Zircon trace element characteristics of intrusions in the Washan iron deposit of Ningwu volcanic basin and their geological significance

Abstract：The Washan iron deposit is a representative porphyrite iron deposit. There are two types of intrusions: One is gabbro-diorite porphyrite closely related to the iron mineralization and serves as the host rocks, and the other is granodiorite porphyry cutting across the ore body, which has been rarely studied. Detailed zircon LA-ICP-MS trace element measurement was performed on these two intrusions. The two intrusions have similar chondrite-normalized REE patterns of zircons and Yb, Hf and Y values, whereas zircons from the granodiorite porphyry have higher U values and U/Yb ratios. In combination with previous studies of isotope geochemistry, the authors infer that these intrusions have similar sources, and much crust material was involved in the formation of granodiorite porphyry during the ascending process. Zircon Ce（Ⅳ）/Ce（Ⅲ）ratios of the granodiorite porphyry are concentrated in the range of 0-100, lower than the values of zircons (>300) from the granite related to the porphyry Cu-Au mineralization; nevertheless, they have similar characteristics of δEu (>0.4). Thus, it is not certain whether the granodiorite porphyry had the potential to form copper and gold deposits, and hence further researches are needed concerning the possible relationship between the granitic stocks and copper and/or gold mineralization.