Uranium and potassium in calc-alkaline volcanic rocks from Sardinia

The U content of major rock-forming minerals in a suite of calc-alkaline volcanic rocks from Sardinia is very low and their partition coefficient of U (D^U = C^S/C^L) is smaller than 0.1. The values of D^U of the mineral phases decrease from basalt to dacite and, in all rocks, the bulk of U and K is present in the groundmass. The apparent close association between K and U in basic and intermediate rocks probably reflects the fact that most of their rock-forming minerals are relatively ‘inert’ with respect to both of these elements.     

Sodium-rich volcanic rocks and their relationships with iron deposits in the Aqishan-Yamansu belt of Eastern Tianshan,NW China

The volcanic rocks hosting the iron deposits in the Aqishan–Yamansu metallogenic belt are sodium-rich.The geochronology,petrography,and geochemistry of minerals and sodium-rich rocks as well as the relationship between these rocks and the iron deposits are studied.Geochemically,the ore-hosting volcanic rocks are sodiumrich(the averages of Na2O and Na2O/K2O are 4.31 wt.%and 8.56,respectively)and belong to the calc-alkaline series.They are enriched in LREEs and LILEs(Ba,U,K,and Sr),but depleted in HFSEs(Nb,Ta,and Ti).SHRIMP zircon U–Pb dating of the crystal tuff in the Aqishan Formation and the dacite in the Tugutu Bulak Formation yields ages of 337.5
2.3 Ma(n?15,MSWD?0.85)and 313.0
3.3 Ma(n?13,MSWD?0.74),respectively,indicating that the sodium-rich volcanic rocks formed from the early–late Carboniferous.Electron microprobe data from plagioclases demonstrate that albites and/or oligoclases were formed in the basic–intermediate–acid volcanic rocks.Two stages of albitization are identified,and the latter is likely attributed to the dissolution of iron in the Aqishan–Yamansu belt.The sodium-rich volcanic rocks probably formed by the interaction between volcanic lava and seawater after volcanoes erupted on the seafloor;meanwhile,the albites formed by element substitution in a low-metamorphic environment.The spatiotemporal coupling relationship between sodium-rich volcanic rocks and iron deposits in the Aqishan–Yamansu belt is favorable.Iron dissolved from the dark minerals of basic–intermediate volcanic rocks through sodium metasomatism is one of the material sources for the iron deposits.     

白云岩成因探讨:新疆三塘湖盆地发现二叠系湖相喷流型热水白云岩

晚石炭世—早二叠世是新疆北部地区构造转换、海陆变迁的重要变革时期,包括三塘湖盆地在内的北疆地区该时期发育多个呈近东西向分布的陆内裂谷,其中存在大量基性、酸性及中性火山岩,它们以裂隙式喷发为特征。中二叠世芦草沟期,北疆地区发育裂谷期后半深湖沉积,沉积了厚层暗色泥岩、凝灰质泥岩、白云质泥岩夹白云质泥晶灰岩、凝灰岩、白云岩及火山岩的岩石组合,在暗色泥岩、凝灰质泥岩中普遍发育吐鲁番鳕鱼、双壳、叶肢介、介形虫等化石。其中的白云岩具如下特征:以铁白云石为主,多呈泥晶和粉晶状,与泥晶石英和有机质（含藻类）构成纹层;与方沸石岩互层,并作为方沸石的胶结物同时交代方沸石;伴生纳长石、伊利石、硬石膏、黄铁矿等多种热液矿物。此类白云岩及其热液矿物为本研究区首次发现,其分布与上石炭统火山岩的分布范围一致,表现出裂隙式、点式分布特点;火山岩中发育丰富的网状、树枝状裂缝并被热液矿物充填,可见火山岩具角砾状构造,可能反映了热液喷流口的沉积特征。初步分析认为该白云岩是一种与岩浆作用、深部热液作用相关的喷流型湖相热水沉积白云岩。     

铀系组分法测定年青火山岩年龄的研究

铀系组分法是测定火山岩不同组分中的２３０Ｔｈ／２３２Ｔｈ值和２３８Ｕ／２３２Ｔｈ值、计算年龄的方法。岩石中的各组分是用磁选或浮选分离的。经过论证，组分法与等时线方法是等价的，但不需要从全岩中精选纯的单矿物，不会发生铀和钍同位素的分馏。根据组分法模式测定了云南腾冲盆地北来凤山、老龟坡山和马鞍山火山岩样品的年龄，分别为０．１１ＭａＢ．Ｐ．、５１０００。Ｂ．Ｐ．和２５０００ａＢ．Ｐ，与地层顺序相吻合。组分法对于年青火山岩定年有着极大的潜力。     

