内蒙古乌努格吐山斑岩铜钼矿床流体包裹体研究

内蒙古乌努格吐山(简称乌山)斑岩铜钼矿床位于得尔布干深断裂北侧的额尔古纳地体。作为兴蒙造山带的一部分,额尔古纳地体经历了古生代俯冲增生、早中生代碰撞造山和晚中生代—新生代期间的与太平洋板块俯冲有关的碰撞后构造演化。乌山矿床形成于侏罗纪,是陆-陆碰撞体制斑岩矿床的典型实例,其地质地球化学特征有助于理解碰撞环境的斑岩矿床的成因,因此本文报道该矿床流体包裹体显微测温学、激光拉曼光谱和扫描电镜/能谱研究结果。乌山矿床流体成矿过程包括早、中、晚3个阶段,分别以石英-钾长石化、石英-绢云母-多金属硫化物化和伊利石-石英-碳酸盐化为特征。石英中可见水溶液包裹体、含子晶和含 CO_2三相流体包裹体,但晚阶段石英中缺乏后两类包裹体。早阶段流体包裹体均一温度>510℃,盐度最高达75.8 wt%Nacl eqv,包裹体的子晶矿物有石盐、黄铜矿以及指示氧化条件的赤铁矿,气相成分富含 CO_2,液相成分以水为主,且多含 CO_3~(2-)。矿化主要发生在中阶段,可分为早期的钼矿化阶段和晚期的铜矿化阶段,其成矿温度分别为340℃～510℃和240℃～340℃。该阶段流体盐度介于6.3～52.0 wt%NaCl eqv。中阶段包裹体含石盐和黄铜矿子矿物,富气相、富液相与含子晶包裹体共存,且具有相近的均一温度,而盐度相差悬殊,指示流体发生沸腾,成矿物质快速沉淀。晚阶段流体温度降低至100℃～240℃,盐度则低于12.4 wt%NaCl eqv。总之,早阶段成矿流体来自岩浆,以高温、高盐度、高氧逸度、富 CO_2为特征;中阶段流体发生沸腾,导致 CO_2逸失、氧逸度降低、成矿物质快速沉淀;晚阶段流体以低温、低盐度、无子晶、贫 CO_2为特征,可能属大气降水热液。     

额尔古纳成矿带西北部金矿床流体包裹体研究

额尔古纳成矿带是中国东北重要的银、铅、锌、铜、钼多金属成矿带,它位于蒙古-鄂霍茨克造山带的东南缘。最近,额尔古纳成矿带西北部发现了砂宝斯、老沟、小伊诺盖沟等金矿床和一些金矿点。这些金矿受洛古河-二根河韧性剪切带和额尔古纳河韧性剪切带控制,矿体常赋存于韧性剪切带的次级张扭性断裂构造中。矿石中硫化物含量一般不超过3%,且硫化物以黄铁矿为主。流体包裹体有气液两相、含 CO_2三相和纯 CO_2包裹体3种类型。气相成分以 H_2O、CO_2和 N_2为主,含少量H_2S、CH_4为特征。流体包裹体的盐度低,介于2.06～8.54%NaCl eqv 之间。老沟金矿流体包裹体均一温度介于171℃～452℃之间,平均295℃,小伊诺盖沟金矿包裹体均一温度为169℃～493℃,平均亦为295℃,均属中温热液矿床。老沟金矿成矿压力为61～122MPa,平均82MPa;小伊诺盖沟金矿成矿压力为38～172MPa,平均93MPa。前者成矿深度介于6～9km,平均7km;后者成矿深度为4～11km,平均8km。上述金矿床的地质-地球化学特征与世界造山型金矿类似,形成于蒙古-中朝板块与西伯利亚板块之间的陆-陆碰撞造山作用。     

Geology,Pb Isotope Geochemistry and Ore Genesis of the Liziyuan Gold Deposit,West Qinling Orogen,Central China

