中国高岭土矿成矿地质特征与资源潜力评价

[研究目的]本文主要对中国高岭土矿开展资源潜力定量评价,指导后期勘查找矿与开发.[研究方法]首先是对中国高岭土矿成矿规律进行研究,按地质成因中国高岭土矿可以分为3种类型:风化型、热液蚀变型和沉积型.然后对中国高岭土矿划分预测类型、总结成矿模式、归纳预测要素,最后对高岭土矿远景区进行划分并估算资源潜力.[研究结果]风化型...     

基于多级次流动单元的砂砾岩储层分类渗透率评价方法——以陆丰油田古近系文昌组W53油藏为例

中国南海东部海域陆丰油田古近系文昌组砂砾岩储层具有岩性复杂、孔隙度低、孔隙结构非均质性较强等特征.不同类型储层渗流特征差异明显,传统的孔渗模型精度难以满足生产开发需要.流动单元能有效刻画储层内部渗流特征,但单纯依据流动单元指标进行流动单元划分就会出现错划的现象.文昌组储层非均质性由宏观到微观具有层次性,综合地质、测井、...     

Varnish microlaminations: new insights from focused ion beam preparation

The cross-sectional texture of rock varnish varies considerably with the scale of analysis and technique used to image a sample. Each jump in resolution results in new insight, with the current state-of-the-art resting at the nanoscale. One key to nanoscale analysis involves focused ion beam (FIB) techniques used most frequently in material science and semiconductor failure analysis. FIB preparation remains challenging, however, for samples like rock coatings with heterogeneous density and abundant porosity. A new technique involving multiangle ion thinning and in situ plan-view lift-out facilitated a scanning transmission electron microscopy study of rock varnish from Death Valley. The results reveal variability in lateral continuity of nanometer microlaminae that can be interrupted by post-depositional diagenesis involving leaching of Mn and Fe, and this variability could explain why some of the visual varnish microlaminations (VML) used in paleoclimatic research can sometimes appear discontinuous. Because these breaks result from post-depositional processes, they do not undermine the paleoclimatic interpretations of VML.     

Contrasted Perceptions of Uluru

Uluru is an inselberg shaped in arkosic sandstone located in the arid plains of central Australia. The indigenous people believed it rose out of a sand hill and has since remained unchanged. The various minor landforms represented mythological animals, people, and events of the Dreamtime. Later investigators interpreted the residual as remaining after long-distance scarp retreat, or as due to scouring by the wind or by the waters of a huge lake. The inselberg and its decorations have been construed in terms of climatic variations. Uluru also has been interpreted as a compressed and resistant compartment that was exposed as a low rise in the latest Mesozoic. The initial rise shed runoff. The steep flanks were shaped in the Eocene by deep subsurface weathering followed by stripping of the regolith and exposure of bedrock forms. Large tafoni and breaks of slope were formed on the southern side where permeable sediments abutted the residual. Following their exposure, basal flares and footcaves were shaped during a later period of subsurface weathering. The inselberg has grown as a relief feature not by uplift, but by the lowering of the surrounding plains. The morphology of Uluru is an expression of episodic exposure.     

农业活动对岩溶作用碳汇的影响:以重庆青木关地下河流域为例

以受农业活动影响强烈的重庆青木关地下河流域为研究对象,利用CTDP300多参数水质自动记录仪、WGZ-1型光电数字水位计、HOBO小型气象站在线自动监测电导率、水位以及降雨等数据,并获取流域耕地面积数据,于2010年分月采集地下水样,分析常规水化学和地下水溶解无机碳δ13C,初步探讨流域农业活动对岩溶作用过程和碳汇的影响,发现农业活动对岩溶作用过程产生明显的影响,进而影响到岩溶地质碳汇。地下水水化学以及地下水δ13CDIC值证实了流域地下水DIC是碳酸、硝酸和硫酸共同溶蚀碳酸盐岩的产物;每月碳酸溶蚀碳酸盐岩产生DIC占地下水中总DIC的比例在55.53%～81.25%之间,雨季(62.98%)普遍低于旱季(74.86%);碳酸溶蚀碳酸盐岩产生的DIC的量为14.67×106mol/a,其中岩溶作用产生的净CO2汇量为7.335×106mol/a,而硝酸和硫酸溶蚀碳酸盐岩产生的DIC总量为7.48×106mol/a,约占地下水中总DIC的33.8%,单位面积耕地上硝酸和硫酸溶蚀碳酸盐岩产生DIC的强度为1.89×106mol/(km2.a)。人类活动引入的硝酸和硫酸参与碳酸盐岩的溶解并改变了区域碳循环。     

陆地硅的生物地球化学循环研究进展

地球表层硅(Si)的生物地球化学循环与大气CO2浓度变化、大洋生物泵作用以及海岸带富营养化等过程密切相关,因此成为全球环境变化研究的核心问题之一。在地质时间尺度上,硅酸盐矿物的化学风化是地球表层所有次生Si的来源。陆地生态系统各次生Si库具有不同的形成机制和驱动因子,这导致各Si库的贮存量和循环周期存在明显差异。土壤Si库中的黏土矿物Si、溶解硅(DSi)和淀积在其他矿物表面的无定形Si都源自硅酸盐矿物的化学风化过程;植物生长过程中吸收土壤中的DSi形成生物Si,然后经微生物分解过程返还给土壤;地表径流将流域陆源Si以悬移质Si和DSi的形式输入河流、海洋。迄今,陆地不同形态Si库的大小及其对全球Si循环的贡献仍不确定。因此,在研究陆地Si的生物地球化学循环过程中,综合考虑各种地表过程及其耦合作用是非常必要的。     

An example of structural and metamorphic relationships in the Musgrave orogenic belt,central Australia

The western Musgrave Ranges are broadly divided into three groups of metamorphic rocks. A central granulite‐facies core is bounded on the north by rocks of amphibolite grade and on the south by rocks transitional between the granulite and amphibolite facies. Faults trending east‐west separate the three groups of rocks.

