金刚石原生矿床类型及安徽省金刚石找矿前景分析

本文对具有经济的金伯利岩和金云火山岩金刚石原生矿两大类型模式特征和产出的构造部位进行了研究.在此基础上,对我省金刚石成矿构造条件进行了分析,并阐述了我省寻找金伯利岩和金云火山岩两大类型金刚石原生矿有利地区.     

Mineralogical studies of pyropes in kimberlites from China

Based on the measurements of refractive index,specific gravity,unit cell parameter,and mineral chemistry and infrared absorption spectrum analyses of pyropes in kimberlites from China,systematic studies of the Physical properties and compositional variations of pyropes of different colors and diverse paragenetic types,within and between kimberlite provinces have been undertaken,The origin of pyropes in the Kimberlites and the depth of their formation have been discussed.Pyropes of the purple series are different from those of the orange series in physical and chemical properties,for exaple,pyropes of the puple series are higher in α0,RI,SG,Cr2O3,MgO,Cr/(Cr Al),Mg/(Mg Fe),and Mg/(Mg Ca),and lower in Al2O3,Fe2O3 FeO than those of the orange series.The classification of garnets in kimberlites from china by the Dawson and Stephens‘ method(1975) has been undertaken and clearly demonstrates that pyropes of diamond-rich kimberlites contain much more groups than those of diamond-poor,especially diamond-free kimberlites.The higher in α0,RI,SG,Cr2O(3.Cr/(Cr Al),knorringite and Cr-component the pyropes are ,the richer in diamond the kimberlites will be.The infrared absorption spectrum patterns of pyropes change with their chemical composition regularly,as reflected in the shape and position of infrared absorption peaks.Two absortpion bands at 862-901 cm^-1 will grade into degeneration from splitting and the absorption band positions of pyropes shift toward lower frequency with increasing Cr2O3 content and Cr/(Cr Al) ratio of pyropes,LREE contents of orange pyrope megacrysts are similar to those of porple pyrope macrocrysts,but the former is higher in HREE than the latter,showing their different chondrite-normalized patterns.The formation pressures of pyropes calculated by Cr-component,Ca-component,knorringite molecules of pyropes show that some pyropes of the purple series in diamondiferous kimberlites fall into the diamond stability field.but all pyropes of diamond-free kimberlites lie outside the diamond stability field.The megacrysts were formed through early crystallization of kimberlites magma at high pressure condition,the majority of the purple pyrope macrocrysts have been derived from disaggregated xenoliths but the minoirty of them appear to be fragments of the discrete megacryst pyropes,or phenocrysts.     

华北克拉通金伯利岩型金刚石矿床含矿性判别

金伯利岩型金刚石原生矿床含矿性评价是了解金刚石成矿规律和指导区域性找矿的重要依据。华北克拉通是我国重要的金刚石成矿远景区,目前已发现了两个重要的含金刚石金伯利岩岩区(山东蒙阴和辽宁瓦房店)。近年来,对岩区内不同品位金刚石典型矿床的研究表明金伯利岩中的金刚石品位取决于以下两个重要的地质过程:金伯利岩岩浆对金刚石的捕获作用和金伯利岩岩浆对金刚石的熔蚀作用。在华北克拉通下方存在一个金刚石稳定区,温度为950～1200℃,压力为4.4～6.1 GPa。山东蒙阴和辽宁瓦房店金伯利岩岩浆在上升过程中穿过该区域并捕获其中的金刚石,成为含矿岩浆;而铁岭和鹤县等金伯利岩岩浆在上升过程中不穿过该区域,成为不含矿岩浆。在穿过金刚石稳定区时,富矿的金伯利岩捕获了更多的金刚石以及金刚石的伴生指示矿物(如镁铝榴石,镁铬铁矿);而贫矿的金伯利岩则相对捕获了少量的金刚石和指示矿物。这些指示矿物往往参加了金刚石的形成过程,有些作为缓冲剂控制了反应(岩浆或熔体)的氧化还原状态,有些则作为反应物或者生成物参与到反应中。部分指示矿物(如镁铝榴石)还进一步地记录了金刚石形成后金伯利岩岩浆对金刚石的交代作用。金伯利岩岩浆温度(T...     

