黑龙江高松山金矿区赋矿火山岩成因及构造意义

Petrogenesis and Tectonic Implications of Volcanic Rocks in the Gaosongshan Gold Deposit,Heilongjiang Province

为探讨高松山金矿床成矿背景和矿床成因,对其主要赋矿围岩下白垩统板子房组火山岩进行了岩相学和地球化学研究.结果显示,该区火山岩以玄武安山岩、安山岩和粗安岩为主,其SiO2含量为51.51％～56.75％,TiO2含量较低（1.02％～1.61％）,MgO含量变化较大（1.51％～7.10％）,Mg#值中等（34～66）,Na2O＋K2O值为3.45％～6.52％,里特曼指数为1.15～3.42,属钙碱系列火山岩.微量元素分析表明,岩石相对富集轻稀土元素,轻、重稀土元素分馏较强,具有弱的Eu负异常（δEu=0.86～1.07）,富集大离子亲石元素和U、Pb等元素,亏损Nb、Ta、Ti、P等高场强元素.上述研究表明,高松山金矿区火山岩的岩浆源区为受俯冲带流体交代的岩石圈地幔,有不同程度的分离结晶,受陆壳混染影响较小.综合区域构造背景,初步认为该区火山岩的形成与古太平洋板块对欧亚大陆下的俯冲作用关系密切,构造环境可能为活动大陆边缘背景下的陆缘弧.

The Gaosongshan gold deposit is spatially closely associated with the volcanic rocks of the Banzifang Formation,which were formed in the Early Cretaceous.The petrogenesis and tectonic settings study about the volcanic rocks will provide an important basis on understanding the metallogenic setting and the ore genesis.Based on petrography and geochemistry study,the volcanic rocks are composed of basaltic andesite,andesite and trachyandesite.Geochemical results indicated that the SiO2 contents are in the range of 51.51％-56.75％,TiO2 and MgO contents are in the range of 1.02％-1.61％ and 1.51％-7.10％,respectively,and Mg# value changes from 34 to 66.The contents of Na2O＋K2O are in the range of 3.45 ％-6.52 ％,which shows the calc-alkaline characteristics based on the Rittmann index.The trace element analysis showed that the rocks are LREE enriched with insignificantly negative Eu anomaly of δEu=0.86-1.07,and that intense fractionation between LREE and HREE exists.The rocks are all enriched in LILE and U,Pb,HFSE,such as Nb,Ta,Ti,P.The petrologic and geochemical study showed that the volcanic rocks in the Gaosongshan Gold Deposit were derived from decompression melting of an enriched continental lithospheric mantle,which had been previously metasomatized by fluids derived from subducted slabs.Crystal fractionation occurred while crustal contamination had insignificant affection during magma was ascenting.It is possibly that the volcanic rocks were formed by the ancient subduction of the Pacific plate beneath the Eurasian continent during the Mesozoic.The tectonic environment most likely was continental marginal arc.