In Situ Analyses of Trace Elements, U–Pb and Lu–Hf Isotopes in Zircons from the Tongshankou Granodiorite Porphyry in Southeast Hubei Province, Middle-Lower Yangtze River Metallogenic Belt, China

The Tongshankou Cu-Mo deposit, located in southeast Hubei province, is a typical skarn–porphyry type ore deposit closely related to the Tongshankou granodiorite porphyry, characterized by a high Sr/Y ratio.Detailed in situ analyses of the trace elements and U–Pb and Lu–Hf isotopes in zircons from the Tongshankou granodiorite porphyry were performed.Scarcely any inherited zircons were observed, and the analyzed zircons yielded highly concordant results with a weighted mean 206Pb/238 U age of 143.5 ± 0.45 Ma（n=20, mean square weighted deviation was 0.75）, which was interpreted to represent the crystallization age of the Tongshankou granodiorite porphyry.The chondrite-normalized rare-earth element pattern was characterized by a slope that steeply rises from the light-group rare-earth elements（LREE） to the heavy-group rare-earth elements（HREE） with a positive Ce-anomaly and inconspicuous Eu-anomaly, which was coincident with the pattern of the zircons from the Chuquicamata West porphyry, Chile.The analyzed zircons also had relatively low 176Hf/177 Hf ratios of 0.282526–0.282604.Assuming t=143 Ma, the corresponding calculated initial Hf isotope compositions（εHf（t）） ranged from-5.6 to-2.9.The results of the in situ analysis of trace elements and U–Pb and Lu–Hf isotopes in zircons from the Tongshankou granodiorite porphyry suggest that a deep-seated process involving a thickened-crust/enriched-mantle interaction may play an important role in the generation of high Sr/Y-ratio magma and potentially in the generation of porphyry Cu-Mo systems.

Cathodoluminescence and Trace Element Composition of Scheelite from the Middle-Lower Yangtze River Metallogenic Belt(MLYB): Implications for Mineralization and Exploration

The Middle-Lower Yangtze River Metallogenic Belt(MLYB)is known to contain abundant copper and iron porphyry-skarn deposits,with an increasing number of tungsten deposits and scheelite in Fe-Cu deposits being discovered in the MLYB during recent decades.The ore genesis of the newly-discovered tungsten mineralization in the MLYB is poorly understood.We investigate four sets of scheelite samples from tungsten,iron and copper deposits,using CL imaging and LA-ICP-MS techniques to reveal internal zonation patterns and trace element compositions.The REE distribution patterns of four studied deposits show varying degrees of LREE enrichment with negative Eu anomalies.The oxygen fugacity of ore-forming fluid increased in Donggushan,while the oxygen fugacity of ore-forming fluid decreased in Ruanjiawan,Guilinzheng and Gaojiabang.The scheelites from the Donggushan,Ruanjiawan,Guilinzheng and Gaojiabang deposits show enrichment in LREEs and HFSE,with Nb/La ratios ranging from 1.217 to 52.455,indicating that the four tungsten deposits are enriched in the volatile fluorine.A plot of(La/Lu)N versus Mo/δEu can be used to distinguish quartz vein type,porphyry and skarn tungsten deposits.This study demonstrates that scheelite grains can be used to infer tungsten mineralization and are effective in identifying magmatic types of tungsten deposits in prospective mining sites.

Molybdenite Re-Os,titanite and garnet U-Pb dating of the Magushan skarn Cu-Mo deposit,Xuancheng district,Middle-Lower Yangtze River Metallogenic Belt