Mantle Degassing and Diamond Genesis：A Carbon Isotope Perspective

The effect of Co2 and CH4 degassing from the mantle on the carbon isotopic composition of diamond has been quantitatively modeled in terms of the principles of Rayleigh distillation.Assuming the δ^13 C value of -5‰ for the mantle,the outgassing of CO2 can result in the large negative δ^13 C values of diamond,whereas the outgassing of CH4 can drive the δ^13C values of diamond in the positive direction.The theoretical expectations can be used to explain the full range of δ^13 C values from-34.4‰5 to 5‰ observed for natural diamonds.It is possible that diamond formation was triggered by the degassing of Co2 and/or CH4 from the mantle and the associated fractional crystallization of carbonate-bearing melt.     

贵州镇远马坪金伯利岩及其捕虏晶对金刚石成矿条件的指示意义

贵州镇远是中国金刚石原生矿找矿的重点区域之一。镇远地区马坪D1号岩体是1965年中国首次发现的含原生金刚石金伯利岩。该岩体岩石具典型的金伯利岩结构和组成特征,其中的锆石捕虏晶U–Pb年代学和Hf同位素分析结果表明,该地区存在未暴露的太古宙基底物质残余。基于壳幔耦合性规律,可能对应有古老的岩石圈地幔,这种古老的克拉通属性是金刚石形成的有利因素。但另一方面,马坪金伯利岩普遍含有伴生矿物含铬镁铝榴石,其CaO含量较高,多数属于G9(二辉橄榄岩)类型,不是全球富含金刚石的方辉橄榄岩原岩类型(G10),暗示当时的岩石圈发生了部分改造而可能不利于高品质金刚石的形成。需要注意的是,在金刚石找矿过程中,应该以详细的野外工作与岩石学对比研究为基础,同时依赖于金伯利岩及其相关的岩浆活动所携带的捕虏体/捕虏晶的研究,配合以岩浆成分来反演地幔源区特征,才能较全面地揭示古老大陆岩石圈的形成年龄与演化历史、物质组成与精细结构,以及大陆岩石圈根的厚度、热状态、氧逸度、流体作用等,进而为寻找金刚石提供重要的依据。     

贵州镇远钾镁煌斑岩原生金刚石微晶貌特征探讨

贵州镇远马坪地区作为中国第一个含金刚石母岩——钾镁煌斑岩的发现地,既是华南地区最重要的、最丰富的含金刚石母岩出露区,也是中国金刚石原生矿找矿的重点区域。以往针对该区的金刚石原生矿勘查工作重点多集中于对其寄主岩石特征的研究上,如岩体侵位方式、矿物组成、岩石地球化学特征以及侵位时代等方面（卢登蓉等,1989;罗会文等,1989;江万,1995;方维萱等,2002;杨光忠,2013）,而对于金刚石本身晶貌学特征的研究较少,且受当时测试技术条件的限制,有关金刚石晶貌特征所对应的找矿信息揭示不够充分。鉴于扬子地台金刚石找矿工作的迫切需要,本文通过对镇远地区钾镁煌斑岩中金刚石矿物自身特点开展晶貌学研究,进而反演、推测其结晶和生长过程,并由此探讨寄主岩石源区特征、母岩形成条件,为扬子地台金刚石原生矿找矿研究提供新的思路。     

博茨瓦纳奥拉帕金刚石矿床成矿地质特征

博茨瓦纳是世界上金刚石资源最为丰富的国家之一。奥拉帕金刚石矿床是该国最大的金刚石矿,矿床的金伯利岩为Ⅰ型,其中的包体可以分为2种:橄榄岩型和榴辉岩型;金刚石可以分为3类:橄榄岩型、榴辉岩型及两者的过渡类型-二辉岩型。其中,橄榄岩型和部分榴辉岩型金刚石来自于地幔结晶堆晶体,而榴辉岩型则与板块俯冲的构造-热事件有关。金伯利岩的形成时代主要为白垩纪,而金刚石则主要形成于元古宙和太古宙,金伯利岩和金刚石为不同时期的产物,金刚石为金伯利岩侵位期间捕获的上地幔物理破碎产物。其中年龄为900~1000Ma的金刚石为板块构造-热事件的产物,并对早期金刚石进行了改造破坏。     