裂谷盆地生油层中火山岩及其矿物与有机质的相互作用——油气生成的催化和加氢作用研究进展及展望

我国裂谷盆地生油层中常有火山岩发育。在研究它们共生模式的基础上,利用地球化学和模拟实验等手段探索埋藏成岩期火山矿物与有机质的相互作用。初步成果表明,一些火山矿物对有机质生烃具有催化和加氢作用,可以使生油岩在较低温度和压力条件下生成较多的油气。但是不同火山矿物对油气生成的催化加氢效果及其动力学特征、这种成因类型的油气识别方法、成藏模式等,还需深入研究。因此,本研究对于丰富油气成因理论、提供新的找油领域具有重要意义。     

Catalysis and hydrogenation: volcanic activity and hydrocarbon generation in rift basins,eastern China

Major oil reserves in rift basins in eastern China are correlated with high quality source rocks. The high quality source rocks and their hydrocarbon generation are often related to volcanic activity in the basins. Three kinds of volcanic rocks in source rocks have been defined in the Songliao, Bohaiwan and North Jiangsu basins. Some of the volcanic rocks were formed in lacustrine environments during the deposition of source rocks. It is remarkable that a part of volcanic-derived materials serves as a source of nutrients for lacustrine organisms which resulted in the formation of the organic matter in source rocks with high organic C contents. Besides hydrothermal alteration, the volcanic minerals contributed catalysis and H₂ to thermal alteration of organic matter into hydrocarbons during burial and diagenesis of source rocks and volcanics. A series of thermal laboratory simulations were performed with various combinations of immature source rocks and natural mineral assemblages. Results indicate that a significant volume of H₂ was produced from the source rock mixed with olivine and zeolite; moreover, this combination provided a 3-fold increase in hydrocarbons. It is proposed that catalysis and hydrogenation by the volcanic minerals promote hydrocarbon generation, although organic matter type is significantly variable. Hydrocarbons are generated at a lower degree of thermal stress when the reaction mixture contains volcanic minerals, and have a heavier C isotopic composition, compared to the control set of experiments.     

Petrochemistry of Volcanic Rocks in the Hishikari Mining Area of Southern Japan, with Implications for the Relative Contribution of Lower Crust and Mantle-derived Basalt

Abstract. This study presents the petrographical, mineralogical, and geochemical characteristics of Late Pliocene‐Pleistocene volcanic rocks distributed in the Hishikari gold mining area of southern Kyushu, Japan, and discusses their origin and evolution. The Hishikari volcanic rocks (HVR), on the basis of age and chemical compositions, are divided into the Kurosonsan (2.4–1.0 Ma) and Shishimano (1.7–0.5 Ma) Groups, which occur in the northern and southern part of the area, respectively. Each group is composed of three andesites and one rhyodacite. HVR are characterized by high concentrations of incompatible elements compared with other volcanic rocks in southern Kyushu, and have low Sr/Nd and high Th/U, Th/Pb, and U/Pb ratios compared with typical subduction‐related arc volcanic rocks. Modal and whole‐rock compositions of the HVR change systematically with the age of the rocks. Mafic mineral and augite/hypersthene ratios of the andesites decrease with decreasing age in the Kurosonsan Group, whereas in the Shishimano Group, these ratios are higher in the youngest andesite. Similarly, major and trace element compositions of the younger andesites in the former group are enriched in felsic components, whereas in the latter group the youngest andesite is more mafic than older andesites. Moreover, the crystallization temperature of phenocryst minerals decreases with younger age in the former group, whereas the opposite trend is seen in the latter group. Another significant feature is that rhyodacite in the Shishimano Group is enriched in felsic minerals and incompatible elements, and exhibits higher crystallization temperatures of phenocryst minerals than the rhyodacite of the Kurosonsan Group. Geochemical attributes of the HVR and other volcanic rocks in southern Kyushu indicate that a lower subcontinental crust, characterized by so‐called EMI‐type Sr‐Nd and DUPAL anomaly‐like Pb isotopic compositions, is distributed beneath the upper to middle crust of the Shimanto Supergroup. The HVR would be more enriched in felsic materials derived from the lower crust by high‐alumina basaltic magma from the mantle than volcanic rocks in other areas of southern Kyushu. The Kurosonsan Group advanced the degree of the lower crust contribution with decreasing age from 51 %, through 61 and 66 % to 77 %. In the Shishimano Group, the younger rhyodacite and andesite are derived from hotter magmas with smaller amounts of lower crust component (58 and 57 %) than the older two andesites (65 % and 68 %). We suggest that the Shishimano rhyodacite, which is considered to be responsible for gold mineralization, was formed by large degree of fractional crystallization of hot basaltic andesite magma with less lower crustal component.     

