成矿岩浆的Cl、S和Cu富集机制及流体出溶过程：以藏北多龙Cu-Au矿集区为例

The enrichment mechanism of Cl, S, Cu and fluid exsolution of ore-forming magma are the key factors that controlling the formation of porphyry Cu-Au deposit. However, the two key problems have not yet been well understood and revealed. In this application, ore-forming/barren porphyries, granodiorite and intermediate-mafic volcanic rocks from the giant Duolong Cu-Au ore district will be used as the main target. Based on the detailed field and peotrographic investigations, Cl-S-Cu and major-trace element composition of apatite, biotite, amphibole, and melt/fluid inclusions will be determined by EMPA and LA-ICP-MS analyses to reveal Cl-S-Cu content and their evolutional trend of ore-forming magma，and to further uncover their ore-forming characteristics. In addition, combing with the detailed studies on O-H-Li stable isotopes of biotite and amphibole, apatite in situ H isotope, zircon in situ Li isotope, and Li and S isotopes of bulk rock, this project tries to investigate the variation of O-H-Li-S isotope value and Cl-S-Cu content of ore-forming magma during fluid exsolution, to further constrain the enrichment mechanism of ore-forming element and the process of fluid exsolution. Finally, this work will deepen our understanding on enrichment mechanism of ore-forming elements during magma evolution-fluid exsolution and further constrains ore-forming theory of porphyry Cu-Au deposit, and has important significance to improve the metallogenesis and exploration of subduction-related porphyry deposit in Tibet.

成矿岩浆Cl-S-Cu富集机制和深部流体出溶过程是斑岩Cu-Au矿床形成的关键控制因素，但对这两个关键问题至今尚未得到很好的揭示。本申请项目拟以西藏班公湖带多龙超大型斑岩Cu-Au矿集区中发育的近同期成矿/不成矿斑岩、花岗闪长岩及中-基性火山岩为研究对象，在详细野外和岩相学基础上，着重对角闪石、黑云母、磷灰石等矿物及熔体/流体包裹体进行电子探针和LA-ICP-MS原位Cu-Cl-S等元素成分分析，反演成矿岩浆Cl-S-Cu的含量及其演化富集过程，揭示成矿岩浆特质。并结合角闪石和黑云母O-H-Li、磷灰石原位H、锆石原位Li及全岩S-Li同位素分析，阐明流体出溶过程中岩浆Cl-S-Cu的含量及同位素变化，限定成矿流体出溶过程及富集机制。以上研究有助于理解岩浆演化-流体出溶过程中成矿元素富集机理，深化斑岩型矿床的成矿理论，在丰富青藏高原早期俯冲阶段的斑岩成矿作用及区域矿产勘查亦具有重要的意义。

成矿岩浆Cl、Cu和S富集机制和流体出溶过程是形成斑岩型Cu-Au矿床的关键控制因素。项目围绕这一关键科学问题，对多龙超大型Cu-Au矿集区同源且与成矿相关的深成岩-浅成斑岩及其重要造岩-副矿物等进行了系统研究。岩浆磷灰石、角闪石和硬石膏的成分揭示未去气的成矿闪长质岩浆具有高氧化性（>NNO+1）、富S（~1800ppm）和Cl（~1.2 wt%）的特征，但并不富Cu（20-40ppm）。磷灰石XF/XCl比值的升高和S含量降低、角闪石Cl含量降低（0.38-0.09 wt%）和低的H同位素（-103 to -113‰）组成，指示在约900°C和深度7-8km的上部岩浆房，岩浆演化到花岗闪长质开始发生流体出溶，初始出溶的流体为高温-高盐度的盐水流体（盐度~50 wt%NaCl equiv.），从而有效地萃取巨量岩浆中Cu而形成成矿流体。蚀变矿物O-H和硫化物S同位素同样也显示成矿流体主要为岩浆来源（δ18O = 2.1-9.9‰和δD = -68.5到-92.9‰）。另外，Fe同位素变化暗示出溶流体具有比成矿岩浆（δ57Fe = 0.03-0.07 ‰）更低的Fe同位素组成（δ57Fe = -0.3~-0.1‰）；并且，从斑岩-高硫型浅成低温阶段热液流体的演化，黄铜矿的Fe同位素呈现逐渐降低的趋势（δ57Fe=-0.6~-0.3‰），主要受控于温度降低、磁铁矿结晶以及氧逸度的变化。最终建立了多龙斑岩-浅成低温Cu-Au成矿系统的岩浆-热液流体演化过程和成矿模式。本项目揭示了多龙成矿岩浆中Cl、S和Cu含量演化及流体出溶过程，认为岩浆富S和Cl以及早期流体出溶是形成超大型斑岩矿集区形成的关键控制因素；并提出角闪石成分和H同位素是有利的区域找矿标志之一。研究结论深化了斑岩型Cu-Au矿床的成矿理论，以及对区域寻找同类型矿床具有一定的借鉴意义。