The Magushan skarn Cu-Mo deposit is a representative example of the skarn mineralization occurring within the Xuancheng ore district of the Middle-Lower Yangtze River Metallogenic Belt of eastern China.The precise age of an ore deposit is important for understanding the timing of mineralization relative to other geological events in a region and to fully place the formation of a mineral deposit within the geological context of other processes that occur within the study area.Here,we present new molybdenite Re-Os and titanite and andradite garnet U-Pb ages for the Magushan deposit and use these data to outline possible approaches for identifying genetic relationships in geologically complex areas.The spatial and paragenetic relationships between the intrusions,alteration,and mineralization within the study area indicates that the formation of the Magushan deposit is genetically associated with the porphyritic granodiorite.However,this is not always the case,as some areas contain complexly zoned plutons with multiple phases of intrusion or mineralization may be distal from or may not have any clear spatial relationship to a pluton.This means that it may not be possible to determine whether the mineralization formed as a result of single or multiple magmatic/hydrothermal events.As such,the approaches presented in this study provide an approach that allows the identification of any geochronological relationships between mineralization and intrusive events in areas more complex than the study area.Previously published zircon U-Pb data for the mineralization-related porphyritic granodiorite in this area yielded an age of 134.2±1.2 Ma(MSWD=1.4)whereas the Re-Os dating of molybdenite from the study area yielded an isochron age of 137.7±2.5 Ma(MSWD=0.43).The timing of the mineralizing event in the study area was further examined by the dating of magmatic accessory titanite and skarn-related andradite garnet,yielding U-Pb ages of 136.3±2.5 Ma(MSWD=3.2)and 135.9±2.7 Ma(MSWD=2.5),respectively.The dating of magmatic and hydrothermal activity within the Magushan area yields ages around 136 Ma,strongly suggesting that the mineralization in this area formed as a result of the emplacement of the intrusion.The dates presented in this study also provide the first indication of the timing of mineralization within the Xuancheng district.providing evidence of a close genetic relationship between the formation of the mineralization within the Xuancheng district and the Early Cretaceous magmatism that occurred in this area.This in turn suggests that other Early Cretaceous intrusive rocks within this region are likely to be associated with mineralization and should be considered highly prospective for future mineral exploration.This study also indicates that the dating of garnet and titanite can also provide reliable geochronological data and evidence of the timing of mineralization and magmatism,respectively,in areas lacking other dateable minerals(e.g.,molybdenite)or where the relationship between mineralization and magmatism is unclear,for example in areas with multiple stages of magmatism,with complexly zoned plutons,and with distal skarn mineralization.

Geological Fluid Mapping in the Tongling Area:Implications for the Paleozoic Submarine Hydrothermal System in the Middle-Lower Yangtze Metallogenic Belt,East China

The Tongling area is one of the 7 ore-cluster areas in the Middle-Lower Yangtze metallogenic belt, East China, and has tectonically undergone a long-term geologic history from the late Paleozoic continental rifting, through the Middle Triassic continent-continent collision to the Jurassic-Cretaceous intracontinental tectono-magmatic activation. The Carboniferous sedimentary-exhalative processes in the area produced widespread massive sulfides with ages of 303-321 Ma, which partly formed massive pyrite-Cu deposits, but mostly provided significant sulfur and metals to the skarn Cu mineralization associated with the Yanshanian felsic intrusions.To understand the Carboniferous submarine hydrothermal system, an area of about 1046 km^2 was chosen to carry out the geological fluid mapping. Associated with massive sulfide formation, footwall sequences 948 m to 1146 m thick, composed of the Lower Silurian-Upper Devonian sandstone, siltstone and thin-layered shale, were widely altered. This hydrothermal alteration is interpreted to reflect largescale hydrothermal fluid flow associated with the late Paleozoic crustal rifting and subsidence. Three hydrothermal alteration types, i.e., deep-level semiconformable siliclfication （S1）, fracture-controlled quartz-sericite-pyrite alteration （S2-3）, and upper-level sub-discordant quartz-sericite-chlorite alteration （D3）, were developed to form distinct zones in the mapped area. About 50-m thick semiconformable silicification zones are located at -1-km depth below massive sulfides and developed between an impermeable shale caprock （S1） and the underlying Ordovician unaltered limestone. Comparisons with modern geothermal systems suggest that the alteration zones record a sub-seafioor aquifer with the most productive hydrothermal fluid flow. Fracture-controlled quartz-sericite-pyrite alteration formed transgressive zones, which downward crosscut the semiconformable alteration zones, and upwards grade into sub-discordant alteration zones that enveloped no economic stringer- stockwork zones beneath massive sulfides. This transgressive zone likely marks an upfiow path of high- flux fluids from the hydrothermal aquifer. Lateral zonation of the sub-discordant alteration zones and their relationship to overlying massive sulfide lenses suggest lateral flows and diffusive discharging of the hydrothermal fluids in a permeable sandstone sequence. Three large-sized, 14 middle-small massive sulfide deposits, and 40 massive sulfide sites have been mapped in detail. They show regional strata- bound characters and two major styles, i.e., the layered sheet plus strata-bound stringer-style and the mound-style. Associated exhalite and chemical sedimentary rock suites include （1） anhydrite-barite, （2） jasper-chert, （3） Mg-rich mudstone-pyrite shale, （4） barite lens, （5） siderite-Fe-bearing dolomite, and （6） Mn-rich shale-mudstone, which usually comprise three sulfide-exhalite cyclic units in the area.The spatial distribution of these alteration zones （minerals） and associated massive sulfdes and exhalites, and regional variation in δ^34S of hydrothermal pyrite and in δ^18O-δ^34C of hanging wall carbonates, suggest three WNW-extending domains of fluid flow, controlled by the basement faults and syn-depositional faults. Each fluid domain appears to have at least two upflow zones, with estimated even spacing of about 5-8 km in the mapped area. The repeated appearance of sulfide-sulfate or sulfide-carbonate rhythmic units in the area suggests episodically venting of fluids through the upfiow conduits by breaking the overlying seals of the hydrothermal aquifer.

