粤西大降坪硫铁矿床地球化学特征及成因探讨

大降坪矿床存在着两种截然不同的矿石类型，Ⅲ号矿体条带状矿石是同生热水沉积作用形成；Ⅳ号矿体块状矿石是后期热液叠加改造形成。两者在微量元素、硫、铅同位素及流体包裹体等地球化学性质方面各具特征。通过矿床地质地球化学等方面研究表明：该矿床为一典型的同生热水沉积－后期热液叠加改造型层控矿床。     

Ga/Mg ratio as a new geochemical tool to differentiate magmatic from metamorphic blue sapphires

Using ICP-MS–LA analyses, we demonstrate that the use of the Ga/Mg ratio, in conjunction with the Fe concentration, is an efficient tool in discriminating between “metamorphic” and “magmatic” blue sapphires. Magmatic blue sapphires found in alkali basalts (e.g. southeastern Asia, China, Africa) are commonly medium-rich to rich in Fe (with average contents between 2000 and 11000 ppm), high in Ga (> 140 ppm), and low in Mg (generally < 20 ppm) with high Ga/Mg ratios (> 10). Conversely, metamorphic blue sapphires found in basalts (e.g. Pailin pastel) and in metamorphic terrains (e.g. Mogok, Sri Lanka, Ilakaka) are characterized by low average iron contents (< 3000 ppm), low Ga contents (< 75 ppm), and high Mg values (> 60 ppm) with low average Ga/Mg ratios (< 10). Basaltic magmatic sapphires have Fe, Ga and Mg contents similar to those obtained for primary magmatic sapphires found in the Garba Tula syenite. This suggests that these both sets of sapphires have a possible common “syenitic” origin, as previously proposed from other criteria. In addition, plumasite-related sapphires and metamorphic sapphires also exhibit similar composition in trace elements. Based on results from the present study, we suggest that fluid circulations during a metamorphic stage produced metasomatic exchanges between mafic and acidic rocks (plumasite model), thus explaining the high Mg contents and converging Ga/Mg ratios observed in metamorphic sapphires.     

黔北普宜地区硫铁多金属矿同位素地球化学特征及成因

正贵州西北部是我国硫铁矿的重要产出地,资源储量排名全国前三位。但研究区的硫铁多金属矿成矿物质来源、成矿环境及伴生有益组分综合利用等科学问题的研究仍不够深入具体,这不仅制约了成矿机制研究和矿床模型的构建,同时因单一硫铁的经济价值及环境污染问题,也会影响到进一步的矿床勘查找矿工作。在野外调查和室内研究基础上,     

云南白秧坪地区东矿带矿床地质地球化学特征及成因分析

东矿带是云南白秧坪矿集区的重要组成部分,矿体明显受逆冲推覆构造主推覆断层及反冲断层的控制,多产于上三叠统三合洞组碳酸盐岩地层中。矿床中发育一套典型的中低温热液成因的矿物组合,成矿流体性质主要为来源于深部的中低温热卤水。硫、铅、碳、氧同位素分析表明成矿物质的深源特征,矿石稀土元素组成显示均有明显的δEu异常,构造热流体活动是成矿的主导因素。矿床地质地球化学特征显示,东矿带的矿床成因类型为与推覆构造有关的中低温热卤水铜银多金属矿床。     

Nephrites of East Siberia: geochemical features and problems of genesis

The largest nephrite-bearing province of Russia is located on the southern folded periphery of the Siberian craton. Deposits of two formation types were established here: apoultrabasic (East Sayan and Dzhida areas, Parama massif) and apocarbonate (Vitim area). Nephrites compose schlieren and lenticular bodies usually in the zones of contact of serpentinous (lizardite–antogorite) dunite–harzburgite rocks and dolomitic marbles with aluminosilicate rocks of different compositions. Significant difference in composition has been established for nephrites of different formations. Apocarbonate nephrites are more magnesian and fluoric and less ferroan. The contents of Li, Be, Rb, and Cs in them are two orders of magnitude higher and the contents of Sc, Ti, and Mn are lower than those in apoultrabasic nephrites. The isotope data evidence that the fluid phase of apoultrabasic nephrites was released from serpentinites during metamorphism, whereas the fluid phase of apocarbonate nephrites is only meteoric water. Oxygen in minerals of metamorphosed carbonate rocks was borrowed from the matrix subjected to replacement, sometimes with the participation of formation waters.     

