浙江安吉多金属矿区石英二长斑岩岩石化学特征和锆石U-Pb年龄及其地质意义

为了解浙江安吉多金属矿区岩浆作用的性质及其与成矿作用的关系,对区内石英二长斑岩的地球化学和年代学展开研究。地球化学结果表明,该岩脉高硅(w(SiO2)=65.91%～66.72%)、富碱(w(K2O+Na2O)=7.82%～8.26%)、高钾(w(K2O)/w(Na2O)=1.58～1.82),铝饱和指数A/CNK=0.86～0.91,轻稀土元素和大离子亲石元素Rb、Th、K相对富集,铕弱负异常,Ba、Sr和高场强元素Nb、Ti、P相对亏损,属准铝质―钾玄岩系列。铝饱和指数及结晶分异指数显示,该岩脉属I型花岗岩系列。年代学结果表明,该岩脉锆石U-Pb年龄为(137.3±1.6)Ma,与区内杂岩体同期。据野外证据,该岩脉的侵位时代指示北东向湖州―学川大断裂在(137.3±1.6)Ma左右再次活动,且该时间也为北西向孝丰―三门湾大断裂再度活跃的最早年龄。区内岩浆作用、成矿作用基本同期,岩体与矿化又具有密切的空间关系,表明区内成矿作用和岩浆活动密切相关。

Geochemical Characteristics and Zircon LA-ICP-MS U-Pb Ages of Quartz-Monzonite Porphyry in Anji Polymetallic Ore District of Zhejiang and Their Geological Implications

In order to get further understanding about the magmatism and its relationship with mineralization,the geochemical characteristics and zircon U-Pb age of quartz-monzonite porphyry in Anji polymetallic ore district in western Zhejiang have been studied.Quartz-monzonite porphyry is characterized by high SiO2(65.91%-66.72%),alkali-rich(Na2O+K2O=7.82%-8.26%),potassium-high(K2O/Na2O=1.58-1.82) and A/CNK=0.86-0.91.Based on the results from A/CNK-A/NK and SiO2-K2O diagrams,quartz-monzonite porphyry belongs to the quasi-aluminous rock and shoshonite series.In chondrite normalized REE distribution patterns,all the samples are LREE-enriched and with weak negative anomaly in Eu(δEu=0.75-0.81).In primitive mantle normalized trace elements spider diagram,the large-ion lithophile elements(e.g.Rb,Th and K) are high concentrations,but Ba,Sr and the high field strength elements(e.g.Nb,Ti and P) are relatively depleted.The aluminized indexes(A/CNK) of all the samples are less than 1.1 and all the differentiation indexes(DI) are about 77,so quartz-monzonite porphyry belongs to I-type granite.Zircon U-Pb dating by LA-ICP-MS shows this porphyry emplaced at(137.3±1.6) Ma of Early Cretaceous and has a similar age with the Wushanguan complex.Considering that quartz-monzonite porphyry exists along Huzhou-Xuechuan fault and is cut off by Xiaofeng-Sanmenwan fault,this age indicates that Huzhou-Xuechuan fault was activated in Early Cretaceous and also constrains the earliest time when Xiaofeng-Sanmenwan fault activated.The magmatism formed in the same time with mineralization,and mineralization also has a close relationship with the complex body in space,so it is believed that the mineralization is related to the magmatism in this study area.