X-ray absorption contrast images of binary chemical reactions     

D. Walker  O.T. Lord  M.J. Walter  S.M. Clark   《Chemical Geology》2009,260(3-4):211-220

Low-divergence synchrotron-sourced X-rays enable a radiographic imaging scheme for full characterization of binary chemical reactions and characterization by type of more complex reactions, in situ, in diamond anvil cells (DAC). Spatially resolved reactants are induced to react by laser heating of their interface. The spatially intermediate products are observed through X-ray absorption contrast. Limits to the technique include the ability to maintain controlled experiment geometry during compression and the ability to resolve chemical differences between reactants and products by X-ray absorption. The ability to make in situ observations at experimental pressure and temperature obviates the problem with quenching techniques for capturing liquid compositions in experiments with dimensions smaller than the diffusion length during quenching time. Partially molten Fe-alloy systems, of poor quenchability, are examined at DAC pressures and temperatures for relevance to Earth's core constitution and evolution. Determinations of eutectic melting in Fe–FeS match known results. Of the probable light elements that may alloy with Fe in the Earth's liquid outer core, Fe–FeS experiments show only modest quenching problems, but C and Si alloy experiments are highly vulnerable to quenching artifacts. The observed reactivity of FeS, Fe₃C, FeSi, and FeO(OH) with Fe in DAC makes the observed non-reactivity between Fe and FeO more significant, reducing the probability that oxygen alone is the major alloy in Earth's molten outer core.  相似文献   

金刚石包裹体中的古地幔信息   总被引：10，自引：1，他引：10  

肖化云  刘丛强  黄智龙 《地球科学进展》2001,16(2):244-250

金刚石在地幔环境生长过程中会捕获一些包裹体，这些包裹体能够被金刚石携带到地球表层，金刚石包裹体保存有其生长时古地幔环境的信息，通过对这些包裹体的研究，,可以获取古地幔环境的信息，阐述了金铡石包裹体的特征，综述了金刚石包裹体在获取古地幔物理化学环境，相环境以及地幔信息方面的取得的一些成果。  相似文献   

山东费县大井头地区金刚石原生矿找矿前景探讨   总被引：3，自引：0，他引：3       下载免费PDF全文

仲卫国  周登诗  刘继太  程晓萍  解丽华 《山东国土资源》2003,19(1):43-49

山东费县大井头地区第四系中金刚石及其指示矿物分布异常丰富 ,并且具有较高的集中度 ;该区的加里东期超基性火山碎屑岩、沉火山碎屑岩及其他一些岩石中均有金刚石和 (或 )指示矿物存在 ;该地区的铬铁矿异常属于矿致异常。研究证明该区第四系中金刚石指示矿物与当地的相关岩体关系密切 ;加里东期超基性火山碎屑岩某些特征与火山口相金伯利岩十分相似。大井头地区所处的构造位置有利于金刚石成矿 ,具有良好的找矿前景 ,值得进一步研究探索。  相似文献   

Recent Developments in Marine Diamond Mining     

Richard H. T. Garnett 《Marine Georesources & Geotechnology》2013,31(2):137-159

The marine diamond deposits of southern Africa owe their existence to fluvial transport down the Orange River to the South Atlantic. On the coast, they were moved, sorted and concentrated by high-energy sea and wind conditions to create a veneer of diamondiferous gravels on the sea floor. Large scale, offshore production by De Beers Marine commenced in 1989 in Namibian waters. The company now acts as a contractor for Namdeb, a corporation owned jointly with the Namibian governments. Some junior public companies also produce diamonds by large-scale mechanized means and conduct extensive exploration programs. Two important developments have occurred recently. Firstly, equipment for the recovery of diamonds from the seabed has been successfully borrowed from other industries. Large drills from onshore civil engineering have been modified for marine sampling and mining. Remotely controlled, seabed-mounted, excavational systems have assumed a major role. The new systems allow both evaluation sampling and subsequent mining to be undertaken by similar or the same equipment, making the results compatible. They permit highly selective extraction and enhanced recovery of the gravels from irregular bedrock in water approaching 200 m deep. But none is universally applicable offshore, each being the preferred system under different conditions. Secondly, the total output of sea diamonds from Namibian waters has increased to 0.8 million carats annually and now exceeds that from all the country's onshore sources. An industry has become established. Corporate and individual perseverence, government encouragement, new technology, shareholders' risk finance, and De Beers' diamond marketing have all played a role in the success. Future diamond production may increase as companies meet the challenge of working lower grade, higher volume deposits, which will require new approaches to the mining process. With a decrease in the physical risk of marine mining, the most variable inputs in operational planning and production forecasting are recovered grade and throughout rate, together with equipment availability. The importance of reliable grade estimation from sufficient sampling density is widely perceived, but the greatest performance risk can involve the predicted excavation rate and ''mineability'' of the seabed sediments. Published reserve statements would benefit from a requirement to specify the planned mining method, the consequent cutoff grade to be employed, and whether or not test mining has been undertaken.  相似文献   