Research and Application of Micromotional Exploration in the Middle-Lower Yangtze Metallogenic Belt of China

Micromotion is the daily tiny vibration of the earth’s surface. Micromotional exploration can use the surface wave information of micro motion to study the shallow structure of underground media. In this study, we collected microtremor data at 68 stations in the Middle-Lower Yangtze Metallogenic Belt (MLYMB) and determined the resonant frequency and obtained the distribution of sedimentary thickness in this area by using H/V spectral ratio. According to the results of H/V, the sedimentary layer in the basin is thick, and the predominant frequency of the basin is 0.05 - 0.1 Hz. There are no obvious lateral changes in the impedance interface between bedrock and sedimentary layer in this area. The basement of Tongling, Anqing and Luzhou mining areas and their adjacent areas is Kongling-Dongling type basement, which is composed of a set of metamorphic core complex. The predominant frequency is 0.05 - 0.1 Hz. The sedimentary thickness gradually thinned from 3800 m in the west to 2100 m in the East. Moreover, this article used SPAC (spatial autocorrelation) method to obtain the S-wave velocity structure of the mining area near Luzong. The SPAC method reveals that the depth of the interface between the loose sediments and the volcanic rocks is about 600 m in the study area near the Luzhou mining area in the Middle-Lower Yangtze Metallogenic Belt, and the average depth of the interface between the volcanic rock section and the intrusive complex section is about 1000 m. The thickness of the intrusive rock is more than 2500 m. Tourmaline is developed in the interior of the intrusive rock, which may have better exploration value.

Basement Characteristics and Crustal Evolution of the Copper-Gold Metallogenic Belt in the Middle and Lower Reaches of the Yangtze River:Some Isotope Constraints

Studies of the Pb, Sr and Nd isotopic composition of Mesozoic intrusive rocks indicate that the basement of the copper-gold metallogenic belt of the middle and lower reaches of the Yangtze River has “two-layer structure” and partly has “multi-layered structure”, and is inhomogeneous and shows the distinct feature of E-W provincialism. The calculated model lead ages (t1) are mostly greater than 2600 Ma, and the model neodymium ages (TDM) vary from 953 to 2276 Ma and concentrate in two time intervals: 1800–2000 Ma and 1200–1600 Ma. It is concluded that the basement of the MBYR is composed of the Late Archaeozoic to Middle Proterozoic metamorphic series and that the crust was initiated in the Archaean and continued to grow in the Early and Middle Proterozoic, and the proportion of new crust formed by mantle differentiation during the Late Proterozoic is low.

Three-dimensional P-wave Velocity Structure Modelling of the Middle and Lower Reaches of the Yangtze River Metallogenic Belt: Crustal Architecture and Metallogenic Implications

