江南造山带湖南段金矿成矿事件及其构造背景

江南造山带湖南段为一重要的金成矿带,目前关于带内金矿形成的时代背景存在较大争议。本文基于区域成岩成矿年代学、矿床(区)地质特征、矿床成因和流体来源、区域构造演化背景等多方面资料,对带内各主要金矿区的成矿时代逐一进行详细解析,以此为基础重新厘定了区域金矿成矿地质事件及其时代,并探讨了各成矿事件的构造背景,初步形成以下认识。江南造山带湖南段主要发生了加里东期、印支晚期和燕山期等3期金成矿事件。加里东期金矿成矿年代为430～410 Ma(志留纪后期),产于同期雪峰冲断带的中段-西南段和东段东部、湘中-湘东南构造岩浆带的东北部等3个地区,各区赋矿地层分别为板溪群、冷家溪群、冷家溪群,前两个地区的成矿与加里东运动变质变形和构造活化作用有关,后一个地区的成矿与志留纪后期花岗质岩浆活动提供热能和流体有关。印支晚期金矿成矿年代为227～202 Ma(晚三叠世),主要分布于同期雪峰冲断带东南缘构造岩浆隆起带,与后碰撞花岗质岩浆活动的热能和热液驱动有关。燕山期金矿成矿年代为152～130 Ma(晚侏罗世—早白垩世初),主要分布于同期雪峰冲断带东南部构造岩浆隆起带的东部,与伸展环境下的花岗质岩浆活动有关。     

吉黑东部Au- Ag- Cu- Mo 石墨成矿带主要地质成矿特征及潜力分析

随着地质大调查的开展,吉黑东部地区新的找矿进展和预测成果不断涌现,使之成为我国下一步找矿的重要地区之一,需要对其开展系统的成矿区划和部署研究工作。本文以新的研究成果和找矿突破为基础,通过综合分析,在该地区划分新的重要成矿部署区带,厘定边界并将其命名为"吉黑东部Au-Ag-Cu-Mo-石墨成矿带"。结合区域成矿地质背景的综合研究,在区内划分了3个III级成矿带,初步建立了Au-Ag-Cu-Mo-石墨成矿带成矿谱系,其成矿作用具有多期次发育和多系统控制的特点,在时间演化上表现为多旋回性、继承性、新生性和叠加性特点,其中海西期与印支末期-燕山期是成矿大爆发期。研究区主要成矿类型为沉积变质型石墨铁金矿、海相火山气液型铜铅锌多金属矿、接触交代型、岩浆热液型多金属矿和岩浆型铜镍矿。结合区域找矿进展和潜力评价最新成果,认为本区Au、Ag、Cu、Mo、石墨潜力巨大,为下一步勘查部署的主攻矿种,同时在本区划分了13个远景区,其中7个为重点远景区,6个为一般远景区,对研究区下一步矿产勘查部署工作有一定指导意义。     

钦-杭成矿带东段村前含矿斑岩地球化学特征及其构造环境与成矿意义

村前铜多金属矿床位于钦杭成矿带东段,为一具有矽卡岩型矿化和斑岩型矿化的铜多金属矿床,含矿岩体为燕山早期花岗闪长斑岩,岩石具有富硅、富铝、富碱的特点,属于偏铝-过铝质钙碱性花岗岩类。岩体具有从深部向浅部蚀变增强,大部分组分活动性不明显,而成矿元素Cu-Mo-Fe-Pb-Zn-Au-Ag含量明显增加,Na2O、Sr含量降低,REE元素除Eu少量丢失外,其余均呈一致的迁入特征。岩体属Ⅰ型花岗质岩石,由具角闪石+石榴子石残留相的火成岩部分熔融形成的熔浆,混合或混染了地壳重熔型岩浆上侵就位而成。钦杭结合带东段,燕山期中酸性岩浆活动具有从176~150Ma的埃达克岩或具岛弧花岗岩特征的Ⅰ型花岗岩,至150~140Ma的S型花岗岩,向140~110Ma的A型花岗岩演化趋势,显示了地壳由厚减薄的过程,暗示其大地构造背景为岩石圈的伸展减薄环境,而形成于169.3±1.1Ma的村前斑岩体正处于伸展阶段早期。综合岩体成矿特征表明,钦杭成矿带东段及邻近地区,176~160Ma主要形成与Ⅰ型花岗质岩石有关的以Cu为主的多金属矿床;160~150Ma主要形成与Ⅰ型花岗质岩石有关的Cu-Mo矿床与W-Sn矿床;150~140Ma主要形成与S型花岗质岩石有关的以W-Sn-Mo为主的多金属矿床,以及以Ag-Pb-Zn为主的多金属矿床;140~110Ma主要形成与A型花岗质岩石有关的以W-Sn-Mo为主的多金属矿床,少量与Ⅰ型花岗质岩石有关的Pb-Zn矿床。     

