秦岭成矿域复合造山过程中印支-燕山期金-多金属成矿作用

The Qinling Orogen in central China has been a long-term geological studied focus for its unique tectonic location，complicated geological history and abundant mineral resources. The Qinling Orogen belt completely records tectonic evolutional processes from breakup of supercontinents, evolution of ocean and continent, continental accretion, collisional orogeny , within-plate stretching and incontinental overprinted orogeny, The belt is also the most important polymetallic metallogenic zone, but the study on metallogenic mechanism of different type deposit in this zone is still very limited. In this study, based on three basins (Xunyang-Zhen’an, Zhashui-Shanyang and Xicheng-Fengxian), four important deposit types, Carlin or Carlin-like and orogenic type gold deposit, porphyry-skarn type copper-gold deposit, sedimentary exhalative-reformed type lead-zinc deposit, and sedimentary -reformed type mercury, antimony and uranium deposit, are selected to study their metallgenic backgrounds, features and origin of ore-forming fluids, detailed deformational processes and the associated inpolymetallic mineralization, crust- mantle interaction and its contribution to polymetallic mineralization, isotope chronology of large-scale polymetallic deposits and their paragenesis-separation mechanism. The study will focus on the geology, geochemistry and their coupling geodynamic setting. And assembly of multi - structure, complex of multi-stage construct, and exchange of crust and mantle materials, transport of the ore-forming fluid, precipitation of the ore -forming matter and mechanism of gold polymetallic deposits will be discussed. Furthermore, the relationship of deformation-thermal-fluid-chemical action with the large-scale gold polymetallic deposit in the transformation geodynamic system will be clarified. This project will also discuss whether there is time and space coupling relation between the process of the Qinling orogen and the mineralization evolution, and further indicate the formation of the ore deposits responding to geological events.

秦岭造山带经历了复杂而漫长的地质演化历史，是中国最重要的多金属富集区和全球罕见的多金属成矿域。本项目以旬阳-镇安、柞水-山阳和西成-凤县三个盆地为研究基地，对斑岩-矽卡岩型铜钼矿床、热水沉积-改造型铅锌矿床、沉积-改造型汞锑铀矿床、卡林-类卡林型及造山型金矿床的成矿地质背景、成矿流体性质及来源、构造变形与金-多金属矿化的耦合关系、壳/幔相互作用与元素富集机制、不同金属矿床的成矿年龄与共生分异机理进行研究，探讨秦岭造山带形成演化过程中的多构造集结、多期构造复合活动、壳幔物质交换与矿源供给、流体输运、矿质聚集和金-多金属矿床定位的耦合关系，阐明由构造动力体制转换引发的构造变形–岩浆侵入–热流体化学作用与金–多金属巨量堆积的成矿机理，揭示秦岭成矿域内众多金属大规模成矿作用在不同成矿阶段对造山地质事件的响应。

为探讨秦岭造山带印支-燕山期中高温、中低温金-多金属矿床之间的成矿联系，本项目对卡林-类卡林型与造山型金、斑岩-矽卡岩型铜钼、低温热液脉型汞锑等矿床开展了成矿构造背景、壳/幔相互作用、构造变形与金-多金属矿化关系、成矿物质来源与流体性质、矿床形成机理研究，取得的成果如下：(1) 西秦岭印支期中-酸性岩浆岩记录了俯冲期亏损地幔组分对地壳生长贡献显著。锆石Hf同位素结果显示壳幔混合作用对铜金成矿作用影响大。晚三叠世秦岭造山带处于由同碰撞挤压向后碰撞伸展转变的过渡构造体制，是造山型金和斑岩-矽卡岩型铜钼成矿的一个关键时期。(2) 秦岭造山带燕山期中-酸性岩浆岩及相关金-多金属矿床集中形成于侏罗纪/白垩纪之交，成岩成矿与秦岭陆内造山事件密切相关，处于陆内造山阶段的挤压向伸展转换的构造背景。(3) 区域构造演化、构造变形与矿床特征显示，卡林-类卡林型金、低温热液脉型汞锑的成矿作用存在统一性和相似性。(4) 金矿床中Au-Ag-Te-Bi矿物组合是指示岩浆热液参与成矿的重要标志；黄铁矿结构及元素分析揭示，不可见金与从成矿流体中抽提出来的金被富砷、贫铁且生长活跃的黄铁矿表面化学吸附相关。(5) 金-多金属矿床中电气石化学组成和汞、锑、铁、镁等同位素变化的协同约束，能有效限定金属物质来源、成矿流体演化，精细刻画成矿过程。(6) 南秦岭斑岩-矽卡岩型矿床成矿岩体为氧化性富水岩浆,形成铜矿床的岩体的εHf(t)值与锆石Eu异常呈正比，而形成钼矿床的岩体εHf(t)值较低，指示花岗岩类岩浆源区不同，是导致燕山期铜、钼在秦岭造山带不同构造单元内发生不同矿化类型和矿化分带的原因。(7) 提出同化混染作用程度的高低决定了非矿、贫矿、富矿花岗伟晶岩脉的地球化学特征与铀赋存状态的差异性。(8) 通过对区域成矿元素地球化学场进行小波分解提取弱异常，建立一种多变量元素地球化学预测建模方法，并得到大水矿区找矿工程验证。