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。     

松辽盆地中生代火山岩中的氟碳钙铈矿特征及成因意义

在松辽盆地深层发育的中生代酸性火山岩中首次发现氟碳钙铈矿.氟碳钙铈矿的寄主岩为球粒流纹岩、流纹岩、流纹质熔结凝灰岩、流纹质凝灰岩,其寄主岩分布深度为2 930～3 830m,形成时代为早白孚世晚期.氟碳钙铈矿常与石英、碳酸盐、钠铁闪石、钠长石、绿泥石、绿帘石、粘土矿物等次生矿物共生,并与天然气储层有着一种内在的联系.氟碳钙铈矿是岩浆后期热液和大气降水多阶段、多次作用萃取的产物,这种相互作用是多无体系参与并经历了多阶段演化,氟碳钙铈矿形成于富Ca2+抖和CO23;的流体及还原环境.松辽盆地周边地区广泛发育的中生代火山岩与松辽盆地深层中生代火山岩十分相似,松辽盆地周边地区是否存在一个巨大的氟碳钙铈矿潜在资源,值得注意.     

中国断陷盆地主要生油岩中的火山活动及其意义

通过对断陷盆地主力生油岩中普遍存在的基碱性火山岩的分析,认为水下火山喷溢环境是优质生油岩赖以形成的主导因素。岩浆、火山的高温无机气液具有加温、加氢、催化作用,是生油岩有机质在浅埋藏的低成熟阶段形成油气的主要动力。这种沉积有机质在火山作用下形成的油气称为有机一无机混合成因的油气。重视油源岩系的火山活动研究,发展多源成烃学说,可以开拓油气勘探新领域。     

西藏吉瓦地区渐新统日贡拉组物源分析及找矿意义

通过详实的野外调查和室内研究,在西藏吉瓦地区新发现了砂岩型铜矿床,赋矿层位为渐新统日贡拉组,矿床类型为层控矿床。为探讨日贡拉组砂岩的物源特征及其构造背景、查明其含矿物质来源,通过碎屑矿物定量分析、元素地球化学方法及重矿物组合分析等一系列物源分析方法对日贡拉组的物质来源进行了研究。结果显示,研究区主要岩性为岩屑砂岩,岩屑主要成分为酸性火山岩,砂岩结构成熟度低,分选磨圆差。碎屑组分分析表明物源集中在火山弧物源区,地球化学特征为硅质含量高、LREE富集、HREE相对亏损、显示Eu负异常,均表明物源与酸性火山岩密切相关;日贡拉组砂岩的大地构造背景主要为大陆岛弧,砂岩碎屑来自上地壳长英质源区。重矿物组合以反映物源为中酸性岩浆岩成分的赤褐铁矿+磁铁矿、锆石、电气石、石榴子石为主,沉积环境为气候干旱、水体较浅的富氧环境。锆石形态特征指示物源距母岩区较近,重矿物的相关性分析也指示了物源与火山岩密切相关。研究区的日贡拉组砂岩与早白垩酸性火山岩微量元素及重矿物的对比表明,碎屑物质源区特点从岩石学特征、地球化学特征及重矿物组合特征上均表现出了亲缘关系,物源成分与火山作用紧密相关,很可能主要来自班公湖-怒江洋壳南向俯冲与雅鲁藏布江洋壳北向俯冲双重制约条件下产生于火山弧环境中的早白垩世火山岩。日贡拉组发现了砂岩型铜矿,火山岩提供了成矿物质来源,为寻找同类型的矿床开启思路。     

Corundum-group minerals in rocks of the Khibiny alkaline pluton,Kola Peninsula

Five minerals of the corundum group have been identified in the Khibiny pluton with certainty. Corundum proper and karelianite occur only in hornfels after volcanic and sedimentary rocks. Xenoliths of hornfels mark the ring faults that bound foidalite within the field of foyaite. Hematite occurs in hydrothermally altered nepheline syenite and crosscutting hydrothermal veins related to the ring faults. Minerals of the ilmenite-pyrophanite series are present in all rocks of the pluton, including veins. Accessory ilmenite in foyaite varies from the manganese variety and pyrophanite in the inner and outer parts of the pluton to manganese-free ilmenite in zone of the Main Ring Fault. In xenoliths of volcanic rocks and alkaline ultramafic rocks, ilmenite is enriched in magnesium. The zoning in distribution of the above-mentioned minerals and the character of variation in their compositions from margins of the pluton to its center are consistent with the petrochemical zoning formed as a result of foyaite alteration of near ring faults.     