Tectonic implications from Re-Os dating of Mesozoic molybdenum deposits in the East Qinling-Dabie orogenic belt

The East Qinling-Dabie molybdenum belt is part of a larger East-West trending metallogenic belt in eastern China. Most of the molybdenum deposits occur as porphyry or porphyry-skarn type, but there are also some vein type deposits. Following systematic Re-Os dating of molybdenite from 13 deposits and comparisons with two previously dated deposits, we have recognized that the molybdenum mineralization in the East Qinling-Dabie belt was developed during hydrothermal activity linked to magmatism and the emplacement of granitoid stocks. Three pulses of granitoid magmatism and Mo mineralization are recognized corresponding to significant tectonic events in the East Qinling-Dabie belt. Vein type deposits dated at 233-221 Ma were formed in detachment fractures, indicating localized extension within the collisional setting of the North China and Yangtze Cratons. I-type and transitional I- and S-type granites and related mineralization dated at 148-138 Ma may have formed part of a continental magmatic arc, with widespread magmatism and back-arc extension caused by subduction of the Izanagi or Paleopacific plate beneath the Eurasian continent in a WNW-ESE direction in the Late Jurassic-Early Cretaceous. Both S-type and transitional S- and I-type granite-associated porphyry molybdenum deposits dated at 131-112 Ma are part of an extensive mineralization event throughout East China that can be ascribed to regional large-scale lithospheric thinning, delamination and thermal erosion.     

Tectonic implications of Re-Os dating of molybdenum deposits in the Tianshan–Xingmeng Orogenic Belt,Central Asia

The Tianshan–Xingmeng molybdenum belt is part of a larger E–W-trending metallogenic belt in northern China. Most of these molybdenum deposits occur as porphyry or porphyry-skarn type, but there are also some vein-type deposits. Following systematic Re-Os dating of molybdenite from four deposits and comparisons with two previously dated deposits, we conclude that molybdenum mineralization in the Tianshan–Xingmeng Orogenic Belt resulted from hydrothermal activity linked to the emplacement of granitoid stocks. Three pulses of granitoid magmatism and Mo mineralization have been recognized in this study, corresponding to tectonic events in the Tianshan–Xingmeng Orogenic Belt. We identify five distinct stages of Mo mineralization events in the Tianshan–Xingmeng Orogenic Belt: 320–250 Ma, 250–200 Ma, 190–155 Ma, 155–140 Ma, and 140–120 Ma. Late Palaeozoic (320–250 Ma) Mo mineralization was closely related to closure of the Palaeo-Asian Ocean and collision between the Siberia and Tarim cratons. Triassic (250–200 Ma) Mo mineralization occurred in a post-collisional tectonic setting. The Early–Middle Jurassic (190–155 Ma) Mo mineralization was related to subduction of the Palaeo-Pacific Ocean on the eastern Asian continental margin, whereas in the Erguna block, the Mo mineralization events were associated with the subduction of the Mongol–Okhotsk Ocean. From 155 to 120 Ma, large-scale continental extension occurred in the Tianshan–Xingmeng Orogenic Belt and surrounding regions. However, the Late Jurassic (150–140 Ma) Mo mineralization events in these areas evolved in a post-orogenic extensional environment of the Mongol–Okhotsk Ocean subduction system. The Early Cretaceous (140–120 Ma) Mo mineralization occurred under the combined effects of the closure of the Mongol–Okhotsk Ocean and subduction of the Palaeo-Pacific Ocean.     

