内蒙古北山额济纳旗小红山钒钛磁铁矿床SHRIMP锆石 U-Pb定年及其意义

小红山钒钛磁铁矿床是近年内蒙古北山地区新发现的一个中型钒钛磁铁矿床,含矿辉长岩体侵位于蓟县系平头山组,岩体具全岩矿化,工业矿体主要赋存于中粗粒辉长岩中。采用SHRIMP锆石U-Pb定年方法对小红山中粗粒辉长岩体进行了年代学研究,获得该岩体的锆石微区原位SHRIMP U-Pb年龄为424±6Ma,表明小红山钒钛磁铁矿成岩成矿事件发生于中志留世。该时期钒钛磁铁矿床的发现,揭示了北山地区早古生代处于陆缘裂谷环境,这对研究和认识北山地区地质构造演化及开展岩浆矿床找矿具有重要意义。     

内蒙古北山额济纳旗小红山钒钛磁铁矿床SHRIMP锆石U-Pb定年及其意义

小红山钒钛磁铁矿床是近年内蒙古北山地区新发现的一个中型钒钛磁铁矿床,含矿辉长岩体侵位于蓟县系平头山组,岩体具全岩矿化,工业矿体主要赋存于中粗粒辉长岩中。采用SHRIMP锆石U-Pb定年方法对小红山中粗粒辉长岩体进行了年代学研究,获得该岩体的锆石微区原位SHRIMP U-Pb年龄为424±6Ma,表明小红山钒钛磁铁矿成岩成矿事件发生于中志留世。该时期钒钛磁铁矿床的发现,揭示了北山地区早古生代处于陆缘裂谷环境,这对研究和认识北山地区地质构造演化及开展岩浆矿床找矿具有重要意义。     

内蒙古小红山钒钛磁铁矿床成矿特征及成因探讨

小红山矿床与河北大庙钒钛铁矿床同产在天山-阴山造山带的两端和相近的纬度上,华力西早期辉长岩为赋矿主岩体,地表多呈脉状贯入型钒钛磁铁矿分布,深部多以隐伏的岩浆-分异型似层状钒钛磁铁矿产出。矿体较稳定、品位较富。矿石矿物以磁铁矿和钛铁矿为主,共伴生有V等元素。属于一种岩浆-分异和分凝-贯入叠加复合型的钒钛磁铁矿类型,为介于攀枝花式和大庙式钒钛磁铁矿特征之间一种新的成矿类型。此类型矿化的发现,对寻找同种钒钛磁铁矿类型具有一定的现实意义。     

秦岭杂岩中侵入体的地球化学及年代学特征

正秦岭造山带由华北板块和扬子板块及其间的微板块经过多期次不同构造运动叠加复合形成,是我国中央造山带的重要组成部分,其形成和演化过程记录了华北板块和扬子板块元古代俯冲消减、古生代弧-陆碰撞和早中生代的陆内造山运动的重要信息(Meng Qingren et al., 2000)。秦岭杂岩(原秦岭岩群)作为秦岭造山带最古老的前寒武纪结晶基底,是研究秦岭造山带构造演化的重要窗口。前人对侵入其中的小型岩体、岩脉研究较少。本次研究     

新疆若羌县沙河湾钛磁铁矿地质特征及找矿意义

沙河湾钛磁铁矿产于笔架山基性-超基性岩带的东部,赋存于层状辉长岩中,目前发现矿体数十条,长数百米至一千米不等,探获资源量达中型规模,为典型的岩浆分异熔离型钛磁铁矿床。在地球物理特征上表现为磁异常与地表基性岩体相吻合,高磁异常中心呈层状展布,与地表钛磁铁矿体分布一致,说明该区仍具找矿潜力。笔者试着从成矿地质特征方面对沙河湾钛磁铁矿进行矿床成因分析,为在该带上寻找同类型矿床提供一定的借鉴。     