应用CH4/N2指标估算塔里木盆地天然气热成熟度

通过对塔里木盆地满加尔凹陷低成熟煤岩在开放在线程序升温体系的热模拟实验,获得煤岩在不同温度点的热分解产物CH4、CO和N2,并对模拟后残留产物进行了镜质体反射率测试,建立了镜质体反射率与对应受热温度之间的关系。煤岩镜质体反射率与热温度之间的二阶关系表达为:Ro=0.0014×T+0.109,r=0.9931(Ro<0.6%);Ro=0.0067×T-1.5855,r=0.9996(Ro>0.6%)。通过上述方程建立CH4/N2值与煤岩镜质体反射率之间的对应关系,并利用CH4/N2值对塔里木盆地库车坳陷天然气热成熟度进行了预测。预测结果与实际地质分析结果相吻合,说明CH4/N2值可以作为塔里木盆地煤成气热成熟度预测指标应用于油气勘探中。     

LA-ICP-MS trace element analysis of pyrite from the Xiaoqinling gold district, China: Implications for ore genesis

The Xiaoqinling district, the second largest gold producing district in China, is located on the southern margin of the North China Craton. It consists of three ore belts, namely, the northern ore belt, the middle ore belt and the southern ore belt. Pyrite from the Dahu gold deposit in the northern ore belt and Wenyu and Yinxin gold deposits in the southern ore belt were investigated using a combination of ore microscopy and in-situ laser-ablation inductively-coupled plasma-mass spectrometry (LA-ICP-MS). A range of trace elements was analyzed, including Au, Te, Ag, Pb, Bi, Cu, Co, Ni, Zn, Mo, Hg, As and Si. The results show that there are no systematic differences between the trace element compositions of pyrite in the three deposits from different ore belts. In general, Au concentrations in pyrite are low (from < 0.01 ppm to 2.2 ppm) but Ni concentrations are rather high (up to 8425 ppm). A four-stage mineralization process is indicated by microscopic and field observations and this can be related to the systematic trace element differences between distinct generations of pyrite. Stage I precedes the main gold mineralization stage; pyrite of this stage has the lowest Au concentrations. Stages II and III contributed most of the gold to the ore-forming system. The corresponding pyrite yielded the highest concentrations of Au and Ni. Our microscopic observations suggest that pyrite in the main gold mineralization stage precipitated simultaneously with molybdenite that has been previously dated as Indosinian (~ 218 Ma by Re–Os molybdenite dating), indicating the Indosinian as the main gold mineralization stage. The Indosinian mineralization age and the geological and geochemical features of these gold deposits (e.g., low salinity, CO₂-rich ore fluids; spatial association with large-scale compressional structures of the Qinling orogen; δ¹⁸O and δD data suggestive of mixing between metamorphic and meteoric waters; δ³⁴S and Pb-isotopic data that point to a mixed crustal-mantle source) all point to typical orogenic-type gold deposits. High Ni concentrations (up to 8425 ppm) of pyrite possibly linked to deep-seated mafic/ultramafic metamorphic rocks provide further evidence on the orogenic gold deposit affinity, but against the model of a granitic derivation of the mineralizing fluid as previously suggested by some workers. Generally low Au concentration in pyrite is also consistent with those from worldwide orogenic gold deposits. Therefore, the gold mineralization in the Xiaoqinling district is described as orogenic type, and is probably related to Indosinian collision between the North China Craton and the Yangtze Craton.     

Some geochemical controls on Ni and Co concentrations in marine ferromanganese deposits

The uptake of Ni and Co in the hydrous Mn oxide or the amorphous Fe-oxide phases of ferromanganese deposits in the oceans was studied by electron-microprobe analyses of 17 natural manganese nodules and by experiments on desorption-dissolution of these metals from synthetic Fe oxide or Mn oxides and natural nodule material. Ni was found to occur nearly always in the Mn-oxide phases of natural nodules, while Co occurs both in the Mn-oxide and Fe-oxide phases, with a slight preference for the latter. The solubility of Ni and Co (from coprecipitates of these metals with Fe hydroxides after aging) in seawater was found to depend strongly on the crystallinity of the host phase. The adsorption of Co by the synthetic Mn oxides from seawater was higher than that of Ni. The experimentally determined solubility of Ni and Co in seawater from natural nodule material is extremely low and matches the concentration range of these metals in ocean water.     

