Kinematic analysis using AMS data from a deformed granitoid

This study highlights the usefulness of anisotropy of magnetic susceptibility data from a deformed granitoid in deciphering its kinematic evolution vis-à-vis shear zone. Data are presented from the Chakradharpur Granitoid (CKPG) that lies to the north of the northerly dipping, ENE–WSW striking Singhbhum Shear Zone (SSZ; eastern India). Whilst the foliation recorded in the field in some parts of the granitoid is parallel to the SSZ, the magnetic foliation is N54°E/90° (mean orientation). It is suggested that the magnetic fabric provides a window into an evolutionary stage prior to the final shearing/thrusting event, the evidence of which is preserved on the mesoscopic scale. It is envisaged that during the initial stages of deformation there was simple shear along the evolving SSZ that resulted in sinistral strike-slip movement; the vorticity axis at this stage was steeply plunging and sense of rotation was anticlockwise. Space was generated in a direction ∼N25°E (perpendicular to maximum-Instantaneous Stretching Axis) into which CKPG emplaced synchronously with regional deformation and evolving SSZ. With continued deformation, there was thrusting along the SSZ. The vorticity axis flipped to a sub-horizontal orientation, thus leading to the development of down-dip stretching lineations and sheath folds within the SSZ. However, at the same time, the vorticity axis responsible for fabric evolution within the syntectonically crystallizing/cooling CKPG was steeply plunging with clockwise rotation. The magnetic foliation (mean orientation N54°E/90°) developed during the final stage of syntectonic crystallization. However, deformation in the region and thrusting along the SSZ continued even after the CKPG had fully crystallized and solidified, which led to the development of the ENE–WSW striking mesoscopic foliation that is parallel with the SSZ. We propose that the angle between the magnetic foliation and the SSZ/foliation recorded in the field, enables to decipher the kinematic vorticity number of flow responsible for fabric evolution of the CKPG. It is concluded that transpression was an important mechanism, and during regional deformation, whilst the SSZ developed structures by dominantly simple shear, the CKPG underwent dominantly pure shear.     

大兴安岭南段热液脉状矿床的流体包裹体和稳定同位素特征:对矿床成因的启示

大兴安岭南段发育大井、双尖子山、布金黑、拜仁达坝、维拉斯托等多个具有典型后生特征的热液脉状铅锌银锡多金属矿床。为了查明上述矿床在成矿流体、成矿物质等方面的特征与差异,进而总结大兴安岭南段热液脉状矿床成矿作用特点,本次研究在野外地质调研的基础上,对上述矿床进行了流体包裹体、激光拉曼和氢氧硫同位素的研究,并取得了如下主要的认识:(1)双尖子山银多金属矿床成矿流体属简单盐水体系热液,维拉斯托和布金黑矿床成矿流体属富碳质盐水体系热液,而大井铜矿成矿流体则为含子矿物的不均匀盐水体系热液;(2)大井、布金黑、拜仁达坝和维拉斯托等矿床早期成矿流体均来自于岩浆热液,但布金黑、拜仁达坝和维拉斯托矿床成矿流体在运移过程中明显地受到了大气降水和地层中有机质的影响;(3)大兴安岭南段多数热液脉状多金属矿床矿石硫同位素δ34S值具有岩浆来源特点,个别矿床硫同位素δ34S值偏高可能是由复杂的岩浆源区性质及地层硫混入所引起。总的来说,大兴安岭南段不同热液脉状矿床在物质来源和流体演化方面的差异明显,而这也体现了该区中生代热液成矿作用的多样性和复杂性特点。     

Deciphering a multistage history affecting U–Cu(–Fe) mineralization in the Singhbhum Shear Zone,eastern India,using pyrite textures and compositions in the Turamdih U–Cu(–Fe) deposit

