青海大场金矿田矿床成因:流体包裹体地球化学及H-O同位素的约束  

The genesis of the Dachang gold ore field in Qinghai Province: Constraints on fluid inclusion geochemistry and H-O isotopes

作　　者：夏锐[1,2] 邓军[1] 卿敏[2] 王长明[1] 李文良[2] 

机构地区：[1]中国地质大学地质过程与矿产资源国家重点实验室,北京100083 [2]武警黄金地质研究所,廊坊065000

出　　处：《岩石学报》2013年第4期1358-1376,共19页Acta Petrologica Sinica

基　　金：国家重点基础研究发展计划(973)项目(2009CB421008);北京市优秀博士学位论文指导老师科研项目(20111141501);武警黄金指挥部专项基金项目(HJ12-03)联合资助

摘　　要：青海大场金矿田位于可可西里-巴颜喀拉晚古生代-中生代浊积盆地褶断带内,是川陕甘交接地区的一个超大型矿田。矿床受NW向构造破碎蚀变带控制,赋矿围岩为三叠系炭质砂板岩,矿石矿物主要为黄铁矿、毒砂和辉锑矿,脉石矿物主要为石英、长石和方解石。金的赋存状态以微细粒金为主。大场金矿田矿石中流体包裹体主要为盐水溶液包裹体(W型)、少量的含CO2包裹体(C型)和富CO2包裹体(PC型)组成。成矿流体具有中低温(180～200℃)、低盐度(2%～5%NaCleqv)、成矿深度为7.9～12.3km的特征。气、液相成分测定显示气相成分以N2、CO2、O2、H2O为主;液相成分中阳离子以Ca2+、Na+、Li+、K+为主,阴离子以富SO42-、Cl-、NO3-、F-为特点,成矿流体属Ca2++Na++SO42-型,有机碳参与了流体成矿作用。氢氧同位素组成分别为δD=-62‰～-106‰,δ18OH2O=3.1‰～10.5‰,说明成矿流体主要为建造水,也有岩浆流体的加入。根据大场金矿田成矿地质背景、流体特征及演化和成矿的构造背景和机制,本文首次提出大场金矿为类卡林型金矿,为研究该区金矿成矿作用提供了参考。The Dachang gold ore field, one of the super large ore field in the Sichuan-Shanxi-Gansu boundary region, is located in the Kekexili-Songpanganze in Late Palaeozoic-Mesozoic turbidite basin and fold and fault belt. It is controlled by an NW-trending structural and altered belt, and hosted in the Triassic carbonaceous sandstone-slate of flysch deposition. The main ore minerals are pyrite, arsenopyrite and stibnite, and gangue minerals are quartz, feldspar and calcite. The gold occurred as grained gold. Microthermometric measurements show that auriferous quartz veins in the Dachang gold ore field have three types of fluid inclusions： NaCl-H2O inclusions （type W）; CO2 brine inclusions （type C） and pure gaseous inclusions （type PC）. The salinity values of NaCl-H2O inclusions have a peak of 2%～5%NaCleqv, homogenization temperature values with a peak of 180～200℃ and metallogenic depths are 7.9～12.3km. The pure gaseous inclusions are dominanted by N2, CO2, O2, H2O, with minor H2S. Liquid phase composition are Ca2＋, Na＋, Li＋, K＋ and SO42-, Cl-, NO3-, F-, with minor Mg2＋. They suggest that the ore-forming fluids of the Dachang gold ore field are characterized by low salinity, low to moderate homogenization temperature. H-O isotopes analyses show that δD=-62‰～-106‰, δ18OH2O=3.1‰ ～10.5‰, indicating that the ore-forming fluids are composed mainly of devolatilization of organic matter, with meteoric water. Geological and fluild features and metallogenic mechanism suggest that the Dachang gold ore field may be Carlin-like gold deposit.

关 键 词：类卡林型金矿 流体包裹体 H-O同位素 大场金矿田 青海 

分 类 号：P618.51[天文地球—矿床学]