辽宁青城子姚家沟斑岩型钼矿流体包裹体

姚家沟钼矿是辽宁青城子矿田中近年来发现的钼矿床,位于华北克拉通北缘,燕辽钼成矿带内。姚家沟花岗斑岩岩体中发现的脑状石英细脉(UST)和石英眼是岩浆出溶热液的直接证据。该矿床蚀变分带特征明显,辉钼矿化主要发育在钾化带及矽卡岩化带中。对姚家沟岩体和钾化钼矿带的5期流体活动进行流体包裹体显微观测表明,其流体包裹体类型丰富,包括单相水包裹体(PW)、两相水包裹体(W)、三相CO_2包裹体(C)、纯CO_2包裹体(PC)和含子矿物包裹体(S),S型流体包裹体中子矿物有赤铁矿、黄铜矿和其他未知矿物,但没有石盐子晶。该矿床流体演化为:1)早期石英眼(均一温度为211.4~515.4℃,盐度(w(NaCl))为0.8%~19.2%)的高中温中低盐度富CO_2体系;2)成矿期石英脉(均一温度为179.5~424.5℃,盐度为2.4%~21.5%)的高中温中低盐度NaCl-H_2O-CO_2体系;3)后期石英脉(均一温度为167.8~353.3℃,盐度为3.4%~15.8%)的中低温中低盐度NaCl-H_2O-CO_2体系;4)晚期方解石脉(均一温度为132.5~234.1℃,盐度为0.9%~11.2%)的中低温中低盐度NaCl-H_2O体系;5)UST(均一温度为158.6~381.7℃,盐度为1.6%~21.5%)为中低温中低盐度NaCl-H_2O-CO_2体系,该期可能与钼矿化关系不大,代表另一期侵位更浅的岩浆出溶热液。流体不混溶、围岩蚀变以及流体混合作用导致流体温度、压力降低,CO_2逸失,体系还原性增强,是成矿金属元素沉淀的主要机理。用等容线相交法对成矿期捕获压力进行估算,为124~180 MPa,对应深度为4.6~7.0km,与同成矿带其他钼矿比较,相对较深。

Fluid Inclusion of Yaojiagou Porphyry Mo Deposit in Qingchengzi in Liaoning Province

The Yaojiagou molybdenum deposit is a newly discovered one in recent years in the ore field of Qingchengzi in Liaoning.It is located in the Yan-Liao Mo metallogenic belt in the northern margin of the North China craton.The quartz veins (UST)and quartz eyes in the Yaojiagou pluton are direct evidence of fluid exsolution from magma.Deposit alteration zonation is significant,and the molybdenum mineralization mainly exists in the potassic and skarn zones.After a microscopic observation,we found various abundant fluid inclusions,including single-phase aqueous (PW-type),twophase aqueous (W-type),three-phase CO2 (C-type),pure CO2 (PC-type),and daughter mineral-bearing inclusions (S-type) in which the daughter minerals are hematite,chalcopyrite,and some other unknown minerals with no halite.The fluid evolution in this deposit are:1) the early quartz eye stage with the homogenization temperature of 211.4-515.4 ℃,salinity of 0.8 ％-19.2 ％,and rich in CO2;2) the quartz veins mineralization stage with the homogenization temperature of 179.5-424.5 ℃ and salinity of 2.4 ％-21.5 ％ in NaC1-H2O-CO2 system;3) the late quartz veins stage with the homogenization temperature of 167.8-353.3 ℃ and salinity of 3.4 ％-15.8 ％ in NaCl-H2O-CO2 system;4) the latest calcite veins stage with the homogenization temperature of 132.5-234.1 ℃ and salinity of 0.9 ％-11.2 ％ in NaCl-H2O system;5)the UST quartz veins stage with the homogenization temperature of 158.6-381.7 ℃ and salinity of 1.6 ％-21.5 ％ in NaCl-H2 O-CO2 system,and this stage represents a immiscible fluid exsolution from a shallower intrusive magma with no mineralization.Wall rock alteration and fluid mixing are the main mechanisms of ore-forming metal elements precipitation,which lead to fluid temperature,pressure reduction,CO2 escaping,and system rebalancing.We obtained the capture pressure of 124-180 MPa with the corresponding depth of 4.6-7.0 km during the ore-forming period by using the method of isochore intersection.It is relatively deeper than that of the other molybdenum deposits in the northern margin of the North China craton.