金伯利岩的物化探异常特征及勘探方法

金伯利岩是金刚石的成矿母岩之一.金伯利岩的分布严格受断裂构造控制,矿体呈管状、脉状,具有成群、结带分布的特征;它具有磁性强、电阻率低、微量元素Cr、Ni 、Nb含量高的特征.地表物化探异常多为椭圆状、条带状且与断裂构造共生.综合物化探异常与矿体吻合较好;金伯利岩岩体形状空间分布与围岩的物性差别,决定了异常大小强弱、反映明显程度; Cr、Ni 、Nb的元素异常范围与金伯利岩管（脉）的形状有直接的对应关系.有针对性选用综合物化探方法、采用合适的测网寻找金伯利岩是行之有效的.     

辽宁复县金伯利岩的磁性特征及其意义

利用磁滞回线、磁畴状态分析、剩磁磁化率和感磁磁化率测量等，对辽宁复县金伯利岩岩体群的磁性矿物成分和成因机制进行了分析．结果表明，该金伯利岩中的磁性矿物成分主要是单畴、似单畴颗粒磁铁矿，它们主要是在金伯利岩岩浆后期，即汽水热液期，在相对快速冷却的环境下形成的原生磁性矿物．在古地磁研究中，利用主成分分析，结合同位素测年结果，给出了该区金伯利岩的古地磁结果，为中国东部早古生代的古地磁研究提供了补充和验证．     

中国的钾镁煌斑岩和金伯利岩与金刚石矿床生成

钾镁煌斑岩产在黔东南和大洪山区 ,副钾镁煌岩散布于华南陆块西半部 .贵州马坪金伯利岩为基性岩 .虽然含矿金伯利岩和钾镁煌斑岩皆产在克拉通区 ,但其地球化学表现出板块俯冲碰撞后岩浆活动特征 .这些含金刚石富钾超镁铁岩岩浆可能由于来自核幔边界的热柱活动在地幔过渡带里古背板消亡的局部地段生成 .基性的金伯利岩岩浆易于保存Ⅱ型金刚石 .     

华北古生代地幔岩捕掳体中石榴石和巨晶石榴石的主、微量元素

山东蒙阴和辽宁复县古生代金伯利岩中产有众多的地慢岩捕掳体（橄榄岩、榴辉岩）和巨晶矿物．通过对这些捕掳体中石榴石以及石榴石巨晶的电子探针、离子探针微区分析及有关模拟计算,发现这些石榴石在捕获前都受到过金伯利岩质的硅酸盐岩浆不同程度的交代改造．其中辽宁复县榴辉岩型石榴石受地慢交代作用的影响很小,反映原亏损地幔石榴石的组成．相反,山东蒙阴橄榄岩中的石榴石和所有石榴石巨晶则受到了交代流体的彻底改造,并与流体相达到完全的平衡,因此反映的是富集地幔的特征,据此可推测中国华北克拉通下古老的岩石圈地幔在古生代金伯利岩岩浆喷出之前已受到过相当强烈的交代作用的改造。     

导电薄层下三维岩脉的CSAMT响应分析

为了研究探测3D导电岩脉状目标体的可控源音频电磁法（CSAMT）的最佳观测装置,我们用压缩积分方程法数值模拟了赋存于导电薄层下的3D导电岩脉的电磁场响应.计算结果表明,最有效的源的位置是把发射源沿岩脉的走向放置.相对于其他几种装置,这种观测装置得到的异常场与主场的比值最大.利用这种最佳的观测装置,通过将异常场E_ya 和 H_xa与噪音作对比,研究了当岩脉的埋深和高度发生变化时岩脉的可探测性问题.当岩脉的顶部埋深增加时,导电岩脉的可探测性降低.岩脉高度的变化对异常场幅值的影响要小于岩脉顶部埋深所产生的影响.所以通常情况下,即便应用了最有效的CSAMT装置,也很难探测到岩脉的高度,应用钻孔中的探测可能会解决这个问题.     

航磁异常分析技术及其在地质构造中的应用

航磁异常在地质构造研究中具有覆盖广、成本低以及横向分辨率高等显著优势,被广泛应用于隐伏岩浆岩及断层探测,俯冲带、大陆裂谷、岩墙群及地幔柱等构造特征分析,磁性界面(包含结晶基底及居里等温面)反演,区域构造划分,以及孕震构造背景研究等领域.近来随着航空磁测技术的发展,积累了越来越多大比例尺、高精度的航磁数据,并在此基础上产...     