The Liziyuan gold deposit, situated on the south side of the Shangdan suture zone, West Qinling Orogen, occurs in metamorphic volcanic rocks(greenschist facies) of the early Paleozoic Liziyuan Group and in Indosinian Tianzishan monzogranite. Orebodies in the Liziyuan gold field are controlled by the ductile-brittle shear zone, and by thrusting nappe faults related to the Indosinian orogeny. In detail, this paper analyzed the geological characteristics of the Liziyuan gold field, and the Pb isotopes of the Lziyuan host rocks, granitoids(Tianzishan monzogranite and Jiancaowan syenite porphyry), sulfides, and auriferous quartz veins by multiple-collector inductively coupled plasma mass spectrometry(MC-ICPMS). In addition, previous data on the sulfur, hydrogen, and oxygen isotopes were employed to discuss the possible sources of the ore-forming fluids and materials, and to further understand the tectonic setting of the Liziyuan gold deposit. The sulfides and their host rocks(Lziyuan Group), Tianzishan monzogranite and Jiancaowan syenite porphyry, and auriferous quartz veins have similar Pb isotopic compositions.Zartman's plumbotectonic model diagram shows that most of the data for the deposit fall near the orogenic Pb evolutionary curve or within the area between the orogenic and mantle Pb evolutionary curves. In the△β-△γ diagram, which genetically classifies the lead isotopes, most of the data fall within the range of the subduction-zone lead mixed with upper crust and mantle. This indicates that a complex source of the ore lead formed in the orogenic environment. The δ~(34)S values of the sulfides range from 3.90 to 8.50‰(average6.80‰), with a pronounced mode at 5.00‰-8.00‰. These values are consistent with that of orogenic gold deposits worldwide, indicating that the sulfur sourced mainly from reduced metamorphic fluids. The isotopic hydrogen and oxygen compositions support a predominantly metamorphic origin of the oreforming fluids, with possible mixing of minor magmatic fluids, but the late stage was dominated by meteoric water. The characteristics of the Liziyuan gold deposit formed in the Indosinian orogenic environment of the Qinling Orogen are consistent with those of orogenic gold deposits found worldwide.     

西秦岭碌础坝石英闪长岩-花岗闪长岩的地球化学、矿物学研究及其地质意义

不同成因类型的花岗岩组合,反映出不同的物源组成或迥异的岩浆演化过程。为了进一步探讨西秦岭造山带中生代花岗质侵入岩的成因、矿物结晶条件和地球动力学背景,选择西秦岭东部碌础坝岩体内的石英闪长岩和花岗闪长岩为研究对象,对其开展详细的野外地质调查以及系统的岩相学、矿物学和岩石地球化学研究。研究结果表明:碌础坝石英闪长岩和花岗闪长岩的SiO₂含量范围为59.65%~67.36%,A/CNK为0.82~1.04,K₂O/Na₂O=1.11~1.74,Mg^#值为47~53,显示出准铝质-弱过铝质特征,属于高钾钙碱性岩石,其中花岗闪长岩为I型花岗岩;岩体具有富集Rb、Th、U、K和Pb等元素,亏损Nb、Ta、P和Ti等元素的特征,具有中等Eu负异常(δEu=0.50~0.77),轻重稀土分馏明显((La/Yb)_N=9.43~30.37)。碌础坝花岗质岩石中斜长石的An值介于18~53之间,以中长石为主,部分斜长石显示振荡环带;角闪石为镁角闪石,部分角闪石具有环带结构,且核部Mg/(Mg+Fe²⁺)值较高(0.88~0.91)并具有富钙特征(CaO含量为17.80%~22.67%),但Al₂O₃含量较低,指示角闪石核部与边部的形成环境具有明显差异;黑云母Mg/(Mg+Fe²⁺)值为0.44~0.57,为镁质黑云母。碌础坝花岗质岩石中全岩和各类矿物的温度计算结果显示,全岩锆饱和温度为736~795 ℃,角闪石结晶温度为704~824 ℃,黑云母结晶温度为700~746 ℃。三种方法计算的结晶温度相近,表明岩体形成于中温环境。碌础坝岩体角闪石全铝压力计结果为1.0~3.5 kbar(1 bar=100 kPa),平均形成深度为6.8 km;黑云母结晶压力为0.9~1.4 kbar,平均形成深度为4.1 km。角闪石湿度及氧逸度计显示其相对氧逸度为ΔNNO=0.1~1.3,含水量为3.9%~6.3%。结合前人资料,认为西秦岭碌础坝岩体由角闪岩为主的变基性岩部分熔融形成,幔源组分的参与导致其具有高Mg^#值、高Cr和Ni等元素含量的特征。碌础坝岩体形成于洋-陆俯冲向陆-陆碰撞转换的阶段。     

西秦岭常家山地区水系沉积物地球化学特征及其地质意义

西秦岭成矿带北亚带是重要的多金属成矿单元。为缩小找矿靶区,在常家山地区开展了1:2.5万水系沉积物测量工作,对采集到的1 141件样品中的Au、Ag、As、Sb、Bi、Cu、Pb、Zn、W、Mo 10种元素进行核密度估算等数理统计分析,结果显示它们的浓度高于全国水系和区域水系沉积物的平均值,表明研究区成矿潜力大。通过因子分析得到F1(Bi、Cu、Zn)、F2(Au、As、Sb)、F3(Ag、Pb)、F4(W、Mo)4个主因子。使用浓度-面积(C-A)分形模型得到各元素和因子的异常阈值,并利用克里金插值法得到相应的地球化学空间分布图;结合区域控矿因素和异常分布特征圈定出Hz1、Hz2、Hz3 3处综合异常,前缘晕、近矿晕和尾晕显示出自西北向东南分布的趋势。水系沉积物地球化学异常分析结果表明,区内构造控矿特征明显,北西方向的礼县—闾井断裂是常家山地区有利的找矿部位。     

