扫描电子显微镜对花岗岩中主要矿物裂隙作用的研究

微裂隙对于岩石的物理性质有重要影响.通过光学显微镜对显微裂隙进行的观察,难以将薄片的制作过程中产生的裂隙同自然裂隙区分;其次,观测的裂隙大小限制在0.1mm或以上数量级,一些重要细节观察不到.扫描电镜的高放大倍数和三维分辨率使其成为适合于裂隙研究的理想工具.利用扫描电镜观测了浙江花岗岩在室温下由51.6MPa压力产生的裂隙的发育过程.观察花岗岩的表面以研究其微裂隙和矿物的解理、晶形及破裂作用.微裂隙分为3种类型:晶体内裂隙(完全发育在颗粒内部),晶体间裂隙(穿过颗粒边界进入其他颗粒中),颗粒边界裂隙(沿颗粒边界发育或与边界重合).本研究中的花岗岩为中-粗粒(1~6mm),经过蚀变,约含40%斜长石,25%钾长石,25%石英,10%镁铁矿物(主要为黑云母和白云母).     

铀矿床定年研究进展评述

往往由于铀矿物(沥青铀矿)颗粒细小、易蚀变成铀的次生矿物及多期铀矿化作用相互叠加等在组成和结构上的固有特点,通常难以用挑选铀矿物(沥青铀矿)样品溶样的传统定年方法精确确定其形成年龄。随着分析技术的不断更新和发展,对铀矿床成矿年代学的研究也不断深入。但受铀矿床中铀矿物U-Pb定年方法本身的制约,以及以往对铀矿物U-Pb定年体系中铀矿物样品要求认识的不足,常常导致获得的年龄无实际地质意义或无法获得理想的等时线年龄。本文针对铀矿化定年方法的发展历程进行了系统梳理和分析,评述了铀矿物定年的五种主要方法:(1)铀矿物U-Th-totalPb化学年龄;(2)铀矿物模式年龄;(3)铀矿物传统等时线年龄;(4)铀矿物矿伴生矿物年龄;(5)原位微区铀矿物U-Pb年龄。在此基础上,深入探讨了铀矿化作用定年研究中存在的问题和对应方案,期望促进未来铀矿床成矿年代学的发展。     

都龙锡锌多金属矿田万龙山矿区矽卡岩矿物特征及成因意义

万龙山锌锡矿床是都龙锡矿田的一个重要矿区。通过矽卡岩岩石化学研究,认为矿区矽卡岩属于钙矽卡岩,在w(SiO_2)—w(CaO)图解中,矿区矽卡岩与花岗岩、大理岩投点区呈线性展布,表明三者之间具有成因联系。对矿区主要的矽卡岩矿物石榴子石、辉石、角闪石、绿帘石和绿泥石进行了电子探针成分分析:石榴子石属于钙铝榴石-钙铁榴石系列,端元组分以钙铝榴石为主(体积分数51.02%～82.63%),钙铁榴石体积分数为12.45%～47.74%;辉石为透辉石-钙铁辉石系列,端元组分以钙铁辉石为主,明显缺乏透辉石;角闪石属于Mg-Fe-Mn-Li组,主要为镁角闪石;绿帘石中Fe的含量较;绿泥石主要为铁镁绿泥石,部分为铁斜绿泥石、密绿泥石或铁绿泥石,显示富镁铁质的特点。依据矽卡岩矿物的组分特征对矿区矽卡岩的成因、成矿条件及矿床成因等进行了讨论,认为矿区矽卡岩及金属矿化主要与晚白垩世老君山花岗岩具有成因关系,锡锌多金属矿床属于岩浆热液渗透交代型矿床。     

中国锗矿成矿规律与开发利用现状

锗是一种银灰色性脆的金属,在地壳中的含量约为0.0007%,属于稀散元素,是制造红外光学仪器的关键材料,2018年被美国内政部列为35种关键性矿产之一。中国的锗资源储量占全球的41%,产量占全世界的71%,拥有类似于稀土的全球影响力。已查明资源储量的锗矿区主要分布在内蒙古和云南等14个省(自治区),其中约一半的查明锗资源储量与煤矿伴生,其余大部分与铅锌矿等有色金属矿产伴生。锗可以出现在不同时代的各种矿床当中,主要包括中低温热液型多金属矿床、含锗有机岩矿床和沉积改造型三大类型,以前二者为主,占所有锗矿资源量的64%。我国高品位的富锗煤矿是世界上少有的优质资源,但尚未得到充分的开发利用。国际上主要从煤灰残渣中回收,我国除了煤矿中回收锗(如云南的临沧含锗煤矿、内蒙的乌兰图嘎)之外,也从有色金属冶炼厂综合回收(如广西大厂、云南会泽)。     

Evidences of felsic volcanism and hydrothermal activities from clays associated with the Palaeoproterozoic Porcellanite Formation of the Vindhyan Supergroup,Central India