In this study,we compiled and analyzed 69310 P-wave travel-time data from 6639 earthquake events.These events(M≥2.0)occurred from 1980 s to June 2019 and were recorded at 319 seismic stations(Chinese Earthquake Networks Center)in the study area.We adopted the double-difference seismic tomographic method(tomo DD)to invert the 3-D P-wave velocity structure and constrain the crust-upper mantle architecture of the Middle and Lower Reaches of the Yangtze River Metallogenic Belt(MLYB).A 1-D initial model extracted from wide-angle seismic profiles was used in the seismic tomography,which greatly reduced the inversion residual.Our results indicate that reliable velocity structure of th e uppermost mantle can be obtained when Pn is involved in the tomography.Our results show that:(1)the pattern of the uppermost mantle velocity structure corresponds well with the geological partitioning:a nearly E-W-trending low-velocity zone is present beneath the Dabie Orogen,in contrast to the mainly NE-trending low-velocity anomalies beneath the Jiangnan Orogen.They suggest the presence of thickened lower crust beneath the orogens in the study area.In contrast,the Yangtze and Cathaysia blocks are characterized by relatively high-velocity anomalies;(2)both the ultra-high-pressure(UHP)metamorphic rocks in the Dabie Orogen and the low-pressure metamorphic rocks in the Zhangbaling dome are characterized by high-velocity anomalies.The upper crust in the Dabie Orogen is characterized by a low-velocity belt,sandwiched between two high velocity zones in a horizontal direction,with discontinuous low-velocity layers in the middle crust.The keel of the Dabie Orogen is mainly preserved beneath its northern section.We infer that the lower crustal delamination may have mainly occurred in the southern Dabie Orogen,which caused the mantle upwelling responsible for the formation of the granitic magmas emplaced in the middle crust as the low-velocity layers observed there.Continuous deep-level compression likely squeezed the granitic magma upward to intrude the upper crustal UHP metamorphic rocks,forming the'sandwich'velocity structure there;(3)high-velocity updoming is widespread in the crust-mantle transition zone beneath the MLYB.From the Anqing-Guichi ore field northeastward to the Luzong,Tongling,Ningwu and Ningzhen orefields,high-velocity anomalies in the crust-mantle transition zone increase rapidly in size and are widely distributed.The updoming also exists in the crust-mantle transition zone beneath the Jiurui and Edongnan orefields,but the high-velocity anomalies are mainly stellate distributed.The updoming high-velocity zone beneath the MLYB generally extends from the crust-mantle transition zone to the middle crust,different from the velocity structure in the upper crust.The upper crust beneath the Early Cretaceous extension-related Luzong and Ningwu volcanic basins is characterized by high velocity zones,in contrast to the low velocity anomalies beneath the Late Jurassic to Early Cretaceous compression-related Tongling ore field.The MLYB may have undergone a compressive-to-extensional transition during the Yanshanian(Jurassic-Cretaceous)period,during which extensive magmatism occurred.The near mantle-crustal boundary updoming was likely caused by asthenospheric underplating at the base of the lower crust.The magmas may have ascended through major crustal faults,undergoing AFC(assimilation and fractional crystallization)processes,became emplaced in the fault-bounded basins or Paleozoic sequences,eventually forming the many Cu-Fe polymetallic deposits there.

Mineralization,Geochemistry and Zircon U-Pb Ages of the Paodaoling Porphyry Gold Deposit in the Guichi Region,Lower Yangtze Metallogenic Belt,Eastern China

The newly discovered Paodaoling porphyry Au deposit from the Guichi region, Lower Yangtze River Metallogenic Belt （LYRB）, contains 〉35 tons of Au at an average grade of -1.7 g/t. It is a porphyry ＇Au-only＇ deposit, as revealed by current exploration in the depths, mostly above -400 m, which is quite uncommon among coeval porphyry mineralization along the LYRB. Additionally, there are also Cu-Au bearing porphyries and barren alkaline granitoids in the Paodaoling district. Zircon LA-ICP-MS U-Pb dating of the Cu-Au-bearing porphyries yield an age of 141-140 Ma, falling within the main magmatic stage of the LYRB, whereas the barren granites give an age of 125-120 Ma, coeval with the regional A- type granites. The Cu-Au-bearing porphyries are LILE-, LREE-enriched and HFSE-depleted, typical of arc magmatic affinities. The barren granites are HFSE-enriched, with lower LREE/HREE ratios and pronounced negative Eu anomalies. The Cu-Au-bearing porphyries in the Paodaoling district have high oxygen fugacities and high water content. Pyrite sulfur isotopes of the Paodaoling gold deposit indicate a magmatic-sedimentary mixed source for the ore-forming fluids. Based on the alteration and poly-metal zonation of the deepest exploration drill hole from the Paodaoling Au deposit, we propose that Cu ore bodies could lie at depth beneath the current Au ore bodies. The magmatism and associated Cu-Au mineralization of the Paodaoling district are likely to have formed in a subduction setting, during slab rollback of the paleo-Pacific plate.

A 3D Investigation of Geological Structure and Its Relationship to Mineralization in the Nanling-Xuancheng Ore District,Middle-Lower Yangtze River Metallogenic Belt,China

The Nanling-Xuancheng ore region of Anhui Province is located in the Middle-Lower Yangtze River metallogenic belt.Insufficient exploration and research have been carried out in this newly defined ore district,although the Chating large porphyry Cu-Au deposit and a few middle-sized skarntype Cu polymetallic deposits have been discovered.In this study,we carried out high-resolution seismic reflection,magnetotelluric,gravity,and magnetic investigations,and constructed the 3 D geological structure of the uppermost crust in a depth range of 0-5 km using a comprehensive inversion of the new data constrained by previous deep-drilling data.We hence proposed some new insights to understand the mineralization processes of this district.A system of alternating ridges and valleys is suggested as the major structure pattern,composed of“two-layer structure”of the basins and“three-layer structure”of anticlines.Moreover,a conjugated fault system and its distribution features are revealed in our models,including the Jiangnan fault,Zhouwang fault,and Kunshan thrust nappe.The Jiangnan and Kunshan faults are suggested to have controlled the diagenesis and metallogenesis.Two deep concealed plutons located in Chating and Magushan are found,forming the Mesozoic diorite-felsic intrusions.These intrusions are believed to be the causes of hydrothermal deposits such as the Chating deposit and the Magushan deposit.

