Re–Os isotope and platinum-group element geochemistry of the Pobei Ni–Cu sulfide-bearing mafic–ultramafic complex in the northeastern part of the Tarim Craton

A number of mafic–ultramafic intrusions that host Ni–Cu sulfide mineralization occur in the northeastern Tarim Craton and the eastern Tianshan Orogenic Belt (NW China). The sulfide-mineralized Pobei mafic–ultramafic complex is located in the northeastern part of the Tarim Craton. The complex is composed of gabbro and olivine gabbro, cut by dunite, wehrlite, and melatroctolite of the Poyi and Poshi intrusions. Disseminated Ni–Cu sulfide mineralization is present towards the base of the ultramafic bodies. The sulfide mineralization is typically low grade (<0.5 wt.% Ni and <2 wt.% S) with low platinum-group element (PGE) concentrations (<24.5 ppb Pt and <69 ppb Pd); the abundance of Cu in 100 % sulfide is 1–8 wt.%, and Ni abundance in 100 % sulfide is typically >4 wt.%. Samples from the Pobei complex have εNd (at 280 Ma) values up to +8.1, consistent with the derivation of the magma from an asthenospheric mantle source. Fo 89.5 mol.% olivine from the ultramafic bodies is consistent with a primitive parental magma. Sulfide-bearing dunite and wehrlite have high Cu/Pd ratios ranging from 24,000 to 218,000, indicating a magma that evolved under conditions of sulfide saturation. The grades of Ni, Cu, and PGE in 100 % sulfide show a strong positive correlation. A model for these variations is proposed where the mantle source of the Pobei magma retained ~0.033 wt.% sulfide during the production of a PGE-depleted parental magma. The parental magma migrated from the mantle to the crust and underwent further S saturation to generate the observed mineralization along with its high Cu/Pd ratio at an R-factor varying from 100 to 1,200. The mineralization at Poshi and Poyi has very high γOs (at 280 Ma) values (+30 to +292) that are negatively correlated with the abundance of Os in 100 % sulfide (5.81–271 ppb) and positively correlated with the Re/Os ratios; this indicates that sulfide saturation was triggered by the assimilation of crustal sulfide with both high γOs and Re/Os ratios. When compared to other Permian mafic–ultramafic intrusions with sulfide mineralization in the East Tianshan, the Poyi and Poshi ultramafic bodies were formed from more primitive magmas, and this helps to explain why the sulfide mineralization has high Ni tenor.     

New textural and mineralogical constraints on the origin of the Hongge Fe-Ti-V oxide deposit, SW China

The Hongge magmatic Fe-Ti-V oxide deposit in the Panxi region, SW China, is hosted in a layered mafic–ultramafic intrusion. This 2.7-km-thick, lopolith-like intrusion consists of the lower, middle, and upper zones, which are composed of olivine clinopyroxenite, clinopyroxenite, and gabbro, respectively. Abundant Fe-Ti oxide layers mainly occur in the middle zone and the lower part of the upper zone. Fe-Ti oxides include Cr-rich and Cr-poor titanomagnetite and granular ilmenite. Cr-rich titanomagnetite is commonly disseminated in the olivine clinopyroxenite of the lower parts of the lower and middle zones and contains 1.89 to 14.9 wt% Cr₂O₃ and 3.20 to 16.2 wt% TiO₂, whereas Cr-poor titanomagnetite typically occurs as net-textured and massive ores in the upper middle and upper zones and contains much lower Cr₂O₃ (<0.4 wt%) but more variable TiO₂ (0.11 to 18.2 wt%). Disseminated Cr-rich titanomagnetite in the ultramafic rocks is commonly enclosed in either olivine or clinopyroxene, whereas Cr-poor titanomangetite of the net-textured and massive ores is mainly interstitial to clinopyroxene and plagioclase. The lithology of the Hongge intrusion is consistent with multiple injections of magmas, the lower zone being derived from a single pulse of less differentiated ferrobasaltic magma and the middle and upper zones from multiple pulses of more differentiated magmas. Cr-rich titanomagnetite in the disseminated ores of the lower and middle zones is interpreted to represent an early crystallization phase whereas clusters of Cr-poor titanomagnetite, granular ilmenite, and apatite in the net-textured ores of the middle and upper zones are thought to have formed from an Fe-Ti-(P)-rich melt segregated from a differentiated ferrobasaltic magma as a result of liquid immiscibility. The dense Fe-Ti-(P)-rich melt percolated downward through the underlying silicate crystal mush to form net-textured and massive Fe-Ti oxide ores, whereas the coexisting Si-rich melt formed the overlying plagioclase-rich rocks in the intrusion.     

