西秦岭夏河—合作地区早子沟和加甘滩金矿床石英微量元素特征及意义

西秦岭造山带发育有大量三叠纪的金矿床,早子沟和加甘滩金矿床是其中最典型的两个矿床,其金资源量分别为116 t和154 t,均为特大型金矿床。早子沟、加甘滩金矿床均位于夏河—合作区域性逆冲推覆断裂以南。早子沟赋矿地层为三叠统古浪堤组,赋矿岩石为泥质板岩、条带状硅质板岩及粉砂质板岩;加甘滩矿区出露地层为三叠统隆务河组,金矿体赋存于长石石英变砂岩夹粉砂质板岩岩性段内。加甘滩金矿床的研究程度相对较低,属中低温构造蚀变岩型金矿床;早子沟金矿床研究程度较高,但是对它的成因仍有不同的认识。石英的微量元素地球化学特征能够提供成矿流体来源与演化的信息,通过对早子沟和加甘滩金矿床开展石英的微量元素地球化学特征研究,探讨其成矿流体来源、成矿条件以及石英微量元素对金矿床形成的指示,为西秦岭造山带金矿床成因研究提供重要的信息。早子沟和加甘滩金矿床不同类型矿石中石英具有相似的稀土元素球粒陨石标准化配分曲线,总体表现出轻稀土元素相对富集、重稀土元素轻微亏损的特征,而且轻稀土元素与重稀土元素分馏程度高,重稀土元素内部分馏程度弱。 早子沟金矿床成矿期热液石英中Rb与Li呈负相关,Rb与Cs呈正相关,而加甘滩金矿床热液石英中Rb与Li、Cs相关性不明显,表明早子沟金矿床石英中Li含量随流体含量的增加而减少,而Cs含量随流体含量的增加而增加。大多数样品具有Eu负异常和弱的Ce正异常,表明早子沟和加甘滩金矿床形成于还原环境,成矿温度较低。样品的(La/Yb)_N较大,反映成矿深度相对较浅。石英的Y/Ho值分别为25.14~30.14和23.40~28.94,指示成矿流体与地壳关系密切。大多数石英样品的Th/La和 Nb/La 值小于1,在大陆地壳标准化图解中具有明显的Sc负异常,Cr、W、Pb和U正异常,表明成矿流体富Cl^-,相对富集Cr、W、Pb和U等元素。结合大地构造背景分析,早子沟和加甘滩金矿形成于大陆边缘环境。     

东天山云海铜镍矿地球化学特征及成因分析

云海铜镍矿位于觉罗塔格构造带西段,成矿岩体为多期次侵入的杂岩体,岩体分异演化充分,镁铁质和超镁铁质岩石均有发育,主要岩石类型为角闪辉石岩、橄榄苏长岩、辉长岩、闪长岩。主量元素化学组成表明,该杂岩体属拉斑玄武岩系列,岩石具同源演化特征,显示高铁、高镁、低钛、低铝特征,富集大离子亲石元素Rb,Ba,亏损Nb,Ta,轻稀土富集。岩浆源区有部分熔融而交代的岩石圈地幔,岩浆在上升过程中受到地壳物质混染,发生橄榄石、斜方辉石、斜长石的分离结晶。岩体形成于早二叠世,为构造活动和地幔柱双重作用下的产物。     

土工试验规范变更对膨胀计算和判定的影响

对土工试验方法标准的新旧规范中无荷膨胀率和有荷膨胀率的变化内容进行对比分析,发现两者的计算公式发生显著变化,新规范的计算结果与旧规范相比,膨胀率明显变大,膨胀量随之增大,这将对工程勘察、设计、施工等产生明显影响。以某工程为例,新规范计算后地层总膨胀量由旧规范的16.7 mm变为51.8 mm,增加了2倍左右,地基土的胀缩等级由Ⅰ级变为Ⅱ级,地基基础设计等级由丙级变为乙级,地基处理措施和施工方案随之也发生改变。因此,工程技术人员对此应综合考虑,严谨对待。     

Effect of the Dry Ashing Method on Cadmium Isotope Measurements in Soil and Plant Samples

A dry ashing method is commonly used to remove organic material from samples prior to geochemical analysis. In the course of this study, the Cd isotope ratios of a series of soil and plant reference materials and samples were studied to evaluate the effect of the dry ashing method on measurement results of Cd isotope ratios. The samples were pre‐treated using the dry ashing method and high‐pressure bomb for comparison. The results show that the digestion using high‐pressure bombs did not lead to Cd loss, but using the dry ashing method would cause different proportions of Cd loss. The whole range of Cd isotope difference between two methods was from ?0.07‰ to 3.01‰. There was also an obvious difference in measured Cd isotope ratios from the same leaf sample pre‐treated independently by the dry ashing method, indicating that the amount of Cd loss and the effect on Cd isotope measurement during dry ashing is related to the properties of the samples. Therefore, dry ashing may not be appropriate for the removal of organic material in Cd isotope ratio measurement, especially for samples with high organic contents. The δ^114/110Cd values of reference materials NIST SRM 1573a and GSD‐30 are reported for the first time in this study.     

