【作者】 吴冉；

【导师】 刘显凡；

【作者基本信息】 成都理工大学 ， 矿物学、岩石学、矿床学， 2011， 硕士

【摘要】 马厂箐铜钼金多金属矿床是“三江”成矿带上与富碱斑岩有关的典型的斑岩型矿床之一。印度-欧亚大陆碰撞在青藏高原东缘形成了巨型的金沙江-哀牢山-红河走滑断裂系统,在断裂系统内分布着一个总体呈北西走向的喜马拉雅期富碱斑岩带[1],该带所处区域岩浆活动频繁,壳幔作用活跃,构造运动复杂,各圈层的物质及能量交换频繁、成矿作用显著。本文通过对马厂箐矿床地质特征的研究,发现马厂箐矿体的产出具有从岩体→接触带→围岩,矿化由钼矿→铜(钼)矿→金矿,成矿温度由高温→高中温→中低温→低温渐变分带的特征,对其围岩蚀变研究发现蚀变可划分出3个带,岩体内发育强硅化核(中心)、石英钾长石化带(中部)、石英绢云母化带(边部)蚀变→接触带发育接触交代型(角岩化、矽卡岩化)蚀变→围岩地层中发育硅化、白云石化、方解石化蚀变,并伴有黑色不透明微晶物质产出,经分析,该黑色不透明物质为地幔流体参与成矿作用的微观踪迹显示,也是引发围岩蚀变和壳幔混染叠加成矿的重要物质源和动力源。通过对矿石、脉体、矿化围岩的稀土及微量元素地球化学研究发现,各类样品的稀土配分模式在明显富集轻稀土的基础上,表现轻微负Eu异常,而LREE富集是地幔流体作用的显著特征之一;矿石、脉体及矿化围岩的微量元素配分模式总体表现大离子亲石元素和高场强元素相对富集。通过对该矿床的岩矿石进行同位素地球化学研究,进一步论证了成矿流体和岩浆流体均来自于富集地幔,并且在马厂箐钼矿段,成矿物质和流体来源显示以幔源为主;在乱硐山铜(钼)矿段,则显示壳幔混源;在金厂箐金矿段,显示以地壳来源为主,由此得到一般规律为:从钼矿段→铜矿段→金矿段,在其成矿物质和流体来源的壳幔混染中,幔源混染逐渐减弱,壳源混染逐渐增强。此外,本文还对马厂箐矿床成岩成矿地质年代学进行了系统研究,提供了花岗斑岩中的LA-ICP-MS锆石U-Pb和辉钼矿Re-Os同位素年代学的研究数据:马厂箐含矿岩体锆石U-Pb年龄为36.17±0.36Ma,代表了富碱斑岩的成岩年龄;辉钼矿Re-Os年龄为34.7～35.1Ma,代表成矿时代。与前人的研究成果对比后得出:马厂箐矿床成矿作用与该区晚期富碱斑岩的岩浆活动有关。结合透岩浆流体成矿理论[61]认为,该区成矿流体是包含于富碱岩浆并与其互不混溶的地幔流体,但在上侵运移过程中伴随富碱岩浆的成岩作用而与富碱岩浆发生不同程度分离,并相应受到不同程度地壳物质的混染,进而形成地幔流体作用的系列成矿效应,表现为产于富碱斑岩体内,属于正岩浆成矿体系的斑岩型钼矿;产于岩体与围岩接触带,属于接触交代成矿体系的矽卡岩型铜(钼)矿和主要赋存于地层围岩中的构造破碎蚀变岩型金矿;某些出现于斑岩体内部的金矿,则一般受控于穿切斑岩体的成岩后断裂。在这一成岩成矿过程中,地幔流体可以随深度和环境变化引起的物理化学条件变化,挥发份逸出,其性质由熔浆→超临界流体→热液转化,并运载和沿途活化成矿物质至适宜容矿部位集中,促使壳幔物质叠加成矿,由此构成马厂箐钼铜金矿床的成矿分带和系列成矿。更多还原

【Abstract】 Machangqing Copper-Molybdenum Polymetallic Deposit is one of theporphyry-type deposits related to alkali-rich porphyries in theNujiang-Lancangjiang-Jinshajiang metallogenic belt. The collision between India andEurasia resulted in the huge Jinshajiang-Ailaoshan-Honghe River strikeslip-faultsystem, where locates a northwest strike Himalayan alkali-rich porphyries. Moreover,the magmatic action and crust-mantle interaction are frequent; therefore this region ischaracterized by complex tectonics and obvious mineralization.By studying the geological characteristics of Machangqing Deposit,we noticethat ore body shows gradient features from rock,contact zone to wall rock,with amineralization change from Molybdenum ore,copper-molybdenum ore to gold oreand temperature changes from high,high-medium,medium-low to low. According toresearch on wall rock alteration , 3 zones are recognized which include strongsilicification in the core,quartz K-feldspar in the center,quartz sericite in the margin .In the contact zone,there is contact Metasomatic(Skarn) alteration while in the wallrock there are silicification,dolomitization and calcilization alteration,associated witha black opaque micro-crystal proved to be an indication of mantle fluid mineralizationand reason for wall rock alteration and crust-mantle overlapping mineralization.Based on trace elements geochemical and REE researches of ores,veins andmineralized wall rocks, we discover that REE patterns show remarkable enrichedLREE as well as slight negative Eu abnormal. The general patterns are rich in largeion lithophile elements(LILE) and high field strength elements(HFSE).Further more,isotope geochemistry suggests that ore-forming fluid and magma originated frommantle. In Machangqing molybdenum(copper)ore block,it is mainly mantle source;In Luantongshan copper ( molybdenum ) ore block , it is mainly crust-mantleoverlapping source ; In Jinchangqing gold ore block , it is mainly crust source.Therefore,conclusion can be made that mantle source effect becomes weaker while crust source effect gets stronger.Besides,systematic geochronology research of rocks and ores forming process inMachangqing deposit supplies the Zircon LA-ICP-MS U-Pb data of ganite-porphyryand molybdenite Re-Os data:the Zircon U-Pb age of Machangqing ore-bearing rockis 36.17±0.36Ma , which is the rock-forming age of alkali-rich porphyries ; Themolybdenite Re-Os age is 34.7～35.1Ma,represents ore-forming epoch. Comparewith formers’results , we believe the Metallogeny of study area is related withmagmatism of late alkali-rich porphyries.Combined with trans-magmatic fluid Metallogeny theory, we believe that theore-forming fluid is mantle source and derives from the alkali-rich magma. During theupwelling of ore-forming fluid , it is separated with the alkali-rich magma andcontaminated with crust , consequently a series of Metallogenies developed. Indetails , molybdenite block of orthomagmatic Metallogeny system is formed inalkali-rich porphyries ; copper ( molybdenum ) block of contact MetasomaticMetallogeny system is found in rock-wall rock contact zones;and the gold block is inwall-rock. Some of the gold blocks occurring in porphyries are often controlled bypost-faults that cut porphyries. With the develop of ore forming,the volatile of mantlefluid escaped,and the characteristics of mantle fluid varied from magma,supercriticalfluid to hydrothermal fluid due to different depths and environments. Meanwhile,activated ore-forming materials were migrated to proper host rock areas and enrichedthere,which finally led to the series of ore-forming belts of molybdenum-copper-golddeposit in Machangqing Area.更多还原