Sm‐Nd and Rb‐Sr dating of Archaean gneisses,eastern Yilgarn Block,Western Australia

Sm‐Nd and Rb‐Sr isotopic data for Archaean gneisses from three localities within the eastern Yilgarn Block of Western Australia indicate that the gneisses define a precise Rb‐Sr whole rock isochron age of 2780 ± 60 Ma and an initial ⁸⁷Sr/⁸⁶Sr of 0.7007 ± 5. The Sm‐Nd isotopic data do not correspond to a single linear array, but form two coherent groups that are consistent with a c. 2800 Ma age of crust formation, with variable initial Nd. These results indicate that the gneiss protoliths existed as continental crust for a maximum period of only c. 100 Ma, and probably for a much shorter time, prior to the formation of the 2790 ±30 Ma greenstones.     

Tourmaline geochemistry and boron isotopic variations as a guide to fluid evolution in the Qiman Tagh W-Sn belt,East Kunlun,China

The Qiman Tagh W-Sn belt lies in the westernmost section of the East Kunlun Orogen, NW China, and is associated with early Paleozoic monzogranites, tourmaline is present throughout this belt. In this paper we report chemical and boron isotopic compositions of tourmaline from wall rocks, monzogranites, and quartz veins within the belt, for studying the evolution of ore-forming fluids. Tourmaline crystals hosted in the monzogranite and wall rocks belong to the alkali group, while those hosted in quartz veins belong to both the alkali and X-site vacancy groups. Tourmaline in the walk rocks lies within the schorl-dravite series and becomes increasingly schorlitic in the monzogranite and quartz veins. Detrital tourmaline in the wall rocks is commonly both optically and chemically zoned,with cores being enriched in Mg compared with the rims. In the Al-Fe-Mg and Ca-Fe-Mg diagrams,tourmaline from the wall rocks plots in the fields of Al-saturated and Ca-poor metapelite, and extends into the field of Li-poor granites, while those from the monzogranite and quartz veins lie within the field of Li-poor granites. Compositional substitution is best represented by the MgFe_(-1), Al(NaR)_(-1), and AlO(Fe(OH))_(-1) exchange vectors. A wider range of δ~(11)B values from -11.1‰ to -7.1‰ is observed in the wall-rock tourmaline crystals, the B isotopic values combining with elemental diagrams indicate a source of metasediments without marine evaporates for the wall rocks in the Qiman Tagh belt. The δ~(11)B values of monzogranite-hosted tourmaline range from -10.7‰ and-9.2‰, corresponding to the continental crust sediments, and indicate a possible connection between the wall rocks and the monzogranite. The overlap in δ~(11)B values between wall rocks and monzogranite implies that a transfer of δ~(11)B values by anataxis with little isotopic fractionation between tourmaline and melts. Tourmaline crystals from quartz veins have δ~(11)B values between -11.0‰ and-9.6‰, combining with the elemental diagrams and geological features, thus indicating a common granite-derived source for the quartz veins and little B isotopic fractionation occurred. Tourmalinite in the wall rocks was formed by metasomatism by a granite-derived hydrothermal fluid, as confirmed by the compositional and geological features.Therefore, we propose a single B-rich sedimentary source in the Qiman Tagh belt, and little boron isotopic fractionation occurred during systematic fluid evolution from the wall rocks, through monzogranite, to quartz veins and tourmalinite.     

新疆阿尔泰巴斯铁列克钨多金属矿矿物特征及其地质意义

巴斯铁列克是在新疆阿尔泰发现的首例中型钨多金属矿床。该矿床赋存于黑云二长花岗岩外接触带的上志留统—下泥盆统康布铁堡组火山沉积岩系中。矿体呈似层状和透镜状分布于矽卡岩中。矽卡岩及金属矿物特征关系到成矿机制研究和矿床模型的构建。文章对矽卡岩矿物和矿石中金属矿物进行了研究,电子探针分析表明,辉石端员组分以透辉石为主,少量钙铁辉石(w(Wo)为49.14%～50.71%,w(En)为24.38%～27.76%,w(Fs)为22.29%～24.27%);石榴子石以钙铝榴石为主;黑云母为铁云母,长石为正长石,绿帘石具有富Ca、Al、贫Fe特征。闪锌矿为铁闪锌矿,磁黄铁矿、黄铜矿、黝锡矿、毒砂、自然铋、辉银矿分子式与标准矿物基本一致。研究表明,矿区矽卡岩为交代成因的钙质矽卡岩,是岩浆热液交代大理岩的产物。通过对矿床地质特征、矽卡岩矿物组合、矽卡岩与矿化关系和矿物成因研究,提出成矿过程经历了早期矽卡岩阶段、退化蚀变阶段和石英硫化物阶段,钨矿化主要形成于退化蚀变阶段,铜锌矿化则形成于石英硫化物阶段。     