The ～200-km-long intensely deformed Singhbhum Shear Zone (SSZ) in eastern India hosts India’s largest U and Cu deposits and related Fe mineralization. The SSZ separates an Archaean cratonic nucleus to the south from a Mesoproterozoic fold belt in the North and has a complex geologic history that obscures the origin of the contained iron-oxide-rich mineral deposits. This study investigates aspects of the history of mineralization in the SSZ by utilizing new petrographic and electron microprobe observations of pyrite textures and zoning in the Turamdih U–Cu(–Fe) deposit. Mineralization at Turamdih is hosted in intensively deformed quartz–chlorite schist. Sulfides and oxides include, in inferred order of development: (a) magmatic Fe(–Ti–Cr) oxide and Fe–Cu(–Ni) sulfide minerals inferred to be magmatic (?) in origin; followed by (b) uranium, Fe-oxide, and Fe–Cu(–Co) sulfide minerals that predate most or all ductile deformation, and are inferred to be of hydrothermal origin; and (c) Fe–Cu sulfides that were generated during and postdating ductile deformation. These features are associated with the formation of three compositionally and texturally distinct pyrites. Pyrite (type-A), typically in globular–semiglobular composite inclusions of pyrite plus chalcopyrite in magnetite, is characterized by very high Ni content (up to 30,700 ppm) and low Co to Ni ratios (0.01–0.61). The textural and compositional characteristics of associated chalcopyrite and rare pyrrhotite suggest that this pyrite could be linked to the magmatic event via selective replacement of magmatic pyrrhotite. Alternatively, this pyrite and associated sulfide inclusions might be cogenetic with hydrothermal Fe-oxide. Type-B pyrite that forms elongate grains and irregular relics and cores of pyrite with high Co contents (up to 23,630 ppm) and high Co to Ni ratios (7.2–140.9) are interpreted to be related to hydrothermal mineralization predating ductile deformation. A third generation of pyrite (type C) with low Co, low Ni, and moderate Co to Ni ratios (0.19–13.93) formed during and postdating the ductile deformation stage overgrowing, replacing, and surrounding type-B pyrite. The textural evolution of pyrite parallels the tectonometamorphic evolution of the shear zone demonstrating grain elongation during progressive ductile deformation and prograde metamorphism, annealing at the peak metamorphic condition, porphyroblastic growth at the retrograde path and cataclasis following porphyroblastic growth. Compositional characteristics of hydrothermal pyrite and available geological information suggest that the U–Cu(–Fe) deposit at Turamdih might be a variant of the Fe oxide (–Cu–U–rare earth elements) family of deposits.     

新疆阿尔泰地区断裂控矿的多重分形机理

新疆阿尔泰地区断裂构造非常发育并对热液成矿有重要控制作用。分形分析表明该区断裂和矿床的空间分布均为多重分形分布,断裂的奇异指数为1.597～2.403,多重分维谱值为0.551～1.706;矿床的奇异指数为0.925～2.287,分维谱值为0.138～1.363。断裂的高的奇异指数和分维谱值表明该区断裂构造具有较高的成熟度和连通性,有利于提高岩石渗透性、促进流体流动和热液矿床的形成。断裂构造的多重分形分布导致该区热液成矿作用的多重分形分布。断裂体系演化过程中不同断裂部位变形和渗透性存在明显差异,数值模拟表明断裂与岩性和流体之间存在强烈的耦合作用并导致不同岩性的断裂具有明显不同的断裂渗透率。断裂-脉体系演化是一个自组织过程,元胞自动机模拟表明只有在分形渗透临界以上连通性较好的脊骨断裂部位是最有利于流体流动和成矿作用的。因此只有在部分有利的断裂部位才能形成矿床,并导致了断裂构造的奇异指数和多重分维谱值明显高于矿床。     

Fault/fracture density and mineralization: a contouring method for targeting in gold exploration

A widely observed correlation between high fracture density and mineralization throughout terranes and geological time indicates a fundamental underlying ore-forming process. In Archaean greenstone-hosted deposits, high-density fracturing was accompanied by enhanced fluid flow during fault/fracture network development, producing regional-scale fluid pressure gradients that focussed hydrothermal fluids into preferentially fractured areas. Fracture density is both increased and decreased during faulting and fault healing, and fracture density accumulates over time, in zones of high palaeo-fluid flow. Localised zones where the density of fracturing is increased by deformation, become permeability nodes for migrating hydrothermal fluids leading to large zones of alteration and gold precipitation. The Ora Banda mining centre in Western Australia contains significant gold deposits that appear to demonstrate a close association between high-density fracturing and gold precipitation. Fracture density in the Ora Banda mines was enhanced by fault–fault intersections, fault–contact intersections and changes in fault geometry. The mine-scale relationships between fracture density and gold mineralization are repeated at smaller and larger scales, hence these relationships may be used in targeting for gold exploration. Contouring the density of fracturing in a region provides a semi-quantitative way to rank areas for exploration and uses data from mapping, drilling and high-quality geophysical data as a basis for analyses. Fracture density contouring is complementary to other prospectivity-analysis methods.     