沉积黄铁矿微量元素和硫同位素组成对黄金洞金矿床的成因约束

黄金洞大型金矿床位于江南造山带湘东北矿集区,矿体主要赋存于沉积黄铁矿发育的新元古代冷家溪群板岩中,含金石英脉为主要的矿化类型。为进一步约束成矿系统中金和硫的来源,揭示赋矿围岩对成矿贡献,深化矿床成因认识,文章以赋矿围岩冷家溪群板岩为研究对象,对其沉积黄铁矿进行了系统的岩相学、电子探针显微结构、激光剥蚀等离子质谱（LA-ICP-MS）原位微量元素和硫同位素分析。研究结果显示,冷家溪群板岩中的沉积黄铁矿主要呈团块状集合体,单个颗粒多为几百~几千微米。微量元素分析结果表明,沉积黄铁矿w(As)变化范围介于796×10^-6~10 667×10^-6,不可见w(Au)多低于1.0×10^-6。沉积黄铁矿的原位δ³⁴S值主要介于-10.7‰~-4.7‰,与矿石中的热液黄铁矿（δ³⁴S=-14.2‰~-0.5‰）具有一定相似性。以上分析结果暗示,沉积黄铁矿提供成矿系统中的金的可能性不大,推测黄金洞金矿床Au主要来自深部过程。成矿流体在与围岩相互作用过程中,沉积成因硫加入成矿系统,为解释热液成因黄铁矿硫同位素组成特征提供关键证据。     

黑龙江省五星Cu-Ni-Pt-Pd矿床的PGE-Au元素地球化学特征与成因探讨

对黑龙江省东部五星Cu-Ni-Pt-Pd矿床的矿体和与成矿有关的镁铁质杂岩的PGE-Au以及铁族、亲铜元素的地球化学特征研究表明：它们均以亏损Cr、IPGE和富集Ni、Co、Cu、Pt和Pd（Pt     

The effect of As, Co, and Ni impurities on pyrite oxidation kinetics: An electrochemical study of synthetic pyrite

Synthetic pyrite crystals doped with As, Co, or Ni, undoped pyrite, and natural arsenian pyrite from Leadville, Colorado were investigated with electrochemical techniques and solid-state measurements of semiconducting properties to determine the effect of impurity content on pyrite’s oxidation behavior. Potential step experiments, cyclic voltammetry, and AC voltammetry were performed in a standard three-electrode electrochemical cell setup. A pH 1.78 sulfuric acid solution containing 1 mM ferric iron, open to atmospheric oxygen, was chosen to approximate water affected by acid drainage. Van der Pauw/Hall effect measurements determined resistivity, carrier concentration and carrier mobility.The anodic dissolution of pyrite and the reduction of ferric iron half-reactions are taken as proxies for natural pyrite oxidation. Pyrite containing no impurities is least reactive. Pyrite with As is more reactive than pyrite with either Ni or Co despite lower dopant concentration. As, Co, and Ni impurities introduce bulk defect states at different energy levels within the band gap. Higher reactivity of impure pyrite suggests that introduced defect levels lead to higher density of occupied surface states at the solid-solution interface and increased metallic behavior. The current density generated from potential step experiments increased with increasing As concentration. The higher reactivity of As-doped pyrite may be related to p-type conductivity and corrosion by holes. The results of this study suggest that considering the impurity content of pyrite in mining waste may lead to more accurate risk assessment of acid producing potential.     