纳米比亚金刚石矿床地质特征、矿床成因及找矿模型

纳米比亚金刚石资源丰富且品质优良,矿床类型以次生砂矿为主。文章对前人的大量研究成果进行分析总结,概述了纳米比亚金刚石矿床的区域地质背景,分析了金刚石矿床的地质特征及矿床成因。对纳米比亚金刚石包裹体氩-氩法定年分析发现,80%的包裹体熔蚀年龄<300Ma,表明大部分纳米比亚碎屑金刚石源自Dwyka期(<300Ma)以后的金伯利岩;纳米比亚金刚石以橄榄岩型(占比46%)和榴辉岩型(占比41%)为主,其余为二辉岩型或介于橄榄岩型-二辉岩型之间;纳米比亚橄榄岩型金刚石包裹体中石榴石-橄榄石平衡矿物的温度为961~1223℃,平均(1107±98)℃;石榴石-斜方辉石的平衡压力多为4.5~6.0GPa。纳米比亚金刚石的找矿有利地区主要为奥兰治河沿线及Oranjemund、卢得立次海岸地区,以次生金刚石砂矿为主。     

辽宁永宁地区含金刚石闪长质岩石显微特征及金刚石来源探讨

辽宁永宁地区发育一套闪长质火山岩，该岩石中曾选获金刚石及其指示矿物，因此成为辽宁省金刚石第Ⅳ成矿带。通过对该岩石矿物组成及其显微结构构造特征研究，表明：(1)闪长质岩石中的斑晶斜长石具有环带结构；(2)橄榄石及金云母具有多世代性，且目估橄榄石+金云母含量在10%以上，局部更为富集；(3)出现“橄榄石+金云母+石榴石”与“斜长石+辉石+角闪石”不平衡的矿物组合；(4)发现橄榄石有碎斑结构和金伯利岩角砾。初步认为，永宁地区的闪长质岩浆在上升过程中捕获了早先已形成的金伯利岩并与之发生熔融混合作用，金刚石来自于深部的金伯利岩。这一认识对该地区寻找金刚石原生矿具有启示意义。     

博茨瓦纳和中国含金刚石金伯利岩的地质特征及对寻找类似岩体的启示

金刚石及其寄主岩石是人类认识地球深部物质组成和性质、壳幔和核幔物质循环重要研究对象。本文总结了中国不同金刚石类型的分布,着重对比了博茨瓦纳和中国含金刚石金伯利岩的地质特征,取得如下认识:(1)博茨瓦纳含矿原生岩石仅为金伯利岩,而中国含矿岩石成分复杂,金伯利岩主要出露在华北克拉通,展布于郯庐、华北中央和华北北缘金伯利岩带,具有工业价值的蒙阴和瓦房店矿床分布于郯庐金伯利岩带中;钾镁煌斑岩主要出露在华南克拉通,重点分布在江南和华南北缘钾镁煌斑岩带中;(2)钙钛矿原位U-Pb年龄和Sr、Nd同位素显示,86～97 Ma奥拉帕金伯利岩群和456～470 Ma蒙阴和瓦房店金伯利岩均具有低87Sr/86Sr(0.703～0.705)和中等εNd(t)(-0.09～+5)特征,指示金伯利岩浆源自弱亏损地幔或初始地幔源区;(3)博茨瓦纳金伯利岩体绝大多数以岩筒产出,而中国以脉状为主岩筒次之;博茨瓦纳岩筒绝大部分为火山口相,中国均为根部相,岩筒地表面积普遍小于前者;(4)奥拉帕A/K1和朱瓦能金伯利岩体是世界上为数不多的主要产出榴辉岩捕虏体和E型金刚石的岩筒之一,而同位于奥拉帕岩群的莱特拉卡内、丹姆沙和卡罗韦岩体与我国郯庐带的金伯利岩体类似,均主要产出地幔橄榄岩捕虏体以及P型和E型金刚石;(5)寻找含矿金伯利岩重点注意以下几点:克拉通内部和周缘深大断裂带是重要的控岩构造;镁铝榴石、镁钛铁矿、铬透辉石、铬尖晶石和铬金红石等是寻找含金刚石金伯利岩重要的指示矿物;航磁等地球物理测量需与土壤取样找矿方法相结合才能取得更好效果;(6)郯庐金伯利岩带、江南钾镁煌斑岩带和塔里木地块是中国重要含矿岩石的找矿靶区,冲积型金刚石成矿潜力巨大。     