Complexity gradients in the Yilgarn Craton: Fundamental controls on crustal-scale fluid flow and the formation of world-class orogenic-gold deposits

Fractal-dimension analysis is an effective means of quantifying complex map patterns of structures and lithological contacts, which are conduits for hydrothermal fluid flow during the formation of orogenic-gold deposits. In this study, fractal dimensions, calculated on a 10 km grid across a geologic map of the Yilgarn Craton of uniform data quality, highlight relationships between geologic complexity and the location and size of Archaean orogenic-gold deposits. In the Kalgoorlie Terrane and Laverton Tectonic Zone, the largest gold deposits occur along steep gradients defined by fractal-dimension values. These steep gradients in the greenstone belts occur between massive sedimentary rock sequences of low complexity, and volcanic and intrusive rock units with more complex map patterns. The formation of world-class orogenic-gold deposits requires that hydrothermal fluids become focused from a large volume of well-connected rocks at depth, towards narrow, high-permeability zones near the location of deposit formation. Connectivity is indirectly related to permeability, and the degree of connectivity is related to the density and orientation of fluid pathways, which are quantified in map patterns using fractal-dimension analysis. Thus, fractal dimensions are a measure of the potential for increased connectivity and the likelihood of increased permeability. Greater complexity, as measured by larger fractal dimensions, implies that a certain area has the potential to produce more interconnected pathways, or zones of high connectivity. Therefore, the steep complexity gradients defined in the Kalgoorlie Terrane and Laverton Tectonic Zone correspond to areas that focused large volumes of hydrothermal fluid and enhanced the potential for significant gold mineralisation. Fractal-dimension analysis thus provides a link between empirical map features and the processes that have enhanced hydrothermal fluid flow and resulted in the formation of larger orogenic-gold deposits.     

Application of stress mapping in cross‐section to understanding ore geometry,predicting ore zones and development of drilling strategies

Stress mapping is a numerical modelling technique used to determine the distribution and relative magnitude of stress during deformation in a mineralised terrane. It is based on the general principle that fluid flow in the Earth's crust is primarily related to pressure gradients. It is best applied to epigenetic hydrothermal mineral deposits, where fluid flow and fluid flux are enhanced in dilational sections of structures and in sites of enhanced rock permeability due to high fracture density. These are defined by sites of low minimum principal stress (σ₃). Most stress mapping is carried out in two dimensions in plan view using geological maps. This is suitable for terranes with steeply dipping lithostratigraphy and structures in which the distribution of mineral deposits is largely controlled by fault structures portrayed on the maps. However, for terranes with gently dipping sequences and structures, and for situations where deposits are sited in and near the hinges of complex fold structures, stress mapping in cross‐section is preferable. The effectiveness of stress mapping is maximised if mineralisation was late in the evolutionary history of the host terrane, and hence the structural geometry of the terrane and contained deposits were essentially that expressed today. The orientation of syn‐mineralisation far‐field stresses must also be inferred. Two examples of orogenic gold deposits, which meet the above criteria, are used to illustrate the potential of stress mapping in cross‐section. Sunrise Dam, located in the Archaean Yilgarn Craton, is a lode‐gold deposit sited in a thrust‐fold belt. Stress mapping illustrates the heterogeneity of stress distribution in the complex structural geometry of the deposit, and predicts the preferential siting of ore zones around the intersections of more steeply dipping, linking thrusts and banded iron‐formation units, and below the controlling more gently dipping basal thrust, the Sunrise Shear. The Howley Anticline in the Pine Creek block hosts several Palaeoproterozoic gold deposits, sited in complex anticlinal structures in greywacke sequences. Stress mapping indicates that gold ores should develop in the hinge zones of symmetrical anticlines, in the hinge zones and more steeply dipping to overturned limbs of asymmetric anticlines, and in and around thrusts in both anticlines and parasitic synclines. The strong correlation between the predictions of the stress mapping, based on the distribution of low σ₃, and the location of gold ores emphasises the potential of stress mapping in cross‐section, not only as an exploration tool for the discovery of additional resources or deposits, but also as a test of geological models. Knowledge of the potential siting of gold ores and their probable orientations also provides a guide to drilling strategies in both mine‐ and regional‐scale exploration.     