下刚果盆地盐相关圈闭储层预测

下刚果盆地是西非被动大陆边缘系列盆地之一,为一大陆裂谷与被动陆缘盆地形成的叠合盆地.盆地储层为渐新统和中新统的浊积砂体.由于早白垩世末期盆地发育大规模蒸发岩层序,上覆沉积负载与非洲板块西倾使得盐岩塑性流动,造成盐上圈闭形成都与盐活动相关.S区块处于盐岩过渡构造带,由于储层分布受沉积相与盐构造的双重控制,难以准确地预测储层,针对上述难点,此文提出了如下的技术思路及流程,即首先利用地震解释得到目的层构造形态,其次综合利用地震属性和地震分频技术得到砂体分布图及沉积相图,并分析构造和砂体的配置关系,寻找有利圈闭,最后利用avo直接烃检测技术对含油气性进行预测.结果显示预测的有利区与已知油田有着很好的对应,且识别的3个未钻圈闭勘探前景良好.应用效果验证了本技术方法对盐相关圈闭具有很好的适用性,可在同类型圈闭中进一步应用.     

高温高压下碳酸盐熔体对地幔岩电导率的影响

为了观测含碳酸盐地幔岩部分熔融过程中电导率的变化,厘清碳酸盐熔体在金伯利岩岩浆形成过程中所起的作用,并探讨Slave克拉通中部Lac de Gras地区约80～120km深处的高导成因,我们利用DS 3600t六面顶压机和Solartron 1260阻抗/增益-相位分析仪在1.0～3.0GPa、673～1873K温压条件下分别测量了含碳酸钠(Na_2CO_3)、碳酸钙(CaCO_3)和大洋中脊玄武岩(MORB)的地幔岩样品的电导率.实验结果表明,地幔岩样品的电导率主要受到温度和组分的影响,而压力对其影响较小.在温度低于1023K时,含Na_2CO_3地幔岩样品的电导率明显高于含同比重CaCO_3和MORB的;温度达到1023K时,含Na_2CO_3地幔岩样品开始熔融;但在之后的200K温度区间内,该部分熔融样品的电导率随温度的增加几乎不发生变化.这一现象或许揭示:地幔深部的碳酸质岩浆在快速上升过程中会同化吸收岩石圈地幔中的斜方辉石(Opx),进而形成金伯利岩岩浆,期间岩浆的电导率几乎不发生变化.含CaCO_3和MORB的地幔岩样品分别在1723K和1423K开始熔融,其部分熔融样品的电导率随温度的增加而快速增加.依据前人的研究结果和我们的实验结果,我们认为可以用含碳酸盐的部分熔融样品来解释Slave克拉通中部Lac de Gras地区约80～120km深处的异常高导现象,并推测熔体中碳酸盐的熔体比例小于2wt.%.     

滇中中元古代昆阳群的地震事件沉积 及其地质意义

地震及其引发的海啸作为一种灾害性的地质事件可以在地层中形成地震-海啸事件沉积记录.云南滇中地区中元古代大龙口组发育地震断裂层、微同沉积断裂、微褶皱纹理、泥晶脉(molartooth构造)、丘状层理等典型的地震-海啸沉积标志,并形成震积岩(A,包括液化泥晶脉灰岩、震裂岩、震褶岩、自碎屑角砾岩和内碎屑副角砾岩等)、海啸岩(B,具丘状层理或平行层理的内碎屑灰岩)及背景沉积(C)三个沉积单元.它们组合成A-B-C,A-C,B-C等3种类型的沉积序列.这些沉积序列分别代表地震-海啸-背景沉积(地震引发海啸)、地震-背景沉积(地震未引发海啸)、海啸-背景沉积(远离地震中心)的事件沉积序列.滇中地区中元古代处于裂谷盆地的构造背景下,大龙口组的地震事件沉积是裂谷盆地构造活动的沉积响应.     

铜陵矿集区浅层含矿岩浆输运网络与运移机制

研究证实铜陵矿集区燕山期岩浆浅表侵入导致了大规模成矿作用, 成矿期区域中部-10 km处存在一个隐伏岩浆房, 成矿岩浆由此处产生并向上运移, 然浅层成矿岩浆输运网络与运移机制这个与成矿作用密切相关问题的探索仍有待深入. 构造力学、分形统计和地质事实综合分析表明北东向高角度褶皱相关断层及棋盘格状基底断裂系是岩浆由浅层岩浆房向盖层褶皱系输运的主要通道, 褶皱核部的虚脱部位是岩浆主要就位空间. 因而, 上褶-下断的构造网络为浅层岩浆的导流-定位系统. 多层结构地质体在变形过程中, 上部地层受下部地层顶托更趋于发生褶皱, 下部地层承受上部地层的载荷易发生断裂, 当下部地层岩石力学强度高于上部时, 上褶-下断构造组合的发育概率会更为增加. 由于存在导流网络, 浅部岩浆房顶部的富含挥发份岩浆以“岩脉式”快速向表层输运, 定位于褶皱虚脱空间中, 并快速充填和改造就位空间; 岩浆顶部的挥发份物质因压力骤降而发生隐爆, 引发多相流体不混溶以及大量成矿元素富集. 脉动式岩脉活动可能是导致铜陵矿集区岩浆岩化学成分互有差异且时空上紧密伴生的主要因素.     