西昆仑南屏雪山地区奥陶纪弧型辉长岩的发现及其地质意义

西昆仑造山带早古生代岩浆岩记录了区内原特提斯构造演化的关键信息。近来,笔者所在课题组在西昆仑造山带南部南屏雪山地区新发现一套奥陶纪辉长岩。LA-MC-ICPMS锆石U-Pb定年结果显示辉长岩形成于476~471 Ma,为早奥陶世岩浆活动的产物。岩石化学特征显示,辉长岩具有高Al₂O₃（14.32%~16.91%）和TiO₂（1.20%~2.53%）,贫P₂O₅（0.22%~0.55%）和低碱（Na₂O+K₂O = 4.03%~5.84%）特征,SiO₂（52.27%~56.65%）与MgO（2.98%~7.59%）变化较大;其中部分样品表现出富Nb特征,相对高SiO₂（53.08%~56.86%）,低MgO（2.98%~6.05%）,高TiO₂（1.48%~2.54%）和Nb（7.64×10^-6~14.08×10^-6）。南屏雪山辉长岩富集大离子亲石元素（Rb、Th、U、K）和轻稀土元素,明显亏损Nb、Ta、Sr等元素,表现出典型岛弧型岩浆岩特征。Sr-Nd同位素方面,南屏雪山辉长岩显示出亏损的ε_Nd（t）值（2.84~4.04）。综合研究表明,南屏雪山奥陶纪弧型辉长岩形成于受俯冲板片熔体交代的亏损地幔发生不同程度的部分熔融过程。结合区域地质特征,我们认为麻扎尔—甜水海地体内大陆弧辉长岩（约530 Ma）、富Nb弧型辉长岩（476~471 Ma）和OIB型枕状玄武岩（约465 Ma）的特殊岩石组合记录了原特提斯洋南向俯冲过程中,俯冲板片后撤诱发的弧后伸展过程。

     

秦岭岩群（杂岩）中侵入体的年代学、地球化学特征及其对古生代构造运动的启示

秦岭岩群（杂岩）是北秦岭构造带主要的构造岩石单元之一,对研究华北板块和扬子板块之间的构造演化具有重要意义。本文对秦岭岩群杂岩中的4个侵入体（包括片麻状变辉长岩、糜棱岩化花岗岩、片麻状石英闪长岩和片麻状花岗岩）进行了地球化学、锆石U-Pb年代学和Lu-Hf同位素分析,以探讨北秦岭在古生代的岩浆作用。结果表明4个样品富集LREE,亏损HREE;片麻状变辉长岩的锆石年龄集中在481Ma~471Ma,糜棱岩化花岗岩锆石年龄具有486Ma的强峰,代表早古生代岩浆热事件;片麻状石英闪长岩和片麻状花岗岩的锆石年龄分别在417Ma~384Ma之间和400Ma~388Ma之间,代表秦岭岩群（杂岩）在晚古生代早期经历的岩浆活动事件。片麻状变辉长岩的εHf(t)值在-5.64~-3.32之间,代表其原岩来自古老地壳;片麻状石英闪长岩和片麻状花岗岩的εHf(t)值均为正值,分别在7.62~11.84和7.50~10.70之间变化,表明其原岩来自亏损地幔。     

Relative timing of igneous intrusion in the Eucalyptus area,northeastern Yilgarn Block,Western Australia

Field studies in the Eucalyptus area, northeastern Yilgarn Block have shown intrusive and extrusive rocks in an Archaean greenstone sequence to be comagma‐tic, and have suggested the sequence of subsequent granitoid intrusion and gold mineralisation. Andesitic volcanic rocks and related subvolcanic granodiorite porphyry and epiclastic sediments were followed by tholeiitic basalt with gabbro/dolerite sills and dykes, which were in turn succeeded by high‐Mg basalt with associated peridotite intrusions. Large, irregular gabbro and peridotite intrusions, which are inferred to represent subvolcanic magma chambers, occur in lower stratigraphic levels, whereas comformable subvolcanic sills occur in higher stratigraphic levels. Granodiorite plutons were followed by adamellite plutons; at least some gold mineralisation was contemporaneous with granitoid emplacement.     