浙闽粤滨海地区成矿演化和矿床时空分布的控制因素

浙闽粤滨海地区中生代的成矿作用主要与岩浆作用有关,矿床在空间上有明显的分带性,在时间上具有明显的迁移性,但这种成矿分带和迁移完全不同于东太平洋安第斯和美国西部平行于俯冲带或垂直海岸线的成矿分带和迁移模式,区域中生代矿床的时空分布和成矿演化明显受着区域的构造应力作用方式,岩浆作用特征,赋矿地层和岩石的含矿性特征以及成岩成矿后的风化剥蚀程度等因素的影响。     

Spatial–temporal relationships of Mesozoic volcanic rocks in NE China: Constraints on tectonic overprinting and transformations between multiple tectonic regimes

LA-ICP-MS zircon U–Pb ages and geochemical data are presented for the Mesozoic volcanic rocks in northeast China, with the aim of determining the tectonic settings of the volcanism and constraining the timing of the overprinting and transformations between the Paleo-Asian Ocean, Mongol–Okhotsk, and circum-Pacific tectonic regimes. The new ages, together with other available age data from the literature, indicate that Mesozoic volcanism in NE China can be subdivided into six episodes: Late Triassic (228–201 Ma), Early–Middle Jurassic (190–173 Ma), Middle–Late Jurassic (166–155 Ma), early Early Cretaceous (145–138 Ma), late Early Cretaceous (133–106 Ma), and Late Cretaceous (97–88 Ma). The Late Triassic volcanic rocks occur in the Lesser Xing’an–Zhangguangcai Ranges, where the volcanic rocks are bimodal, and in the eastern Heilongjiang–Jilin provinces where the volcanics are A-type rhyolites, implying that they formed in an extensional environment after the final closure of the Paleo-Asian Ocean. The Early–Middle Jurassic (190–173 Ma) volcanic rocks, both in the Erguna Massif and the eastern Heilongjiang–Jilin provinces, belong chemically to the calc-alkaline series, implying an active continental margin setting. The volcanics in the Erguna Massif are related to the subduction of the Mongol–Okhotsk oceanic plate beneath the Massif, and those in the eastern Jilin–Heilongjiang provinces are related to the subduction of the Paleo-Pacific Plate beneath the Eurasian continent. The coeval bimodal volcanic rocks in the Lesser Xing’an–Zhangguangcai Ranges were probably formed under an extensional environment similar to a backarc setting of double-direction subduction. Volcanic rocks of Middle–Late Jurassic (155–166 Ma) and early Early Cretaceous (145–138 Ma) age only occur in the Great Xing’an Range and the northern Hebei and western Liaoning provinces (limited to the west of the Songliao Basin), and they belong chemically to high-K calc-alkaline series and A-type rhyolites, respectively. Combined with the regional unconformity and thrust structures in the northern Hebei and western Liaoning provinces, we conclude that these volcanics formed during a collapse or delamination of a thickened continental crust related to the evolution of the Mongol–Okhotsk suture belt. The late Early Cretaceous volcanic rocks, widely distributed in NE China, belong chemically to a low- to medium-K calc-alkaline series in the eastern Heilongjiang–Jilin provinces (i.e., the Eurasian continental margin), and to a bimodal volcanic rock association within both the Songliao Basin and the Great Xing’an Range. The volcanics in the eastern Heilongjiang–Jilin provinces formed in an active continental margin setting related to the subduction of the Paleo-Pacific Plate beneath the Eurasian continent, and the bimodal volcanics formed under an extensional environment related either to a backarc setting or to delamination of a thickened crust, or both. Late Cretaceous volcanics, limited to the eastern Heilongjiang–Jilin provinces and the eastern North China Craton (NCC), consist of calc-alkaline rocks in the eastern Heilongjiang–Jilin provinces and alkaline basalts in the eastern NCC, suggesting that the former originated during subduction of the Paleo-Pacific Plate beneath the Eurasian continent, whereas the latter formed in an extensional environment similar to a backarc setting. Taking all this into account, we conclude that (1) the transformation from the Paleo-Asian Ocean regime to the circum-Pacific tectonic regime happened during the Late Triassic to Early Jurassic; (2) the effect of the Mongol–Okhotsk suture belt on NE China was mainly in the Early Jurassic, Middle–Late Jurassic, and early Early Cretaceous; and (3) the late Early Cretaceous and Late Cretaceous volcanics can be attributed to the subduction of the Paleo-Pacific Plate beneath the Eurasian continent.     

