Laboratory simulation of the salt weathering of schist: II. Fragmentation of fine schist particles

Recent developments in long term landform evolution modelling have created a new demand for quantitative salt weathering data, and in particular data describing the size distribution of the weathered rock fragments. To enable future development of rock breakdown models for use in landscape evolution and soil production models, laboratory work was undertaken to extend existing schist/salt weathering fragmentation studies to include an examination of the breakdown of sub‐millimetre quartz chlorite schist particles in a seasonally wet tropical climate. Laser particle sizing was used to assess the impact of different experimental procedures on the resulting particle size distribution. The results reveal that salt weathering under a range of realistic simulated tropical wet season conditions produces a significant degree of schist particle breakdown. The fragmentation of the schist is characterized by splitting of the larger fragments into mid‐sized product with finer material produced, possibly from the breakdown of mid‐sized fragments when weathering is more advanced. Salinity, the salt addition method and temperature were all found to affect weathering rates. Subtle differences in mineralogy also produce variations in weathering patterns and rates. It is also shown that an increase in drying temperature leads to accelerated weathering rates, however, the geometry of the fracture process is not significantly affected. Copyright © 2006 John Wiley & Sons, Ltd.     

从成矿构造动力学探讨脉状金矿床成矿深度

在综述国内外与韧性剪切带有关的脉状金矿床成矿动力学的新近研究成果后,根据成矿控矿构造动力学特征及其与成矿流体运移机制、矿物结晶特点的关系认为矿物结晶发生于地震微破裂导致成矿流体压力骤降后的低压力阶段,由矿物包裹体压力并按静岩压力梯度推算的成矿深度要明显小于矿床的实际成矿深度.本文提出一种新的成矿深度估算方法,其估算的成矿深度与目前大多数脉状金矿床中石英具有明显的韧性变形的特点相吻合.     

A model of the early evolution of karst aquifers in limestone in the dimensions of length and depth

A new model of the early evolution of limestone karst aquifers in the dimensions of length and depth is presented. In its initial state the aquifer consists of a rock massive with evenly spaced fractures of about 50 μm aperture widths with an hydraulic conductivity of 10⁻⁷ ms⁻¹. In addition to this a coarser network of prominent fractures with aperture widths of several 100 μm is also present. Boundary conditions of constant recharge 450 mm/year, or constant head from the input of allogenic streams are imposed. First the position of the water table in the aquifer is calculated, then dissolutional widening during a time step in all the fractures below the water table is found by use of the well-known nonlinear dissolution kinetics of limestone. This is iterated and the position of the water table as well as the fracture widths are found as a function of time. In the case of constant recharge to a karst plateau, the water table in any case drops to base level and conduits there propagate from the spring headwards. If constant head conditions are valid the position of the water table remains almost stable and conduits propagate along the water table from the input towards the spring. There is competition between conduit evolution along prominent fractures and along tight fissures close to the water table. In any case under constant head conditions one of these pathways wins, and early karst evolution is terminated by a breakthrough event with an explosive increase of the flow through the aquifer until constant head conditions break down. Depending on the boundary conditions of constant head or constant recharge or a combination of both it is possible to describe models of cave genesis, which have been derived from field evidence, such as the water table models of Swinnerton and Rhoades as well as the four-state model by Ford and Ewers (Can. J. Earth Sci., 15 (1978) 1783).     

碳酸盐岩红土风化壳主要特征及红土成因探讨—以贵州典型剖面为例

本文总结提出了碳酸盐岩风化壳成因证据及其演化特点，对风化壳红土成因进行了讨论。     

Variations in chemical compositions of the eolian dust in Chinese Loess Plateau over the past 2.5 Ma and chemical weathering in the Asian inland

Major and trace elements as well as strontium isotopic composition have been analyzed on the acid-insoluble (AI) phase of the loess-paleosol sequence from Luochuan, Shaanxi Province, China. Results show that the chemical composition of AI phase of loess and paleosols is distinctive to the average composition of upper continental crust (UCC), characterized by depletion of mobile elements Na, Ca and Sr. The distribution pattern of elements in AI phase reveals that initial dust, derived from a vast area of Asian inland, has suffered from Na- and Ca-removed chemical weathering compared to UCC. Some geochemical parameters (such as CIA values, Na/K, Rb/Sr and⁸⁷Sr/⁸⁶Sr ratios) display a regular variation and evolution, reflecting that the chemical weathering in the source region of loess deposits has decreased gradually since 2.5 Ma with the general increase of global ice volume. This coincidence reflects that the aridity of Asian inland since the Quaternary is a possible regional response to the global climate change.     

