西藏邦铺斑岩钼(铜)矿床钾硅酸盐化热液黑云母电子探针分析及早期成矿流体特征

热液黑云母的化学组成对于揭示早期成矿流体的物理化学性质和流体演化过程具有重要意义。邦铺矿床是冈底斯成矿带东段一个大型的斑岩型钼(铜)矿床,其钾硅酸盐化蚀变带内热液黑云母广泛发育,本文对采自该矿床闪长玢岩钾硅酸盐化蚀变带内的热液黑云母进行了电子探针分析。结果表明,热液黑云母的SiO_2、TiO_2、Al_2O_3、FeO~T、MgO和K_2O等主要氧化物的平均含量为38.95%、1.42%、13.55%、14.22%、16.23%和9.77%,具有明显的高镁低铁、高钾低钠钙等特征,且异常高的K/Na值(82.5)可能是指示斑岩型钼矿化的重要指标。依据化学组成估算热液黑云母结晶时流体的氧逸度和温度,显示钾硅酸盐化蚀变带内早期成矿流体具有高温、高氧逸度特征,且深部流体平均温度(458℃)明显高于浅部流体(366℃),成矿流体从深部向浅部运移的过程中,温度和压力逐渐降低,导致钼、铜硫化物从流体中析出从而成矿。该成果为进一步研究矿床成矿流体的演化和成矿机制提供了重要线索。     

利用高分辨率3D技术和荧光强度变化精确测量烃类包裹体体积的方法

烃类包裹体气液比的精度对PVT模拟结果可靠性有重要影响,而气液相边界的判断对气液比测定准确性至关重要。本文开发了一种精确测量烃类包裹体体积的方法,即利用高分辨率激光共聚焦显微扫描技术获取烃类包裹体3D图,在透射及荧光模式下用三维坐标标定液相的边界,利用3Dfor LSM软件计算烃类包裹体液相的体积;同时利用激光共聚焦显微荧光技术对横穿气液两相的直线进行线扫描,根据扫描线上荧光强度的突变判断气相边界,多次扫描求平均值作为气相直径。本方法避免了人为判断包裹体气相边界的不可靠性,对气液边界的确定精度可达0.02μm,提高了气液比测试精度,使得利用包裹体恢复古压力结果更加可靠。     

西藏雄梅铜矿区含矿斑岩与非含矿斑岩成因对比研究

西藏雄梅铜矿床是近年来在班公湖_怒江成矿带中段新发现的一处斑岩铜矿床,该矿床的发现使得班公湖_怒江成矿带真正具备了"带"的概念,大大地拓宽了找矿远景。文章通过对雄梅铜矿区斑岩体的LA_ICP_MS锆石U_Pb定年,发现矿区存在2套斑岩:一套是前人测定的年龄为106.7 Ma的含矿斑岩;另一套是本文测定的非含矿斑岩,3个年龄分别是(121.8±2.3)Ma(MSWD=0.32)、(122.8±2.1)Ma(MSWD=1.16)、(121.5±2.5)Ma(MSWD=0.54)。两套斑岩的岩性虽然都是花岗闪长斑岩,但非含矿斑岩比含矿斑岩含有更多的钾长石,矿化强度大大减弱。岩石地球化学分析结果表明,两套斑岩虽然都富集大离子亲石元素(LILE)Rb、Ba、Th、U、K、Pb,亏损高场强元素(HFSE)Nb、Ta、Ti,具有碰撞后岩浆作用的共同特征,但在岩浆源区和成因上显示出明显的差异。含矿斑岩和非含矿斑岩均属于强过铝质S型花岗岩,然而前者源区组成为杂砂岩,后者源区则以泥质岩为主。岩浆分异过程中,含矿斑岩受斜长石和钾长石的分离结晶控制,非含矿斑岩则受钾长石和黑云母的分离结晶控制。     