The Narryer Gneiss Complex of the Yilgarn Block, Western Australia: a segment of Archaean lower crust uplifted during Proterozoic orogeny

The Narryer Gneiss Complex of the Yilgarn Block is a key segment of the Western Australian Precambrian Shield. It is a regional granulite facies terrain comprised of predominantly quartzo-feldspathic gneisses derived from granitic intrusions c. 3.6–3.4 Ga old. Granulite facies metamorphism occurred c. 3.3 Ga ago, and conditions of 750–850°C and 7–10 kbar are estimated for the Mukalo Creek Area (MCA) near Errabiddy in the north. The P–T path of the MCA has been derived from metamorphic assemblages in younger rocks that intruded the gneisses during at least three subsequent events, and this path is supported by reaction coronas in the older gneisses. There is no evidence for uplift immediately following peak metamorphism of the MCA, and a period of isobaric cooling is inferred from the pressures recorded in younger rocks. Pressures and temperatures estimated from metadolerites, which intruded the older gneisses during ‘granite–greenstone’tectonism at about 2.6 Ga and during early Proterozoic thrusting show that the Errabiddy area remained in the lower crust, although it was probably reheated during the younger events. Isothermal uplift to upper crustal levels occurred at c. 1.6 Ga ago, and was followed by further deformation and patchy retrogression of high-grade assemblages. The effects of younger deformation, cooling and reheating can be discerned in the older gneisses, but as there has been no pervasive deformation or rehydration, the minerals and microstructures formed during early Archaean granulite facies metamorphism for the most part are retained. The MCA remained in the lower crust for about 1700 Ma following peak metamorphism and some event unrelated to the original metamorphism was required to exhume it. Uplift occurred during development of the Capricorn Orogen, when some 30–35 km were added to the crust beneath the Errabiddy area. The recognition of early Proterozoic thrusting, plus crustal thickening, suggests that the Capricorn Orogen is a belt of regional compression which resulted from convergence of the Yilgarn and Pilbara Cratons.     

Geochemistry, Petrogenesis and Metallogenesis of the Panzhihua Gabbroic Layered Intrusion and Associated Fe-Ti-V Oxide Deposits, Sichuan Province, SW China

The Panzhihua gabbroic layered intrusion is associated withthe 260 Ma Emeishan Large Igneous Province in SW China. Thissill-like body hosts a giant Fe–Ti–V oxide depositwith 1333 million ton ore reserves, which makes China a majorproducer of these metals. The intrusion has a Marginal zoneof fine-grained hornblende-bearing gabbro and olivine gabbro,followed upward by Lower, Middle, and Upper zones. The Lowerand Middle zones consist of layered melanogabbro and gabbrocomposed of cumulate clinopyroxene, plagioclase, and olivine.These zones also contain magnetite layers. The Upper zone consistschiefly of leucogabbro composed of plagioclase and clinopyroxenewith minor olivine. Most rocks in the body show variable-scalerhythmic modal layering in which dark minerals, primarily clinopyroxene,dominate in the lower parts of each layer, and lighter minerals,primarily plagioclase, dominate in the upper parts. The oxideores occur as layers and lenses within the gabbros and are concentratedin the lower parts of the intrusion. Ore textures and associatedmineral assemblages indicate that the ore bodies formed by verylate-stage crystallization of V-rich titanomagnetite from animmiscible oxide liquid in a fluid-rich environment. The rocksof the Panzhihua intrusion become more evolved in chemistryupward and follow a tholeiitic differentiation trend with enrichmentin Fe, Ti, and V. They are enriched in light rare earth elementsrelative to heavy rare earth elements, and exhibit positiveNb, Ta, and Ti anomalies and negative Zr and Hf anomalies. Thesilicate rocks and oxide ores of the Panzhihua intrusion formedfrom highly evolved Fe–Ti–V-rich ferrobasaltic orferropicritic magmas. The textures of the ores and the abundanceof minor hydrous phases indicate that addition of fluids fromupper crustal wall-rocks induced the separation of the immiscibleoxide melts from which the Fe–Ti–V oxide ore bodiesin the lower part of the intrusion crystallized. KEY WORDS: magnetite; Fe–Ti-rich gabbro; layered intrusion; Panzhihua; SW China     