Sr isotope evolution during chemical weathering of granites -- impact of relative weathering rates of minerals

The Sr isotopic systematics in the weathering profiles of biotite granite and granite porphyry in southern Jiangxi Province were investigated. The results showed that during the chemical weathering of granites, remarked fractionation occurred between Rb and Sr. During the early stages of chemical weathering of granites, the released Sr/Si and Sr/Ca ratios are larger than those of the parent rocks, and the leaching rate of Sr is higher than those of Si, Ca, K, Rb, etc. Dynamic variations in relative weathering rates of the main Sr-contributing minerals led to fluctuation with time in 87Sr/86Sr ratios of inherent and released Sr in the weathering crust of granite. Successive weathering of biotite, plagioclase and K-feldspar made 87Sr/86Sr ratios in the weathering residues show such a fluctuation trend as to decrease first, increase, and then decrease again till they maintain stable. This work further indicates that when Sr isotopes are used to trace biogeochemical processes on both the catchment and global scales, one must seriously take account of the prefer-ential release of Sr from dissolving solid phase and the fluctuation of 87Sr/86Sr ratios caused by the variations of relative weathering rates of Sr-contributing minerals.     

Chemical Characteristics of Stream Draining fromDudu Glacier: An Alpine Meltwater Stream inGanga Headwater, Garhwal Himalaya

I-DtjcrONAlpine environment enjoys a distinct set of physicochemical conditions asl compared to other aqueous systems. Thehydrochemical characteristics of meltwater draining from thisenvironment are different from the other aqueous ecosystemsdue to their mountainous nature and extreme cold climatic conditions. The high concentration of various chemical constitu.ents in meltwater shows the intensive chemical weathering inthe basin. The rapid physical weathering due tO grinding actionof the gl…     

湘潭石潭海泡石粘土矿床特征及找矿方向

赋存于茅口组下部含泥质灰岩段的矿体呈似层状、透镜状，长3500－5600m，平均厚4.39-5.15m，矿石品位一般8%-20%，最高可达65％。矿石有原岩型和粘土型两类，粘土型矿石一般呈灰－深灰色，干燥后呈灰白色，硬度1－2，比重1.6-2.3t/m^3，粘性强，可塑性好，透水性强。主要矿物成分有海泡石、石英、方解石、滑石、蒙脱石、伊利石和氟磷石等,矿石富Si、Mg、贫K、Na,CaO、Al2O3含量偏高。早二叠世江南古陆两侧局限（浅）海或海湾环境有利于海泡石沉积。在永顺－石门、安化－浏阳、怀化－浏阳成矿带，具有良好的找矿前景，估计海泡石资源量在3000万吨以上。     

澧县曾家河芒硝岩盐矿床开发浅析

本文在分析矿床内外部建设条件的基础上,根据芒硝岩盐原料市场行情,着重对矿床开发的经济社会效益进行了评价,初步评价表明:国家和企业均可获得较丰厚的利润,还可安置1400多人就业。建议进一步开展地质勘查工作。     

包心构造是铝土矿床的成因标志

铝土矿床的包心构造,即粘土岩层包裹铝土矿体,是腐植酸长期分解土壤硅酸盐,而导致土壤剖面的垂直分层。具备垂直渗水系统的地形,如岩溶洼地、平顶山丘,是成矿的先决条件之一。铝岩系是一套陆相地层,夹在地层剖面的基底岩层风化侵蚀面之上,和其上发育植被的沉积间断面之下。铝土矿是陆上成矿,是植物化学风化残积矿床。