大兴安岭北段岔路口巨型斑岩钼多金属矿床的岩浆演化、流体出溶与成矿机理

The Chalukou porphyry Mo polymetallic deposit, a newly discovered world-class deposit in northern Great Khingan Mts, is controlled by volcanic mechanism and poly-stage porphyries with high silicon and rich in alkali. Characterized by well developing of fluorite, magnetite and hematite, special texture such as unidirectional solidification texture (UST) and quartz shell, it creates a precious opportunity for the research on the transition process from magma to fluids of high fluorine porphyry Mo deposit. Taking the differentiation evolution of multi-stage magmatism, transition process from magma to fluids and construction of alteration and mineralization as major threads, we will determine the time interval of magmatism, hydrothermal activity and mineralization interval by SIMS, LA-ICPMS and Ar-Ar geochronological methods after detailed field geological survey, core documentation of four exploration profiles, field mapping of detailed veins and alteration and systematical sampling. Through the comprehensive study on petrology, ore microscopy, mineralogy and chemical composition of elements, in combination with analysis on Sr-Nd-Pb, zircon Hf-O and in-situ S isotopes, as well as analysis on ore-forming elements of melt inclusions, melt-fluid inclusions and fluid inclusions by LA-ICPMS, we will reveal the differentiation evolution, emplacement mechanism and source region of magma, switching process from magma to fluids, development of hydrothermal alteration-mineralization-vein system, assemblage and separation mechanism for Mo and Pb-Zn of the composite volcano-intrusive complex. This research will promote our understanding for the formation and evolution of this kind of high fluorine porphyry Mo deposits, and also will provide theoretical basis for further exploration in the region.

大兴安岭北段新近发现的岔路口世界级斑岩钼多金属矿，受控于火山机构与高硅富碱多期斑岩，以发育萤石和磁铁矿为特色,并发育UST、硅化壳等特殊结构，为高F斑岩钼矿的岩浆-流体转换研究提供了难得机遇。拟以多期岩浆分异演化、岩浆-流体转换和蚀变-矿化结构为主线，通过细致的地表观察、4条钻孔剖面岩芯编录、脉系与蚀变精细填图和系统采样，采用SIMS和LA-ICPMS及Ar-Ar等定年方法，确定岩浆活动和热液-矿化时限。通过系统的岩石学、矿相学、矿物学、元素化学成分研究，辅以Sr-Nd-Pb、锆石Hf-O及原位S同位素分析，结合熔融包裹体、熔流包裹体和流体包裹体中成矿元素的LA-ICPMS分析，揭示复式火成杂岩体内岩浆分异演化、就位过程及其源区性质、岩浆-流体转换过程、热液-矿化-脉系演进及其对钼-铅锌分离富集的控制机理。该研究将增进对该类高F斑岩钼矿床形成演化的理解，并为区域同类矿床的勘查提供理论依据。

岔路口斑岩钼多金属矿床的发现和勘探是近年来大兴安岭北段森林覆盖区找矿的重大突破，探获钼金属量246万吨，资源储量居全国钼矿之首。其成矿岩浆-热液以高氟高氧化、成矿系统以下部斑岩钼矿化-上部脉状铅锌矿化而别具特色。本次以多期次岩浆分异演化、蚀变-脉系-矿化精细刻画、成矿流体演化、成矿物质来源为研究主线，通过多种研究手段，取得以下重要研究成果：（1）厘定了成岩成矿时代，矿区发育三期岩浆活动，即成矿前花岗岩(172~163Ma)，成矿期细晶斑岩、花岗斑岩和石英斑岩（147~148Ma）和成矿后脉岩(145~129Ma)，成矿时代为145.7±1.5Ma，岩浆-热液-矿化演化时限约2.5Ma。（2）成矿期斑岩体具有高硅、富碱、富氟的特征，岩浆起源于新生下地壳，有少量的古老物质加入，并经历过强烈的分异结晶过程。（3）确认岔路口矿床为典型的高氟高氧化斑岩矿床，并精细刻画了其热液脉系-蚀变-矿化特征，识别出热液系统具有多期脉动特征。（4）通过硫化物和蚀变矿物的成分，查明了岔路口Mo-Zn-Pb系统蚀变-矿化过程的微量元素行为。（5）通过各阶段脉系石英CL图像、石英微量元素和流体包裹体研究，揭示了成矿系统的流体演化过程，岔路口矿床初始成矿流体为单一富气相、低盐度、高温、富金属流体，随着流体上升、降压、冷却，伴随着增强的水岩反应、大气水混合过程，形成斑岩钼矿化以及脉状铅锌矿化。（6）H-O-S同位素揭示岔路口热液流体为岩浆来源，早期以岩浆水为主的流体控制了钼矿的形成，晚期铅锌成矿期间有较多大气降水的加入，结合黄铁矿微量元素特征，指示Mo-Zn-Pb成矿系统具有相同物质来源且经历不同演化过程。（7）分析了矿床控矿因素并建立了成岩成矿模式。研究成果不仅深化了斑岩钼矿成矿理论与Mo-Pb-Zn成矿系统的认识，对区带找矿也具有重要借鉴意义。