Quantification of electrical resistance to estimate NaCl behavior in a column under controlled conditions

Accurate prediction of solute transport processes in surface water and its underlying bed is an important task not only for proper management of the surface water but also for pollution control in these water bodies. Key issue in this task is an estimation of parameters as diffusion coefficient and velocity for solute transport both in water body and in the underlying bed. This estimation would greatly help us to understand the deposition and release mechanism of solute across the water-bed interface. In this study, a column experiment was conducted in laboratory to estimate the velocity and diffusion coefficient of sodium chloride (NaCl) in water body and underlying sand layer (bed). The column used with a diameter of 30 cm and a height of 100 cm, was filled with sand at the lower half part and water at the upper half part. Total 64 stainless steel electrodes were installed on its surface around. The sodium chloride solution was injected from the top of the column, and electrical resistance between electrodes was monitored for 71 h. Then the dimensionless resistance breakthrough curve was fitted with one dimensional analytic solution for solute transport and the related diffusion coefficient and velocity parameters were estimated. The results show that the NaCl transport velocity was high in the water body but extremely low in the underlying sand layer (bed). The diffusion coefficient estimated in sand layer coincides with those reported well. This indicates that the electrical resistance based solute transport parameter estimation method is not only effective but also has an advantage of multipoints monitoring. This is useful both in mapping solute transport parameter for solute transport process analysis and in providing parameter input for solute transport numerical modeling.     

Statistical Analysis of Anisotropic Damage of the Bukit Timah Granite

Summary This paper presents a method to analyze probabilistic anisotropic initial damage of a rock mass. A three-dimensional geometric model of cracks in a rock mass is established in terms of several parameters, such as orientations, spacing and normalized sizes of cracks in the rock mass. The dip, dip direction, spacing, and normalized size of cracks of the Bukit Timah granite in Singapore were obtained from visual inspection of rock cores, color TV imaging, and impression packer tests in the boreholes at a site of geological investigation. Using the measured data, probabilistic distribution laws of geometric parameters of cracks on the surface of the boreholes are derived. Based on these statistical distributions and using Monte-Carlo simulation method, the distribution of anisotropic initial damage of the Bukit Timah granite is derived and found to have a beta distribution. This anisotropic initial damage distribution of a rock mass can be used in probabilistic analysis of rock mass responses to both static and dynamic loads.     

碳酸盐岩差异性风化成土特征及其对石漠化形成的影响

碳酸盐岩极低的酸不溶物含量使岩石风化产生的残积土壤物质数量极少，并产生巨大的体积缩小，促使早期形成的残积土在重力作用下不断向下塌陷。显著的差异性风化使基岩面强烈起伏，甚至形成大量的岩溶尘洼地、裂隙、地下管道、洞穴系统等。在重力和水的作用下，土粒沿垂直和水平方向上经微距离或短距离搬运到上述低洼或地下空间中，甚至由地下河带到更远的地方，这是碳酸盐岩地区土壤丢失的重要方式，也是形成石漠化最主要的地质因素。土壤在地表分布高度不均匀，是碳酸盐岩地区的地表少土的重要原因。对于酸不溶物含量相当的石灰岩和白云岩而言，由于白云岩的差异性风化明显弱于石灰岩，以及受各种应力作用后，白云岩形成的节理及裂隙密集而均匀，从而提高了近地表白云岩的含水能力，延长了风化过程中的水－岩反应时间，使风化作用可以相对集中于地表或近地表进行，有利于岩石的整体风化作用的进行，同时使白云岩风化壳基岩面起伏相对较小，风化残积形成的土壤分布也相对均匀。因此，白云岩区地表土层较厚，石漠化程度也稍弱于灰岩区。     