吉林敦化大石河钼矿床成因与辉钼矿Re-Os 同位素测年

大石河钼矿床是近年来在小兴安岭-张广才岭钼成矿带南缘新发现的一个大型钼矿床。深部矿体产于似斑状花岗闪长岩体顶部,呈细脉浸染型; 近地表矿体主要呈含辉钼矿石英脉,赋存于浅变质岩中。钼矿化受隐爆角砾岩筒及构造裂隙控制,矿化与蚀变具有明显的分带性,属斑岩型钼矿床。对采自矿区浅部矿体中的5 件辉钼矿样品进行了Re-Os 同位素测年,获得模式年龄( 182. 1 ± 2. 7) ～ ( 191. 9 ± 2. 6) Ma,加权平均年龄( 186. 7 ± 5. 0) Ma,MSWD 值为11. 8,表明大石河钼矿形成于燕山早期。结合近年来小兴安岭-张广才岭钼成矿带上所获得的成岩成矿年龄数据,认为160 ～ 190 Ma 是该钼成矿带的钼矿成矿作用的集中期。辉钼矿样品中Re 含量为3. 549 ～ 4. 362 μg·g － 1,指示成矿物质为壳源。综合分析认为,大石河钼矿床为该区燕山早期大规模成矿事件的产物,形成于古亚洲构造域和环太平洋构造域叠加和转换期的构造环境。     

云南格咱岛弧斑岩-矽卡岩铜、钼（金）矿床成矿系统

格咱岛弧带是西南三江多岛弧盆系中一个主要的地质构造单元,它始于晚三叠世甘孜—理塘洋壳的向西俯冲,燕山期经历了陆内汇聚和造山后伸展作用阶段,区内岩浆活动和成矿作用强烈,是近年来新发现的重要铜多金属成矿带。根据区内岩浆岩和矿床的时空分布,同位素年代学证据,构造环境及成矿作用,将格咱岛弧成矿系统划分为印支期成矿亚系统和燕山期成矿亚系统。印支期主要发育了与安山岩同源的壳幔型中酸性岩浆作用,形成斑岩型Cu矿成矿系统,燕山期伴随着同碰撞中酸性岩浆活动形成斑岩型Mo(Cu)及热液型W(Mo)成矿系统。研究表明,格咱岛弧深部找矿具有较好的资源潜力,其中燕山期Mo多金属成矿已显现出良好的找矿前景。     

藏东类乌齐-左贡成矿带构造演化与成矿作用

藏东类乌齐-左贡成矿带(简称类-左带)是三江特提斯成矿域内一条重要的成矿带,其整体的研究较为薄弱、零散.本文基于最新的研究成果,按照成矿时代、地质背景、成矿作用及成矿元素组合将带内矿床划分为了6个成矿系列,包括:(1)印支期晶质石墨矿系列;(2)印支期蛇绿岩相关风化淋滤型菱镁矿系列;(3)印支期沉积-改造型Fe-Cu多...     

