Detailed <Superscript>40</Superscript>Ar/<Superscript>39</Superscript>Ar dating of geologic events associated with the Mantos Blancos copper deposit,northern Chile

The ⁴⁰Ar/³⁹Ar geochronological method was applied to date magmatic and hydrothermal alteration events in the Mantos Blancos mining district in the Coastal Cordillera of northern Chile, allowing the distinction of two separate mineralization events. The Late Jurassic Mantos Blancos orebody, hosted in Jurassic volcanic rocks, is a magmatic-hydrothermal breccia-style Cu deposit. Two superimposed mineralization events have been recently proposed. The first event is accompanied by a phyllic hydrothermal alteration affecting a rhyolitic dome. The second mineralization event is related to the intrusion of bimodal stocks and sills inside the deposit. Because of the superposition of several magmatic and hydrothermal events, the obtained ⁴⁰Ar/³⁹Ar age data are complex; however, with a careful interpretation of the age spectra, it is possible to detect complex histories of successive emplacement, alteration, mineralization, and thermal resetting. The extrusion of Jurassic basic to intermediate volcanic rocks of the La Negra Formation is dated at 156.3 ± 1.4 Ma (2σ) using plagioclase from an andesitic lava flow. The first mineralization event and associated phyllic alteration affecting the rhyolitic dome occurred around 155–156 Ma. A younger bimodal intrusive event, supposed to be equivalent to the bimodal stock and sill system inside the deposit, is probably responsible for the second mineralization event dated at ca. 142 Ma. Other low-temperature alteration events have been dated on sericitized plagioclase at ca. 145–146, 125, and 101 Ma. This is the first time that two distinct mineralization events have been documented from radiometric data for a copper deposit in the metallogenic belt of the Coastal Cordillera of northern Chile. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Sensitivity analysis of support safety factor for predicting the effects of contributing parameters on roof falls in underground coal mines

Roof falls accounted for 18.18% of all fatal accidents in Indian coal mines, contributing about 35.29% of all fatal accidents in below-ground operations in 2005. The support safety factor, always preferred in support planning and design of underground coal mines, may be an important predictor for roof falls. In this paper, geotechnical data were collected from 14 roof fall incident places in an underground coal mine, located in the Eastern India, which has bord and pillar method of workings. The mean value of probabilistic support safety factor for the case study mine was found to be 1.24. However, the probability, of the estimated support safety factor of less than or equal to one, was found to be 0.246. Sensitivity analysis was conducted to analyze the effects of the contributing parameters on support safety factor and the likelihood of the roof fall. The multi-variate regression analysis was carried out for the data generated by Monte Carlo method to correlate the contributing factors to support safety factor. It ranked gallery width as the first parameter to control the support safety factor.     

内蒙古敖包吐萤石矿床的Sr、Nd、Pb同位素地球化学特征

敖包吐萤石矿床是内蒙古北部苏莫查干地区单一萤石矿集区中的一个代表性矿床,产于早二叠世大石寨组火山-沉积岩与早白垩世敖包吐花岗岩的接触带上。文章通过分析该矿床岩、矿石的微量元素和稀土元素,揭示出萤石的成矿作用可分为2个阶段,即交代作用和充填作用。交代作用过程中大石寨组的结晶灰岩可能为萤石的形成提供了部分Ca来源,萤石矿石的稀土元素配分模式与海水基本类似,具有Ce负异常;成矿作用后期主要表现为充填作用,形成颗粒粗大的萤石,表现为重稀土元素富集的特征,并随着萤石的沉淀析出,稀土元素总量逐渐下降,反映出成矿流体经历了较长期的演化过程。各地层单元、花岗岩体和萤石矿石的Sr、Nd、Pb同位素研究表明,萤石的放射性同位素组成具有壳、幔源混合的特点,成矿物质来源具有多源性。早白垩世敖包吐花岗岩可能是萤石中F的主要来源,而大石寨组的结晶灰岩则可能提供了Ca。另外,Pb、Nd同位素的极大不均一性,有可能是成矿流体在运移过程中对艾力格庙群放射性组分的选择性吸收的结果。萤石成矿作用与钾玄岩的时空关系暗示了萤石的成矿过程可能是中国东部岩石圈减薄和下地壳的置换地质事件的结果。在构造转型的过程中,燕山中期富碱的酸性花岗岩浆的活动分异出富含F的成矿流体,与幔源流体混合,沿区域重新活化的深大断裂和大石寨组的层间破碎带上升,交代其间的灰岩透镜体,从而形成敖包吐中型萤石矿床。     

金川镍铜矿床数学模型对深部矿化变化趋势的指示

按矿化特征将金川X矿区主矿体分为致密块状特富矿、海绵状富矿和浸染状贫矿.应用MicroMine软件对3类矿化体分别建立了数学模型,并应用距离平方反比法对模型单元块进行了镍、铜品位估值.通过分析和对比矿床数学模型900m至1300m不同水平剖面上的Ni、Cu品位及Ni/Cu比值的变化,得出在X矿区的中部西侧是一个Ni和Cu的矿化中心,并且向深部Cu的矿化强度高于Ni.     

