青海都兰白石崖M20矿床成矿流体特征

Characteristics of ore-forming fluid of Baishiya M20 deposit,Dulan of Qinghai

都兰白石崖地区位于柴达木盆地东南缘,柴北缘成矿带和柴南缘成矿带交汇部位。矿床赋存于印支期中酸性花岗岩体与石炭系碳酸盐岩地层接触带中,矿体以铁及铁多金属矿为主要特征,属典型的矽卡岩型铁多金属矿床。成矿物质主要来源于与中酸性岩浆有关的含矿流体,流体作用于元古界大肯达坂群、沙柳河群及奥陶纪滩间山群,随印支—燕山期岩浆上侵形成本区富有特色的矽卡岩型矿床,流体包裹体测试分析,测得均一温度介于194°C^388°C,流体盐度为0.331%~10.978(wt%NaCl equiv),估算流体密度为0.550~0.892g/cm^3,流体平均压力为106bar。成矿温度(捕获温度)201℃~399℃,平均299℃,属中-低温流体。静岩压力深度值为2.7km,成矿深度应为中浅环境。通过C、H、O同位素研究表明,成矿流体可能来源于地幔岩浆热液,部分来自大气水及变质水。成矿物质既有来自深部地幔及岩浆,也有来自石炭-奥陶系,矿床应属中低温热液矿床。

The Baishiyan area in Dulan is located in the southeastern margin of Qaidam Basin in the junction of the northern margin ore belt and southern margin ore belt of Qaidam Basin.The deposit is mainly hosted at the contact zone of medium acid granite and carbonate strata of Carboniferous system.The ore body is characterized by iron and iron-polymetallic ore,and the deposit is belonged to a typical polymetallic skarn type.The ore-forming material mainly derived from the ore-bearing fluid associated with the medium-acid magma.The fluid acts on Proterozoic Dakengdaban Group,Shaliuhe Group and Ordovician Tanjianshan Group.With the upward migration of Indosinian Yanshan magma,the typical skarn type deposit formed.The results of test on fluid inclusions showed that the uniformity temperature is between 194°C and 388°C and the fluid salinity is 0.331%-10.978%(wt% NaCl equiv),and the fluid density is estimated to be 0.550 to 0.892 g/cm^3,and the fluid average pressure is 106 bar.Mineralization temperature(capture temperature)is 201℃-399℃,with an average value of 299 ℃.Rock depth of static pressure is 2.7 km,and mineralization depth should be shallow environment.The C,H,O isotopic study has shown that ore-forming fluids might be derived from mantle magmatic hydrothermal fluids,partly from atmospheric and metamorphic water.Oreforming material is from both of the deep mantle magma,and from the Carboniferous-Ordovician system.The deposit is belonged to a hydrothermal deposit of middle-low temperature.