中国西北部成矿地质特征及找矿新发现

西北地区地处中亚构造域和特提斯构造域的交汇处,中间夹有塔里木克拉通和华北克拉通的西段。地质历史上,两个克拉通及其裂解的微陆块的形成和运动史,基本约束了中国西北部的构造发展历程。围绕克拉通及微陆块的显生宙造山带基本是其周缘增生的结果,由于大陆运移,其他大陆边缘增生的产物,在早三叠世(210 Ma)大陆汇聚中也添加了进来,这些造山带及其陆块边缘的增生是西北各种内生金属矿床的重要形成背景。同时,新元古代、晚古生代陆内与地幔柱有关的大火成岩省的发育,为铜镍等重要矿床的形成提供了条件。此外,在克拉通及其微陆块形成和后期的叠生盆地中,形成了重要的沉积和沉积变质矿床。西北地区近年来重要找矿发现,不断印证了西北克拉通边缘板块构造增生和板内幔源构造岩浆作用成矿的特点,并对传统的地质背景构造认识提出了挑战。这其中,最具经济价值和地质意义的是3个超大型金属矿床的发现:西天山早石炭世阿吾拉勒火山-次火山岩浆喷溢型磁铁矿矿床、东昆仑早泥盆世夏日哈木岩浆深部熔离-贯入型铜镍矿床和西昆仑侏罗—白垩纪火烧云构造热液型铅锌矿床。阿吾拉勒磁铁矿矿床是中国首例火山-次火山岩浆喷溢型磁铁矿矿床,可与智利的拉科超大型典型磁铁矿矿床对比,且更具有经济价值,该矿床的勘查和研究为深入理解中亚造山带天山及其邻区石炭纪裂谷型火山岩浆作用与成矿提供了研究的范例;夏日哈木铜镍矿是中国近年来最重要的铜镍矿发现,探明镍资源量已达百万吨以上,该矿床的发现为查明中国早古生代末期新的岩浆铜镍成矿事件及其找矿潜力提供了研究新区;火烧云铅锌矿床是新近发现的具有超大型资源潜力的铅锌矿床,也是喀喇昆仑—三江造山带中蕴藏的中新生代巨型铅锌成矿带上最重要的成矿发现,为深化研究青藏高原东北缘巨型铅锌成矿带的成矿物质来源和构造控矿机制提供了新的基地。     

吉黑东部中生代晚期中酸性岩浆活动与金成矿作用

吉黑东部金矿床集中分布于小兴安岭北麓、完达山和太平岭（东宁-延边）,矿床类型以斑岩型-浅成低温热液型矿床为主。成矿年代大约为110 Ma左右。稳定同位素显示成矿流体具有岩浆水特征,而成矿物质则主要来源于深源岩浆,这说明吉黑东部金成矿可能与岩浆活动有关。同时,研究显示吉黑东部广泛发育一套120~95 Ma的中酸性火山-侵入岩,其与110 Ma金成矿事件时空关系密切。这套火山-侵入岩在矿区表现为英安-流纹质或安山-英安质火山岩组合和闪长玢岩、花岗斑岩及花岗岩等脉岩和小侵入体。而岩石化学特征则表明其属中酸性的钙碱性系列,为一套俯冲流体交代地幔楔起源的岩浆。区域对比研究表明,吉黑东部金成矿与俄罗斯远东地区Sikhote-Alin锡成矿、韩国南部金-银成矿可能处于同一大地构造环境的不同构造部位。成矿年代从吉黑东部向东南方向有变年轻的趋势,且成矿岩浆岩的酸性成分增强而幔源成分减少。综合区域岩浆岩和区域成矿特征,表明吉黑东部存在一期110 Ma的金成矿事件,其与中生代晚期板块俯冲及其后的岩石圈拆沉作用和弧后伸展有关,成矿大地构造环境为大陆边缘弧。     