High-resolution 3D crustal S-wave velocity structure of the MiddleLower Yangtze River Metallogenic Belt and implications for its deep geodynamic setting

The Middle-Lower Yangtze River Metallogenic Belt(MLYMB) is an important mineral resource region in China.High-resolution crustal models can provide crucial constraints to understand the ore-forming processes and geodynamic setting in this region. Using ambient seismic noise from 107 permanent and 82 portable stations in the MLYMB and the adjacent area,we present a new high-resolution 3D S-wave velocity model of this region. We first extract 5–50 s Rayleigh wave phase velocity dispersion data by calculating ambient noise cross-correlation functions(CFs) and then use the surface wave direct inversion method to invert the mixed path travel times for the 3D S-wave velocity structure. Checkerboard tests show that the horizontal resolution of the 3D S-wave velocity model is approximately 0.5°–1.0° and that the vertical resolution decreases with increasing noise and depth. Our high-resolution 3D S-wave velocity model reveals:(1) AV-shaped high-velocity zone(HVZ) is located in the lower crust and the uppermost mantle in the study region. The western branch of the HVZ passes through the Jianghan Basin,the Qinling-Dabie orogenic belt and the Nanxiang Basin. The eastern branch, which almost completely covers the main body of the MLYMB, is located near the Tanlu Fault. The low-velocity anomalies between the western and eastern branches are located in the area of the Qinling-Dabie orogenic belt.(2) High-velocity uplifts(HVUs) are common in the crust of the MLYMB,especially in the areas near the Tanlu Fault, the Changjiang Fault and the Yangxin-Changzhou Fault. The intensities of the HVUs gradually weaken from west to east. The V-shaped HVZ in the lower crust and uppermost mantle and the HVUs in the middle and lower crust likely represent cooled mantle intrusive rocks. During the Yanshanian period, fault systems formed in the MLYMB due to the convergence between the South China Plate and the North China Plate, the multiple-direction drifting of the PaleoPacific Plate and its subduction beneath the Eurasian Plate. The dehydration of the cold oceanic crust led to partial melting in the upper mantle. Temperature differences caused strong convection of the upper mantle material that underplated the lower crust and rose to near the surface along the deep fault systems. After mixing with the crustal materials, mineralization processes, such as assimilation and fractional crystallization, occurred in the MLYMB.

长江中下游成矿带南陵—宣城矿集区中生代构造—岩浆—成矿特征及其地质意义

安徽南陵—宣城矿集区是长江中下游成矿带中一个新确立的矿集区,近年来找矿勘查工作取得重要进展。笔者等在广泛收集以往区域地质调查以及最新地球物理探测和矿床地质勘查成果的基础上,系统总结了矿集区地质构造、岩浆岩和铜多金属矿床的地质和地球化学特征,探讨了中生代时期区域构造作用与岩浆作用和成矿作用的相互关系。研究认为,南陵—宣城矿集区构造上为一个受深大断裂控制的中生代—新生代陆相凹陷—断陷火山—沉积盆地,盆地之上叠置古生代地层构成的NE向指状展布的复背斜/逆冲推覆体,盆地基底地层组成和构造特征与盆地之上叠置的复背斜/逆冲推覆体基本一致,且两者均发育相同时代和特征的侵入岩及相关铜多金属矿床。南陵—宣城矿集区构造—岩浆—成矿特征总体上与长江中下游成矿带其他地区基本一致,反映自中生代以来受古太平洋板块向欧亚板块之下俯冲作用的控制,经历了强烈的陆内变形改造以及相应的多期次NW—SE向挤压作用和拉张作用。南陵—宣城矿集区构造—岩浆—成矿特征同时又具有其独特性,表现在其地质构造格架、侵入岩和矿床特征与长江中下游成矿带其他火山—沉积盆地明显不同,反映其在区域构造空间以及地壳基底结构和组成上的差异,同时揭示南陵—宣城矿集区是长江中下游成矿带跨构造单元复合系统的典型代表。