Geology,fluid inclusions,and geochemistry of the Zhazixi Sb–W deposit,Hunan, South China

The Zhazixi Sb–W deposit in the Xuefeng uplift, South China, exhibits a unique metal association of W and Sb, where the W orebodies are hosted by interlayer fractures and the Sb orebodies are contained within NW-trending faults. This study proposes that the W and Sb mineralization took place in two separate periods. The mineral paragenesis of the W mineralization reveals a mass of quartz, scheelite and minor calcite. The mineral assemblage of the Sb mineralization developed after W mineralization and consists of predominantly quartz and stibnite, and small amounts of native Sb, berthierite, chalcostibnite, pyrite, and chalcopyrite. Fluid inclusions in quartz and coexisting scheelite are dominated by two-phase, liquid-rich, aqueous inclusions at room temperature. Microthermometric studies suggest that ore-forming fluids for W mineralization are characterized by moderate temperatures (170–270 °C), low salinity (3–7 wt% NaCl equiv.), low density (0.75–0.95 g/cm³), and moderate to high pressure (57.2–99.7 MPa) and these fluids experienced a cooling and dilution evolution during W mineralization. Ore-forming fluids for Sb mineralization are epithermal types with low temperatures (150–230 °C), low salinity (4–6 wt% NaCl equiv.), moderate density (0.82–0.94 g/cm³), and high pressure (42.2–122.5 MPa) and these fluids display an evident decline in homogenization temperature during Sb mineralization. Laser Raman analyses of the vapor phase indicate that the ore-forming fluids for both W and Sb mineralization contain a small amount of CO₂.The ore-forming fluids for Sb mineralization are identified as predominantly originating from the continental crust, as suggested by the low ³He values (0.009 × 10⁻¹² cc.STP/g) and ³He/⁴He ratios (0.002–0.056 Ra) as well as high ³⁶Ar values (1.93 × 10⁻⁹ cc.STP/g) and ⁴⁰Ar/³⁶Ar ratios (909.5–2279.7). The source of S is identified to be the Neoproterozoic Wuqiangxi Formation, as traced by the δ³⁴S_V-CDT values of stibnite (3.1–9.4‰). The ²⁰⁸Pb/²⁰⁴Pb (37.643–40.222), ²⁰⁷Pb/²⁰⁴Pb (15.456–15.681), and ²⁰⁶Pb/²⁰⁴Pb (17.093–20.042) ratios suggest a mixture of lower crustal and supracrustal Pb sources.It is thus concluded that the ore genesis of the Zhazixi Sb–W deposit is related to the intracontinental orogeny during the early Mesozoic. Fluid mixing is considered to be the critical mechanism involved in W mineralization, whereas a fluid cooling process is responsible for Sb mineralization. Furthermore, the absence of Au is attributed to the low Σa_s content in Sb-mineralizing fluids.     

内蒙古东山湾钨钼多金属矿床成矿流体地球化学特征及成因

东山湾钨钼多金属矿床为大兴安岭南段新发现的一斑岩型矿床,产于燕山晚期花岗斑岩体与二叠系的接触带附近。该矿床主要发育细脉、微细脉浸染型矿化,其钨钼银多金属热液成矿作用划分为黑钨矿-锡石-毒砂-石英阶段(Ⅰ)、毒砂-辉钼矿-石英阶段(Ⅱ)、银多金属硫化物-石英阶段(Ⅲ) 3个阶段。为了系统研究该矿床不同成矿阶段成矿流体的来源、性质及其演化特点,对不同成矿阶段样品进行了流体包裹体岩相学、显微测温学及碳、氢、氧同位素研究。结果表明:Ⅰ、Ⅱ阶段石英中流体包裹体的均一温度分别为232.7~321.7 ℃和201.2~352.7 ℃,盐度(w(NaCl))分别为3.4%~9.8%和4.1%~10.4%,成矿流体属中温、中等盐度不均匀的NaCl-H₂O体系型热液;Ⅲ阶段石英中流体包裹体的均一温度变化范围为198.6~273.5 ℃,盐度为5.0%~8.4%,成矿流体属中低温、中低盐度均匀的NaCl-H₂O体系型热液;Ⅱ阶段石英样品的δ¹⁸O值为7.5‰~9.0‰,石英中流体包裹体的δD_H2O-SMOW值与δ¹³C_PDB值分别为-175.6‰~-160.3‰与-23.5‰~-20.1‰。成矿流体具有岩浆分异热液的特点,并伴随大气降水的大量加入,流体运移过程中地层有机质的加入导致了成矿流体具有较低的δD_H2O-SMOW值、δ¹³C_PDB值;成矿流体的不混容作用、大气降水的加入是导致区内钨钼沉淀、成矿的主要机制,而银多金属矿化则可能由成矿流体的降温冷却所引起。     