钪的地球化学与铁矿石成因

一、钪的地球化学特征钪在元素周期表上位于第四周期第三族,属过渡元素类的稀土元素。它的原子序为21,是一个奇数元素,具有奇数的原子量(44.956≈45)和奇数的电价( 3)。在戈尔德施密特的元素地球化学分类中,钪属于亲石元素,位于戈氏原子容积曲线第三个凹陷的上升部分。Рехарский(1976)将其归为基性元素。在费尔斯曼的对角线系列中,钪的离子半径(0.81)与Li~(1 )(0.82)、Mg~(2 )(0·80)、Zr~(4 )     

Cobalt,nickel and selenium in sulphides as indicators of ore genesis

Trace element studies of sulphides have been used to estimate temperatures of mineral formation, to identify metallogenic provinces, and to investigate the environment of mineral deposition. In the investigation of depositional environments, the Co:Ni and S:Se ratios are potentially useful as discriminators between magmatic-hydrothermal and sedimentary environments. A wide range of ore-types occurs in the Lower Palaeozoic rocks of West Tasmania (Australia) which lies in the southern part of the Tasman Geosyncline. The cobalt and nickel contents of pyrites from a number of these ores have been determined by atomic absorption spectrophotometry. Preliminary results show that the pyrites may be grouped as follows: a) those of sedimentary or diagenetic origin in shales (high cobalt and nickel and Co:Ni<1), b) those of probable volcanic origin without accompanying lead and zinc minerals (Co:Ni>1), and c) those of probable volcanic origin associated with lead and zinc minerals, and those with cassiterite or argentiferous galena related to granitic intrusions (low cobalt and nickel and Co:Ni<1). In some areas there is evidence that relatively high cobalt and selenium contents in pyrite may be related to volcanic processes.

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Zusammenfassung Mit Hilfe von Untersuchungen des Spurenelement-Gehaltes von Sulfiden wurden die Temperaturen der Mineralbildung abgeschätzt. Ziel war es, metallogene Zonen zu indentifizieren und das Milieu von Mineralablagerungen zu erforschen. Bei den Untersuchungen der Ablagerungsbedingungen können die Co:Ni- und S:Se-Verhältnisse unter Umständen zur Unterscheidung zwischen magma-hydrothermalem und sedimentärem Milieu dienen. Eine beachtliche Vielfalt von Erzarten ist in den Unter-Paläozoischen Gesteinen von West-Tasmanien (Australien) vorhanden, welches im südlichen Teil der Tasman-Geosynklinale liegt. Die Kobalt- und Nickelgehalte von Pyriten und einer Reihe entsprechender Erze wurden durch Atom-Absorptions-Spektrophotometrie bestimmt. Vorläufige Ergebnisse zeigen, daß die Pyrite in folgender Weise klassifiziert werden können: a) Pyrite sedimentärer oder diagenetischer Herkunft in Schiefern, mit hohem Kobalt- und Nickelgehalt und Co:Ni<1; b) Pyrite wahrscheinlich vulkanischen Ursprungs, frei von Blei und Zinkmineralien (Co:Ni>1); c) Pyrite wahrscheinlich vulkanischen Ursprungs verbunden mit Blei- und Zinkmineralien, und solche mit Kassiterit oder silberhaltigem Bleiglanz, verbunden mit Granit-Eindringungen (mit einem niedrigen Kobalt- und Nickelgehalt und Co:Ni<1). In manchen Gegenden sind Anzeichen dafür vorhanden, daß verhältnismäßig hohe Kobalt- und Selengehalte in Pyriten mit vulkanischen Prozessen zusammenhängen.

     

祁连山白银厂黄铁矿型矿床成因探讨

白银厂黄铁矿型矿区,共有五个矿床,已相继开采四个。其中有以铜为主的含铜黄铁矿型矿床,如折腰山、火焰山、铜厂沟;有以铜-铅-锌为主的多金属黄铁矿型矿床,如小铁山。这两种类型矿床均赋存在白银厂细碧-角斑岩内,且矿体相距很近,构造、岩相相似。说明在同一构造单元、同一火山岩系内可以生成两种不同类型的矿床。该区矿床位于北祁连加里东地槽东部火山岩系内,对其成因一直有争议。有人认为矿床     

