Sm-Nd and Ar-Ar Isotopic Dating of the Nuri Cu-W-Mo Deposit in the Southern Gangdese, Tibet: Implications for the Porphyry-Skarn Metallogenic System and Metallogenetic Epochs of the Eastern Gangdese

The Nuri Cu-W-Mo deposit is a large newly explored deposit located at the southern margin of the Gangdese metallogenic belt. There are skarn and porphyry mineralizations in the deposit, but the formation age of the skarn and the relationship between the skarn and porphyry mineralizations are controversial. Constraints on the precise chronology are of fundamental importance for understanding the ore genesis of the Nuri deposit. To determine the formation age of the skarn, we chose garnets and whole rock skarn samples for Sm-Nd dating. We also selected biotite associated with potassic alteration for Ar-Ar dating to confirm the ore formation age of the porphyry mineralizations. The Sm-Nd ages of the skarn are 25.73 +/- 0.92 - 25.2 +/- 3.9Ma, and the age of the potassic alteration is 24.37 +/- 0.32Ma. The results indicate that the skarn and porphyry mineralization are coeval and belong to a unified magmatic hydrothermal system. Combined with a previous molybdenite Re-Os age, we think that the hydrothermal activity of the Nuri deposit lasted for 1.2 - 2.1 Myr, which indicates that the mineralization formed rapidly. The chronologic results indicate that the Nuri deposit formed in the period of transformation from compression to extension in the late collisional stage of the collision between the Indian and Eurasian continents.