西南三江地区沉积岩容矿型铅锌矿成矿特征和成矿规律

以沉积岩为容矿围岩的铅锌矿床种类繁多,储量巨大,是世界上铅、锌资源的主要来源,因此,一直受到矿床学家和地质工作者的重视.近年来,三江特提斯地区因其得天独厚的成矿条件和丰富的金属矿产资源而成为矿床学界研究的热点和前沿.研究区广泛发育沉积岩容矿型铅锌矿床,空间上与自北向南发育的各新生代沉积盆地密切相伴;成矿发生在喜马拉雅碰撞造山挤压向伸展的构造转换阶段,成矿时代主要集中在41～20 Ma之间;矿床主要赋存在二叠统和三叠统灰岩地层中;矿床分布受区域逆冲-推覆系统控制,表现为近NS向断层控制矿床分布的区域性特点;矿化主要表现为热液充填逆冲断层上盘中各次级构造、裂隙和开放空间成矿;围岩蚀变较弱,主要为方解石化;主成矿元素Pb+Zn外,往往还伴生大量诸如Ag、Sr、Sb、Cu等元素.基于区域成矿特征和成矿规律,总结了找矿标志并指明了找矿方向.     

甘肃中秦岭成矿带成矿规律及找矿远景

文章在全面揭示甘肃中秦岭成矿带23种矿产成矿规律的基础上,圈定找矿远景区。通过成矿地质背景和成矿过程研究,建立主要矿床类型的成矿模式;以主要地质事件和成矿作用为主线,归纳矿床的时空分布规律和矿床成矿系列;通过矿床成矿系列与成矿模式相结合的方法预测找矿远景区。结果表明,浅成中-低温热液型铅锌矿由有地幔流体和岩浆流体参与的变质流体和建造水混合或沸腾形成;岩浆热液型金矿由源于下地壳的岩浆热液与大气水混合和沸腾形成,或由源于中地壳的岩浆热液与变质水混合后再与建造水或大气水混合形成;研究区存在7个矿床成矿系列。结论认为,中秦岭华力西期—印支期含矿流体矿床成矿系列分布区中,夏河-两当弧形断裂与近东西向断裂的交汇部位是该矿床成矿系列的成矿有利部位,中秦岭华力西期—印支期岩浆相关矿床成矿系列分布区中,中酸性岩体与近东西向断裂耦合部位是该成矿系列的成矿有利部位。文章圈定找矿远景区12处。     

First results on the LPO-derived seismic properties of iron ores from the Quadrilátero Ferrífero region, southeastern Brazil

The role of hydrothermal fluids in assisting the activity of strike-slip faults is investigated using a range of new geological, geophysical, and geochemical data obtained on the Argentat fault, Massif Central, France. This fault zone, 180-km-long and 6 to 8 km-width, has experienced coeval intense channeling of hydrothermal fluids and brittle deformation during a short time span (300–295 Ma). According to seismic data, the fault core is a 4-km-wide, vertical zone of high fracture density that rooted in the middle crust (~ 13 km) and that involved fluids in its deeper parts (9–13 km depth). If stress analyses in the fault core and strain analyses in the damage zone both support a left-lateral movement along the fault zone, it is inferred that hydrothermal fluids have strongly influenced fault development, and the resulting fault has influenced fluid flow. Fluid pressure made easier fracturing and faulting in zones of competent rocks units and along rheological boundaries. Repeated cycles of increase of fault-fracture permeability then overpressure of hydrothermal fluids at fault extremity favored strong and fast development of the crustal-scale strike-slip fault. The high permeability obtained along the fault zone permitted a decrease of coupling across the weak fault core. Connections between shallower and lower crustal fluids reservoirs precipitate the decrease of fault activity by quartz precipitation and sulfides deposition. The zones of intense hydrothermal alteration at shallows crustal levels and the zones of fluid overpressure at the base of the upper crust both controlled the final geometry of the crustal-scale fault zone.     

Cretaceous crustal thinning in North Africa: Implications for magmatic and thermal events in the Eastern Tunisian margin and the Pelagic Sea

The integrated use of geological, geophysical, and geochemical data from Eastern Tunisia onshore and offshore samples indicate a crustal thinning induced from the Tethyan rifting. This is responsible for the subsequent evolution of the North African passive margin during the Late Cretaceous, and the creation of the fold–thrust belt and associated foreland deformations. This thinned crust was an area of mantle upwelling that favoured the increase of isotherms, the uprise of basalt magma, and the circulation of hydrothermal fluids. The Cretaceous magmatism generated a major hydrothermal event characterised by the circulation of hot fluids along faults and a relatively high heat flow in the basin. Temperature elevation and hydrothermal conditions led to alteration of basalts and generated a new mineral equilibrium around the enclosing sedimentary deposits.     