祁连山白银厂黄铁矿型矿床成因探讨

The Baiyinchang mining area, an important industrial base of base metals in China, consists of five pyrite type deposits of different sizes, four of which have already been worked. These five deposits might be grouped into two types: Cu-bearing (predominatingly Cu) pyrite type deposits, such as Zheyaoshan, Huoyanshan and Tongchanggou, and polymetallic pyrite deposits containing principally Cu, Pb and Zn, such as Xiaotieshan and Sigejuan. These two types of deposits occur close to each other in the same formation-Baiyinchang spilite-keratophyre sequence and have similar structures and petrofacies, suggesting the possibility of forming two different types of deposits in the same tectonic unit and volcanic rock series. The deposit lies in the eastern part of the volcanic complex within the Qilian eugeosyncline, its genesis remains a problem of much controversy. Ln recent years, the author has made an integrated study and analysis of the data accumulated over the past thirty years and also performed some field investigation to check up these references. The results acquired have led him to postulate the hypothesis that the deposit was formed by the concentration of volcanic hydrothermal fluids in depression and the activity of subvolcano-magmatic fluids. The formation of the massive pyrite in the main ore body of Zheyaoshan is believed to be the result of the lateral effusion from the Qingshanbao vent of the third subcycle appearing presently as silicic rock formation, i.e., the result of the accumulation in the second subcycle crater depression of the ore material effused from the pyrrhotite ore chimney. This might be borne out by the existence of abundant massive copper-bearing pynhotite ore with well-developed textures of corrosion and replacement in the chimney as well as by the ring-like distribution of the metallic minerals around the chimney caused by the spread of the fluids from this center. Geological mapping and analyses of the data of drill core and petrofacies support the claim that the ore body is located at the crater depression. Minerals in massive pyrite ore body are coarse in the west and fine in the east, suggesting also the migration of ore fluids from east to west into the center of depression. The massive ore body cutting obliquely the strata, the relatively weak alteration of country rocks and the remarkable variation in copper content of the ore body all seem to have resulted from the ascending movement of the copper-bearing ore fluids brought by subvolcanic activity along the ore chimney and its fracture zone formed during the crustal reversion. The Xiaotieshan polymetallic pyrite deposit is of subvolcano-magmatic fluids type. Its ore-forming processes were strictly controlled by late subvolcanic activity which, in turn, was governed by fracturing. The ore body overlies the hanging wall of quartz albitophyre and shows close relationships with subvolcanic rocks in dimension and grade while the texture and structure of ore and the mineral constituents vary in accordance with the diverse country rocks. The examination of the structure of volcanos, fractures, variation in petrofacies, regularity of subvolcanic activity, the extent of wall rock alteration and characteristics of mineralization, therefore, makes up the prerequisite for the search of such concealed ore deposits. The Jinfangou ore belt expends along a EW striking fracture zone characterized by complex lithological characters and petrofacies as well as by frequent subvolcanic activities. Mineralization and ore bodies are exclusively confined to the fracture zone. The repeated crustal reversion during: the late stage of the development of rock formation resulted in the folding and faulting of the strata, thus facilitating the differentiation and migration of the magma. The intrusion of the subvolcanic magma not only brought sufficient ore-bearing fluids for mineralization, but supplied heat for their migration. This is due to the fact that heat: accelerated the circulation of the ore fluids, which dissolved ore elements dispersed in the volcanic rock and unceasingly infiltrated into and replaced the country rocks as well. As a result ore fluids concentrated to form ore deposits at places with favorable structure and country rock conditions.     

The effect of As, Co, and Ni impurities on pyrite oxidation kinetics: Batch and flow-through reactor experiments with synthetic pyrite

Pyrite samples synthesized with As, Co, or Ni impurities and without added impurities were oxidized in batch and mixed flow-through reactors in the presence of 1 mM ferric iron, at pH 2. Six samples from each dopant population were used to provide a statistically robust comparison; two natural samples from Leadville, CO (major impurities Pb, As, Bi, Ag, Zn) and Elba, Italy (Co, As) were also included. In each experiment, three reaction progress variables were monitored: ferric iron, ferrous iron, and sulfate. The pyrite samples with impurities have average oxidation rates that are faster than the undoped samples, with As- and Co-doped pyrite having the highest rates. As, Co, and Ni were released to solution in accordance with their concentrations in the solid samples. As concentrations in the batch reactor experiments tended to remain constant, in contrast to Co and Ni, which increased over time. Initial rates, calculated from the batch reactor experiments, were faster than the steady-state rates calculated from the mixed flow-through reactor experiments. Apparent rates calculated using sulfate were faster than apparent rates calculated using ferric and ferrous iron, reflecting oxidation of ferrous iron in solution by dissolved oxygen. The results imply that impurities in pyrite do contribute to its reactivity, in agreement with studies using electrochemical methods. Oxidation rate differences among pyrite samples with different impurities are probably too small to warrant explicit consideration in environmental modeling applications, but are important to understanding pyrite oxidation mechanisms and semiconducting properties.     

