长江中下游成矿带三维S波速度结构及对深部过程的约束

利用73个固定台站记录的163个远震事件数据,采用多道互相关技术挑选了5524条S波到时数据,并对S波到时数据进行地壳校正,在此基础上采用天然地震层析成像方法和远震S波到时信息,获得了长江中下游成矿带上地幔的三维S波速度结构模型.研究结果表明:(1)研究区域上地幔存在着明显的低速异常,且走向与成矿带相同,可能为上涌的软流圈热物质;(2)研究区域地幔过渡带和上地幔底部存在着明显的高速异常,可能为俯冲的古太平洋板块和拆沉的岩石圈;(3)成矿带上地幔的低速异常呈现由南向北逐渐变浅的空间分布特征,该特征表明软流圈热物质由南向北上涌.综合分析认为,成矿带中生代大规模岩浆活动和成矿作用的深部过程主要与岩石圈的拆沉密切相关.     

闽西南多金属成矿带地质地球物理特征综合研究——以永定大排多金属矿区为例

闽西南地区位于福建武夷山成矿带西南部,自远古宙以来经历了多期次的构造演化.该区地处东南沿海构造-岩浆-成矿带上,为环太平洋大陆边缘多金属成矿带与南岭多金属成矿带复合部位,是我国重要的多金属矿产地.永定大排多金属矿区作为近年来武夷山成矿带新发现的大型多金属矿,区内叠加作用和控矿作用相对复杂,现有的地质地球物理工作程度不足以满足对该区域成矿规律的深入认识,一些基础地质问题亟待解决.因此,本文在深入收集永定大排矿区地质地球物理资料基础上,综合分析区域成矿背景与成矿构造,在重点区域布设综合地球物理勘探工作,包括1：1万高精度磁测、可控源音频大地电磁剖面及反射地震剖面.基于上述工作：1）开展了研究区航磁数据三维磁化率反演与分布特征分析与大地电磁二维电阻率反演与分布特征分析,开展了地震资料真地表深度偏移成像,获得了更加准确的地震剖面成像结果.2）结合推覆体控矿特征,地震剖面和电阻率剖面、航磁反演结果相互验证和约束,勾画了地下构造形态.地表地质剖面延伸和标定了构造形态的地质内涵,获得了从地表到3000 m深度的构造解释结果.解释结果清晰地显示了与推覆相关的构造、控矿层位以及岩体信息,为三位一体的找矿思路提供了地球物理依据.     

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.     

基于GIS成矿预测中几个关键问题的探讨

在前人研究结果和实践的基础上,提出了基于GIS成矿预测需要解决的几个关键问题,包括矿产地质数据处理、专家的知识经验、成矿预测数学方法的选取、数字化的成矿预测数据在不同GIS软件间的转换等,对其中一些关键问题提出相应的研究思路及解决办法。     

核幔成矿物质与地幔热柱多级演化成矿

研究认为金等成矿物质主要来自核-幔源区,以气态-气液混合态、含矿流体的形式,通过地幔热柱→地幔亚热柱→幔枝构造→有利构造扩容带,迁移到幔枝构造外围的韧脆性剪切带、侵入岩体的内、外接触带、各种脉岩与围岩的接触带等有利部位集聚成矿,并构成矿田→矿床→矿体(脉)的有序排列组合,表现出不同的矿床类型。因此,应侧重研究构造成矿控矿作用,以指导新一轮地质找矿和矿产资源评价。文中还举例分析了胶西北焦家断裂与三山岛断裂的交切关系及其控矿作用。     

The oldest Mo porphyry mineralization in the Yangtze Valley Metallogenic Belt of eastern China: Constraints on its origin from geochemistry,geochronology and fluid inclusion studies at Matou