Cretaceous crustal thinning in North Africa: Implications for magmatic and thermal events in the Eastern Tunisian margin and the Pelagic Sea

The integrated use of geological, geophysical, and geochemical data from Eastern Tunisia onshore and offshore samples indicate a crustal thinning induced from the Tethyan rifting. This is responsible for the subsequent evolution of the North African passive margin during the Late Cretaceous, and the creation of the fold–thrust belt and associated foreland deformations. This thinned crust was an area of mantle upwelling that favoured the increase of isotherms, the uprise of basalt magma, and the circulation of hydrothermal fluids. The Cretaceous magmatism generated a major hydrothermal event characterised by the circulation of hot fluids along faults and a relatively high heat flow in the basin. Temperature elevation and hydrothermal conditions led to alteration of basalts and generated a new mineral equilibrium around the enclosing sedimentary deposits.     

巴音戈壁盆地塔木素铀矿床含矿砂岩成岩作用类型、演化序列及其对铀成矿的约束

勘查和研究发现部分砂岩型铀矿床中不仅有表生氧化流体作用还存在深部流体的参与,这类砂岩型铀矿床蚀变类型多样且成因复杂.塔木素砂岩型铀矿表生流体和深部流体活动都很明显,砂岩普遍固结且后生蚀变类型独特,因此,恢复成岩成矿事件及其演化过程,对揭示铀沉淀富集机理至关重要.本文通过镜下鉴定、电子探针、扫描电镜分析等,系统研究了塔木素矿床含矿砂岩成岩作用特征与后生蚀变矿物生成序列,重塑了成岩成矿事件的演化过程.研究结果显示,塔木素矿床砂岩中压实作用较弱而胶结作用很强,重结晶作用普遍,是造成目的层致密的主要原因,赤铁矿、褐铁矿化、碳酸盐化、石膏化是该地区主要的胶结类型.将该地区的成岩演化划分为沉积-早成岩阶段、早期氧化流体作用阶段、热流体改造阶段和晚期氧化流体弱改造阶段.成岩环境由弱碱性向酸性环境转变的过程中的氧化还原过渡部位是造成铀沉淀的关键,大规模的氧化作用是矿床形成的基础,后期热流体活动对早期形成的低品位铀矿石进行叠加改造,是成矿的关键环节.     

Structures and Implications for Fluid Migration in the Jiadi Carlin‐Type Gold Deposit,Guizhou Province,Southwest China

The Jiadi gold deposit is a newly discovered Carlin‐type gold deposit in the Guizhou Province, Southwest China. This deposit is structurally controlled by a shallow fold–fault superimposed system along the Lianhuashan trend. Field geological investigations, structural analysis, and mathematical research are conducted to study its structures and hydrothermal fluid flow process. Geological investigations (i.e. sections, stope, and drill hole) indicate that the structures are dominated by NE‐trending folds, NWW‐trending folds, and faults. A trend‐surface analysis of the low interformational fracture zone suggests that the overall distribution of the Lianhuashan trend is controlled by the NE‐trending Lianhuashan anticline. Nearly all primary Carlin‐type gold deposits are distributed along the southeastern flank where the fold axis changes from NE to EW. Gold orebodies are hosted by the interformational fracture zones and primarily situated at the transitions from the high‐value areas to the low‐value areas of the interformational fracture zones. A stress analysis on the hydrothermal veins indicates that they are of tenso‐shear properties. The ore‐forming elements (Au, As, Sb, Hg, and Tl) of the hydrothermal veins from the interformational fracture zones and intrusive breccia body present strong positive anomalies compared with those from the adjacent wall rocks. According to the development patterns of the ore‐forming elements and hydrothermal veins, a migration process of the ore‐forming fluids is proposed: the deeply sourced ore‐forming fluids migrated vertically to shallow crust along an intrusive breccia body, subsequently flowed horizontally along the interformational fracture zones accompanied by gold precipitation in the early stage, and finally migrated outward along steep micro‐fractures during following stages.     