Gold distribution and lithogeochemical discrimination of residual regolith and transported overburden,Minotaur gold deposit,Lake Lefroy,Western Australia

Abstract

The Yilgarn Craton of Western Australia hosts a number of Cenozoic paleochannels, which have been incised into the underlying Paleozoic and Precambrian rocks, filled with sediments and subsequently weathered. The paleochannels are of particular interest in mineral exploration as they may not only host placer-type deposits but also overlie significant supergene and primary mineralisation. Paleochannels also pose particular challenges during exploration as they mask underlying geochemical anomalies, including gold and pathfinder elements. This study investigates a method of distinguishing transported overburden from residual regolith utilising a combination of field and laboratory-based techniques. At the Minotaur deposit, the residual regolith and transported overburden are mineralogically similar, although the presence of biotite, chlorite and muscovite is more characteristic of the residual regolith. Geochemically, Zr, Ti, Co and Sc ratios form distinct groupings allowing more confident discrimination of transported overburden from the underlying residual regolith units. The presence of a distinct gold depletion zone at the redox front was also identified to be a feature of the Minotaur deposit, with Au enrichment occurring above (within transported overburden) and below (within saprolite) the redox front, similar to other gold deposits on Lake Lefroy. The lithological, stratigraphic and Au-enrichment characteristics at Minotaur have also been compared with regional studies and suggest the long-lived impact of paleovalleys on the depositional systems and Au distribution of Lake Lefroy. This work provides a basis for future studies of the region in particular the variation of depositional sequences within regional paleochannel networks.     

基于3DMine软件的地质统计学在洋县毕机沟钒钛磁铁矿资源量计算中的应用

毕机构钒钛磁铁矿床是陕南目前正在开发利用的钒钛磁铁矿床,矿体产出于辉长岩中,属岩浆分异—后期热液改造型钒钛磁铁矿床,本文以3DMine软件为操作平台,运用地质统计学法,通过数据整理—建库—半变异函数分析—普通克里格插值—资源储量计算等步骤,对毕机构矿床进行了资源储量计算,论证了合适的圈矿工业指标。充分体现了地质统计学法在复杂矿区资源储量计算过程中较传统资源储量计算方法表现出的优势和便利。     

X射线荧光光谱法测定钒钛磁铁矿石中的主次量组分

采用熔融玻璃片制样,选用ZSX Primus Ⅱ X射线荧光光谱仪对钒钛磁铁矿样品中的V₂O₅、TiO₂、TFe、CaO、MgO、Al₂O₃、SiO₂、P₂O₅、MnO等组分进行测定,分析结果与标准值和及化学值相吻合,10次测定的相对标准偏差小于10%。     

云开地区早古生代竹雅-石板辉长岩锆石U-Pb定年与Lu-Hf同位素特征

华夏地块西段的云开地区出露少量早古生代基性侵入岩,多以小岩株状侵入前寒武纪变质地层或与同期片麻状花岗岩共生,岩石类型主要为辉长岩和苏长辉长岩。LA-ICP-MS锆石U-Pb测年显示,信宜竹雅和高州石板辉长岩结晶年龄约为445Ma。辉长岩岩石地球化学以富MgO、CaO,相对贫TiO_2为特征,具有极低的稀土元素总量(∑REE=20.8×10~(-6)~26.6×10~(-6)),轻稀土元素略微富集,亏损Nb、Zr、Ti、P等高场强元素。锆石ε_(Hf)(t)均为弱的负值,Hf同位素一阶段模式年龄介于1.1~1.4Ga之间,显示富集地幔源区特征。构造环境分析表明,辉长岩与火山弧玄武岩相似。综合前人研究认为,华夏地块早古生代存在一系列具典型弧火山岩特征的基性岩类,这对早古生代构造运动的认识具有重要的限定作用。     