Numerical characterization of slope rock mass through considerations of hydraulic and mechanical properties

Landslides - In this paper, the slope rock mass is numerically characterized by considering hydraulic and mechanical properties using two distinct element models. The flow rate and permeability are...     

Failure mechanisms and dynamics of the Shanzao rockslide in Yongjia County,China on 10 August 2019

Landslides - At about 04:00 on 10 August 2019, the heavy rainfall carried by Typhoon Lekima induced a catastrophic rockslide in Shanzao Village, Yongjia County, China. The heavy rainfall triggered...     

Movement process analysis of the high-speed long-runout Shuicheng landslide over 3-D complex terrain using a depth-averaged numerical model

Landslides - Flow-like landslide is one of the most catastrophic types of natural hazards due to its high velocity and long travel distance. In 2019, a large catastrophic landslide was triggered by...     

A three-dimensional large-deformation random finite-element study of landslide runout considering spatially varying soil

Landslides - Landslide is a uniquely dynamic large-deformation process that can present serious threat to human lives and infrastructures. The natural soil properties often exhibit inherent spatial...     

四川盆地东部中二叠统茅口组热液活动特征

四川盆地中二叠统茅口组存在丰富的热液流体活动。在野外剖面和岩心观察的基础上,利用多种分析测试方法,对四川盆地东部茅口组碳酸盐岩中的热液活动特征进行了探讨。研究区茅口组热液活动包括2类,一类为硅质热液,表现为薄层硅质岩或硅质团块;另一类为碳酸盐型热液,表现为粗晶方解石和白云石充填在张性构造裂缝中或呈"雪片状"集合体,偶见少量黄铁矿、闪锌矿等金属硫化物伴生。硅质岩主量元素之间的关系表明硅质来源具有多样性,是热液硅与壳源硅的混合;黄铁矿、闪锌矿原位S同位素δ34S介于-3.91‰~-6.87‰之间,推测可能受到了微生物和基性岩浆岩的双重影响;方解石脉和具鞍状双晶的白云石脉普遍具有Ca O高于标准计量、相对富Sr和U、贫REE和Ti、Ce/Ce*明显负异常、Eu/Eu*主体正异常、Y正异常等特征,表明碳酸盐脉为热液活动的产物,流体来源也呈现出火山活动相关流体与富钙地下水混合的特点。闪锌矿富集Ge和Cd,Zn/Cd及Zn/Fe值反映了中等成矿温度。硅质岩和碳酸盐流体包裹体均一温度变化范围较大,介于54.7~294.3℃之间,与稀土元素和微量元素比值所揭示的特征吻合。研究结果表明,穿层状硅质结核和团块的首次出现往往标志着茅口组热液活动的开始,而张性构造裂缝和碳酸盐型热液活动带来的围岩白云化作用则有效地改善了白云岩储集层的物性。     

豫西宜阳上二叠统孙家沟组孢粉组合及其地质意义*

豫西宜阳上二叠统孙家沟组为一套陆相碎屑岩,在该组中部土门段砂泥互层中发现大量的植物化石碎片和孢粉化石。文中依据孙家沟组沉积特征及孢粉组合区域对比,厘定了土门段的地质时代,并依据孢粉化石的亲缘植物关系和信息函数,结合微量元素Sr/Cu值指标,定性和半定量分析了宜阳地区的古气候特征。结果显示: 土门段共发现52属孢粉化石,以裸子植物花粉占优势,与华北地区晚二叠世孢粉组合特征有很大的相似性,推测其地质时代相当于晚二叠世长兴期。孢粉化石属种的植物亲缘关系与欧美镁灰岩统植物成分类似,表明整体上为较炎热的半干旱古气候。该成果可为华北地区晚二叠世晚期的陆相沉积环境、古植物背景以及古气候演化研究提供参考依据。