The Yangla copper deposit is a large skarn copper deposit in the Jinsha River suture line in the Sanjiang tectonic domain. The mineralization process can be divided into 3 stages and 5 sub-stages: (1) the skarn stage can be further divided into skarn and degeneration alteration sub-stages; (2) the quartz sulfide stage includes the quartz-sulfide and the quartz-carbonate sub-stages; (3) the supergene stage is mainly the supergene oxidation sub-stage. The skarn minerals are mainly garnet and diopside in the Linong section. According to field observation, microscopic identification and LA-ICP-MS in situ microanalysis, garnet in the deposit can be divided into two generations. The early-stage garnet (Grt Ⅰ) is mainly calcium aluminum garnet (And24.81Gro72.40–And57.92Gro30.02), and the late-stage garnet (GrtⅡ), which has oscillatory rings, is mainly calcium iron garnet (And61.64Gro37.18–And90.96Gro7.81). Both of them belong to the andraditegrossularite series. The garnet has relatively low REE contents (ΣREE=3.74×10−6–111×10−6), high LREE/HREE ratios (LREE/HREE=0.72–31.72), and dominantly positive Eu anomalies (δEu=0.83–8.40). GrtⅠ shows depletion of light rare earth elements (LREE) and enrichment of heavy rare earth elements (HREE), showing left inclined REE patterns. GrtⅡ shows enrichment of LREE and depletion of HREE as a whole, and right inclined REE patterns. In comparison, the ΣREE, LREE/HREE ratios and δEu of GrtⅡ are generally higher than those of GrtⅠ, the ratio of LREE/HREE has a clear positive correlation with δEu, the ΣREE has a weakly positive correlation with U and Y, but GrtⅠ has no significant correlation. Both GrtⅠ and GrtⅡ are strongly depleted in large ion lithophile elements including Rb, Ba, and Sr, and enriched in high field strength elements such as Ta, Th and U. The contents of Cu, Mo, Sn and Pb in GrtⅡ are significantly higher than those in GrtⅠ. The contents and variations of major and trace elements in garnet indicate that the oxygen fugacity of GrtⅠ is higher than that of GrtⅠ, and the fluids are more neutral or alkaline, which suggest that GrtⅠ was formed through diffusion metasomatism, whereas GrtⅡ closely related to Cu-Mo mineralization was formed via percolation metasomatism. The in situ LA-sf-ICP-MS U-Pb dating of garnet closely associated with chalcopyrite yielded an age of 236±5 Ma (MSWD=0.8, n=23), which accurately determined that the Yangla copper deposit was formed in the early Late Triassic. This age is consistent with the zircon U-Pb age from the first-stage granodiorite and molybdenite Re-Os ages within the error ranges, forming a reliable time frame for the Yangla copper deposit which supports a genetic link with the first magmatic event. © 2023 Science Press. All rights reserved.