Decompressional coronas and symplectites in granulites of the Musgrave Complex, central Australia

Abstract In granulite facies metapelitic rocks in the Musgrave Complex, central Australia, reaction between S1 garnet and sillimanite involves the development in S2 of both garnet + cordierite + hercynitic spinel + biotite and hercynitic spinel + cordierite + sillimanite + biotite. The S2 assemblages occur either in coronas and symplectites, mainly around garnet, or, in rocks in which S2 is more strongly developed, as recrystallized assemblages. Ignoring the presence of biotite and ilmenite, the mineral textures can be accounted for qualitatively by a consideration of the model system FeO-MgO-Al₂O₃-SiO₂ (FMAS); the textural relationships accord with decompression accompanying the change from S1 to S2. However, since biotite and ilmenite are involved in the assemblages, the parageneses are better accounted for in terms of equilibria in the expanded model system K₂O-FeO-MgO-Al₂O₃-SiO₂-H₂-TiO₂-Fe₂O₃ (KFMASHTO), i.e. AFM + TiO₂+ Fe₂O₃. The coronas reflect the tectonic unroofing of at least part of the Musgrave Complex from peak S1 conditions of about 8 kbar to S2 conditions of about 4 kbar.     

福建李家坊金矿床磁铁矿成因及其对金矿化过程的指示

福建泰宁李家坊金矿床位于武夷山成矿带中段,为闽西北何宝山矿田内新发现的一个中型金矿床,成因类型尚未明确。磁铁矿是该矿床中常见的氧化物,文章应用磁铁矿微量元素特征对李家坊金矿床成矿过程与成因类型进行约束。基于野外地质踏勘和钻孔岩芯编录,结合室内详细的岩相学观察,依据磁铁矿的结构和矿物共生组合,文章将其分为4种类型（Mt1a、Mt1b、Mt2和Mt3）。其中,Mt1a位于铜金矿脉边缘,呈板柱状,与绿泥石共生; Mt1b位于铜金矿脉边缘,呈自形-半自形粒状,与绿泥石-赤铁矿共生; Mt2位于铜金矿脉中,呈脉状产出,穿插早阶段的石英-黄铁矿脉,与绿泥石-绿帘石共生; Mt3位于铜金矿脉中,呈半自形-他形粒状,与绿帘石-赤铁矿共生,被后阶段黄铜矿包裹、交代。金主要以自然金和银金矿的形式赋存于Mt3中。原位微区分析结果表明,李家坊金矿不同类型磁铁矿均属于热液型磁铁矿。此外,从Mt1a型到Mt3型磁铁矿,w（Ti）呈逐渐降低的趋势,指示热液流体逐渐向低温条件演化; w（V）表现出先降低后升高再降低的变化规律,暗示热液流体的氧逸度有明显波动,但总体呈升高趋势。磁铁矿的显微结构和化学组成具矽卡岩型矿化特征,是判断矿床成因类型的证据。其中,Mt3型磁铁矿与Au矿化密切相关,其矿物组合与微量元素特征可指示金在低温高氧逸度的环境下沉淀。     