Phosphate minerals as a recorder of P-T-fluid regimes of metamorphic belts: example from the Palaeoproterozoic Singhbhum Shear Zone of the East Indian shield

The Arcuate Singhbhum Shear Zone (SSZ) forms an integral part and occurs at the southern fringe of the Palaeoproterozoic North Singhbhum Fold Belt (NSFB) of the East Indian Shield. Repeated folding, ductile shearing, and accompanying hydrothermal activities in the SSZ during the late Palaeoproterozoic (ca. 1.66–1.60 Ga) orogeny resulted in a highly tectonized ensemble of rocks including a suite of peraluminous kyanite-rich quartzite (KQR). Near Kanyaluka village, the KQR shows millimetre- to decimetre-thick alternation of kyanite- and quartz-rich bands. The banded rock is intensely sheared and is cross-cut by weakly deformed to undeformed kyanite-quartz veins. In many places, kyanite-rich bands show sea-green coloured pods rich in lazulite. Textural studies reveal that deformed kyanite and quartz grains are sequentially replaced by augelite and lazulite (X_Mg > 0.97) at the terminal phase of shearing in the SSZ. Modelling of observed textures and mineral compositions with the C-Space program shows the following augelite- and lazulite-forming reactions:

1. 1.829Kyanite + 0.998P + 1.5H₂O + 0.001Ca = 1Augelite + 1.666Al + 0.001 Mg + 1.822SiO₂ + 0.002Fe + 0.0002Na

2. 1.778Kyanite + 0.667Augelite + 1.294P + 1.011 Mg + 0.011Fe + 0.0001Na = 1Lazulite + 2.833Al + 1.78SiO₂ + 0.001 Ca

Stoichiometry of the balanced chemical reactions suggests that a significant amount of P, Mg, and H₂O were added to, and Al and SiO₂ were subtracted from, the host kyanite-rich rock to produce augelite and lazulite. Experimental studies in the system Al₂O₃-SiO₂-FeO-MgO-P₂O₅-H₂O and the results of quantitative geothermobarometry suggest that lazulite and augelite were formed in a narrow temperature (440 ± 40°C) and pressure (~6.3 ± 1 kbar) range. Ductile shearing along the SSZ channelized the P- and Mg-rich fluids that metasomatized the kyanite-rich bands and veins to produce lazulite. The inferred P-T conditions can be explained by burial of the studied rock under an ~25 km-thick thrust sheet of NSFB during the Palaeoproterozoic orogenesis.     

Reappraisal of the structure of the Western Iron Ore Group, Singhbhum craton, eastern India: Implications for the exploration of BIF-hosted iron ore deposits

The middle to late Archean Iron Ore Group rocks occurring along the western margin (the Western Iron Ore basin) of the Singhbhum Granite massif in the Singhbhum craton were deformed during Iron Ore orogeny and are disposed in a horseshoe-shaped synclinal structure in the eastern part of the Indian shield. The Western Iron Ore basin hosts almost all the major high-grade iron ore deposits of eastern India. Contrary to the established view, present analysis emphasizes that the horseshoe fold in reality is a synclinorium consisting of a syncline–anticline fold pair which were later cross-folded along an east–west axis.

Structural analysis in the eastern anticline of the ‘horseshoe synclinorium’ suggests that the BIF hosting the high-grade iron ore bodies are disposed in three linear NNE–SSW trending belts, each showing an open synclinal geometry. Later cross folding produced development of widespread dome and basin pattern at the sub-horizontal hinge zones of these synclinal fold belts. The major iron ore deposits in the eastern anticline at the present level of erosion are preferentially localized within shallow elongated basinal structures only. The axis of the adjoining western syncline was similarly uplifted as partial culminations where cross-folded against E–W anticlinal axes. But here, the BIF-iron ore bodies are preferentially localized within elongated domal structures in contrast to the basinal sites in the adjacent eastern anticline. Such an inference based on structural analysis could probably be utilized as a potential tool for all future explorations, reserve estimation and recovery of the iron ore deposits in the terrain.     

