赣北昆山钨钼铜矿床花岗岩地球化学及Hf同位素研究

Geochemical and Hf Isotopes of Granites in the Kunshan W-Mo-Cu Deposit,Northern Jiangxi Province

昆山钨钼铜矿床地处赣北九岭钨钼铜矿集区中部,是大湖塘超大型钨矿床南部发现的中-大型钨多金属矿床。石英脉型W-Mo-Cu矿体主要产于燕山期似斑状花岗岩(~152Ma)与上元古界双桥山群的外接触带。除似斑状花岗岩外,矿区内发育成矿后花岗斑岩脉(~136Ma)。本文对昆山矿床似斑状花岗岩及花岗斑岩开展了系统的岩石学、地球化学研究,并对与成矿密切相关的似斑状花岗岩进行了锆石Hf同位素测试分析。似斑状花岗岩与晚期花岗斑岩均为高硅(SiO——2=71.35%~76.55%、73.12%~75.15%)、高钾(K——2O=3.81%~5.25%、5.14%~6.26%)、钙碱性系列、过铝质岩石(A/CNK值分别为1.07~1.26、1.06~1.43,平均大于1.1);轻稀土元素富集,轻重稀土分馏强烈,具有明显的负Eu异常(δEu=0.34~0.58、0.20~0.32);锆饱和温度较低,分别为711~761℃、727~766℃,显示了高分异S型花岗岩的特征。锆石Hf同位素组成表明,似斑状花岗岩的ε_(Hf)(t)为-8.80~4.48,二阶段Hf模式年龄tDM2=917~1757Ma,推测其源区主要来自于双桥山群浅变质岩系,岩浆活动与下扬子地区构造格局大转换有关。总结发现,昆山矿床与大湖塘矿床具有相似的岩浆岩演化序列,大湖塘地区燕山期花岗岩岩石学、成岩年龄、地球化学及Nd-Hf同位素等特征显示其是起源于同一深部岩浆房的岩浆,经深部岩浆房分异演化,脉动侵位所形成。

The Kunshan W-Mo-Cu deposit in Northern Jiangxi which is located in the central area of Jiuling tungsten-polymetallic ore concentration region, is a medium-large scale tungsten-polymetallic deposit discovered in Dahutang area recently. Ore bodies in the form of quartz vein occur in the external contact zone between the Yanshanian porphyritic granite （-152Ma） and the low grade metamorphic rock of Neoproterozoic Shuangqiaoshan Group. In addition to porphyritic granite, there are granite porphyry veins （-136Ma） outcropped in the Kunshan deposit. In this peper, detailed studies on the petrology, geochemistry of Yanshanian intrusions and analysis of zircon Hf isotopes of porphyritic granite which is closely related to mineralization in the deposit are conducted. Both porphyritic granite and granite porphyry are characterized as high silicon （SiO2 =71.35%-76.55%, 73.12%-75.15%）, high potassium （K20= 3.81%-5.25%, 5.14%-6.26%）, calc-alkaline series of peraluminous granite （A/CNK=1.07-1.26, 1.06-1.43, and the average is more than 1.1） ;enrichment in LREEs, strong LREE/HREE fractionation and significant negative Eu anomalies （c？Eu=0.34-0.58,0.20-0.32） ; low zircon saturation temperatures （711-761℃ and 727-766℃ respectively）, which suggest that they are both high fractional S-type granites. The eHf（t） values of porphyritic granite vary from --8.80 to 4.48 with the two-stage model ages tDM2 of 917Ma to 1757Ma. It is indicated that the source region of the granite were mostly from the Neoproterozoic Shuangqiaoshan Group, and the Yanshanian magmatic activity is related to the tectonic conversion of The Lower Yangtze region in Late Jurassic. Based on the petrologic, geochronological, geochemical and Nd-Hf isotopes characters of granites in Dahutang area, it is concluded that the Kunshan deposit has a similar magmatic evolution sequence with the Dahutang deposit which originated from the same deep magma chamber, and then intruded discontinuously after differentiation process.