冀东峪耳崖金矿区闪长岩脉地球化学特征及其地质意义

Geochemical Characteristics and Geological Significance of Diorite of Yu’erya Gold Deposit Area in Eastern Hebei Province

冀东地区位于华北板块北缘燕山造山带东部,矿产资源丰富,是中国金矿的主要产地之一,尤其是热液型金矿。峪耳崖金矿床是冀东众多热液型金矿床的典型代表,金矿主体赋存于侏罗纪峪耳崖花岗岩体内,少部分赋存于侵入花岗岩体的侏罗纪闪长岩脉中。闪长岩脉元素地球化学分析显示:w(SiO2)为51.99%~61.88%、Mg#值为0.37~0.64,w(Na2O+K2O)为5.07%~8.89%,A/NK为1.37~2.26,A/CNK为0.73~0.96,属准铝质高钾钙碱性系列;富集轻稀土元素和大离子亲石元素Rb、Ba、K、Sr,亏损重稀土元素和高场强元素Nb、Ta、Ti。锆石原位Hf同位素测试表明,εHf(t)为负值,介于-16.5~-6.5之间。综合研究认为:峪耳崖金矿区侏罗纪闪长岩浆源于俯冲流体交代的富集岩石圈地幔,岩浆上侵过程中受到华北板块古老下地壳物质的有限混染;成矿期闪长岩浆为金成矿提供了部分物质来源;峪耳崖金矿区闪长岩脉形成于古太平洋板块向欧亚大陆俯冲的动力学背景。

Located in the eastern part of the Yanshan orogenic belt on the northern margin of the North China plate in eastern Hebei Province, Yu’erya is one of the main gold producing areas especially with hydrothermal gold deposits. The Yu’erya deposit is representative in eastern Hebei Province, which occurs mainly in the granite of the Jurassic Yu’erya pluton with a few orebodies in the Jurassic diorite that intruded into the granite. The geochemical data show that the w(SiO2) of diorites is 51.99%-61.88% and w(Na2O+K2O) is 5.07%-8.89%, with Mg# values between 0.37 to 0.64. They are high-potassium calc-alkaline and quasi-aluminum with A/CNK and A/NK values ranging from 0.73 to 0.96 and 1.37 to 2.26, respectively. All samples are rich in LREE and LILE including Rb, Ba, K,and Sr, and are depleted of HREE and HFSE such as Nb, Ta and Ti. The zircon Hf isotope studies show that the εHf(t) values of the diorites range from-16.5 to-6.5. These data indicate that the Jurassic diorite magma originated from the enriched lithospheric mantle replaced by subduction fluids, and was contaminated limitedly by the ancient lower crust material of the North China plate during magma upwelling. In the ore-forming period, the diorite magma provided part of the material for the gold mineralization. Combined with other regional results, this study suggests that the magmatism is likely associated with the subduction of the paleo-Pacific plate beneath Eurasia.