新疆西天山达巴特斑岩铜钼矿床成矿流体演化

新疆达巴特铜钼矿床位于天山造山带的北缘,赛里木地块的中部,成矿与晚石炭世-早二叠世浅成侵入体有关。对该矿床详细的矿石组构、流体包裹体显微测温和激光拉曼光谱分析揭示,其流体成矿先后经历了辉钼矿-黄铜矿-石英脉(Ⅰ)、无矿石英脉(Ⅱ)、辉钼矿-石英脉(Ⅲ)和方解石-石英脉(Ⅳ)等4个阶段。从早到晚不同阶段,包裹体均一温度集中分布在336~414℃、276~393℃、221~396℃、192~287℃,盐度为(4.5~9.9)%Na Cleq、(1.6~8.4)%Na Cleq、(1.2~45.6)%Na Cleq、(1.6~7.5)%Na Cleq,密度为0.57~0.76 g/cm3、0.54~0.80 g/cm3、0.51~1.11 g/cm3、0.76~0.91 g/cm3,随成矿流体温度、盐度降低,密度渐升,还原性增强。Ⅰ、Ⅲ阶段都发育矿化,包裹体具有明显的沸腾特征,且气相成分中均发现CO2,表明Ⅰ和Ⅲ阶段的流体沸腾可能导致金属沉淀,且CO2对金属运移可能具有重要作用。压力估算得到达巴特矿床Ⅰ、Ⅱ、Ⅲ、Ⅳ阶段脉体的成矿深度分别为0.5~1.1 km、0.3~1.0 km、0.5~1.0km、0.4~1.0km。矿体矿石、围岩蚀变和流体包裹体具有斑岩型矿床的特点。结合前人资料,认为达巴特为一典型斑岩型矿床。     

云南姚安老街子铅银矿床岩性-断裂控矿特征与找矿预测—以2108m中段为例

云南姚安铅银矿床与富碱斑岩、构造活动密切相关。在矿床深部2108m中段开展大比例尺地质填图,选取3号、5号穿脉建立岩性-断裂地质剖面,分析岩性-断裂控矿特征,总结铅矿化规律,提出深部找矿预测区。研究认为,条带状、网脉状铅矿脉主要分布于肉红—灰白色正长斑岩内NE向断裂或不同方向断裂交汇处;NE向灰紫色黑云母正长斑岩脉、灰白色正长斑岩脉上盘,铅矿脉变厚、加富,岩脉侵入正长斑岩较侵入砂岩,铅矿化更强。隐爆角砾岩(筒)中方铅矿呈细脉状、散点状及浸染状,沿角砾裂隙及角砾的边缘充填,深部铅矿化加强。早期NNW向背斜与一系列NW向扭—扭张性断裂(F3、F4),限制了矿床就位的空间,总体控制矿床展布;后期NE—SW向主应力作用形成的NE向张性空间(F1及NE向断裂、岩脉)为矿区火成岩喷溢和矿液上升提供了通道,是主要的成矿构造,控制铅矿脉、正长斑岩脉产出。正长斑岩脉与断裂的空间位置一致,产状一致,岩脉上盘矿化强、品位高,构造—岩脉—矿化三者耦合作用,具密切的时空关系与成因联系。铅矿化为岩浆期后热液沿断裂充填作用产物,同时或稍晚于岩脉就位。姚安老街子铅银矿体主要受岩性、构造控制。总结了岩性-断裂控矿特征及铅矿化规律,提出四个深部找矿预测区。     

Millennial timescale resolution of rhyolite magma recharge at Tarawera volcano: insights from quartz chemistry and melt inclusions

Most rhyolite eruption episodes of Tarawera volcano have emitted several physiochemically distinct magma batches (∼1–10 km³). These episodes were separated on a millennial timescale. The magma batches were relatively homogeneous in temperature and composition at pumice scale (>4 cm), but experienced isolated crystallisation histories. At the sub-cm scale, matrix glasses have trace element compositions (Sr, Ba, Rb) that vary by factors up to 2.5, indicating incomplete mixing of separate melts. Some quartz-hosted melt inclusions are depleted in compatible trace elements (Sr, Ti, Ba) compared to enclosing matrix glasses. This could reflect re-melting of felsic crystals deeper in the crystal pile. Individual quartz crystals display a variety of cathodoluminescence brightness and Ti zoning patterns including rapid changes in melt chemistry and/or temperature (∼50–100°C), and point to multi-cycle crystallisation histories. The Tarawera magma system consisted of a crystal-rich mass containing waxing and waning melt pockets that were periodically recharged by silicic melts driven by basaltic intrusion. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Tectonic configuration of the Apuseni–Banat—Timok–Srednogorie belt, Balkans-South Carpathians, constrained by high precision Re–Os molybdenite ages

