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内华达州斯利泊(Sleeper)矿床富矿脉型金矿石,系在小于500米的深度范围内沉淀形成,并具有细粒石英胶状条带与含有大量银金矿的蛋白石质氧化硅胶状条带交替的特殊结构.这种结构迹象表明石英条带是从原始的胶状非晶质状态重结晶而来,而富金条带系由氧化硅与金颗粒凝胶组成的非晶质析出物原始沉积而成.金与氧化硅首先在热液体系的较深部位以胶体形式析出,然后由成矿溶液的水力作用向上机械搬运,由于溶液的冷却或沸腾,并在复合阳离子Al~(3+)的水化物的催化下产生胶粒凝结。浅成低温热液体系中金以胶粒形式搬运表明,至少在某些条件下胶体中的金含量比真溶液中要高.欲解释斯利泊矿床富矿石的成因,需存在一种富金的成矿溶液;而胶体金的局部搬运可能对浸染状低温热液金矿床的形成起了一定的作用. 相似文献
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通过分析整个世界太古宇和元古宇地区的地震波速模型，发现太古宇地区的厚度为３５ｋｍ左右（碰撞带边缘除外），而元古宇地壳的厚度则显然要大得多，大致为４５ｋｍ，并且在其基底有一较厚的高速层（＞７ｋｍ／ｓ）．我们认为有两种模式可以解释这些差异。第一种模型把这种差异归因于上地幔成分的改变。太古宇地幔中的温度较高，因而导致了科马提熔岩的喷发，结果使得岩石圈过分贫化而不能产生大量的玄武质熔体。元古宇地是在富地幔 相似文献
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自然灾害是给人类及其设施带来严重难的危害。本文试图在了解灾害的危害性基础上，以火山作用为例，在核废料处置库选址中，通过圈定灾害高发区、确定内险评价参数、划出高风险区及风险等级三步骤，对灾害风险性进行评价。 相似文献
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吴伟成 《华东地质学院学报》1993,(4)
第二届全国同位素水文地质方法学术讨论会于1993年9月4日至8日在长春召开。出席会议共60人,其中第一论文作者28人。学部委员张宗祜研究员、南大薛禹群教授等知名学者参加了会议。长春地院正、副院长山席了开、闭幕式。本届会议由地矿部水文地质工程地质研究所、小国地质学会水文地质专业委员会和吉林省地质学会联合举办。会前由天津大学出版社出版了会议论文汇编《中国同位素水文地质学之进展》(1988—1993)。 相似文献
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加筋土桥台因其具有良好的复合体特性,被广泛应用于各项工程建设,研究它在实际工程条件下的工作性能对其设计和推广具有重要意义。加筋土桥台在服役过程中主要承受交通荷载作用,通过室内大比例缩尺模型的加速应力试验,研究交通荷载条件下加筋土桥台的工作性能,考虑加筋间距与筋材刚度的影响,综合分析了不同交通荷载等级和循环次数下桥台变形与筋材应变的变化规律。研究结果表明,加筋土桥台在交通荷载作用下整体变形随循环次数趋于收敛,其顶部沉降、面板水平位移与筋材应变均远小于规范给出的阈值;各变形值随加载时间呈阶梯状发展,不同条件下变形收敛趋势有所差异;增大筋材刚度和减小加筋层间距有利于控制桥台的变形,筋材刚度对变形的控制作用要优于加筋间距;交通荷载作用下面板水平应变与顶部竖向应变并不满足2倍关系,二者之间的定量关系有待进一步研究。 相似文献
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Nutrient and suspended sediment concentrations were measured in the dry season and during the rising and falling stages of flood events in the Annan and Daintree rivers to estimate catchment exports. These flood events were also sampled along the salinity gradient in the estuary and nearshore shelf to quantify the modification of terrestrial sediment and nutrient loads as they pass through estuaries into the Great Barrier Reef lagoon. In the Daintree River TSS concentrations were found to increase between the catchment and the estuary plume. The source of TSS may have been scour of the estuarine channel or from land use in the catchment of the lower estuary. In the dry season nitrogen enters the Annan and Daintree estuaries predominantly in the form of PON and DON in roughly equal proportions. Nitrogen exports to the GBR are mostly in the form of DON. In the wet season the majority of nitrogen enters the estuaries as DON and leaves as PON. Nitrogen removal in the estuaries and plumes appears to be biologically mediated once suspended sediment concentrations decrease to a point where phytoplankton growth is not light limited. In the dry season phosphorus enters and leaves the estuaries primarily in organic form. PIP is the dominant form of phosphorus in river water, but leaves the estuary more evenly distributed between all forms. These estuarine processes result in less nitrogen and phosphorus being delivered to the GBR lagoon than is exported from the catchment. The differences between these estuaries highlights the need for further work to explore modifications in estuaries that drain into the Great Barrier Reef lagoon. 相似文献
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1.引言高层和低层等熵位涡(IPV)距平的相互作用,对斜压不稳定和温带气旋的形成提供了一种简明的描述(Hoskins等,1985).最近,这种提法作为背风坡气旋产生的一种似乎可信的理由,已经引起人们的注意(如,Mattocks和Bleck,1986).但是,这种机制能否成立还需由理论的和观测的依据所证实.这里,用戈达德大气实验室(GLA)的资 相似文献
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Trace metal uptake by the Chinese mitten crab Eriocheir sinensis: the role of osmoregulation 总被引：2，自引：0，他引：2
Changes in salinity affect the bioavailability and consequent uptake of trace metals by euryhaline invertebrates. In many cases, salinity-related effects on metal uptake can be explained by changes in chemical speciation but salinity may also influence uptake indirectly through its action on osmoregulatory mechanisms. Specifically, it can be hypothesised that trace metal uptake may be reduced at salinities approaching the isosmotic point of a species because, at this point, there is reduced activity of ionic exchange pumps. The present study tested this hypothesis using the Chinese mitten crab, Eriocheir sinensis, a hyper-hypoosmoregulator with an isosmotic point around 33 per thousand. Crabs were exposed to radio-labelled cadmium and zinc at 23, 33 and 43 per thousand for 4 days. To eradicate speciation effects, crabs were exposed to the same concentration of the radio-labelled free metal ion (estimated using MineQL computer software) at each salinity. Haemolymph samples were taken daily and radio-labelled metal concentrations were estimated from radioactivity counts and used to provide relative measures of metal uptake. Neither cadmium nor zinc uptake was lowest at the isosmotic point. The uptake of cadmium increased significantly with increase in salinity, while the uptake of zinc showed no significant change with increased salinity. Thus changes in trace metal uptake rates in E. sinensis do not appear to be controlled only by changes in free metal ion concentrations. The different effects of salinity change on the uptake of cadmium and zinc (in the absence of free metal ion change) also indicate that physiological responses to osmotic change alone do not control metal uptake rates for this species. 相似文献