization temperatures of melt and liquid inclusions in minerals vary from 185 to 920℃,which are comparable to the inclusions observed in banded migmatites and ptygmatic quartz veins in the surrounding metamorphic rocks. The mineralization fluids of the pegmatite were rich in HCO_3 and CO_2,and their compositional assemblages are comparable to metamorphic fluids.Results of H,O,C,Si etc.isotopic analyses and REE,and Be analyses indicates that the sources of mineralization components that formed the pegmatites are closely associated with metamorphic fluids and the enclosing metamorphic rocks. A pegmatite structure simulation experiment was conducted at high temperature and pressure(840℃and 1,500×105Pa.),with various metamorphic rock samples in a water-rich and volatile-rich environment.When the liquidus was reached,the temperature was gradually decreased at the rate of 5～10℃/day over a time period of three months.SEM energy-dispersive spectrum analyses were performed on the experimental products.A series of pegmatoid textures were observed including zonal texture,megacryst texture,drusy cavities,crystal druses,and vesicular texture along with more than ten types of minerals including plagioclase,microcline,quartz and biotite.Different metamorphic rock melts generated different mineral assemblages.Experiment results revealed that the partial melting of metamorphic rocks could form melts similar to pegmatite magmas. Based upon the geological characteristics,geochemistry,and pegmatite texture simulation experimental results,it is concluded that the mineralization components of Ailaoshan aquamarine-bearing pegmatites came from metamorphic rocks.The petrogenetic model for the origin of pegmatites is related to ultrametamorphism and metamorphic anatexis.