Petrography,chemical composition,and Raman spectra of chrome spinel: Constraints on the diamond potential of the No. 30 pipe kimberlite in Wafangdian,North China Craton     

《Ore Geology Reviews》2017

Conventional diamond exploration seldom searches directly for diamonds in rock and soil samples. Instead, it focuses on the search for indicator minerals like chrome spinel, which can be used to evaluate diamond potential. Chrome spinels are preserved as pristine minerals in the early Paleozoic (∼465 Ma), hydrothermally altered, Group I No. 30 pipe kimberlite that intruded the Neoproterozoic Qingbaikou strata in Wafangdian, North China Craton (NCC). The characteristics of the chrome spinels were investigated by petrographic observation (BSE imaging), quantitative chemical analysis (EPMA), and Raman spectral analysis. The results show that the chrome spinels are mostly sub-rounded with extremely few grains being subhedral, and these spinels are macrocrystic, more than 500 µm in size. The chrome spinels also have compositional zones: the cores are classified as magnesiochromite as they have distinctly chromium-rich (Cr₂O₃ up to 66.56 wt%) and titanium-poor (TiO₂ < 1 wt%) compositions; and the rims are classified as magnetite as they have chromium-poor and iron-rich composition. In the cores of chrome spinels, compositional variations are controlled by Al³⁺-Cr³⁺ isomorphism, which results in a strong Raman spectra peak (A_1g mode) varying from 690 cm⁻¹ to 702.9 cm⁻¹. In the rims of chrome spinel, compositional variations result in the A_1g peak varying from 660 cm⁻¹ to 672 cm⁻¹. The morphology and chemical compositions indicate that the chrome spinels are mantle xenocrysts. The cores of the spinel are remnants of primary mantle xenocrysts that have been resorbed, and the rims were formed during kimberlite magmatism. The compositions of the cores are used to evaluate the diamond potential of this kimberlite through comparison with the compositions of chrome spinels from the Changmazhuang and No. 50 pipe kimberlites in the NCC. In MgO, Al₂O₃ and TiO₂ versus Cr₂O₃ plots, the chrome spinels from the Changmazhuang and No. 50 pipe kimberlites are mostly located in the diamond stability field. However, only a small proportion of chrome spinels from No. 30 pipe kimberlite have same behavior, which indicates that the diamond potential of the former two kimberlites is greater than that of the No. 30 pipe kimberlite. This is also supported by compositional zones in the spinel grains: there is with an increase in Fe³⁺ in the rims, which suggests that the chrome spinels experienced highly oxidizing conditions. Oxidizing conditions may have been imparted by fluids/melts that have a great influence on diamond destruction. Here, we suggest that chrome spinel compositions can be a useful tool for identifying the target for diamond potential in the North China Craton.  相似文献   

预压层叠式钻齿型孕镶金刚石钻头的研制          下载免费PDF全文

刘全心  刘青  南建平  柯文斌 《探矿工程》2012,39(Z1):94-96

分析了高品质钻头的应用需求,指明了高品质钻头的研究方向。设计了一种层叠式结构钻齿,采用预冷压工艺进行压制后,再经过装模热压烧结的新型孕镶金刚石钻头。给出了此类钻头的原材料选择和制作工艺参数,分析了钻探试验结果。结果表明：预压层叠式钻齿型孕镶金刚石钻头,有利于改善钻进条件,提高钻进效率,有效地实现钻头制造过程中节能降耗,是一种广谱性应用前景的孕镶金刚石钻头新型式。  相似文献   

Petrogenesis of lherzolites from the Purang ophiolite,Yarlung-Zangbo suture zone,Tibet: origin and significance of ultra-high pressure and other ‘unusual’ minerals in the Neo-Tethyan lithospheric mantle     