江南造山带西段桂北四堡地区830 Ma辉长岩锆石SIMS U-Pb年代学和岩石地球化学特征及其岩石成因研究

本次研究对象为江南造山带西段桂北四堡地区新元古代辉长岩,主要由斜长石和单斜辉石组成,含有少量的橄榄石和钛铁氧化物,表明在岩浆演化过程中发生了斜长石和单斜辉石以及少量橄榄石的分离结晶作用。辉长岩锆石SIMS U-Pb谐和年龄为(830±7)Ma,指示其侵位年龄约为830 Ma。全岩具有低SiO₂含量(48.46%~53.99%)、高MgO含量(9.27%~25.22%)、Mg^#值较高(62~79)的特征。辉长岩为钙碱性系列岩石,其稀土元素球粒陨石标准化和微量元素原始地幔标准化与典型的弧岩浆相似,具有相对富集轻稀土元素((La/Yb)_N=2.2~3.7,(La/Sm)_N=2.5~2.9)和大离子亲石元素,明显的高场强元素(Nb、Ta和Ti)亏损的特征,还具有较高的Th/Nb比值(0.7~0.8)和低Nb/La比值(0.4~0.6)。辉长岩具有负的ε_Nd(t)值(-6.3~-3.0)和正的ε_Hf(t)值(8.0~12.1),指示其源区为亏损地幔,但有富集组分加入。结合区域地质特征,推测辉长岩形成于活动大陆边缘俯冲构造背景,起源于受沉积物流体交代了的楔地幔。     

Hunter–Bowen deformation in South Percy Island,northeastern Australia

South Percy Island is located approximately 50 km off the central Queensland coast and comprises a disrupted ophiolite mass alongside a diverse array of metamorphosed felsic and mafic rocks that record several episodes of magmatism, volcanism and deformation from the Permian to Early Cretaceous. This paper aims to constrain the age, affinity and deformation history of these units, as well as to establish the tectonic significance of the terrane. The trace-element compositions of mafic and felsic meta-igneous rocks record a change from MORB-like prior to ca 277 Ma to subduction-related by ca 258 Ma. Overprinting relationships between intrusive phases and deformation features reveal a relative chronology for the tectonothermal evolution of the area, while U–Pb and ⁴⁰Ar/³⁹Ar geochronology provides absolute age constraints. Deformation is localised around a NNE-striking tectonic contact that separates serpentinised ultramafic rocks from metamorphosed pillow lavas. Early formed ductile fabrics associated with the main episode of deformation (D₁) preserve bulk flattening strains at greenschist-facies conditions. Emplacement and post-kinematic cooling ages of a pre-D₁ quartz-monzonite dyke constrain the age of D₁/M₁ deformation and metamorphism to the period between ca 258 and ca 248 Ma. Minor brittle deformation (D₂) occurred at ca 230 Ma, based on U–Pb dating of a syn-D₂ diorite dyke (ca 231 ± 10 Ma) and several ca 230 Ma ⁴⁰Ar/³⁹Ar cooling ages. The deformation, metamorphism, and supra-subduction zone magmatism preserved on South Percy Island is correlated with the nearby Marlborough Terrane and more broadly with the second pulse of the Hunter–Bowen Orogeny, which affected much of the central and northern parts of eastern Australia in the late Permian and Early Triassic. Our results support previous suggestions that the second pulse of the Hunter–Bowen Orogeny involved coeval thrust systems in both the inboard and outboard parts of the orogen.     

High-temperature–low-pressure metamorphism and the production of S-type granites of the Hillgrove Supersuite,southern New England Orogen,NSW, Australia