A conceptual model for kimberlite emplacement by solitary interfacial mega-waves on the core mantle boundary

If convection in the Earth's liquid outer core is disrupted, degrades to turbulence and begins to behave in a chaotic manner, it will destabilize the Earth's magnetic field and provide the seeds for kimberlite melts via turbulent jets of silicate rich core material which invade the lower mantle. These (proto-) melts may then be captured by extreme amplitude solitary nonlinear waves generated through interaction of the outer core surface with the base of the mantle. A pressure differential behind the wave front then provides a mechanism for the captured melt to ascend to the upper mantle and crust so quickly that emplacement may indirectly promote a type of impact fracture cone within the relatively brittle crust. These waves are very rare but of finite probability. The assumption of turbulence transmission between layers is justified using a simple three-layer liquid model. The core derived melts eventually become frozen in place as localised topographic highs in the Mohorovicic discontinuity (Moho), or as deep rooted intrusive events. The intrusion's final composition is a function of melt contamination by two separate sources: the core contaminated mantle base and subducted Archean crust. The mega-wave hypothesis offers a plausible vehicle for early stage emplacement of kimberlite pipes and explains the age association of diamondiferous kimberlites with magnetic reversals and tectonic plate rearrangements.     

Fragmentation in kimberlite: products and intensity of explosive eruption

The explosive eruption of kimberlite magma is capable of producing a variety of pyroclast sizes, shapes, and textures. However, all pyroclastic deposits of kimberlite comprise two main types of pyroclasts: (1) pyroclasts of kimberlite with or without enclosed olivine crystals and (2) olivine crystals which lack coatings of kimberlite. Here, we propose two hypotheses for how kimberlite magmas are modified due to explosive eruption: (1) olivine crystals break during kimberlite eruption, and (2) kimberlite melt can be efficiently separated from crystals during eruption. These ideas are tested against data collected from field study and image analysis of coherent kimberlite and fragmental kimberlite from kimberlite pipes at Diavik, NT. Olivines are expected to break because of rapid pressure changes during the explosive eruption. Disruption of kimberlite magma, and pyroclast production, is driven by ductile deformation processes, rather than by brittle fragmentation. The extent to which melt separates from olivine crystals to produce kimberlite-free crystals is a direct consequence of the relative proportions of gas, melt and crystals. Lastly, the properties of juvenile pyroclasts in deposits of pyroclastic kimberlite are used to index the relative intensity of kimberlite eruptions. A fragmentation index is proposed for kimberlite eruption based on: (a) crystal size distributions of olivine and on (b) ratios of selvage-free olivine pyroclasts to pyroclasts of kimberlite with or without olivine crystals.     

Geology of the BK9 kimberlite (Damtshaa,Botswana): implications for the formation of dark volcaniclastic kimberlite

The BK9 kimberlite consists of three overlapping pipes. It contains two dark varieties of massive volcaniclastic kimberlite, informally termed dark volcaniclastic kimberlite (DVK). DVK(ns) is present in the north and south pipes and is interbedded with lenses of basalt breccia at the margins of the pipes. DVK(c) is present within the central pipe where it is overlain by a sequence of basalt breccias with interbedded volcanogenic sediments. The features observed within the DVK units of the BK9 kimberlite provide strong evidence for gas fluidisation of the accumulating pyroclastic material. These include the massive interior of the pipes, marginal epiclastic units, well-dispersed country-rock xenoliths and small-scale heterogeneities in lithic clast abundance. The upper portions of the central pipe provide a record of the transition from pyroclastic eruption and infill to passive epiclastic infilling of the crater, after the eruption has ceased. The wall-rock of the BK9 kimberlite dips inwards and is interpreted as post pipe-fill subsidence of the adjacent country rock. The two DVK units contain interstitial, silt-sized pyroclasts. The DVK(ns) has a higher fraction of former melt and displays evidence of incipient welding, as a result of differences in eruption dynamics. These units demonstrate that whilst DVK is comparable in many respects to MVK and forms part of a spectrum of volcaniclastic rocks formed by fluidisation, it differs in frequently containing silt-sized particles and including agglutinated and welded varieties with a high melt fraction. The DVK varieties, studied here, also have a distinctive hydrothermal assemblage, resulting from the abundance of low-silica accidental lithic clasts. Both the hydrothermal alteration and the abundance of silt-sized particles contribute to the DVKs distinctive dark colour.     