内蒙古白乃庙铜-金-钼矿床成矿机制——来自流体包裹体和He-Ar同位素的证据

白乃庙铜-金-钼矿是华北板块北缘中段一个重要矿床,其矿化特征既显示斑岩型蚀变特征,同时又表现出明显的后期造山作用改造的特点。本次研究通过系统的流体包裹体显微测温、激光拉曼和气液相色谱分析揭示其成矿流体为中—低温、中低盐度的CO_2(CO)-H_2O-CH_4(C_2H_2+C_2H_4)-NaCl-CaCl_2体系,流体混合作用和CO_2逃逸为成矿主要因素。富还原性流体的存在可能促使气相流体携带大量的Cu、Au等成矿元素迁移至较远点的白乃庙群地层,沿着片理或裂隙沉淀成矿。对不同成矿阶段矿石中黄铁矿的He-Ar同位素组成测试结果显示白乃庙矿床黄铁矿流体包裹体的~3He/~4He比值在0.06~0.71Ra之间,~(40)Ar/~(36)Ar比值为375.5~1436.3,指示成矿体系由不同性质和组成的两个端元流体混合而成,即混入了类似于MORB型地幔端元的高温高盐度流体和富含地壳放射成因氦但具有空气氩同位素组成特征的低温大气降水。白乃庙矿床属受后期造山作用改造的斑岩型铜-金-钼矿床,形成于古亚洲洋板块持续向南俯冲背景。     

黑龙江省塔河绿林林场一带兴华渡口群岩石地球化学特征

黑龙江省塔河西北绿林林场一带原划分的兴华渡口群的岩石地球化学成分可与太古宙绿岩带对比,该区的兴华渡口群为低级地体（火山沉积盆地）,ＳｍＮｄ模式年龄及单阶段演化年龄为（１２５２±２８～１４６３±２０）Ｍａ。     

皖南花山锑金矿床硫化物电子探针分析及其指示意义

花山锑金矿床位于皖南东至县境内, 是皖南地区代表性金-多金属矿床之一。 本次工作对花山锑金矿床开展了野外地质、岩相学特征观察以及金属硫化物电子探针分析, 得到以下结论：1） 花山锑金矿床主要成矿阶段可分为毒砂-黄铁矿（PyⅠ）阶段、黄铜矿-黄铁矿 （PyⅡ）阶段和方解石-辉锑矿阶段。 2） 金在不同阶段硫化物中均有赋存, 其矿化伴随整个热液成矿过程, 且以毒砂-PyⅠ阶段和黄铜矿-PyⅡ阶段为主。 毒砂-PyⅠ阶段和黄铜矿-PyⅡ阶段发育金矿化, 无锑矿化, 方解石-辉锑矿阶段发育锑、金共生矿化。 3） 早阶段即毒砂 -PyⅠ阶段和黄铜矿-PyⅡ阶段载金矿物为黄铁矿、毒砂及黄铜矿, 成矿物质来源以地层为 主;晚阶段即方解石-辉锑矿阶段载金矿物为辉锑矿, 成矿物质来源以燕山期岩浆岩为主。 本次工作对东至及皖南地区金矿床的寻找勘探具有重要的指示意义。     

淮南矿区煤矸石的物质组成特征及资源化评价

本文利用各种测试方法,对淮南谢桥、新庄孜和张集煤矿采集的不同层位来源的240个煤矸石样品的化学成分、矿物成分和微量元素的进行测试与分析,得出了淮南矿区不同煤矿煤矸石的化学成分特征及其中微量元素的含量变化,评价了煤矸石中有害元素的环境影响作用。结合煤矸石基本特征,提出了合理的资源化利用途径,为煤矿开采过程的主要固体废物煤矸石综合利用和资源化、煤矿环境保护提供了参考资料。     

锶矿X

研究了找锶矿的