AG MP-1阴离子交换树脂元素分离方法再研究

目前不同实验室建立的用于MC-ICP-MS铜铁锌同位素测定的离子交换分离方法多适用于一般地质样品的Fe同位素高精度测定,而对于一些类似于白云鄂博Fe-Nb-REE矿床的特殊地质样品,这些分离方法的适用情况有待进一步研究。为研究REE、Nb、Ta、Co、Cu、W等元素是否能够和Fe有效分离,采用AG MP-1阴离子交换树脂,依次以6 mol/L HCl和2 mol/L HCl为介质对这些元素进行淋洗,并利用ICP-AES和ICP MS对淋洗液中的各元素含量进行测定。实验结果表明,在6 mol/L HCl介质条件下,运用AG MP-1树脂可以将REE、W与Fe有效地分离,能够将Nb、Ta的含量降低一个数量级;Fe、Co、Cu的淋洗行为和前人研究结果一致。     

Faroe Shelf Water

Faroe Shelf Water (FSW) is the water mass that occupies the shallow parts of the Faroe Shelf, surrounding the Faroe Islands (62°N, 7°W). Intensive tidal mixing induces a high degree of homogeneity and the circulation system allows a partial isolation from surrounding waters. This water mass, therefore, supports a unique ecosystem of great importance for commercial fish stocks and studies have shown a clear dependence of the ecosystem on the physical processes that maintain this system and control the exchange between the FSW and the off-shelf waters. In order to identify and quantify these processes, a large observational dataset has been analysed and related to alternative theories. From this analysis, the extent and properties of the FSW have been quantified and the degree of stratification explained in terms of the Simpson–Hunter theory. The residual clockwise circulation system, which is responsible for the partial isolation from off-shelf waters, is shown to be mainly generated by tidal rectification. The typical exchange rate of water between the FSW and the off-shelf regimes has been determined by the use of simple models based on the heat and the salt budgets but the actual exchange rate is found to vary considerably in time and space. These results support earlier suggestions that this exchange is the main limiting factor for the phytoplankton spring bloom on the Faroe Shelf and that variations in exchange rate are responsible for the large inter-annual variation in spring bloom timing and intensity. The observations indicate that the on-shelf/off-shelf exchange intensity is not symmetrically distributed around the shelf, but rather concentrated around the narrow southern tip of the Faroe Shelf, where off-shelf waters during intensive exchange events may be imported all the way to the shore.     

东昆仑西段黑山-祁漫塔格成矿带钨锡成矿地质条件及找矿方向

从沉积建造、岩浆侵入、构造活动等方面探讨了新疆东昆仑西段黑山-祁漫塔格成矿带钨锡元素的成矿地质条件,利用1：10万水系沉积物测量成果,结合成矿地质条件,初步划分了钨锡的找矿靶区,为钨锡矿产的寻找指出了方向.     

济南高陡土质边坡稳定性分析及治理方法探讨——以济南南部山区山间平原为例

在济南山前及山间倾斜平原区常见土质边坡存在较大安全隐患,本文结合实例,对此类边坡开展稳定性评价及治理方法研究,对不稳定边坡的成因做了详细分析,并采用毕肖普条分法对边坡稳定性进行了定量计算,提出清坡+格构+钢筋混凝土挡板+截水沟的方案解决土质边坡失稳问题。治理后边坡滑动安全系数为1.673,实现了土质边坡的有效防治,为此类土质边坡失稳问题提供了新的治理思路。     

成都地区隐伏构造元素的地球化学特征

通过对成都市多目标地球化学资料的研究，认为深层样的Hg,W,Au,Sc和浅层样的Hg,W,Au,B可以指示隐伏构造，而深层样的指示作用优于浅层样，在深层样反映好的隐伏构造可能与地热发育有关。低温热液、农业有毒元素和油气指示元素指标在隐伏构造上表明明显。在今后多目标地球化学测量中，必需进行深层样的采样。