《International Geology Review》2012,54(17):2184-2210

ABSTRACT

The Purang ultramafic massif, located in the Yarlung-Zangbo Suture Zone (YZSZ) of the Tibetan Plateau, consists mainly of harzburgites and minor lherzolites. The spinel-bearing lherzolites of the NW part of the massif display a granular texture, consisting of large olivine and pyroxene crystals with curvilinear grain boundaries. These lherzolites contain chromian spinel (Cr-spinel) of low Cr# [100 × Cr/(Cr +Al) = 24.7–30.2], enstatite with high Mg# [100 × Mg/(Mg + Fe²⁺) = 90.0–91.2] and relatively high Al₂O₃ content (3.3–4.1 wt%), and diopside with high Mg# (90.2–93.3) and Al₂O₃ content (4.6–5.0 wt%). These compositions are analogous to those of spinel and pyroxenes from residual peridotites. However, the Purang lherzolites show U-shaped primitive mantle (PM)-normalized rare earth element (REE)-profiles, which are not consistent with a potential origin as melting residues. The high LREE contents and positive Ti anomalies shown by the investigated lherzolites coupled with the low TiO₂ content of their mineral constituents imply that these rocks possibly stored LREE- and Ti-bearing arc-related melts/fluids in their groundmass.

A mineral assemblage composed of diamond, super-reduced [(SuR) moissanite, native Cr] and crustal-derived minerals (zircon, corundum, rutile), has been separated from the Purang lherzolites. Uranium-Pb geochronological dating of zircons yielded an age range between 1718 and 465 Ma, indicating that they represent ancient crustal material delivered into the upper mantle via previous subduction events. Diamonds and old zircons (± crustal minerals) were carried to shallow mantle levels by asthenospheric magmas produced during a slab rollback-induced decompression melting process. The recovery of SuR minerals is consistent with fluid percolation and crystallization of alteration-related minerals in the lithospheric parts of a (hydrated) mantle wedge, resulting in the formation of highly reduced micro-environments.  相似文献   

Diamond economics of the Prairie Creek lamproite, Murfreesboro, AR, USA     

Dennis P. Dunn 《Ore Geology Reviews》2003,22(3-4):251-262

The Prairie Creek lamproite is the largest of seven ultramafic vents that make up the Prairie Creek lamproite province. Diamonds were first discovered in 1906, and commercial mining continued intermittently until about 1931. The evaluation program undertaken by the Arkansas State Parks Commission in the 1990s resulted in the mapping and evaluation of four major vent facies rock types: olivine lamproite, epiclastic sediments, phlogopite-rich tuff and olivine-rich tuff. Significant diamond contents were found only within the phlogopite-rich tuff (0.11 carat/100 tonnes) and olivine-rich tuff (1.1 carats/100 tonnes).Stratigraphic relationships indicate that the diamondiferous tuffs have undergone <50 m of erosion. Extrapolation of the surface rock units and their diamond contents to the pre-erosion surface suggests that 93,000 carats of diamonds were liberated and then concentrated as a natural surface enrichment. Early commercial production focused on the natural surface concentrations, an assumption supported by historic mining records. Historical grades suggest that 58,000 carats were contained in these surface deposits, about half of those diamonds being recovered during commercial operation. These relationships suggest that 35,000 carats remain as eluvial and alluvial deposits adjacent to the existing tourist area. This erosion model minimizes the prospects for either primary or alluvial commercial mining; however, it does validate early historic mining records and suggests areas for further tourist development within existing park boundaries.  相似文献   

金刚石形成的微观解释及其保存条件     

肖湘萍 《国土资源》1992,(1)

作者讨论了石墨转化为金刚石时的自由能变化和影响金刚石保存的物理化学因素。提出了复位效应这一概念,分析了释压速率、催化剂和水份等因素对金刚石保存的影响。人工合成金刚石的生产实践证实,在压力降低时,由于上述因素的影响,金刚石不稳定,并向石墨转化,金伯利岩中金刚石含矿性取决于多种因素:岩浆侵位的速度、冷凝速度、围岩水份以及岩浆化学成分。现有资料发明,金伯利岩体上部富金刚石,而往深部品位变贫且质量差,在一个岩管中往往中部富而边部渐贫。  相似文献   

胶辽台隆金刚石原生矿多旋回成矿作用讨论     

庄德厚 《国土资源》1988,(2)

辽东复县和鲁西蒙阴金刚石原生矿带产于中朝准地台的胶辽台隆次级凸起与凹陷的衔接带。胶辽台隆自晚前寒武纪以来,经历了扬子、晚加里东、华力西、印支、燕山等构造岩浆旋回,并在地台多旋回升降运动中,由于地壳产生减薄和水平引张作用,使富镁铁橄榄岩浆沿岩石圈断裂反复上涌,充填于基底断裂和盖层断裂中,形成了金伯利岩管和岩脉。依此,金刚石的成矿作用可划分为4个旋回;前寒武纪成矿旋回;加里东成矿旋回;华力西成矿旋回;燕山成矿旋回,其中以晚加里东—华力西成矿旋回和燕山成矿旋回最为重要。  相似文献