长江中下游斑岩-矽卡岩铜多金属矿床共伴生碲、硒资源现状和成矿规律浅析

斑岩-矽卡岩铜多金属矿床常伴生大量的碲、硒资源,提供了全球目前几乎所有的碲、硒产量,但碲、硒在这些矿床中的成矿规律还不清楚。长江中下游成矿带多处铜多金属矿床都伴生有硒和/或碲资源,但其资源现状、赋存状态和成矿规律的研究还较为薄弱。本文基于已有的研究资料,对长江中下游伴生碲、硒资源量进行了估算,对碲、硒的赋存状态和分布规律以及成矿规律进行了探讨。目前长江中下游已探明的伴生碲、硒资源量分别为9061 t和10574 t,相当于18个大型碲矿床、21个大型硒矿床,这些矿产资源已部分回收利用。其中九瑞矿集区的资源量最大。碲、硒主要以独立矿物形式存在,发育4种产状碲的独立矿物和2种产状硒的独立矿物,它们均形成于硫化物阶段,后者主要形成于晚硫化物阶段。根据资源量相对规模,该成矿带上的矿床类型可分为硒矿床、碲硒和硒碲矿床三种。以岩体为中心向外,碲、硒含量由低到高依次为斑岩型矿体、矽卡岩型矿体和层间交代型矿体。本文初步揭示了长江中下游成矿带碲、硒矿化的成矿规律,可为资源评价和找矿勘查提供科学依据。今后应加强对斑岩-矽卡岩铜金成矿系统中碲、硒富集机制的研究。

长江中下游成矿带物性结构揭示的成矿深部背景和过程

长江中下游成矿带是中国重要的铁-铜多金属资源宝库,而成矿带岩石圈构造演化是成矿带成矿全过程和矿床预测的关键。然而,构造对岩浆-成矿作用深部背景和过程的控制仍存在较大争议,主要包括上地幔对流引起的岩石圈伸展和下地壳熔融,以及与古太平洋板块俯冲有关的应力体制转换和岩浆活动两类认识。而且,这一关键地质问题仍然缺乏地球物理深探测资料的约束。为此,基于自然资源部“深部矿产资源探测与评价创新团队”在成矿带主体地区获得的地球物理探测成果,本文分析了壳幔/岩石圈、地壳及上地壳/地壳浅表不同尺度的探测结果和物性模型,总结和补充了长江中下游成矿带成矿深部背景和过程的相关认识,并提出成矿带深部的陆内俯冲板片断离引发的地幔物质上涌控制成矿带成矿系统的深部物源和通道要素。此外,铁-铜成矿系统虽然具有统一的深部背景,但受控于板片下沉引起的应力体制转换,形成于随时间变化的不同构造背景和深部过程。

安徽安庆铜铁矿床钴的赋存状态、分布与富集规律研究

长江中下游成矿带是我国东部最重要的成矿带之一,广泛发育矽卡岩型铜铁矿床且伴生Co资源,而成矿带内的矽卡岩型铜铁矿床中关键金属Co元素的赋存状态、分布以及富集规律研究尚未系统开展。本文以矽卡岩型铜铁矿床——安庆铜矿为研究对象,通过系统采样、显微观察、扫描电子显微镜、全岩化学分析及矿物原位LA-ICP MS微量成分测试手段,初步估算矿床中伴生Co的资源量约为8769t,达到中型规模,查明了伴生Co的平均含量为166×10^(-6),综合利用潜力较大。查明了铜矿石中Co含量(平均含量为166×10^(-6))明显高于铁矿石(平均含量为126×10^(-6)),尤其是含铜磁黄铁矿型矿石中Co元素富集程度最高,且计算得出磁黄铁矿、黄铁矿、磁铁矿和黄铜矿分别赋存矿石Co含量的45.1%、52.8%、0.5%和1.6%。此外,矿床内不同类型矿化蚀变岩中Co含量与磁黄铁矿和黄铁矿总量具有较强的正相关性,Co主要以类质同像的形式赋存于黄铁矿和磁黄铁矿内,黄铁矿中Co的含量变化范围较大,早石英硫化物阶段的黄铁矿(Py1)中Co含量为258×10^(-6)~25920×10^(-6),晚石英硫化物阶段的黄铁矿(Py2)中Co含量为0.3×10^(-6)~594×10^(-6),磁黄铁矿中Co含量变化范围较小,主要集中于311×10^(-6)~1181×10^(-6),Co主要富集于早石英硫化物阶段,晚石英硫化物阶段不富集。含铜磁黄铁矿型矿石中Co元素变化范围大(85×10^(-6)~430×10^(-6))是由于矿石中黄铁矿和磁黄铁矿的含量以及黄铁矿Co含量极不均匀造成的。综合前人研究,本次工作认为大气降水混入引起的成矿流体冷却和稀释可能是导致安庆铜矿中Co元素沉淀富集在黄铁矿和磁黄铁矿内的主要因素。