复合成矿与构造转换——以长江中下游成矿带为例

复合成因矿床分布广泛,把它们单独划分出来进行研究,对于深入认识成矿过程、发展成矿理论和指导找矿勘探,均有重要意义.鉴于中国大陆东部中生代岩浆作用强烈,对前期成矿作用的影响也很明显,因此本文以长江中下游成矿带为例,评介了复合成矿作用的几种主要机理,认同前人提出的叠加和改造是其基本类型,但预富集作用也应重视,同时也不能忽视继承成矿和再生成矿,特别是继承和预富集联合多次出现时,可以形成区域性成矿元素大规模富集.同时,本文还将它们放在区域构造体制和机制转化演化过程中加以考察,进一步明确它们在中生代构造体制转换以前主要以沉积(含热水沉积)成因的含矿建造、矿源层或矿(胚)层产出,而矿床的最终形成与就位则主要与新构造体制下由挤压向引张转化的过渡环境中构造-岩浆活动有关,呈现出“成矿大爆发”的现象.其中早期( 145～136Ma)构造机制是以走滑挤压作用为主,形成与高钾钙碱性岩系有关的铜金矿化.晚期(135 ～ 127Ma)以走滑引张作用为主,形成了与橄榄安粗岩系有关的铁硫矿化.但这两期都有广泛发育的以叠加改造为主的复合成因铜、金、铁、硫及铅锌矿床,从而在典型的岩浆热液矿床和沉积矿床之间形成了一套过渡性矿床序列(层控矽卡岩型→沉积热液叠加型→层控叠改型→迁移式改造型→原地式改造型),构建了一个矿床“家族”.末期( 126 ～ 123Ma)以引张作用为主,出现碱性火山岩和A型花岗岩类,伴随铁、金、钼、铀等矿化,成矿带的成矿活动随之进入尾声.     

老挝-越南长山成矿带古特提斯构造岩浆演化与成矿作用

老挝-越南长山成矿带位于特提斯构造成矿域东南段,发育大量古特提斯旋回岩浆岩和铜-金-铁-锡等多金属矿床,是研究东特提斯构造岩浆演化与成矿作用的天然实验室。本文系统梳理了长山成矿带的成岩成矿时代、矿床组合和岩石地球化学研究成果,揭示了长山成矿带古特提斯时期的岩浆岩时空格架,构建了晚石炭—中二叠世(317~264 Ma)哀牢山-马江洋的俯冲、中二叠—晚三叠世(263~235 Ma)华南地体与印支地体的碰撞以及晚三叠世(234~202 Ma)碰撞后伸展等构造演化过程。初步建立了长山成矿带各阶段的成矿模式,包括俯冲期斑岩-矽卡岩型Fe-Cu-Au和浅成低温热液型Cu-Au-Ag成矿(305~279 Ma)、碰撞期斑岩-矽卡岩型Sn和矽卡岩型Fe-Au成矿(249~236 Ma)、伸展期热液脉型Au矿化(212~204 Ma)。受限于晚三叠世晚期岩浆活动和成矿作用研究资料的缺乏,碰撞后伸展阶段的成矿作用仍有待进一步研究。     

南秦岭宁陕地区月河坪夕卡岩型钼矿Re-Os年龄和矿床学特征

宁陕地区月河坪钼矿床位于南秦岭多金属成矿带,属于夕卡岩型钼矿。本文采用辉钼矿Re-Os同位素定年方法,精确地测定月河坪钼矿的成矿时代。分析结果显示,5件辉钼矿样品Re-Os同位素模式年龄的变化范围小,集中在189.8Ma和195.4Ma之间,获得加权平均年龄值191.4±1.6Ma,与等时线回归计算得到的年龄值193.6±3.5Ma在误差范围内相吻合。结果说明成矿时代为早侏罗纪,成矿作用属于中国北部燕山期大规模成矿期的一部分。结合已报道的成矿年龄资料,月河坪钼矿床可能形成于扬子板块与华北板块的后碰撞造山作用过程,但有可能受到后期岩浆活动的改造和破坏。同时推测在南秦岭地区存在印支末期到燕山早期的成矿事件,这对于秦岭造山带尤其是南秦岭地区钼矿资源勘探具有借鉴意义。     

Magmatism, Deep Processes and Gold Deposits in Eastern Hebei, China

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Gold and silver metallogeny of the South China Fold Belt: a consequence of multiple mineralizing events?

