Mineralogy, geochemistry, and petrogenesis of nephrite from Panshi, Jilin, Northeast China

Abstract

Nephrite is an important variety of jade that is of great significance in prospecting management. Little research has been carried out on the newly discovered nephrite deposit in Panshi, Jilin Province, Northeast China. This paper presents the first systematic study of this new deposit. The mineralogical, petrological, and geochemical characteristics along with the petrogenesis of samples from this deposit were evaluated by microscopic observation, scanning electron microscopy, electron probe microanalysis, and laser ablation inductively coupled plasma mass spectrometry. The main mineral component of the Panshi nephrite was determined to be tremolite, and diopside, chlorite, apatite, calcite, and dolomite were observed as secondary minerals. The tremolite presented two microstructures: feltlike and fibroblastic. All the examined tremolite samples contained low amounts of FeO (0.006–0.249 wt%), Cr2O3 (0.000–0.047 wt%), and NiO (0.000–0.053 wt%) along with high values (>0.99) of Mg2+/(Mg2++Fe2+) relative to dolomite-related nephrites. The nephrite samples all exhibited very low total rare earth element contents ranging from 1.831 to 5.121 ppm and were characterized by positive and negative Eu anomalies (0.267–4.446), negative Ce anomalies (0.283–0.650), positive U anomalies, and negative Ba, Nb, Ti, and Ce anomalies. These characteristics indicate a multistage, superimposed mineralization formation mechanism for the Panshi nephrite. The test results and regional geological survey results indicate that the Panshi nephrite deposit was likely formed by intermediate-felsicmagmas that intruded into dolomitic marble in many stages during the Variscan–Indosinian epoch. Generally, the genesis of the Panshi nephrite can be ascribed to two typical processes, contact metasomatism and late metamorphism, and the Panshi nephrite is of dolomite-related origin. The results of this study provide theoretical guidance for the search for nephrite deposits of dolomite-related origin.