邹平王家庄铜矿床成矿地球化学及成因探讨

王家庄铜矿床的矿化脉石英中流体包裹体均一温度介于116 ~ 566 ℃之间,均值为 289 ℃;盐度介于7.2%～63.2% NaCleq,均值为21.1% NaCleq。流体的气相成分主要为H2O和CO2。在均一温度为240 ~ 440 ℃区间内,出现了富气相的两相水溶液包裹体、富液相的两相水溶液包裹体和含子晶的三相水溶液包裹体共存现象,以及加温后富气相包裹体均一到气相和同期富液相包裹体均一到液相的特征,表明成矿流体曾发生过沸腾作用;其中第一次发生于360 ~ 400 ℃,主要形成高温、高盐度含子晶的三相水溶液包裹体和高温、中盐度富液相的两相水溶液包裹体及高温、低盐度富气相的两相水溶液包裹体;第二次发生于240 ~ 320 ℃,主要形成高—中温、高盐度的含子晶的三相水溶液包裹体和高—中温、中盐度富液相的两相水溶液包裹体及高—中温、低盐度富气相的两相水溶液包裹体;之后主要形成富液相的两相水溶液包裹体,具有中低温和中盐度的特征。矿化脉石英中的δ18OH2O介于-1.14‰ ~ 1.79‰之间,均值为0.94‰;δD介于-63.70‰ ~ -56.50‰之间,均值为-59.8‰;说明王家庄铜矿床的成矿流体主要来源于岩浆,后期混入大气降水。矿石矿物的δ34S变化于-8.80‰ ~ -2.80‰之间,均值为-6.33‰。矿石矿物的n(206Pb)/n(204Pb)介于18.1684 ~ 18.3637之间,均值为18.2892;n(207Pb)/n(204Pb)介于155546 ~ 156342之间,均值为155777;n(208Pb)/n(204Pb)介于38.1286 ~ 38.4840之间,均值为38.2780。说明矿石具有贫重硫和富放射性成因铅的特征,硫、铅主要来源于深部,后期可能受到地壳物质或大气降水的混染。     

河南洛宁段河金矿流体包裹体研究和矿床成因

河南省洛宁县段河石英脉型金矿主要包括石寨沟和岭东两个矿区,分别由3～4条含金石英脉构成。矿化过程从早到晚包括石英-黄铁矿、石英-多金属硫化物和石英-碳酸盐等3个阶段．其中中阶段金矿化最强,次为早阶段。各阶段石英中流体包裹体以气液两相包裹体为主．次为纯液体包裹体。激光拉曼测试表明,气液两相包裹体的液相为H2O,气相主要为Ho和CO2混合、纯H2O,次为纯CO2;纯液体包裹体为纯H2O。石寨沟矿区包裹体均一温度从早到晚依次为240．9～315．9℃．188．7～304．5℃,137．3～259．3℃：流体盐度变化依次为（6．74～12．85）wt%NaCl．eq,（2．41～8．68）wt％NaCl．eq,（2．24-7．86）wt%NaCl．eq。岭东矿区均一温度从早到晚依次为303．7-343．1℃,251．8-325．4℃,305．7～355．0℃：流体盐度变化依次为（5．11～11．70）wt％NaCl．eq,（2．74-10．11）wt％NaCl．eq,（0．53-6．74）wt％NaCl．eq。两矿区主成矿期流体均为中温、低盐度,早阶段流体为改造热液和变质热液的混合体,含一定量CO2,且流体CO2含量和盐度从早到晚逐渐降低。石寨沟矿区包裹体均一温度逐渐降低,而岭东矿区包裹体均一温度先降后升,加之岭东矿区各阶段成矿温度均高于石寨沟矿区．表明成矿流体系统主要受岩浆热驱动,岭东矿区更靠近岩体,且在晚阶段又有脉动性的岩浆加热．段河金矿区南部存在隐伏岩体。     

强降雨条件下土质边坡瞬态稳定性分析

基于实际降雨气象资料,设计了单峰降雨和8个不同时间间隔的双峰降雨计算方案,利用非饱和土力学理论,对边坡的瞬态稳定性进行了计算和分析,研究了水分在坡体内的运移对边坡稳定性的时间空间影响效应,同时考察了降雨入渗造成的土性渗透特性的改变。分析发现：一次降雨的影响历时约12 d,降雨后约0.5 d该类土质边坡最危险;不同时间间隔的两次降雨对边坡稳定的影响比单峰降雨的最小安全系数滞后约0.3 d～0.8 d,影响历时基本保持不变;土体物理力学性质、边坡最危险滑动面及其对应的安全系数随水分在坡体内渗透运移而变化。     

豫南灵山岩体铀矿化特征

地处豫南的灵山岩体,分布着丰富的矿产资源。笔者以灵山岩体铀矿化分布特征为切入点,阐述灵山岩体铀矿化特征。该岩体铀矿化受构造、裂隙的控制,有利成矿部位在岩体中构造带与脉岩相交复合部位,矿化富集地段多含铁质、锰质和泥质,且热液蚀变发育。铀源来自岩体。具有4种矿化类型。总结其矿化特征,对豫南新县岩体、商城岩体的找矿具有一定指导意义。     

鲢鱼(Hypophthalmichthys molitrix)摄食强度和节律的实验研究

报道用室内实验方法对鲢鱼摄食强度和摄食节律的研究结果,探讨了影响它们的因子。提出鲢鱼在不同水温、不同花粉密度及不同鱼规格下的摄食量的统计分析。指出:食粒密度和水温与摄食量正相关,而鱼规格与摄食量负相关;食粒密度对摄食量影响最大(P<0.01),其次为水温;水温和食粒密度在影响摄食量的过程中可能有一定的交互作用。鲢鱼摄食强度在室内条件下也具明显的昼夜节律。在食粒规格较小、密度较低且溶氧充足条件下,鲢鱼夜晚非但不停食且出现摄食率次高峰。在本实验条件下,鲢鱼的日摄食节律与水温和光照无关,可能受饵料可得性和自身的生物钟节律等制约。