安徽庐枞盆地西湾铅锌矿床闪锌矿中镉的赋存状态和富集机制研究

镉(Cd)是一种重要的关键金属元素,对国家安全和新兴产业发展具有重大意义。闪锌矿是最具经济意义的富镉矿物,查明闪锌矿中镉的赋存状态,对研究镉的富集机制具有重要的意义;但受限于研究手段,闪锌矿纳米尺度上镉的赋存状态研究仍相对薄弱。西湾矿床是长江中下游成矿带庐枞矿集区内新发现的大型铅锌矿床,矿床中产出富镉闪锌矿。本次研究使用LA-ICP-MS对闪锌矿进行原位微量元素含量和Mapping分析,查明闪锌矿微米尺度镉的分布规律;在此基础上使用扫描透射电镜(STEM)查明纳米级闪锌矿的微观形貌和高分辨原子像,明确纳米尺度镉的赋存状态。研究结果表明,西湾矿床闪锌矿中镉含量的变化范围为2186×10^(-6)~9859×10^(-6),镉在闪锌矿中分布不均匀,闪锌矿孔洞发育的区域相对富镉,而闪锌矿均质区域相对贫镉。通过高分辨原子像的晶面间距和原子线扫描结果,确定西湾矿床闪锌矿中Cd原子以原位替代Zn原子的形式赋存在闪锌矿晶格中,未发现纳米级镉的独立矿物。对比金顶和牛角塘等富镉铅锌矿床,长江中下游成矿带的铅锌矿床中平均镉含量不高,推测成矿带可能缺乏充足的镉物质来源。

长江中下游转换构造结与区域成矿背景分析

中国东部中生代以来的地壳运动频繁,构造演化复杂,岩浆活动剧烈,成矿作用多样,是不同体制构造转换的重要地区。长江中下游地区是中生代特提斯构造体制与太平洋构造体制转换的经典地区,是两大构造体制交汇和转换的焦点部位,具有岩石圈物质重组、结构重建的时-空演化关系。长江中下游转换构造结由是中国东部中生代特提斯构造体制与太平洋构造体制转换的产物,大别造山带、郯庐断裂带和长江中下游成矿带直接记录了两大构造体制转换的过程、沉积-构造-岩浆-成矿的时空关系和动力学背景。长江中下游转换构造结内构造叠加强烈,规律明显,以长江复合构造带和铜陵-杭州构造带为代表的NE-SW向构造带和NW-SE向构造带,严格控制着区内燕山期岩浆活动和长江中下游成矿带的展布;长江中下游转换构造结内具有结点成矿的规律,不同规模的NE-SW向构造带与NW-SE向构造带的交切处正是区内矿集区和重要矿床的分布位置。

长江中下游成矿带火山岩盆地的成岩成矿作用

长江中下游成矿带是我国重要的铜铁多金属成矿带,其中发育溧水、溧阳、宁芜、繁昌、庐枞、怀宁和金牛盆地等火山岩盆地。与成矿带中断隆区相比,火山岩盆地内的成岩成矿作用研究仍显滞后。本文综合已有研究工作和资料,以庐枞盆地和宁芜盆地为主,探讨长江中下游地区火山岩盆地的地质特征、岩浆岩时空格架、地球化学特征及成矿作用和成矿模式等。长江中下游成矿带火山岩盆地内岩浆岩的年代学研究表明,各陆相火山岩盆地内岩浆岩均形成于早白垩世(135～123Ma),不同盆地内各旋回火山活动时间几乎相同,盆地中侵入岩的分期、岩性和成岩时代也大致可以对比。地球化学特征研究表明,盆地内早晚两旋回火山岩与两期侵入岩在岩浆起源、岩浆演化特征、岩石成因等方面一致,可以完全对应。岩浆源区为成分接近富集的交代地幔,交代地幔的形成与古板块的俯冲交代作用有关。岩浆演化经历了结晶分异作用和同化混染作用,岩浆结晶分异作用主要发生于深部岩浆房中。长江中下游成矿带火山岩盆地中成矿作用以铁矿化为主,产出以著名的"玢岩铁矿"矿床组合为特征的一系列不同类型的火山-次火山热液型和沉积改造型等铁矿床及硫铁矿、硬石膏和明矾石矿床。矿床地质地球化学特征研究表明,铁矿床和次火山岩(闪长玢岩)关系密切,其形成还受火山构造和基底膏盐层等控制和影响。成矿年代学研究证实不同玢岩型矿床的成矿时代基本一致,均为130Ma左右,盆地内铁成矿作用是在较短时间(1～2Ma)内集中"爆发式"形成的。综合火山岩盆地成岩成矿作用特征,本文建立了长江中下游成矿带火山岩盆地的成岩成矿模式,并认为火山岩盆地成岩成矿作用是中国东部中生代构造-岩浆-成矿系统演化的有机组成部分,受中国东部中生代地球动力学背景的制约。