The South China Fold Belt is part of the South China Block that is interpreted to be the result of multiple tectonic and magmatic events that formed a collage of accreted Proterozoic and Phanerozoic terranes. The Jurassic to early Cretaceous Yanshanian period (180–90 Ma), a time of major tectono-thermal events that affected much of eastern and southeastern China, is of great metallogenic importance in the fold belt. This period is linked to subduction of the Pacific plate beneath the Eurasian continent, and is manifested by voluminous volcano-plutonic activity of predominantly calc-alkaline affinity.The distribution of gold and silver deposits in the South China Fold Belt indicates the presence of two distinct metallogenic provinces. A region of basement uplifts, which are controlled by shear zones and form Neoproterozoic inliers of metamorphosed iron-rich rock types, defines the first province. In this province, orogenic lodes and volcanic-related epithermal deposits represent the more significant precious-metal mineralization. The second province is essentially confined to a belt of Yanshanian felsic–intermediate volcanic and subvolcanic rocks that extends along most of the southeastern China coast in an area known as the Coastal Volcanic Belt. Deposits in the Coastal Volcanic Belt are silver- and/or copper-rich, volcanic-hosted and epithermal in character.The precious-metal metallogeny of the South China Fold Belt is interpreted to have developed in at least three stages: one as a result of collision events, during the Caledonian Orogeny (ca. 400 Ma), the second during the Indosinian Orogeny (ca. 200 Ma) and the third during or soon after the formation of the Yanshanian magmatic belt (Yanshanian Orogeny; 180–90 Ma). The latter was responsible for a hydrothermal event that affected large sections of the belt and its Proterozoic substrate. This may have resulted in the redistribution and enrichment of precious metals from preexisting orogenic gold lodes in Neoproterozoic basement rocks, which are now exposed as windows in zones of tectonic uplift. The Yanshanian hydrothermal activity was particularly widespread in the Coastal Volcanic Belt and resulted in the formation of both low- and high-sulfidation epithermal gold and silver, and locally copper and other base-metal mineralization. It is suggested that the Coastal Volcanic Belt has greater potential for world-class epithermal and porphyry deposits than previously realised.     

Triassic magmatism and Mo mineralization in Northeast China: geochronological and isotopic constraints from the Laojiagou porphyry Mo deposit

The Laojiagou Mo deposit is a newly discovered porphyry Mo deposit located in the Xilamulun Mo metallogenic belt, Northeast China. Mo mineralization mainly occurred within the monzogranite and monzogranite porphyry. Re–Os isochron dating of molybdenites indicate a mineralization age of 234.9 ± 3.1 Ma. Zircon LA–ICP–MS U–Pb analysis for monzogranite porphyry and monzogranite yield ²⁰⁶Pb/²³⁸U ages of 238.6 ± 1.8 and 241.3 ± 1.5 Ma, respectively, indicating that Laojiagou Mo mineralization is related to Middle Triassic magmatism. Hf isotopic compositions of zircons from both monzogranite porphyry and monzogranite are characterized by positive ε_Hf(t) values [ε_Hf(t) = 2.9–7.3 and 1.5–7.9, respectively] and young T_DM2 model ages, which implies that the magma was derived from juvenile crust created during accretion of the Central Asian Orogenic Belt (CAOB). Identification of the Laojiagou Mo deposit adds another important example of Triassic Mo mineralization in the Xilamulun Mo metallogenic belt where most Triassic Mo deposits in northeast China cluster around the northern margin of North China Craton. Based on the regional geological setting and geochronological and Hf isotope characteristics, we propose that Triassic Mo deposits and related magmatic rocks in northeast China formed during the last stages of evolution of the CAOB. These deposits formed during post-collisional extension after the closure of the Palaeo-Asian Ocean and amalgamation of the North China–Mongolian Block with the Siberian Craton.     