安徽铜陵新桥Cu-Au-S矿床黄铁矿微量元素LA-ICP-MS原位测定及其对矿床成因的制约

激光剥蚀电感耦合等离子体质谱(LA-ICP-MS)是一种固体微区分析新技术。用该技术来分析矿床中硫化物的微量元素组成可以为研究成矿流体特征、矿床成因及找矿勘探提供有关的科学信息。文中以安徽铜陵矿集区内新桥Cu-Au-S矿床中的黄铁矿为研究对象,在详细的野外观察和室内鉴定的基础上,将矿床中的黄铁矿分为具有沉积特征的胶状黄铁矿(PyⅠ)、具有变形重结晶和热液叠加作用特征的细粒他形黄铁矿(PyⅡ)和具热液成因特征的中—粗粒自形黄铁矿(PyⅢ)3种类型。LA-ICP-MS原位微量元素测定结果显示,PyⅠ中相对富含Ti、Co、Ni、As、Se、Te;PyⅡ继承了PyⅠ中富含Ti、Co、Ni、As、Se、Te、Bi的特征,同时还含有不均匀分布的少量成矿元素(Cu、Pb、Zn、Au、Ag);PyⅢ中成矿元素Cu、Pb、Zn、Ag、Au以及Bi元素的含量较高,Co、Ni、As的含量较低。在元素赋存状态方面,Co、Ni、As、Se和Te均以类质同象的形式进入到了黄铁矿的晶格中;Bi在PyⅡ中主要以含Bi矿物的微细包裹体形式存在,而在PyⅢ中的Bi还部分取代了Fe而占据了晶格;Cu、Pb、Zn、Au、Ag这些成矿元素中,Cu和Zn分别以黄铜矿和闪锌矿的矿物包裹体存在于黄铁矿中;PyⅡ中所含的少量Au、Ag,可能分别以自然金和自然银的形式存在,而在PyⅢ中Au可能主要以银金矿的形式存在,Ag除了以银金矿的形式存在以外还可能赋存于黄铁矿中含铋的矿物包裹体内;Pb主要赋存于黄铁矿中的方铅矿或含铋矿物的包裹体中。在综合分析黄铁矿的结构形态和微量元素组成特征的基础上认为,PyⅠ型黄铁矿可能形成于前人提出的晚古生代海底沉积或喷流沉积环境,PyⅡ和PyⅢ型黄铁矿分别形成于中生代区域构造变形-热液叠加改造的过渡环境和热液环境,PyⅡ和PyⅢ的形成时间相近。新桥矿床的形成可能经历了晚古生代海底沉积或喷流沉积期和燕山期热液期,胶黄铁矿主要形成于沉积成矿期,而矿床中成矿物质Cu、Pb、Zn、Au、Ag等主要来自燕山期岩浆侵入作用形成的热液成矿系统。     