宁芜盆地闪长玢岩的形成时代及对成矿的指示意义

宁芜盆地是长江中下游成矿带的重要组成部分和玢岩型铁矿床的主要产地,盆地内广泛产出闪长玢岩,这类岩体与铁矿床的形成关系密切,但其精确的成岩成矿时代及其形成构造背景的研究仍十分薄弱。本次工作在详细野外地质工作的基础上,系统开展了盆地内与铁矿床有关的7个闪长玢岩体的年代学研究,通过对闪长玢岩锆石LA-ICP-MS同位素定年方法,确定了盆地内主要闪长玢岩体,凹山岩体、陶村岩体、和尚桥岩体、东山岩体、白象山岩体、和睦山岩体和姑山岩体的成岩时代分别为130.2±2.0Ma、130.7±1.8Ma、131.1±1.5Ma、131.1±3.1Ma、130.0±1.4Ma、131.1±1.9Ma和129.2±1.7Ma。定年结果表明盆地内闪长玢岩成岩年龄均为130Ma左右,其成岩年龄可以近似代表铁矿床的成矿年龄。长江中下游地区存在145～136Ma、135～127Ma、126～123Ma三期成岩(成矿)作用,宁芜盆地内闪长玢岩是第二期岩浆活动的产物,其形成时代明显晚于长江中下游成矿带断隆区内与斑岩型-矽卡岩型铜(铁)、金矿床有关的高钾钙碱性岩体。宁芜盆地内闪长玢岩及玢岩型铁矿床形成于区域岩石圈伸展构造环境。

长江中下游成矿带成矿规律和成矿模式

长江中下游成矿带作为中国东部重要的成矿带之一,成矿地质条件、成矿规律和成矿模式的相关研究已经十分深入,形成了一系列公认的理论研究成果,本文重点论述了成矿带成矿地质条件和成矿规律方面研究的新进展,并在此基础上构筑了成矿带的成矿模式。本文主要开展了以下总结工作:(1)将成矿带的构造要素突破以往按构造单元分解的做法,确立跨构造单元的"复合构造系统",结合成矿带成岩成矿作用特点,重新确定了长江中下游成矿带的范围,并对成矿亚带进行了重新划分;(2)收集汇总了长江中下游成矿带近年来国内外学者最新的成岩成矿年龄数据,总结了矿床时空分布规律;(3)从地质,地球物理和地球化学等方面,总结归纳了沿基底结合带复活的网状断裂系统,阐明了成矿带的控矿构造格架,分析了长江中下游成矿带的成因规律;(4)补充和完善了断隆区和断凹区的成矿模式,并初步构筑了长江中下游成矿带综合成矿模式。提出长江中下游成矿带内主体成岩成矿作用总体上分为走滑挤压阶段(146~135Ma)、走滑引张阶段(135~126Ma)和拉张伸展阶段(126~123Ma)等三个阶段,古太平洋板块作用导致的壳幔过程,引发含元古代弧岩浆岩源区活化和中生代的构造活化("双活化")是长江中下游成矿带形成的主要机制。

安徽庐枞盆地泥河铁矿床年代学研究及其意义

庐枞盆地位于长江中下游断陷带内,地处扬子板块北缘,是长江中下游成矿带中重要的铁铜多金属成矿区。庐枞盆地内火山岩和侵入岩分布广泛,包括龙门院、砖桥、双庙和浮山4组火山岩以及34个出露地表的侵入岩体。泥河铁矿床是盆地西北部新勘探发现的大型铁矿床,其精确的成岩成矿时代及其形成构造背景研究仍十分薄弱。本次工作在详细野外地质工作的基础上,系统开展了泥河铁矿床成岩成矿年代学研究,通过对岩浆岩锆石LA ICP-MS和金云母40Ar-39Ar定年方法,确定矿区中的辉石闪长玢岩、正长斑岩和粗安斑岩的成岩时代分别为132.4±1.5Ma、129.4±2.0Ma和134.3±1.2Ma,成矿时代为130.9±2.6Ma。矿床地质特征表明辉石闪长玢岩是成矿母岩,粗安斑岩形成于成矿作用之前,正长斑岩为成矿期后形成的脉岩,穿切火山岩地层和矿体。上述定年结果与地质事实吻合,表明泥河铁矿床的成岩成矿作用几乎同时发生。通过与庐枞盆地和区域成岩成矿时代对比,认为盆地内玢岩型铁矿床集中形成于130Ma左右,是长江中下游成矿第二期成矿作用活动的产物,庐枞盆地内130Ma左右的辉石闪长玢岩侵入体是寻找泥河式玢岩型铁矿床的勘探靶区。