The Apuseni–Banat–Timok–Srednogorie magmatic–metallogenic belt (ABTS belt), forms a substantial metallogenic province in the Balkan-South Carpathian system in southeastern Europe. The belt hosts porphyry, skarn, and epithermal deposits mined since pre-Roman times. Generally, the deposits, prospects, and occurrences within the belt are linked to magmatic centers of calc-alkaline affinity. Fifty-one rhenium-osmium (Re–Os) ages and Re concentration data for molybdenites define systematic geochronologic trends and constrain the geochemical-metallogenic evolution of the belt in space and time. From these data and additional existing geologic-geochemical data, a general tectonic history for the belt is proposed. Mineralization ages in Apuseni-Banat, Timok, and Panagyurishte (the central district of the larger E–W Srednogorie Zone) range from 72–83, 81–88, and 87–92 Ma, respectively, and clearly document increasing age from the northwestern districts to the southeastern districts. Further, Re–Os ages suggest rapidly migrating pulses of Late Cretaceous magmatic–hydrothermal activity with construction of deposits in ~1 m.y., districts in ~10 m.y., and the entire 1,500 km belt in ~20 m.y. Ages in both Timok and Panagyurishte show systematic younging, while deposit ages in Banat and Apuseni are less systematic reflecting a restricted evolution of the tectonic system. Systematic differences are also observed for molybdenite Re concentrations on the belt scale. Re concentrations generally range from hundreds to thousands of parts per million, typical of subduction-related Cu–Au–Mo–(PGE) porphyry systems associated with the generation of juvenile crust. The geochronologic and geochemical trends are compatible with proposed steepening of subducting oceanic slab and relaxation of upper continental plate compression. Resulting influx of sub-continental mantle lithosphere (SCML) and asthenosphere provide a fertile metal source and heat, while the subducting slab contributes connate and mineral dehydration fluids, which facilitate partial melting and metal leaching of SCML and asthenosphere. Cu–Au–Mo–(PGE) porphyry deposits may develop where melts are trapped at shallow crustal levels, often with associated volcanism and epithermal-style deposits (South Banat, Timok, and Panagyurishte). Mo–Fe–Pb–Zn skarn deposits may develop where felsic melts are trapped adjacent to Mesozoic limestones at moderate crustal levels (North Banat and Apuseni). Systematic spatial variations in deposit style, commodity enrichment, Re–Os ages, and Re concentrations support specific tectonic processes that led to ore formation. In a post-collisional setting, subduction of Vardar oceanic crust may have stalled, causing slab steepening and rollback. The slab rollback relaxes compression, facilitating and enhancing orogenic collapse of previously thickened Balkan-South Carpathian crust. The progression of coupled rollback-orogenic collapse is evidenced by the width of Late Cretaceous extensional basins and northward younging of Re–Os ages, from Panagyurishte (~60 km; 92–87 Ma) to Timok (~20 km; 88–81 Ma) to Apuseni-Banat (~5 km; 83–72 Ma). Generation of a well-endowed mineral belt, such as the ABTS, requires a temporally and spatially restricted window of magmatic–hydrothermal activity. This window is quickly opened as upper plate compression relaxes, thereby inducing melt generation and ingress of melt to higher crustal levels. The window is just as quickly closed as upper plate compression is reinstated. The transient tectonic state responsible for economic mineralization in the ABTS belt may be a paleo-analogue to transient intervals in the present subduction tectonics of SE Asia where much mineral wealth has been created in the last few million years.     

Late Cenozoic to recent transtensional deformation across the Southern part of the Gaoligong shear zone between the Indian plate and SE margin of the Tibetan plateau and its tectonic origin