青城子层状/脉状铅锌矿床稀土元素地球化学特征及地质意义

位处华北板块北缘东段的辽吉裂谷带内发育有多处中、小型铅锌矿床,其中,同时发育层状和脉状铅锌矿的青城子矿床是典型的代表。为了探讨青城子层状铅锌矿和脉状铅锌矿矿质来源及成因的异同及其所代表的地质意义,利用ICP-MS对层状铅锌矿及其围岩、脉状铅锌矿及其围岩和后期穿矿脉岩进行了稀土元素测试。结果表明,所有样品均具有轻稀土元素（LREE）富集和明显分异的特点。层状铅锌矿及其围岩具有Eu正异常和较弱的Ce负异常,表明其成矿物质均来自上升的深部热水流体与海水的混合热液,在高温、还原流体和海水的参与下成矿。脉状铅锌矿及其围岩稀土元素配分模式与层状铅锌矿及其围岩相似,但其Eu为负异常和Ce异常不明显,部分样品出现较弱的Ce正异常,对比分析穿矿脉岩明显的Eu负异常和Ce正异常以及二者稀土元素总量稍大于层状铅锌矿的特点,文章认为青城子层状矿石为沉积成矿,成矿热液为深部热水流体与海水的混合热液,但后期受到岩浆侵入叠加改造的影响而在局部形成脉状铅锌矿体,引起了Eu负异常和局部Ce正异常的出现以及稀土元素总量的增加。     

LCT型伟晶岩及其锂矿床成因概述

花岗伟晶岩具有与低共熔花岗岩相似的矿物和化学组成,通常与高分异花岗岩具有成因联系。花岗伟晶岩划分为富Li-Cs-Ta (LCT)、富Nb-Y-F (NYF)和混合的LCT+NYF型,其中LCT型伟晶岩以过铝质,富集助熔组分(H₂O、F、P、B)、稀有元素(Li、Rb、Cs、Nb、Ta、Be、Sn),极其低的Nb/Ta比值(<5)为特征。通常LCT型伟晶岩显示内部分带,主要包括边界带、壁带、中间带和核部带;此外,可能还发育交代体、层状细晶岩和晶洞。大多数LCT型伟晶岩形成与(同造山)-晚造山的过铝质S型、I型或混合的S+I型花岗岩具有成因联系。对于壳源沉积岩小比例部分熔融直接形成的伟晶岩,通常形成于伸展背景下的晚造山和造山后阶段,侵入于典型的低压角闪岩-高绿片岩相的变沉积岩中。伟晶岩外带(包括边缘带、壁带、细晶岩)中的细粒和细晶岩结构、UST (单向固结结构)是液相线过冷所致,而伟晶岩内带(中间带、核部带)中粗大矿物形成、矿物分带以及稀有金属矿物的饱和结晶是助熔组分(H₂O、B、P、F)、稀有金属(Li、Rb、Cs、Be、Nb、Ta)通过...     

东升庙多金属硫化物矿床主要含矿岩系地质地球化学特征及对矿床成因的指示意义

东升庙矿床是内蒙古狼山-渣尔泰山成矿带上最大的锌多金属矿床,主要含矿岩系是狼山群第2岩组。通过对矿区地质现象的野外观察和钻孔样品地球化学特征的研究,结合国际上同类矿床最新研究进展,对东升庙矿床主矿体的成矿过程提出了新观点。岩、矿石样品的岩相学研究结果显示,不同岩段的岩、矿石有不同的组构特征：第4岩性段中部菱铁矿矿石为典型的细粒镶嵌结构和块状构造,具明显的化学沉积特征;第4岩性段底部②号矿体中的闪锌矿矿石具半自形-它形晶粒结构或溶蚀结构,多为角砾状构造或块状构造,有明显的充填-交代现象;第3岩性段以绢云石墨片岩为主的黑色岩系网脉状矿化普遍,常见后期热液充填现象。岩矿石样品的地球化学研究结果显示,菱铁矿矿石和闪锌矿矿石有相似的微量元素富集特征和稀土元素配分曲线,可能具有同一物质来源。而第3岩性段的绢云石墨片岩有不同的微量元素富集特征和稀土元素配分曲线,可能是多期热液活动作用的结果。值得一提的是,在②号主矿体硫化物矿石中不但发现有来自于矿体下部的有一定磨圆度的绢云石墨片岩碎屑角砾,还有一些来自上部围岩的含炭质白云大理岩角砾。此类碎屑角砾可能是交代残余或者交代过程中垮塌的产物,无法用同时沉积解释。综合分析认为第3岩性段的网脉状矿化是后期热液充填的结果,而第4岩性段底部的②号矿体是含矿热液选择性交代碳酸盐地层而成矿,菱铁矿矿体是富铁热液运移到海底后沉积生成。相对于传统的喷流沉积成矿方式,本文认为交代作用对东升庙主矿体的形成起到了关键作用。