隐伏岩体顶上带与深部成矿预测

岩浆侵入的流体流动模拟表明,侵入体上方是流体聚焦流动的位置,流体通量远大于旁侧围岩,流体在此产生沸腾作用。随温度降低,侵入体上方渗透率逐渐增大,最大渗透率出现在侵入体的顶部。含水岩浆侵位后在其顶上带发生二次沸腾和减压过程,释放出的巨大机械能远大于围岩的抗张强度,足以引起围岩发生脆性破坏。岩浆岩顶上带的水饱和外壳及其围岩发生破裂形成陡倾裂隙和水力破裂。直立长椭球状岩浆体的侵入会在岩浆岩顶上带产生放射状和同心圆状裂隙,同时产生爆破角砾岩筒。因此侵入体顶上带的岩钟、岩枝、岩脉,放射状、同心圆状裂隙和角砾岩筒均为构造弱化带,是热液矿脉密集发育的部位。矿床地质学研究已充分证明,岩浆岩顶上带确是容纳与中酸性岩浆有关的热液矿床的最佳部位。在开展深部成矿预测和找矿的过程中,探寻隐伏岩体顶上带和/或岩钟,是寻找深部与花岗岩类有关的多金属矿床的捷径。     

Palaeozoic oolitic ironstone of the French Armorican Massif: a chemical and structural trap for orogenic base metal–As–Sb–Au mineralisation during Hercynian strike-slip deformation

In the Saint-Aubin-des-Chateaux quarry (Armorican Hercynian belt, western France), an epigenetic hydrothermal alteration affects an oolitic ironstone layer intercalated within the Lower Ordovician Grès armoricain Formation. The hydrothermal overprint produced pervasive and massive sulphidation with stratoid pyritised lenticular bodies within the oolitic ironstone layer. These sulphide lenses are spatially associated with strike-slip faults and extend laterally from them. After the massive sulphidation stage (Fe–As, stage 1), subsequent fracturing allowed the deposition of base metals (stage 2) and Pb–Sb–Au (stage 3) parageneses in veins. The dominant brittle structures are vertical extension veins, conjugate shear veins and strike-slip faults of various orders. All these structures are filled with the same paragenetic sequence. Deformation analysis allows the identification of structures that developed incrementally via right-lateral simple shear compatible with bulk strain affecting the Central Armorican Domain. Each increment corresponds to a fracture set filled with specific parageneses. Successive hydrothermal pulses reflect clockwise rotation of the horizontal shortening direction. Geothermometry on chlorite and arsenopyrite shows an input of hot hydrothermal fluids (maximum of 390–350°C) during the main sulphide stage 1. The subsequent stages present a marked temperature drop (300–275°C). Lead isotopes suggest that the lead source is similar for all hydrothermal stages and corresponds to the underlying Neo-Proterozoic basement. Lead isotope data, relative ages of deformation and comparison with neighbouring deposits suggest that large-scale fluid pulses occurred during the whole Hercynian orogeny rather than pulses restricted to the late Hercynian period. The vicinity of the Hercynian internal domain appears as a key control for deformation and fluid flow in the oolitic ironstones, which acted as a chemical and structural trap for the hydrothermal fluids. The epigenetic mineralisation of Saint-Aubin-des-Chateaux appears to be very similar to epigenetic sulphidation described in banded iron formation-hosted gold deposits.     

岩浆 热液过渡型矿床的若干特征

摘　 要　 在内生成矿作用中成矿流体有 3 种:岩浆、 热液和岩浆 热液过渡性流体。 从地质研 究、 矿物包裹体、 成矿实验 3 个方面简介了岩浆 热液过渡型矿床研究的进展。 指出岩浆 热 液过渡性流体有 2种形成方式:一是在岩浆结晶过程中挥发分不断集中而形成, 另一是由熔 离作用所形成。 并从矿体与岩浆岩的关系、 矿体与围岩的关系、 矿石的结构构造、 围岩蚀变、 分带现象、 矿物包裹体 6 个方面总结了岩浆 热液过渡型矿床的特征。     

煌斑岩与某些热液矿床关系新探──兼论幔源C－H－O流体的分异演化

本文指出了煌斑岩与某些热液矿床之间在大的时、空尺度上密切相关，而在小尺度上刚具有明显的独立性，提出并论证了煌斑岩及某些热液矿床形成过程中的幔源Ｃ－Ｈ－Ｏ流体的分异演化模式，即溶解了大量常量及微量元素的高温幔源Ｃ－Ｈ－Ｏ流体上升进入地壳后，因压力降低及挥发分组成的岩化发生分异作用，形成相对富含铁镁质的硅酸盐流体及相对富含硅碱质的Ｃ－Ｈ－Ｏ流体，前者在地壳浅部定位形成钙碱性煌斑岩，而后者则引发并参与了