The Matou Mo(-Cu) deposit, located in the Yangtze Valley Metallogenic Belt of central-eastern China, is a typical porphyry-type Mo deposit. The orebodies at the deposit are hosted by Matou porphyritic granodiorite, which is the largest intrusive in the area. Quartz vein-type and disseminated sulfide mineralization are well developed in the porphyry and near its contact with Silurian sandstone. Crosscutting relationships indicate that porphyritic granodiorite is the oldest phase in the pluton, which is crosscut by a porphyritic diorite containing traces of chalcopyrite, and later dolerite dykes. These phases have U-Pb zircon dates of 147 ± 3, 140 ± 1 and 135 ± 1 Ma, which confirms the cross-cutting relationships observed in the field. A Re-Os molybdenite isochron age of 147 ± 4 Ma indicates that the porphyritic granodiorite is the source of the oldest Mo mineralization in the metallogenic belt and was formed during a change of the tectonic setting in the area, from an intracontinental orogeny to extensional tectonics. From 147 to 135 Ma, crust-mantle interaction played an important role in the formation of magmatic rocks at Matou. Systematic petrological and geochemistry investigations reveal that the three phases have a crust source with minor input from the mantle. Investigation of ore-forming fluid, H-O isotopes, S isotopes, and the Re content of molybdenite indicate that the ore-forming fluid and metals were derived from the lower crust. During the evolution of fluid from initial magmatic fluids (stage I) to ore-forming fluids (stage II), fluid boiling accompanied by the input of relatively cooler meteoric water led to the deposition of the Mo mineralization.     

A prediction model for important mineral resources in China

Prediction models for mineral resources provide an analytical foundation and method to express the results of resource evaluations. The project “China National Mineral Resources Assessment Initiative” was conducted during 2006–2013, with the aim to determine the location, quantity, and quality of 25 important mineral resources occurring at depths of <1 km. There are currently 80 integrated prediction models on the scale of III–level metallogenic belts in use across China. The Huangshaping Pb–Zn polymetallic deposit, Hunan province, China, is used as a case study to establish methods and processes for developing a mineral resource prediction model that would be used for exploration targeting. The construction of prediction models requires the development of a classification scheme for the proposed prediction method appropriate for the prediction area. An initial metallogenic model is quantitatively transformed to a prospecting model, and then a prediction model. The incorporation of additional methodology, analysis of a comprehensive geological database, and correlation of asymmetric information between the well–explored typical deposit area and regional prediction area, yield an integrated prediction model. This paper also discusses the prediction modeling theory, and presents 12 models used for mineral assessments.     

滇西镇康水头山Pb-Zn矿床成矿流体及矿质来源探讨——H、O、S、Pb同位素地球化学证据

滇西镇康水头山Pb-Zn矿床是保山地块镇康Pb-Zn-Fe-Cu多金属矿集区内又一重要找矿成果。矿体呈似层状、透镜状产于上寒武统保山组大理岩化灰岩中,呈NEE向顺层产出,矿石矿物主要为闪锌矿和方铅矿,偶见黄铜矿和黄铁矿等;脉石矿物主要有白云石、绿泥石、方解石、石英和绢云母等。本文基于对矿床地质特征的详细研究,结合矿床H、O、S、Pb同位素组成,对其成矿流体和矿质来源进行了探讨,同时与毗邻的芦子园超大型Pb-Zn-Fe-Cu多金属矿床进行了对比。研究表明:该矿床石英的δD值介于-101.1‰~-93.3‰之间,均值为-96.85‰(n=4),δ~(18)O_(H_2O)值为3.37‰~3.77‰之间,均值为3.57‰(n=4),表明成矿流体早期以原生岩浆水为主,有大气降水的混入。矿床金属硫化物的δ~(34)S值均为正值,介于4.1‰~12.2‰,均值为8.23‰(n=10),与旁侧的芦子园矿床δ~(34)S值(8.9‰~12‰)较为接近。该矿床可划分出三个成矿阶段,阶段Ⅱ为以闪锌矿和方铅矿为主的主要成矿阶段(δ~(34)S主要集中在4.1‰~6.2‰之间),其δ~(34)S均值可近似代表成矿热液中的δ~(34)S∑S值,即δ~(34)S∑S≈δ~(34)S均值=6.56‰(n=7),闪锌矿和方铅矿δ~(34)S值有部分重叠,但总体上具有δ~(34)S闪锌矿δ~(34)S方铅矿以及不同颜色闪锌矿之间δ~(34)S深棕色闪锌矿δ~(34)S棕褐色闪锌矿δ~(34)S浅棕色闪锌矿的分布特征,暗示硫同位素在硫化物间的分馏达到平衡,表明S同位素组成较为稳定,显示水头山矿床具有深部壳源岩浆成因的特征。矿床金属硫化物的Pb同位素分析显示,Pb同位素组成非常集中(~(206)Pb/~(204)Pb=18.3408~18.4483,均值为18.3815,~(207)Pb/~(204)Pb=15.8337~15.9440,均值为15.8745,~(208)Pb/~(204)Pb=38.8224~39.4391,均值为38.9941,n=10),投点主要分布在上地壳演化线上方,表明其Pb主要来自于以岩浆作用为主的上地壳物质。本文认为矿区深部壳源岩浆热液是水头山矿床最重要的成矿流体与矿质来源,流体的混合作用是矿床金属元素沉淀和富集的重要机制,矿床具有低温、后生成矿特征,推测矿床的形成与燕山晚期的岩浆热液作用有关。     

