福建上杭县浸铜湖矿床成矿岩体的地球化学特征及其地质意义

Geochemical signatures and geological implications of metallogenic rockbodies in Jintonghu deposit,Shanghang,Fujian province

华南晚中生代发育大规模的岩浆活动及巨量金属成矿,成岩成矿作用一直是大花岗岩成矿省研究的主要内容。闽西浸铜湖铜钼矿床中发育有与矿化同时代的花岗闪长斑岩及花岗斑岩。为查明这两个岩体与矿化的关系,对其进行详细的岩石地球化学分析。研究表明:花岗闪长斑岩属弱过铝质岩,具埃达克质岩石的亲缘性。元素和同位素特征指示其为俯冲交代富集地幔来源,分离结晶作用控制着岩体的形成。花岗斑岩属过铝质岩,发生斜长石的分离结晶。花岗斑岩的Sr-Nd同位素组成排除华夏元古代陆壳基底物质及幔源岩浆参与的可能,指示其物质来源应为早期就位的火成岩或正变质岩。浸铜湖矿床形成于受古太平洋板块俯冲、折返影响而形成的伸展构造环境。

South China was characterized as widespread magmatic activities during the Late Mesozoic and of particular close association with economically abundant mineralization according to the accumulation of metal elements, in which diagenesis and ore-forming processes has been the main involved contents of research objectives for the Mesozoic great granite province. Granodiorite porphyries and granites are almost simultaneous with the Cu-Mo mineralization within the Jintonghu orefield. In order to determine the genetic relationship between these intrusions and Cu-Mo mineralization, whole rock major, trace element and Sr-Nd isotope analyses of the granodiorite porphyries and granites in the Jintonghu deposit were carried out. The granodiorite porphyries were classified as weakly pre-aluminous granites, showing an adakitic affinity. Detailed petrologic and geochemical data indicate that these granodioritic intrusions are derived directly from a metasomatized enriched mantle source, and the fractional crystallization processes play a key role in the formation of them. By contrast, the granites are classified as pre-aluminous, demonstrating that the intrusion might have undergone the fractional crystallization of plagioclase during magma ascent. The Sr-Nd isotopic compositions preclude that the initial magmas of the granites are dominantly sourced from the Proterozoic crustal basement metirals and juvenile or enriched mantle compositions. Interpretation of the elemental and isotopic data suggests that the granite is likely derived from partial melting of the early deep-seated magmatic rocks. The granodiorite porphyries and granites are emplaced in a back-arc extensional setting resulted from a forward and roll-back of the subducted paleo-Pacific slab under an active continental margin environment.