大兴安岭岔路口斑岩钼矿床流体成分及成矿意义

Compositions and Microthermometry of Fluid Inclusions of Chalukou Porphyry Mo Deposit from Great Xing'an Range:Implications for Ore Genesis

岔路口超大型斑岩型钼矿床位于大兴安岭北段,以网脉状和角砾岩型矿化为主.该矿床经历了4个成矿阶段:Ⅰ.石英-钾长石;Ⅱ.石英-辉钼矿;Ⅲ.石英-多金属硫化物;Ⅳ.石英-萤石-方解石.包裹体的岩相学及激光拉曼研究揭示,石英斑晶内的熔体-流体包裹体中熔体成分有更长石和钠长石,为岩浆出溶作用形成;子矿物多相包裹体(S型)中含有钾盐、石盐、赤铁矿和石膏等子矿物,显示出成矿流体为高氧逸度.第Ⅰ成矿阶段包裹体有气液两相(L+V型)、富CO2三相(C型)和含石盐、钾盐、赤铁矿及硬石膏等子矿物的多相(S型)等类型,第Ⅱ成矿阶段除了有L+V型、C型以及含钾盐、石盐、黄铜矿和辉钼矿等子矿物多相(S型)外,还可以见到S型包裹体与气相包裹体(V型)共存;第Ⅲ成矿阶段以L+V型和含方解石的S型包裹体为主;第Ⅳ成矿阶段除见到L+V型包裹体外,还可以见到液相包裹体(L型).显微测温结果显示从早到晚,流体包裹体均一温度从530℃变为120℃、盐度从66.7%NaCl equiv变为1.2%NaCl equiv,呈现逐渐降低的趋势.群体包裹体成分显示各阶段均含有气相CO2,液相成分中Na+,K+,Ca2+,SO42-,Cl-含量很高,而F-含量极少.成矿流体总体属于富含CO2的高盐度、高氧逸度的NaCl-H2O-CO2体系,在流体演化过程中温度、氧逸度、盐度和CO2含量逐渐降低.温度、盐度、CO2含量逐渐降低及绢云母化影响了矿石沉淀.

The Chalukou Mo deposit lies in the northern Great Xing？an Range,in which veinlet and breccia dominate mineraliza-tion.The whole hydrothermal ore-forming processes involve the following four stages：I.quartz-potash feldspar stage;II. quartz-molybdenite stage;III.quartz-polymetallic sulfide stage;IV.quartz-fluorite-calcite stage.The petrographic and laser Ra-man spectroscopy study show that the melt-fluid inclusions in quartz phenocryst contain component of oligoclase and albite,in-dicating they directly exsolved from primary magma.Halite,sylvite,hematite,and gypsum are recognized as daughter miner-als in S-type inclusions of granite porphyry,suggesting high oxygen fugacity.The stageⅠquartz captures （L＋V）-type,C-type,and S-type （contain halite,sylvite,hematite,and anhydrite daughter minerals）fluid inclusions.The stage Ⅱ quartz cap-tures （L＋V）-type,C-type,and S-type （contain halite,sylvite,chalcopyrite,and molybdenite daughter minerals）fluid inclu-sions,in addition,V-type and S-type fluid inclusions are coexistent.In the stage III,there are （L＋V）-type and S-type with calcite as daughter minerals.Stage IV develops （L＋V）-type and L-type fluid inclusions.Microthermometric data show the＆amp;nbsp;homogenization temperatures （530 ℃→120 ℃）and salinities （66.7% NaCl equiv→1.2% NaCl equiv）decrease gradually.The gas components have a certain amount of CO2 in every stage,and the liquid components in fluid inclusions have Na^＋,K^＋,Ca^2＋,SO4^2-,and small amount of F^-.The initial fluids are high oxygen fugacity and salinity NaCl-H2 O-CO2 fluid system with abundant CO2 .The homogenization temperatures,salinities,lgfO2 ,and CO2 content tend to fall from the early to late stage.The decline of homogenization temperatures,salinities,and CO2 content as well as sericitization greatly hinder the depositing of metallogenic elements.