津巴布韦奇拉色卡矿区金刚石古砂矿地质特征及成因

通过对津巴布韦奇拉色卡矿区金刚石古砂矿的地质特征、矿层特征、赋矿规律等的研究,建立了该区矿床勘查模型。研究表明,该区构造上处于太古宙津巴布韦克拉通东部边缘,西部紧邻林波波造山带、莫桑比克造山带,而林波波带为重要的金刚石产地,该区处于金刚石古砂矿成矿的有利位置;矿层赋存于中元古代乌肯多群砂砾岩组沉积岩中。该区金刚石古砂矿为沉积型金刚石古砂矿类型,属滨海环境沉积建造。在中元古代,原生矿中的金刚石被风化剥蚀出来,经流水的搬运,在滨海地区沉积,固结形成金刚石古砂矿床。津巴布韦奇拉色卡矿区金刚石古砂矿的发现及研究对指导中国境内寻找金刚石古砂矿具有重要的意义。     

山东省平邑县大井头钾镁煌斑岩地质特征及金刚石含矿性

平邑县大井头岩体发现以来,其岩性界定和金刚石含矿性始终悬而未解。近期针对其深部施工2个钻孔,在钻孔人工重砂样中选获原生金刚石3颗。结合岩矿鉴定、岩石地球化学和重砂矿物特征,认为大井头岩体为含金刚石的钾镁煌斑岩管,岩体下游的金刚石及其重砂矿物异常应由该岩体引起。结合周边存在的金刚石指示矿物异常和多处尚未查明的疑似岩体,认为该地区具有广阔的金刚石原生矿找矿前景。     

大同火山群新生代火山岩成因相平衡实验约束

通过常压控制氧逸度熔融相平衡实验结果可探讨一些火山岩岩石学的基本问题及火山岩成因机制问题。在Ｏｌ－Ｄｉ－Ｎｅ三元相图上，不同大地构造环境中产出的碱性玄武岩的Ｏｌ＋ＣＰｘ－Ｐｌ饱和同结线不重合，相同构造环境中产出的碱性玄武岩的Ｏｌ＋ＣＰｘ＋Ｐｌ饱和同结线随ｆｏ＿２升高只是简单地朝Ｏｌ端移动。在ＬｅＢａＳ（１９８６）ＴＡＳ图内火山岩低压结晶作用硅─碱演化趋势呈正斜率并近似与ＴＡＳ图内火山岩系列分界线相近。由低压液相成分演化线与大同火山群岩石化学变异趋势对比，以及高压控制下的结晶作用特点的分析，大同火山群中更新世早期岩浆向中更新世晚期岩浆的演化不能用简单的低压结晶作用解释，而高压控制下的结晶作用可能是主要的控制因素。     

鲁西大井头地区金刚石找矿指示矿物特征及其研究意义

鲁西大井头地区自然重砂中的金刚石及其找矿指示矿物发现已久,然而找矿工作尚未能取得实质性突破。本文从金刚石找矿指示矿物角度入手,在研究该地区指示矿物晶体形貌特征和化学成分特征的基础上,通过对比大井头地区自然重砂与大井头岩体中的指示矿物特征、大井头地区与其它地区金伯利岩、钾镁煌斑岩中的指示矿物特征后得出:大井头地区既存在金刚石指示矿物,又含有金刚石母岩指示矿物,是鲁西金刚石找矿的有利地区;第四系自然重砂中的指示矿物类型和所占比重与大井头岩体较为一致,认为第四系中的指示矿物由大井头岩体供源;大井头岩体含有较大比重的榴辉岩相指示矿物,如G4组镁铝-铁铝榴石和绿辉石,且其中金刚石多为Ib型,表现出与蒙阴地区金刚石原生矿不同的特征,认为大井头岩体为穿越金刚石生成区边部、并携带了其中特征性矿物成分的钾镁煌斑岩。结合大井头周边地区发现的三处重砂矿物异常和多个可疑岩体,依据钾镁煌斑岩集群分布的特点,认为大井头及周边地区是新区、新类型金刚石找矿的优质靶区,建议今后找矿方向和工作重点向钾镁煌斑岩型金刚石原生矿转移。     

