In situ major-, trace-elements and Sr-Nd isotopic compositions of apatite from the Luming porphyry Mo deposit, NE China: Constraints on the petrogenetic-metallogenic features

Abstract

Apatite is an important accessory mineral in granitic rocks and can record important petrogenetic-metallogenic information. In particular, magmatic apatite can provide information on the volatile composition and magma source of the ore-forming rocks in porphyry deposits. This work focuses on magmatic apatite within the ore-forming intrusion of the Luming super-large porphyry Mo deposit. We use electron probe micro-analyzer (EPMA) and laser ablation multi-collector inductively coupled plasma mass spectrometry (LA-MC-ICP-MS) analytical methods to analyze the major- and trace-element and Sr-Nd isotopic compositions of the apatite. The results show that the apatite grains are magmatic apatite, classified as fluorapatite. The trace-element patterns of the apatites feature clearly negative Sr, Ba, and Zr anomalies and Ba, Nb, Sr, Zr and Eu depletions that are more distinct than those in the granite porphyry and monzogranite in the Luming deposit. The apatites exhibit slight LREE enrichment and distinctly negative Eu anomalies. The positive Eu/Eu∗ (δEu)-Ga correlation and the strongly negative Eu anomaly indicate that the magma of this granite porphyry may have been in a relatively reductive state. The apatites also indicate that the granite porphyry is a non-adakitic rock, which is consistent with the whole-rock geochemical characteristics. Furthermore, the apatites feature low Sr contents and δEu values and high F/Cl ratios, similar to the characteristics of typical Mo deposits. The 87Rb/86Sr and 87Sr/86Sr ratios of the apatites are 0.012811–0.037958 and 0.710897–0.714423, respectively. The (87Sr/86Sr)i (ISr) values are 0.710865–0.721183. The 147Sm/144Nd and 143Nd/144Nd ratios are 0.132166–0.225171 and 0.512520–0.512681, respectively. The εNd(t) values are −1.78–0.21, and the two-stage Nd model ages are 949–1065 Ma. The approximately positive εNd(t) values and young Nd model ages of the apatite are similar to those of the ore-forming rocks in Early Jurassic Mo deposits in NE China, indicating that these rocks shared the same magma source, which originated from the partial melting of juvenile crust.