福建政和地区熊山岩体锆石U-Pb定年、地球化学特征及其成矿意义

Zircon U-Pb dating,geochemistry and metallogenic significance of Xiongshan intrusion in Zhenghe area,Fujian

熊山岩体分布于福建政和地区,大地构造位置位于华南褶皱系东部的闽中裂谷带中西部,岩性总体上属基性岩。浅部主要为细粒辉长岩、辉绿玢岩,深部出现粗粒闪长岩和花岗闪长岩类。细粒辉长岩的LA-ICP-MS锆石U-Pb测年结果为(463.9±6.2)Ma,粗粒闪长岩的LA-ICP-MS锆石U-Pb测年结果为(465.7±6.1)Ma,表明熊山岩体的结晶年龄为465.7~463.9 Ma。样品在TAS图解中主要投影在辉长岩范围内。细粒辉长岩中稀土元素总量偏低,(La/Yb)N为1.08,LREE/HREE比值为1.94;δEu为0.83,表现为较弱的负异常;δCe为0.92,基本无异常;LILE(K、Sr、Ba)含量较低,HFSE(U、Zr、Nb)和Ti表现为较弱的正异常。粗粒闪长岩及花岗闪长岩中稀土元素总量中等,(La/Yb)N为8.68和8.91,LREE/HREE比值为8.60和8.50,富集轻稀土元素;δEu为0.95和0.87,表现为较弱的负异常;δCe为0.96和0.99,无明显异常;样品中LILE(K、Rb、Ba、Sr)相对富集,HFSE(U、Th、Nb)、Ti和P亏损。根据岩体地球化学特征,认为形成熊山岩体早期细粒辉长岩的岩浆来自于深部的地幔橄榄岩,而形成较晚期的粗粒闪长岩和花岗闪长岩类的岩浆则来自于玄武质和榴辉岩熔体区。熊山岩体成岩时间早于大药坑金矿床形成时间,不是成矿岩体,但在后期成矿过程中可提供成矿物质,是金矿形成的"矿源岩"。

The Xiongshan intrusion is located in Zhenghe area of Fujian,and tectonically it lies in middlewest of central Fujian rifting zone in the east of South China fold system,belonging to basic rock mass.The shallow part of the intrusion is mainly composed of fine gabbro and diabasite and the deep part mainly consists of coarse diorite and granodiorite.According to the LA-ICP-MS zircon U-Pb dating of fine gabbro(463.9 ± 6.2 Ma) and coarse diorite(465.7 ± 6.1 Ma),the crystallization age of the Xiongshan intrusion is 465.7 ~ 463.9 Ma.The samples are mainly projected in the gabbro area in the TAS diagram.The ∑REE content in fine gabbro is low,the(La/Yb)Nratio is 1.08 and the LREE/HREE ratio is 1.94;δEu is 0.83 which means weak negative anomaly;δCe is 0.92 which means no anomaly;the content of LILE(K,Sr,Ba) are low,while HFSE(U,Zr,Nb) and Ti show weak positive anomaly.The ∑REE content in coarse diorite and granodiorite is medium,with(La/Yb)N ratio of 8.68 and 8.91,the LREE/HREE ratio of 8.60 and 8.50,respectively,showing enrichment in LREE;δEu is 0.95 and 0.87,respectively which means weak negative anomaly;δCe is 0.96 and 0.99 which means no anomaly;the samples are characterized by enrichment in LILE(K,Rb,Ba,K) and depletion in HFSE(U,Th,Nb),Ti and P.According to the geochemical characteristics of the Xiongshan intrusion,it is believed that the older fine gabbro came from the deep mantle peridotite,and the younger coarse diorite and granodiorite were from the eclogite and basaltic melting zone.The age of the Xiongshan intrusion is older than that of the Dayaokeng gold deposit,implying the intrusion was not metallogenic rock body,but could serve as the host rock of the deposit,providing some ore-forming material during the later metallogenic process.