Geology of a complex kimberlite pipe (K2 pipe,Venetia Mine,South Africa): insights into conduit processes during explosive ultrabasic eruptions

K2 is a steep-sided kimberlite pipe with a complex internal geology. Geological mapping, logging of drillcore and petrographic studies indicate that it comprises layered breccias and pyroclastic rocks of various grain sizes, lithic contents and internal structures. The pipe comprises two geologically distinct parts: K2 West is a layered sequence of juvenile- and lithic-rich breccias, which dip 20–45° inwards, and K2 East consists of a steep-sided pipe-like body filled with massive volcaniclastic kimberlite nested within the K2 pipe. The layered sequence in K2 West is present to > 900 m below present surface and is interpreted as a sequence of pyroclastic rocks generated by explosive eruptions and mass-wasting breccias generated by rock fall and sector collapse of the pipe walls: both processes occurred in tandem during the infill of the pipe. Several breccia lobes extend across the pipe and are truncated by the steep contact with K2 East. Dense pyroclastic rocks within the layered sequence are interpreted as welded deposits. K2 East represents a conduit that was blasted through the layered breccia sequence at a late stage in the eruption. This phase may have involved fluidisation of trapped pyroclasts, with loss of fine particles and comminution of coarse clasts. We conclude that the K2 kimberlite pipe was emplaced in several distinct stages that consisted of an initial explosive enlargement, followed by alternating phases of accumulation and ejection.     

The palaeomagnetism of some Upper Cretaceous kimberlite occurrences in South Africa

Palaeomagnetic results are reported from the De Beers, DuToitspan and Wesselton kimberlite pipes (86 ± 3Ma) at Kimberley and from the Finsch and Koffyfontein pipes. The latter are both less than 150 km from Kimberley and although undated are geologically correlated with the Kimberley pipes. Eighty blocks, oriented without recourse to magnetic methods, have been collected from the five pipes. The samples comprise kimberlite, accidental inclusions of widely varying lithologies and wall rock thus enabling inclusion and baked contact tests to be performed. Extensive alternating field and thermal demagnetization experiments show that the magnetization of the kimberlite is primary. Secular variation is not averaged out in any one pipe (with the possible exception of Finsch) and it is suggested the three Kimberley pipes were emplaced simultaneously. The mean pole position of the five pipes (57.2°E, 58.2°S withK = 25.8 andA₉₅ = 15.3°) is believed to be a good estimate of the palaeomagnetic pole86 ± 3Ma ago. It is now possible to state that the African Mesozoic palaeomagnetic pole remained essentially in the same position until at least86 ± 3Ma ago.     

A rare occurrence of a crater-filling clastogenic extrusive coherent kimberlite,Victor Northwest (Ontario,Canada)

Kimberlite pipes can contain significant proportions of dark and dense kimberlite that have mostly been interpreted as intrusive coherent (hypabyssal) in origin. This study reports a well-documented occurrence of a fresh intra-crater clastogenic extrusive coherent kimberlite that is concluded to have formed as a result of lava fountaining. This paper focuses on a dark, dense, competent, generally crystal-rich, massive kimberlite unit within the Victor Northwest kimberlite pipe (Ontario, Canada). Using a comprehensive volcanological and petrographic analysis of all available drill cores, it is shown that this unit has a fresh well-crystallised coherent groundmass and is extrusive and pyroclastic in origin. The proposed clastogenic coherent extrusive origin is based on deposit morphology, gradational contacts to enveloping pyroclastic units, as well as the presence of remnant pyroclast outlines and angular broken olivines. This paper, and an increasing number of other studies, suggest that fragmental extrusive coherent kimberlite in intra-crater settings may be more common than previously thought. The emplacement history and volcanology of these pipes need to be reconsidered based on the emerging importance of this particular kimberlite facies.     

