云南格咱岛弧带欠虽铜矿石英闪长玢岩年代学、岩石地球化学特征及成岩成矿的制约

摘要

欠虽铜矿床位于西南三江地区义敦岛弧南段的格咱岛弧中南部,是近年来该区新发现的铜多金属矿床,具有良好的找矿前景.目前该地区已发现若干印支期成矿事件中形成的中大型矿床,是中国重要的多金属矿集区.本文通过LA-ICP-MS锆石U-Pb定年方法对欠虽铜矿石英闪长玢岩进行了年代学研究,获得铜矿化石英闪长玢岩的形成年龄为(220.3±0.66)Ma(MSWD=0.99).岩石地球化学特征研究表明,欠虽石英闪长玢岩具有富钠(K2O/Na2O为0.05~1.42,平均值为0.86)、准铝质(0.82~1.19,平均值为1.07)的特征,岩石富集轻稀土元素(LREE),轻重稀土元素分馏明显(LaN/YbN=19.6~28.8),富集大离子亲石元素(LILE,Ba、Th、U、Sr),亏损高场强元素(HFSF,Ta、Nb、Ce、P、Ti),属于典型的I型花岗岩.欠虽铜矿成矿岩体成岩时代发生在印支晚期,含矿斑岩的微量元素特征、构造背景及同位素特征反映欠虽岩体形成于岛弧环境,与格咱岛弧印支期洋壳的俯冲造山作用密切联系.通过地球化学特征及成岩成矿年代的研究,表明欠虽多金属矿的形成年限与甘孜—理塘洋壳俯冲造山作用时限相近,且与普朗铜矿、红山铜矿是同期次同源构造-岩浆演化的产物,这对探讨格咱岛弧构造-岩浆演化及成岩成矿作用的研究具有重要意义.%The Indosinian Qianui copper polymetallic deposit discovered in recent years is located in the central and southern segment of the eastern Geza porphyry belt of southern Yidun arc in Southwest China. A large number of indo-Chinese large-size ore deposits were formed in the metallogenic area,which is hence an important polymetallic belt in China. In this paper, the authors studied the ages of the Qiansui quartz diorite porphyry with zircon LA-ICP-MS U-Pb dating method and obtained the formation age of the copper mineralized quartz diorite porphyry of 220.3 ± 0.66 Ma (MSWD=0.99). Geochemical characteristics indicate that Qiansui ore-bearing quartz diorite porphyry is characterized by rich Na (K2O/Na2O=0.05-1.42, averagely 0.86), metaluminous nature (0.82-1.19, averagely 1.07), enrichment of light rare earth elements (LREE,Ba, Th, U, Sr),obvious REE fractionation (LaN/YbN=19.6-28.8), enrichment of large ion lithophile elements (LILE, Ba, Th, U, Sr), and depletion of high field strength elements (HFSF, Ta, Nb, Ce, P, Ti). The rock belongs to typical I-type granite. The ore-forming process of Qiansui metallogenic rock body occurred in the late Indosinian, and the trace element characteristics, tectonic background and isotopic characteristics of the ore-bearing porphyry suggest that Qiansui rock was formed in an island arc environment, and that its formation was probably related to the subduction of oceanic crust in Indosinian.The study of geochemical characteristics and petrogenetic age of Qiansui reveals the fixed formation age of Qiansui and the time limit of Ganzi-Litang oceanic crust subduction orogeny, suggesting that Pulang and Hongshan copper deposits were the products of the evolution of magma structure in the same period. The results obtained by the authors have important significance for the study of Gezan island arc tectonic magmatic evolution and petrogenetic mineralization.