Chemico-mineralogical attributes of authigenic clays associated with the altered volcanic tuffs that occur in the Palaeoproterozoic Porcellanite Formation contain evidences of hydrothermal alteration and diagenetic processes in a marine environment. Previous sedimentological and geochemical studies on Porcellanite Formation were restricted to the Chopan area, but, the details related to provenance, nature and source of volcanism archived in these clays have not been ascertained. In order to understand these aspects, present study on these authigenic clays were carried out. Clay minerals represent dominance of illite with subordinate amount of montmorillonite. Moreover, low abundance of kaolinite is also noticed. The illite fibers and plates associated with the kaolinite indicate illitization. The kaolinite to illite transformation is favoured by incorporation of K⁺ ions, derived from the K-feldspar dissolution and its overgrowth. Major oxide contents of these clays and their ratios when plotted over diagrams marked with standard illite, kaolinite, smectite and chlorite compositional fields show clustering within or close to the illite field. Thermodynamic components calculated for these clays when plotted over AR₂³⁺AlSi₃O₁₀(OH)₂ − R₂³⁺Si₄O₁₀(OH)₂ − AR²⁺R³⁺Si₄O₁₀(OH)₂ ternary diagram, data plots lie within the illite, mixed layer I/S and smectite fields. Binary major oxide data plots between bulk rock and authigenic clay compositions showed felsic affinity. Montmorillonite and illite predominated in the eastern and western marginal areas of the Vindhyan Basin, respectively. However, former resulted from the hydrothermal alteration of volcanic glass associated with the ferruginous breccia and altered tuffs and remnants of the volcanic vents, whereas, later is associated with the tuffaceous beds. Owing to the adsorption, Ba, Rb and Sr is enriched in clays comparing to the bulk rock composition. Low (< 15 ppm) Sc values suggested major contribution from the felsic component. Also, low Rb/Sr and Th/U values revealed moderate insitu weathering. The dominance of K-feldspar alteration and insitu weathering is also evident from clustering of clay data plots in the A-CN-K ternary diagram. Pronounced negative Eu anomaly together with higher LREE/HREE values associated with these clay minerals implied proximity to source and their possible derivation from the silicified felsic tuffs available in the provenance.     

Climatic and sea‐level control of Jurassic (Pliensbachian) clay mineral sedimentation in the Cardigan Bay Basin,Llanbedr (Mochras Farm) borehole,Wales

Early Jurassic climate is characterized by alternating cold and warm periods highlighted by studies based notably on oxygen isotopes measured on belemnite guards and other marine invertebrate shells. These climatic changes include changes in the hydrological cycle, and consequently weathering and runoff conditions. In order to clarify the erosion and weathering conditions during the Pliensbachian, this study determined the mineralogical composition of the clay fraction of 132 samples taken from the entire stage drilled in the Llanbedr (Mochras Farm) borehole (Cardigan Bay Basin). The clay mineral assemblages are composed of various proportions of chlorite, illite, illite/smectite mixed‐layers (R1 I–S), smectite and kaolinite, with possibly occasional traces of berthierine. The occurrence of abundant smectite indicates that the maximum burial temperature never exceeded 70°C. Consequently, clay minerals are considered mainly detrital, and their fluctuations likely reflect environmental changes. The variations in the proportions of smectite and kaolinite are opposite to each other. Kaolinite is particularly abundant at the base of the jamesoni Zone, in part coinciding with the δ¹³C negative excursion corresponding to the Sinemurian/Pliensbachian Boundary Event, and through the davoei Zone, whilst smectite is abundant in the upper part of jamesoni and base of ibex zones and through the subnodosus/gibbosus subzones of the margaritatus Zone. The kaolinite‐rich intervals reflect an intensification of hydrolysis and an acceleration of the hydrological cycle, while the smectite‐rich intervals indicate a more arid climate. The spinatum Zone is characterized by a distinct clay assemblage with abundant primary minerals, R1 I–S, kaolinite reworked from previously deposited sediments or from Palaeozoic rocks, and probably berthierine originating from contemporaneous ironstone‐generating environments of shallower waters. This mineralogical change by the end of the Pliensbachian likely reflects a transition from a dominant chemical weathering to a deeper physical erosion of the continent, probably related to a significant sea‐level fall consistent with a glacio‐eustatic origin.     