老挝帕莱通铁矿床西矿段磁铁矿地球化学特征及其成矿意义

帕莱通铁矿床是老挝万象—呵叻中新生代盆地中最大规模的铁矿床,分为东、西2个矿段,西矿段为豆状、块状富磁铁矿矿体,东部则主要发育角砾状贫赤铁矿矿体。其中,西矿段主要产于新生代富铁质玄武岩中。文章对西矿段中豆状、块状磁铁矿进行了详细的野外地质调查和显微结构分析,发现块状磁铁矿具有细粒他形结构特征,豆状磁铁矿具有球粒同心圆状结构特征。对较为新鲜的磁铁矿进行电子探针(EPMA)以及激光剥蚀电感耦合等离子质谱(LA-ICP-MS)分析显示:帕莱通铁矿床磁铁矿TiO_2-Al_2O_3-MgO三角图落入岩浆岩区域;微量元素富集V、Ti、Cr、Co、Ni及Ga等元素,亏损Sr、Ba及Mg等不相容元素;w(Co)和w(Ni)较高,且较高的Ni/Co比值可以反映成因与深源物质;w(Ti)较高且Ni/Cr比值≤1,在Ti-Ni/Cr图中落入了热液型磁铁矿的范围;Ga-Sn图解表明磁铁矿属于斑岩型热液成因;(Ca+Al+Mn)-(Ti+V)或Ni/(Cr+Mn)-(Ti+V)成因判别图显示该矿床兼具Kiruna型和斑岩型矿床的特征;w(V)表明磁铁矿在较低氧化环境中形成;(Al+Mn)-(Ti+V)形成温度判别图表明磁铁矿形成温度处于300～500℃范围内。文章认为帕莱通铁矿床成矿物质主要源于岩浆演化作用形成的富铁流体,后期由于岩浆热液流体的交代作用,使得磁铁矿具有了热液成因的特征。岩浆型矿床类型在老挝及邻区分布较为广泛,研究帕莱通铁矿的成因,对于总结区域成矿规律,指导同类型矿床找矿预测具有重要意义。     

阜平杂岩中低品位磁铁矿的形成与深熔作用的关系

在中-高级变质的阜平杂岩中可以形成低品位磁铁矿.除碎屑岩中继承的磁铁矿外,新生变质磁铁矿多呈斑晶,可出现于多种岩石类型,如变基性岩、中性岩、酸性岩和变沉积岩中,表明新生磁铁矿的形成不受层位控制.磁铁矿可由物理重结晶和化学反应2种形式形成,重结晶过程主要为矿物颗粒的加粗,但没有明显的脱水反应.变质化学反应形成的磁铁矿与各单元所经受的后期变质事件改造有关,这类磁铁矿的出现与岩石中TFe的含量没有必然的联系,关键在于变质反应中是否有适量的铁组分的迁移和富集.变质反应过程中,初期黑云母变质转化形成角闪石,即变质反应不全是脱水或吸水过程,表明阜平杂岩主要的变质过程发生在含水体系中.在进一步的变质改造中,黑云母、角闪石可深熔转化形成磁铁矿.在片麻岩的含水熔融过程中,Mg、Ca优先迁移,而Fe(Ti,Al)迁移微弱,造成Fe(Ti,Al)与Mg组分的分离,残留的相对富铁组分形成磁铁矿、钛铁矿.磁铁矿结晶时没有明显的挤压或剪切,张应力可能占主导地位,相应的深熔作用主要发生在构造静应力期或体系略微抬升的过程中.     

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.     

攀西裂谷带内超基性碱性岩和层状辉长岩^40Ar-^39Ar年龄——以鸡街、大向坪和太和岩体为例

对分布在攀西古裂谷带内的禄丰县鸡街和大向坪超基性碱性环状杂岩体中霞辉岩，以及西昌太和层状辉长岩等两类岩石进行全岩^40Ar-^39Ar坪年龄测定，结果表明鸡街岩体和大向坪岩体中霞辉岩年龄范围在214～193Ma，相当于晚三叠世，属于印支期。总体上，超基性碱性环状杂岩的侵位时间略晚于含矿辉长岩；太和层状辉长岩^40Ar-^39Ar坪年龄，由于过剩Ar等原因的扰动，使其年龄值远远高于成岩年龄。暗示全岩或辉石单矿物等不适合作为攀西地区层状辉长岩定年的对象。