矿床地球化学国家重点实验室知识库

In order to constrain its petrogenesis and mineralization, a detailed study of Miocene quartz diorite porphyry from the Ciemas area of West Java, Indonesia, was undertaken, including geochronology and major and trace element analyses. Ciemas quartz diorite porphyry contains medium–coarse-grained quartz and hornblende phenocrysts in a matrix of primarily cryptocrystalline quartz and feldspar. The rocks belong to the calc-alkaline-high K calc-alkaline series. The quartz diorite porphyry and Miocene dacite and andesite wall rocks have similar compositions, both being enriched in large-ion lithophile elements (LILEs) K, Rb, Th, and U, depleted in high-field strength elements (HFSEs) Nb, Ta, Zr, Hf, and P; with light rare earth element (LREE)-enriched patterns and negative Eu anomalies, which are typical for arc magmatic rocks. LA-ICP-MS U-Pb zircon ages of andesite, amphibolic tuff breccia, and quartz diorite porphyry are 17.5 ± 0.3, 16.9 ± 0.3, and 17.1 ± 0.4 Ma, respectively. The quartz diorite porphyry formed by mid-Miocene arc magmatism. This intrusion and surrounding volcanics developed together as the Indian–Australian Plate subducted northward beneath Java, releasing fluids that triggered partial melting of the overlying mantle wedge and felsic melts that evolved further in the crust. Petrogenesis and ages of Ciemas magmatic rocks are important to gaining an understanding of Cenozoic Sunda Arc magmatism, and also provide insights into related epithermal gold deposits.