安徽庐枞盆地罗河铁矿床中榍石LA-ICP-MS U-Pb定年及其意义

罗河铁矿床位于长江中下游铁铜金成矿带庐枞矿集区,已探明资源量约10亿吨,是成矿带内最大的铁矿床。矿床主成矿阶段广泛发育热液成因榍石,以榍石-硬石膏-磷灰石组合为特征,在矿床-800~-900m和-1500~-1600m两个不同深度稳定发育,为确定成矿时代和成矿流体演化提供了良好的研究对象。本次工作对罗河铁矿床深部和浅部两层矿体中热液榍石开展了年代学及地球化学研究,结果表明榍石中存在(Al,Fe)~(3+)+(F,OH)~-=Ti~(4+)+O~(2-)置换反应,并富含Zr、Nb和REE等元素。榍石中Zr含量估算矿床成矿温度约700℃,指示玢岩型矿床比矽卡岩型铁矿床具有更高的成矿温度,高温条件有利于Ti元素的迁移。榍石的稀土元素配分图均呈现出明显右倾,并具较高的稀土元素总量以及明显的负Eu异常特征,轻稀土富集表明其结晶早于磷灰石和绿帘石等矿物,形成于高温热液环境,不同深度榍石的Eu异常变化表明成矿流体的氧逸度从深部到浅部有所升高。热液榍石原位微区LA-ICPMS U-Pb定年结果表明,上、下两层榍石形成时代分别为130.0±0.9Ma和129.1±0.8Ma~129.7±0.8Ma,表明罗河铁矿床两层矿体是同一成矿系统的在不同深度的产物。矿床成矿时代与区内隐伏闪长岩体成岩时代一致,结合矿床地质特征研究,本文认为闪长玢岩是矿床的成矿母岩。罗河铁矿床属于燕山晚期岩浆热液活动的产物,形成于区域早白垩世岩石圈减薄的环境。     

Geological and Geochemical Constraints on the Newly Discovered Yangchongli Gold Deposit in Tongling Region, Lower Yangtze Metallogenic Belt

The newly discovered Yangchongli gold deposit is a unique independent gold deposit in the Tongling ore-cluster region controlled by the tectonic alteration firstly discovered in the Lower Yangtze Metallogenic Belt(LYMB). The host magmatic rocks mainly consist of monzodiorite and K-feldspar granite. The LA-ICP-MS U-Pb zircons dating yielded weighted mean ~(206)Pb/~(238)U ages of 140.7 ± 1.8 Ma and 126.4 ± 1.2 Ma for the monzodiorite and K-feldspar granite, respectively. Monzodiorites are enriched in Sr, Ba, Rb, and depleted in Y, Yb with high Sr/Y and La/Yb ratios, similar to the geochemical features of adakite, considered as products of differentiation of mafic magmas originating from lithospheric mantle melt/fluids caused by metasomatism during paleo-Pacific Plate subduction in the Mesozic. In contrast, the compositions of K-feldspar granites are A-type granites, indicating an extensional tectonic background. Gold ores hosted in the fracture zone occurred as quartz vein within cataclastic rock. Sulfur and lead isotopes from pyrites show crust-mantle mixing characteristics. Metal components from strata also took part in the gold mineralization, and resulted from two episodes of magmatism that were probably related to tectonic transition from a compressive to an extensional setting between 140–126 Ma, which led to the Mesozoic large-scale polymetallic mineralization events in eastern China.