The detailed structural relationships between the granulites and the lower grade rocks are described and discussed. The granulites are structurally relatively simple and are characterised by the presence of a strong southwesterly‐plunging, mineral‐streaking lineation. In marked contrast, the transitional rocks are more complexly folded on a macroscopic scale and they also have a well‐developed mineral lineation plunging to the southeast. These two lineation orientations are considered to be directions of maximum elongation. The amphibolite‐facies rocks are also complexly folded and at least two lineations related to different phases of deformation have been recognized.

A suite of foliated and lineated dolerite dykes which occurs throughout the area inherited their fabric during a period of intense deformation and recrystallization, which resulted in the development of numerous mylonite zones.

It is suggested that the granulite‐facies rocks may represent a suite of cover rocks which have been thrust in a northerly direction over a pre‐existing amphibolite‐facies basement.     

The Cainozoic geology of the Middle Shoalhaven Plain

The Middle Shoalhaven Plain is a large, tray‐like depression bounded in the west by the Mulwaree fault and in the east by cliffed Permian sediments. The plain is probably Mesozoic in origin and was partially alluviated during the Early to mid‐Eocene. Much of the plain and sediments were covered by basalts during the Late Eocene. This was followed by an episode of deep weathering, which culminated in the formation of widespread bauxitic and lateritic crusts and manganocrete and silcrete during the mid‐Tertiary. A second minor weathering event is recorded during the latest Tertiary to Early Pleistocene. Two new basalt dates are consistent with earlier ones at about 43 Ma. Palaeomagnetism shows bauxites and ferricretes to be mid‐Tertiary.     

Mapping bedrock lithologies through in situ regolith using retained element ratios: a case study from the Agnew-Lawlers area,Western Australia

Large, high-quality multi-element geochemical datasets are becoming widely available in the exploration industry, and afford excellent opportunities to investigate geochemical processes. A dataset of over 2500 analyses of unweathered and variably weathered mafic and ultramafic rocks for over 50 elements has been collected by Gold Fields Ltd. in the auriferous Agnew-Lawlers area of the eastern Yilgarn Craton of Western Australia. This dataset is used to investigate changes in element abundances and inter-element ratios through varying degrees and styles of weathering in an area of thick regolith characterised by deep in situ weathering. Systematic interrogation of the data, using lithostratigraphic controls derived from regional mapping and geophysics, reveals that a suite of elements, including Ti, Al, Zr, Th, La, Sc and Nb, and to a lesser extent Cr and Ni, behave as essentially immobile components during saprolite formation. In some cases diagnostic element ratios persist into siliceous duricrust. Ratios of these elements are used as reliable discriminants of bedrock type, and delineate features such as cryptic layering within fractionated sills and subtle geochemical variants in a sequence of tholeiitic and komatiitic basalts. Mapping on the basis of discriminant element ratios greatly extends previous trace-element ratio-based schemes for rock type discrimination. The potential to determine several of these elements with adequate precision and accuracy using portable XRF technology opens a potentially useful technique for rapid geochemical bedrock mapping in residual terrains.     

Traces from the past: the Cenozoic regolith and intraplate neotectonic history of the Gun Emplacement,a ferricreted bench on the western margin of the Mt Lofty Ranges,South Australia

The Gun Emplacement is a small but distinctive bench on the Eden–Burnside Fault Escarpment near Anstey Hill, in the northeastern suburbs of Adelaide, South Australia, occurring at an elevation of ～210–220 m asl. It is underlain by Middle Eocene North Maslin Sand and is capped by resistant, ferricreted colluvium. Paleomagnetic dating of hematitic mottles in the ferricreted colluvium, immediately underlying the emplacement, returned a Pliocene/Early Pleistocene age. This age is equivalent to that obtained for summit surface weathering. Fault scarps and exposures, including slickensides and fault gouge material, suggest that the Eden–Burnside Fault at this location has a strong en échelon pattern developed in response to reverse-sinistral oblique-slip faulting, reflecting continental stress fields. Remnants of ferricrete cappings forming stranded benches on the Eden–Burnside Fault Escarpment at elevations up to 25 m above the Gun Emplacement demonstrate recurrent tectonism of the South Mt Lofty Ranges related to intraplate deformation. There are at least four distinct ferricrete benches preserved on the eastern side of the active fault leading up from the Gun Emplacement surface. These benches demonstrate alternating periods of stability and tectonic activity disrupting and uplifting the ferricreted surfaces. A fresh surface rupture occurs and may be related to a recent seismic event.