Chuquicamata, in northern Chile, is one of the largest porphyry copper deposits in the world; the western side of its orebody is bounded by a major longitudinal fault, the West fault. We report paleomagnetic results from surface sites and drill cores from different geological units at Chuquicamata, especially within the late Eocene Fiesta granodiorite of the western block of the West fault. Characteristic remanent magnetizations (ChRM) were determined after detailed thermal or alternating field demagnetization. Soft components carried by multidomain magnetite crystals in the Fiesta granodiorite were removed by AF demagnetization at 10–20 mT. The ChRMs, not demagnetized by alternating fields up to 100 mT, have unblocking temperatures above 580 °C with ~ 75% of the magnetization removed in the temperature range of 580–590 °C. Optical and SEM mineralogical observations, and microprobe data indicate the occurrence of multidomain magnetite formed during a late magmatic stage of alteration coeval with strong oxidation of primary titanomagnetite and formation of ilmenite, hematite, pseudobrookite, and rutile. The characteristic directions have negative inclinations and declinations (330° to 230°); strongly deflected from the expected Eocene direction. Anisotropy of magnetic susceptibility (AMS), with degree up to 1.4, is carried by multidomain magnetite. AMS ellipsoids have subvertical foliations with azimuth varying strongly from N280° to N20°. We show that both the ChRMs and the AMS fabrics record the same apparent relative rotations between sites. Although the AMS anisotropy is high, there is no evidence for a solid-state deformation and the apparent rotation of the magnetic fabric is interpreted to be the consequence of small-block rotation. The apparent large (> 100°) counterclockwise rotations of small blocks within the Fiesta granodiorite suggest a wide damaged zone related to sinistral displacement along the West fault. This interpretation is consistent with previous models indicating that the Fiesta granodiorite was sinistrally translated and brought in front of the early Oligocene porphyry copper deposit during the Oligocene–early Miocene. This study shows that paleomagnetic markers are useful for improving the quantification and understanding of small-scale deformation within plutons adjacent to major fault zones.     

河南汤家坪钼矿床流体成矿作用研究

汤家坪大型斑岩型钼矿床位于大别造山带。对流体包裹体的岩相学、显微测温及激光拉曼显微探针分析表明,汤家坪钼矿床的流体包裹体可划分为富（含）CO2包裹体、水溶液包裹体和含子晶包裹体3类;均～温度集中在126,7-472．1℃,盐度集中在（0．18-14．21）wt％和（33．10～54．37）wt％．密度为O．38～1．21g／cm^3;子矿物含石盐及金属硫化物等。从矿体中心向外围．流体包裹体的温度、盐度有逐渐变小的趋势;从成矿早阶段到晚阶段．由高盐度低密度岩浆流体逐渐变为低盐度低密度流体,压力逐渐变小,深度变浅。辉钥矿的Re-Os模式年龄集巾在113～118Ma．表明成矿略晚于母岩岩体的成岩时代．其成岩成矿的构造背景为华北与扬子板块碰撞造山晚期的伸展构造体制。     

Geology and Re-Os Geochronology of Mineralization of the Miduk Porphyry Copper Deposit, Iran

The Miduk porphyry copper deposit is located in Kerman province, 85 km northwest of the Sar Cheshmeh porphyry copper deposit, Iran. The deposit is hosted by Eocene volcanic rocks of andesitic–basaltic composition. The porphyry‐type mineralization is associated with two Miocene calc‐alkaline intrusive phases (P1 and P2, respectively). Five hypogene alteration zones are distinguished at the Miduk deposit, including magnetite‐rich potassic, potassic, potassic–phyllic, phyllic and propylitic. Mineralization occurs as stockwork, dissemination and nine generations (magnetite, quartz–magnetite, barren quartz, quartz‐magnetite‐chalcopyrite‐anhydrite, chalcopyrite–anhydrite, quartz‐chalcopyrite‐anhydrite‐pyrite, quartz‐molybdenite‐anhydrite ± chalcopyrite ± magnetite, pyrite, and quartz‐pyrite‐anhydrite ± sericite) of veinlets and veins. Early stages of mineralization consist of magnetite rich veins in the deepest part of the deposit and the main stage of mineralization contains chalcopyrite, magnetite and anhydrite in the potassic zone. The high intensity of mineralization is associated with P2 porphyry (Miduk porphyry). Based on petrography, mineralogy, alteration halos and geochemistry, the Miduk porphyry copper deposit is similar to those of continental arc setting porphyry copper deposits. The Re‐Os molybdenite dates provide the timing of sulfide mineralization at 12.23 ± 0.07 Ma, coincident with U/Pb zircon ages of the P2 porphyry. This evidence indicates a direct genetic relationship between the Miduk porphyry stock and molybdenite mineralization. The Re‐Os age of the Miduk deposit marks the main stage of magmatism and porphyry copper formation in the Central Iranian volcano‐plutonic belt.