柴北缘阿日特克山斑岩型铜钼矿床流体包裹体、稳定同位素特征及其地质意义

Fluid Inclusions,Stable Isotope Characteristics and Geological Significance of Aritekeshan Porphyry Cu Mo Deposit in Northern Qaidam Basin

阿日特克山铜钼矿床位于柴北缘中北段,为近年来新发现的隐伏斑岩型矿床,矿体产出于海西晚期—印支期花岗闪长(斑)岩和古元古代达肯大坂岩群接触部位。为探讨该矿床成矿流体特征和成矿机制,本文对矿床野外地质特征、流体包裹体及稳定同位素组成进行了系统的研究。根据不同类型矿脉之间的相互关系,可将热液成矿期次划分为成矿早期石英阶段、成矿期辉钼矿-多金属硫化物-石英阶段和成矿晚期石英-方解石阶段。流体包裹体岩相学研究表明,阿日特克山铜钼矿床流体包裹体以Ⅰ型(富液相L+V两相水溶液包裹体)、Ⅱ型(富气相L+V两相水溶液包裹体)和Ⅲ型(含子矿物三相水溶液包裹体)为主。显微测温及包裹体拉曼光谱分析结果显示,成矿流体体系为中高温、中低盐度、中高密度的NaCl-H_(2)O体系,至成矿晚期,流体性质变化为低温、低盐度、高密度流体,矿床形成深度为0.40~4.00 km。氢氧同位素分析测试结果显示,δD_(V-SMOW)值为-92.9‰~-78.4‰,δ^(18)O_(H_(2)O)值为-7.4‰~2.0‰,表明成矿流体以混合流体为主,随着成矿流体的演化,有更多的大气降水不断混入。矿石中金属硫化物δ^(34)S值处于9.4‰~11.7‰之间,平均值为10.2‰,表现出明显的地层硫特征,为岩浆热液与围岩地层相互作用所致。综上认为,阿日特克山铜钼矿床为矽卡岩型-斑岩型矿床,形成于海西晚期—印支期俯冲碰撞构造环境,混合成矿流体强烈的不混溶作用为斑岩型铜钼矿床形成的主要机制。

Aritekshan Cu-Mo deposit is a newly discovered concealed porphyry deposit,located in the central-north part of the northern Qaidam basin.The orebodies occurred in the contact area between the Late Hercynian-Indosinian granodiorite(porphyry)and Paleoproterozoic Dakendaban Group.In order to explore the characteristics of ore-forming fluids,the ore-forming mechanism and genesis of the deposit,this paper systematically studied the field geological characteristics,fluid inclusions and stable isotope composition of the deposit.According to the relationship between different types of ore veins,the hydrothermal metallogenic stages can be divided into the early mineralization quartz stage,molybdenum-polymetallic sulfide-quartz stage and late mineralization quartz-calcite stage.The fluid inclusions are mainly TypeⅠ(liquid-rich L+V two-phase aqueous inclusions),TypeⅡ(gas-rich L+V two-phase aqueous inclusions)and TypeⅢ(three-phase aqueous solution inclusions containing daughter minerals).The results of microthermometry and inclusion Raman spectrum analysis show that the ore-forming fluid system is NaCl-H_(2)O system with medium-high temperature,medium-low salinity,and medium-high density.In the late stage of mineralization,the properties of the fluids changed to low temperature,low salinity and high density fluid,with the deposit formation depth of 0.40-4.00 km.The values of DV-SMOW andδ^(18)OH_(2)O range from-92.9‰to-78.4‰and-7.4‰to 2.0‰respectively,indicating that the ore-forming fluids are mainly mixed fluids.With the evolution of ore-forming fluids,the continuous mixing of meteoric water affects mineralization.Theδ^(34)S of metal sulfide in the ore ranges from 9.4‰to 11.7‰,with an average value of 10.2‰,showing obvious characteristics of strata sulfur,which is caused by the interaction between magmatic hydrothermal fluid and surrounding rock strata.It is believed that Aritekshan Cu-Mo deposit is a skarn-porphyry type deposit,which was formed in the subduction and collision during Late Hercynian-Indosinian,which is consistent with the diagenetic age of granodiorite.The strong immiscibility of mixed ore-forming fluids is the main mechanism of the formation of porphyry Cu-Mo deposit.