Petrophysical properties of kimberlites from the Komsomolsky Pipe and their relationship to its composition,formation conditions,and diamond content

The paper discusses the petrophysical properties of kimberlites from the Komsomolsky Pipe and statistical analysis of their relationships with the data of petrographic and ore microscopic studies. Comparison of the obtained results with data of analogous studies in other Yakutian kimberlite pipes showed that these data can be applied for prognostic evaluation of kimberlite contents in kimberlite bodies of this region.     

鄂尔多斯古陆金刚石成矿条件及找矿潜力

鄂尔多斯古陆具有稳定的结晶基底和沉积盖层,也存在有利于金伯利岩形成的深切地幔的深大断裂构造。在山西柳林尖家沟地区发现众多金伯利岩,在山西应县和大同地区发现金伯利岩、钾镁煌斑岩及似金伯利岩等与金刚石形成有关的岩体,在这些地区也发现少量微粒金刚石和大量指示矿物;圈出内蒙古新庙、陕西店塔2个铬尖晶石指示矿物异常区。陕西店塔地区还发现与金伯利岩岩浆活动有关的环状构造。鄂尔多斯古陆区具备原生金刚石形成条件,具有良好的找矿潜力。     

Redox state of eclogites and peridotites from sub-cratonic upper mantle and a connection with diamond genesis

Pressure–Temperature- conditions and fluid compositions estimated for mineral parageneses from inclusions in diamonds, diamond-bearing and diamond-free xenoliths using a garnet–clinopyroxene–silica oxygen barometer data indicate that the upper mantle is zoned, with a relatively oxidized lithosphere and a reduced asthenosphere. Calculations in the C–O–H system indicate that eclogite inclusions within diamonds and xenoliths have formed mainly in equilibrium with water-rich fluids.     

辽宁省南部金刚石分布及找矿预测

详细地介绍了辽宁省南部发现的金伯利岩岩体和金刚石砂矿形成地质条件、分布范围,特别是金刚石砂矿成因类型、分布规律及成矿远景区预测。     

Prospects of search for diamondiferous kimberlites in the northeastern Siberian Platform

The objects of study are Triassic hypabyssal diamondiferous kimberlites with an age of 220-245 Ma, containing macrocrysts of unaltered olivine. The latter are close in the time of formation to the main stage of intrusion of the Siberian Trap Province (252 Ma), which lasted less than 1 Myr. A comparative high-precision analytical study of the Ti, Ca, Cr, and Al impurity patterns in about 1000 olivine macrocryst samples with a forsterite content Fo = (100Mg/(Mg + Fe)) of 78 to 93 has demonstrated the effect of traps on the lithospheric composition. A comprehensive comparative study of diamonds from northern placers and Triassic kimberlites, including determination of their carbon isotope composition, was performed. Chromatography-mass-spectroscopic analysis of submicron fluid inclusions in diamonds from northern placers and kimberlites has shown predominant hydrocarbons of a wide range of compositions and subordinate contents of N₂, H₂O, and CO₂. These findings, together with the results of previous studies of subcalcic Cr-pyropes and diamonds found in the Lower Carboniferous gritstones of the Kyutyungde graben, lead to the conclusion that the Toluopka kimberlite field is promising for Paleozoic kimberlites. The results of comprehensive studies of diamonds and indicator minerals and U/Pb isotope dating of numerous detrital zircon samples from the basal horizon of the Carnian Stage (Upper Triassic) of the Bulkur site in the lower reaches of the Lena River suggest the presence of diamondiferous kimberlites within the northeastern Siberian Platform. The age of the probable primary diamond sources in the study area can be evaluated by an integrated U/Pb isotope dating of zircons, perovskites, and rutiles from the developed diamond placers and the basal horizon of the Carnian Stage.     

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

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.