Kimberlite wall-rock fragmentation processes: Venetia K08 pipe development

Current kimberlite pipe development models strongly advocate a downward growth process with the pipe cutting down onto its feeder dyke by means of volcanic explosions. Evidence is presented from the K08 kimberlite pipe in Venetia Mine, South Africa, which suggests that some pipes or sub-components of pipes develop upwards. The K08 pipe in pit exposure comprises >90 vol.% chaotic mega-breccia of country rock clasts (gneiss and schist) and <10 vol.% coherent kimberlite. Sub-horizontal breccia layers, tens of metres thick, are defined by lithic clast size variations and contain zones of shearing and secondary fragmentation. Textural studies of the breccias and fractal statistics on clast size distributions are used to characterize sheared and non-sheared breccia zones and to deduce a fragmentation mechanism. Breccia statistics are compared directly with the statistics of fragmented rock produced from mining processes in order to support interpretations. Results are consistent with an initial stage of brecciation formed by upward-moving collapse of an explosively pre-conditioned hanging wall into a sub-terranean volcanic excavation. Our analysis suggests that the pre-conditioning is most likely to have been caused by explosions, either phreatic or phreatomagmatic in nature, with a total energy output of 2.7 × 10⁹ kJ (656 t of TNT). A second stage of fragmentation is interpreted as shearing of the breccia caused by multiple late kimberlite intrusions and possible bulk movement of material in the pipe conduit related to adjacent volcanism in the K02 pipe.     

Factors controlling the internal facies architecture of maar-diatreme volcanoes

Most if not all kimberlite pipes show a multitude of facies types, which imply that the pipes were emplaced under an episodic re-occurrence of eruptive phases, often with intermittent phases of volcanic quiescence. The majority of these facies can be related to either the fragmentation behaviour of the magma during emplacement or changing conditions during sedimentation of volcaniclastic deposits, as well as their alteration and compaction after deposition. An additional factor controlling pipe-facies architecture is the degree of mobility of the loci of explosions in the explosion chambers of the root zone or root zones at the base of the maar-diatreme volcano. In a growing pipe, the root zone moves downward and, with that movement, the overlying diatreme enlarges both in size and diameter. However, during the life span of the volcano, the explosion chamber can also move upward, back into the lower diatreme, where renewed explosions result in the destruction of older deposits and their structures. Next to vertical shifts of explosion chambers, the loci of explosions can also move laterally along the feeder dyke or dyke swarm. This mobility of explosion chambers results in a highly complex facies architecture in which a pipe can be composed of several separate root zones that are overlain by an amalgamated, crosscutting diatreme and maar crater with several lobes. Pipe complexity is amplified by periodic changes of the fragmentation behaviour and explosivity of kimberlite magma. Recent mapping and logging results of Canadian and African kimberlite pipes suggest that kimberlite magma fragmentation ranges from highly explosive with abundant entrained country rock fragments to weakly explosive spatter-like production with scarce xenoliths. On occasions, spatter may even reconstitute and form a texturally coherent deposit on the crater floor. In addition, ascending kimberlite magma can pass the loci of earlier fragmentation events in the root zone and intrudes as coherent hypabyssal kimberlite dykes in high pipe levels or forms extrusive lava lakes or flows on the crater floor or the syneruptive land surface, respectively. This highly variable emplacement behaviour is typical for basaltic maar-diatreme volcanoes and since similar deposits can also be found in kimberlites, it can be concluded that also the volcanological processes leading to these deposits are similar to the ones observed in basaltic pipes.     

H2O and CO2 in kimberlitic fluid as recorded by diamonds and olivines in several Ekati Diamond Mine kimberlites,Northwest Territories,Canada

Surface dissolution features on diamonds and Fourier Transform Infra Red spectroscopy (FTIR) of phenocrystal and xenocrystal olivines from kimberlites contain a record of magmatic fluid in kimberlite magmas. We investigated composition and behavior of kimberlitic fluid and the effect of volatiles on the eruption style and geology of kimberlites using microdiamonds and olivine concentrates from six kimberlite pipes with different lithologies and the character of diamond resorption (Ekati Diamond Mine, Northwest Territories, Canada). The study showed a clear correlation between the resorption style of diamond population of the kimberlites and the type of infrared (IR) spectra of their olivines. Four kimberlites have high quality diamonds with smooth regular surface features and high H₂O content of the olivines indicating the presence of H₂O-rich fluid during the emplacement. Fast ascent rates of fluid-rich magma can explain explosive eruption and filling the pipes with volcaniclastic kimberlite facies. Conversely, Grizzly and Leslie kimberlites have diamonds with complex sharp features diminishing diamond quality and indicating loss of the fluid. The slower ascent rates and less explosive eruption of the fluid-free magmas produced kimberlite pipes filled with magmatic facies kimberlite. Distinctive peaks in olivine IR spectra at 3356 and 3327 cm^? 1 were found to correlate with the presence of hydrous magmatic fluid. Character of diamond morphology suggests that during the whole ascent of all six kimberlites, the magmatic fluid when present had a high H₂O:CO₂ ratio.