砂岩型铀矿中铀矿物U-Pb年代学研究现状及研究方向

该文基于中国地质调查局天津地质调查中心研究团队近年来的研究工作及对相关文献的综合研究,对砂岩型铀矿中一些重要铀矿物如沥青铀矿(晶质铀矿)、铀石、钛铀矿等的微区原位成因矿物学和U-Pb年代学研究现状进行了深入分析,提出新的研究方向,即通过采用二次离子质谱法、激光剥蚀多接收器电感耦合等离子体质谱法与电子探针化学分析法和同位素稀释热电离质谱法相结合的方式,综合研究砂岩型铀矿中沥青铀矿(晶质铀矿)、铀石、钛铀矿等铀矿物和金红石、磷灰石等含铀矿物的微区原位成因矿物学和U-Pb年代学,探索砂岩型铀矿中矿石矿物的U-Pb同位素测年新方法,获取更精确的砂岩型铀矿成岩成矿的年代学信息。这对于全面准确地认识砂岩型铀矿床的生成和演化历史,建立砂岩型铀矿床的成矿新理论具有十分重要的科学意义。铀矿物测年新方法在砂岩型铀矿床的地质勘探中也有广阔的应用前景。     

Experimental investigation on thermochemical sulfate reduction in the presence of 1-pentanethiol at 200 and 250 °C: Implications for in situ TSR processes occurring in some MVT deposits

Organic sulfur compounds are ubiquitous in natural oil and gas fields and moderate-low temperature sulfide ore deposits. Previous studies have shown that organic sulfur compounds are important in enhancing the rates of thermochemical sulfate reduction (TSR) reactions, but the details of these reaction mechanisms remain unclear. In order to assess the extent of sulfate reduction in the presence of labile sulfur species at temperature conditions near to those where TSR occurs in nature, we conducted a series of experiments using the fused silica capillary capsule (FCSS) method. The tested systems containing labile sulfur species are MgSO₄ + 1-pentanethiol (C₅H₁₁SH) + 1-octene (C₈H₁₆), MgSO₄ + 1-octene (C₈H₁₆), MgSO₄ + 1-pentanethiol (C₅H₁₁SH), 1-pentanethiol (C₅H₁₁SH)+H₂O, and MgSO₄ + 1-pentanethiol (C₅H₁₁SH) + ZnBr₂ systems. Our results show that: (1) intermediate oxidized carbon species (ethanol and acetic acid) are formed during TSR simulation experiments when 1-pentanethiol is present; (2) in the presence of ZnBr₂, 1-pentanethiol can be oxidized by sulfate to CO₂ at 200 °C, which is within the temperature range observed in natural TSR; and (3) the precipitation of sulfide minerals may significantly promote the rate of TSR, indicating that the rates of in situ TSR reactions in ore deposits could be much faster than previously thought. This may be important for understanding the possibility of in situ TSR as a mechanism for the precipitation of metal sulfides in some ore deposits. These findings provide important experimental evidence for understanding the role of organic sulfur compounds in TSR reactions and the pathway of TSR reactions initiated by organic sulfur compounds under natural conditions.     

Mineral carbon MinC(%) from Rock-Eval analysis as a reliable and cost-effective measurement of carbonate contents in shale source and reservoir rocks

The abundance of carbonate minerals in rocks is an important element for petroleum geochemists, geologists and engineers to consider during hydrocarbon exploration and production. Carbonate minerals can be related to the depositional environments of the source rocks and hence the type of organic matter that can be subsequently modified through diagenetic processes. The total carbonate content in shales can also be used to deduce their fracability as reservoir rock for shale gas/oil extraction. At present, mineralogical analysis by X-ray diffraction (XRD) is the most widely used technique in the oil and gas-related petrophysical and geochemical laboratories for identifying and quantifying carbonate minerals in rock samples. In contrast, the use of the total mineral carbon content parameter MinC (%) from Rock-Eval analysis has been limited despite (1) the parameter's effectiveness as demonstrated through instrument and methodology development; and (2) the presence of a large volume of Rock-Eval results due to its widespread use in the oil and gas industry.In this study, we acquired XRD and Rock-Eval analytical results on over nine hundred rock samples ranging from Ordovician to Cretaceous age from four petroleum sedimentary basins in Canada. Least-squares regression analyses produce empirical equations with R² values greater than 0.92 for the correlations between XRD total carbonate contents and the Rock-Eval MinC (%) values of six different suites of samples. This indicates that the MinC (%) values generated by Rock-Eval 6 and other instruments of similar capability can be used with confidence for estimating the amounts of total carbonates in sedimentary rock samples. While the correlation between the two types of carbonate content measurements is geology-specific, a global linear regression model (R² of 0.97) based on the large combined data set has been proposed for approximating the total carbonate abundances based on Rock-Eval MinC (%) values.     

Should deep seabed mining be allowed?

Commercial interest in deep sea minerals in the area beyond the limits of national jurisdiction has rapidly increased in recent years. The International Seabed Authority has already given out 26 exploration contracts and it is currently in the process of developing the Mining Code for eventual exploitation of the mineral resources. Priority issues have so far been feasibility and profitability of this emerging industry, while relatively little consideration has been given as to how, and to an even lesser extent, whether deep seabed mining should proceed. This article makes a case that the global community should question and scrutinize the underlying assumption that deep seabed mining is going benefit humankind as a whole before commercializing the common heritage of humankind.