The high-temperature–low-pressure Wongwibinda Metamorphic Complex of the southern New England Orogen is bound by S-type granite plutons of the Hillgrove Supersuite to the north, east and south. New U–Pb geochronology of five samples of the Hillgrove Supersuite demonstrates that plutonism in the complex involved two pulses: ca 300 Ma and ca 292 Ma. This indicates that plutonism partially overlaps the age of high-T–low-P metamorphism (296.8 ± 1.5 Ma), but also postdates it. Zircon grains identified as xenocrysts based on age (≥310 Ma) have U–Pb–Hf isotopic character that largely overlaps detrital grains in the host Girrakool Beds, indicating that accretionary complex crust is the likely source of these xenocrysts. The ¹⁷⁶Hf/¹⁷⁷Hf initial character for zircon for the ca 300 Ma plutons (three samples) is less radiogenic than those in the ca 292 Ma plutons (two samples). The progression in ¹⁷⁶Hf/¹⁷⁷Hf initial character for zircon infers an increasing mantle component in the Hillgrove Supersuite with time. These data are evidence of a rift tectonic setting, where mantle-derived magmas are predicted to more readily migrate to shallower crustal levels as the crust thins and becomes hotter. Additionally, early episodes of partial melting in the system melt-depleted the metasedimentary sources, thus reducing the S-type component as anatexis progressed. The evolution of the Hillgrove Supersuite coincides with a period of early Permian slab roll back and extension accompanied by crustal rifting and thinning, leading to high-T–low-P metamorphism, anatexis and S-type granite production and the development of rift basins such as the Sydney–Gunnedah–Bowen system.     

Petrology,geochemistry and a probable late Cambrian age for harzburgites of the Coolac Serpentinite,New South Wales,Australia

The Coolac Serpentinite, in the Tumut region of southeastern NSW, is one of many Alpine-type, linear ultramafic bodies exposed in the Lachlan Orogen of New South Wales. Despite the significance of such oceanic lithosphere throughout the orogen to tectonic models, few studies on the genesis of these bodies in the Lachlan Orogen have been documented. A significant proportion of the Coolac ultramafic rocks are only partially serpentinised, making them good candidates for detailed petrological and geochemical studies. The Coolac peridotites include harzburgites with mineral compositions and bulk-rock REE concentrations similar to abyssal peridotites. Assuming depleted mantle compositions, HREE concentrations are limited (0.2–0.3 × primitive mantle) implying melt extraction of 15–20%. Conversely, some Cr-spinel data within the harzburgites (Cr# = 0.22–0.27) indicate partial melting of only 9–11%. Adsorbed mantle pyroxenes, excess olivine and LREE enrichment suggest melt–rock interactions led to the refertilisation of the harzburgites. Isotope characteristics of a ca 501 Ma allochthonous tonalite block derived from melting of altered oceanic crust and a ca 439 Ma oceanic granite intrusion indicate an identical source that separated from the fertile mantle at 660 Ma. This places chronological constraints on the harzburgites, which are the result of two-stage melting involving a lherzolite protolith formed during the break-up of Rodinia followed by harzburgite formation during a further melt extraction event within an extensional phase of the Delamerian Orogeny. The harzburgites were enriched via melt–rock interactions soon after formation as well as during phases of the Benambran Orogeny beginning at ca 439 Ma and ending around ca 427 Ma with the emplacement of the North Mooney Complex, a layered ultramafic–gabbro association that has characteristics of Alaskan-style intrusions similar to the Fifield complexes of the central Lachlan Orogen.     

Mélanges and other types of block-in-matrix formations in the Cantabrian Zone (Variscan Orogen,northwest Spain): origin and significance

Block-in-matrix formations in the Variscan foreland of Spain (Cantabrian Zone) occur in two different geological settings. The major block-in-matrix formations are mélanges, which appear as carpets beneath or ahead of submarine thrust systems. These mélanges may reach up to kilometric thickness and are mostly composed of broken formations (boudinaged sequences) of late Carboniferous age and scattered ‘exotic’ blocks derived from older Palaeozoic formations. Moreover, the mélanges in the Cantabrian Zone also include subordinate debris flow deposits with a chaotic block-in-matrix fabric (olistostromes). The source of the mélange blocks was the front of advancing nappes, chiefly the upper part of the nappe stacks. Therefore, the Cantabrian mélanges are interpreted as originated through submarine sliding and slumping associated with steep slopes at the orogenic front. The different types of rock bodies of these mélanges may be related to the degree of lithification of the sediments or rocks during slumping. So, broken formations are boudinaged sequences where the boudins or blocks resulted from extensional faults developed in lithified or semilithified limestones and sandstones, whereas the unlithified muddy matrix underwent continuous deformation. The scattered ‘exotic’ blocks ranging in age from early Cambrian to early Carboniferous were incorporated into the mélanges as individual blocks from competent well-lithified formations, originally located in the lower part of the nappe stacks. Although the Cantabrian Zone mélanges include olistostromic intervals, most of the olistostromes of this zone occur in a different geological setting. They are usually intercalated in the normal marine deposits of the Variscan foreland basin and, in contrast to the mélanges, they are mostly related to the margins of carbonate platforms, ahead of moving nappes. Finally, other instances of olistostromes are related to slopes generated by limb rotation of growth folds, which developed on submarine wedge-top successions.