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。     

云南省龙脖河铜矿区火山岩地质及岩石化学特征研究

龙脖河铜矿床的成矿与该区火山岩关系密切，加强对其进行岩石化学的研究，对在本区和区域上同类矿床的勘查找矿和成因研究具有重要的指导意义。在大量野外调查和室内综合分析基础上，研究了龙脖河铜矿区典型火山岩及其组构特征、副矿物特征、蚀变特点和岩石化学特征，认为龙脖河铜矿区火山岩是一套富钠质的碱性玄武岩系列岩石，与大红山群变钠质火山岩岩石组合十分相似。     

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.     

Carbonatitic Volcanic Genesis of Hetaoqing Fe-Cu Deposit in Central Yunnan, China

Abstract. The Kunyang rift on western margin of Yangtze Platform is a continental rift, and also a rare Precambrian Fe-Cu mineralization zone in China. The Wuding-Lufeng mineralization area in the middle section of the rift is an important part of the zone, and an elliptic-shaped volcanic collapsed basin, controlled by a ring fracture system with carbonatitic volcanic rocks mainly occurring along the northwestern edge of the basin. The Hetaoqing Fe-Cu ore deposit at the western side of the basin is hosted in carbonatitic volcanic rocks and pyroclastic sedimentary rocks. The original ore bodies occur as layers, bands and lenses conformable to the host carbonatitic rocks. The ores usually appear as massive, impregnated and granular in carbonatitic rocks, and as brecciform and sandy in pyroclastic sedimentary rocks. Ore-forming minerals are magnetite, hematite, chalcopy-rite, bornite, pyrite, carrollite, molybdenite, cobaltite and skinnerite, and secondary minerals limonite, chalcocite, azurite, malachite and tenorite. Gangue minerals are calcite, dolomite, ankerite, common hornblende, arfvedsonite, augite, aegirine-augite, albite, phlogopite, biotite, chlorite and apatite. Evidences of mineral chemistry, trace elements and isotopic ratios of ores, as well as geological features, suggest that the original ores are igneous in origin. Chemical features of magnetites in the deposit belong to carbonatite type, and are similar to those from the Bayan Obo carbonatites. The ores are rich in iron, titanium, rare earth elements, niobium, tantalum, gold, silver, phosphor and sulfur. These features indicate that the Fe-Cu deposit associated with volcanic activity in the Wuding-Lufeng basin is alkali-carbonatite volcanic type.     

陕西秦巴火山岩的分布特征及其与成矿的关系

陕西秦巴区元古宙和早古生代火山活动强烈,火山岩发育。经研究,其火山岩形成机制,多与裂谷构造有关。这些火山岩中与之相关的矿产有钼、铼、钨、金、铅、银、锌、铜、铁、金红石及有关的非金属矿等。本文从该区火山岩的特征出发,分析其所产出的大地构造环境,并探讨火山岩与矿产之间的关系,最后提出进一步找矿的建议。     

长白山天池火山晚更新世以来的喷发活动：

应用高精度铀系不平衡TIMS法测定了吉林长白山天池火山岩锥体中上部的11个熔岩、浮岩样品的年龄，并据此划分出晚更新世、全新世以来6个喷发活动期次，分别为：＞350ka、70ka、18－25ka、10ka、4－5ka和1－0．75ka。此外，还介绍了铀系不平衡法火山岩年代学的基本原理和试验流程，讨论了样品封闭等问题。     

燕山中段大红峪组火山岩的古风化特征

燕山中段 (主要是指北京市平谷县内 )大红峪组火山岩 ,在火山活动的间歇期 ,存在古风化现象。古风化使火山岩的成分、结构遭受改变 ,以致影响对岩石岩性的确定及同位素年龄的测定等。不同的地质环境 ,其风化情景不同。文中论述了火山岩的三种风化带及其不同的风化环境特征 ,并与现代风化带进行了对比。研究大红峪组的古风化现象 ,有利于更好地认识当时的地质环境。     

我国东北小古里河-科洛-五大连池-二克山火山带钾质矿物成因及地质意义

东北黑龙江小古里河-科洛-五大连池-二克山火山岩带是我国近代保存最好的火山群之一,此带火山岩的岩石化学特点全都强碱富钾,K₂O/Na₂O>1.2,属于一套高钾过碱性火山岩。通过对东北钾质火山岩及金云母橄榄岩地幔捕虏体中钾质矿物金云母、白榴石的成分、结晶环境与岩浆成分及来源关系的研究,认为在岩石圈伸展构造背景下,地幔金云母橄榄岩的低度部分熔融形成钾质岩浆,钾质岩浆上升到地壳浅部经历了白榴石的结晶作用。岩浆演化晚期,因钾质矿物大量晶出导致岩浆相对富钠而出现他形霞石和方钠石等填隙矿物。火山岩及地幔捕虏体中富挥发分矿物金云母、白榴石、磷灰石、霞石和方钠石还提供了钾质岩浆富含H₂O、F、Cl、P等挥发分的证据。