Origin of the subduction-related Tieli nephrite deposit in Northeast China: Constraints from halogens, trace elements, and Sr isotopes in apatite group minerals

Abstract

Apatite, which is an excellent tracer of geological processes and magma evolution, can record a variety of information about melt and/or ore-fluid evolution by incorporating large amounts of trace elements. In this study, we conducted an in situ geochemical analysis of apatite from the Tieli nephrite deposit in Northeast China and evaluated the genetic mechanism along with the source. The apatite from the Tieli nephrite deposit in Northeast China is magmatic apatite characterized by positive Ce anomalies, negative or positive Eu anomalies, enrichment in light rare earth elements, depletion in heavy rare earth elements, and high F content. The apatite coincides with plagioclase crystallization with positive Sr-(La/Yb)N/(Sm/Yb)N correlations. The geochemical characteristics of the redox-sensitive elements (Eu, V, As, and Mn) in apatite indicate that the parental magma has a high oxygen fugacity between HM (Hematite–Magnetite) and NNO (Ni-NiO). The estimated F and Cl contents of the source area (average values of 1694 and 2328 ppm, respectively) are higher than the average values of the continental crust and primitive mantle, indicating a convergence process of halogens in the source area. The non-chondritic Y/Ho ratios of the apatite (3.34–53.64) imply that the magma interacted with a high volume of fluids. Combined with the findings of previous studies, the 87Sr/86Sr values in apatite suggest contributions from crust and mantle materials. Moreover, the positive correlation between Sr and 87Sr/86Sr may indicate that the subducted sediments altered by seawater were added into the magma chamber. Based on the above findings, the subduction of the Pacific Plate may supply source material and power for magmatism and mineralization in the Tieli nephrite deposit.