Study of late-Mesozoic magmatic rocks and their related copper-gold-polymetallic deposits in the Guichi ore-cluster district,Lower Yangtze River Metallogenic Belt,East China

ABSTRACT

The Guichi ore-cluster district in the Lower Yangtze River Metallogenic Belt hosts extensive Cu–Au–Mo polymetallic deposits including the Tongshan Cu–Mo, Paodaoling Au, Matou Cu–Mo, Anzishan Cu–Mo, Guilinzheng Mo and Zhaceqiao Au deposits, mostly associated with the late Mesozoic magmatic rocks, which has been drawn to attention of study and exploration. However, the metallogenic relationship between magmatic rocks and the Cu–Au-polymetallic deposits is not well constrained. In this study, we report new zircon U–Pb ages, Hf isotopic, and geochemical data for the ore-bearing intrusions of Guichi region. LA-ICP-MS U–Pb ages for the Anzishan quartz diorite porphyrite is 143.9 ± 1.0 Ma. Integrated with previous geochronological data, these late Mesozoic magmatic rocks can be subdivided into two stages of magmatic activities. The first stage (150–132 Ma) is characterized by high-K calc-alkaline intrusions closely associated with Cu–Au polymetallic ore deposits. Whereas, the second stage (130–125 Ma) produced granites and syenites and is mainly characterized by shoshonite series that are related to Mo–Cu mineralization. The first stage of magmatic rocks is considered to be formed by partial melting of subducted Palaeo-Pacific Plate, assimilated with Yangtze lower crust and remelting Meso-Neoproterozoic crust/sediments. The second stage of magmatism is originated from partial melting of Mesoproterozoic-Neoproterozoic crust, mixed with juvenile crustal materials. The depression cross to the uplift zone of the Jiangnan Ancient Continent forms a gradual transition relation, and the hydrothermal mineralization composite with two stages have certain characteristics along the regional fault (Gaotan Fault). Guichi region results from two episodes of magmatism probably related to tectonic transition from subduction of Palaeo-Pacific Plate to back-arc extensional setting between 150 and 125 Ma, which lead to the Mesozoic large-scale polymetallic mineralization events in southeast China.     

皖南东至兆吉口铅锌矿床成矿时代的厘定及其找矿指示意义

皖南东至兆吉口铅锌矿床是近年来在江南过渡带西段新发现的一个规模达中型的中-低温热液型矿床。目前揭露的铅锌矿体均赋存于东至断裂带及其西侧次级张(扭)性断裂及裂隙中。文章选取了该矿床主要矿石矿物闪锌矿以及与主成矿阶段金属硫化物紧密共生的石英,分别采用流体包裹体Rb-Sr法和40Ar-39Ar法进行同位素地质年龄测定。4件闪锌矿样品获得流体包裹体Rb-Sr等时线年龄为(128±1)Ma;2件石英样品获得流体包裹体40Ar-39Ar坪年龄分别为(128.74±3.02)Ma和(128.19±1.98)Ma,等时线年龄分别为(128.81±5.25)Ma和(128.30±3.47)Ma,反等时线年龄分别为(128.82±5.24)Ma和(128.31±3.47)Ma。同位素地质年龄测试结果基本一致,表明兆吉口铅锌矿床形成于128 Ma左右,成矿时代为早白垩世。该成矿年龄与赋矿闪长玢岩的形成时间((129.0±2.3)Ma~(128.4±2.7)Ma)一致,也与东至断裂燕山晚期的活动年龄((126.3±2.2)Ma)相近,表明该矿床成矿与燕山晚期的构造-岩浆活动密切相关,此时区域构造背景为强烈挤压后的伸展环境。这一矿化事件在成矿时代上明显晚于长江中下游成矿带中的断隆区(如铜陵、安庆-贵池等矿集区)的铜金多金属矿床和皖南成矿带中的钨钼多金属矿床(136 Ma),而与长江中下游成矿带断坳区的玢岩铁矿床的成矿时间(135~127 Ma)相近,指示长江中下游成矿带与皖南成矿带之间的江南过渡带中发育有燕山晚期较晚阶段(128 Ma左右)的铅锌矿化事件,为今后在该区开展铅锌多金属矿床找矿勘探提供了重要依据。