Haijun Yu

1. A-type granites were proposed by Loiselle and Wones (1979) and are characterized by their distinct alkalic, relatively anhydrous, and anorogenic nature. Geochemically, A-type granites are distin...

The Zhongdian Arc is an important copper polymetallic ore cluster in China’s Sanjiang Tethyan Metallogenic Domain, and the Langdu deposit is a representative porphyry–skarn Cu deposit in this region. This study aims to constrain the timing of magmatic activity at the Langdu deposit. It also seeks to reveal the magma’s physical–chemical properties and evolution, and to identify the factors controlling mineralization. To achieve these objectives, this study used LA-ICP-MS zircon U-Pb dating and elemental analysis, combined with halogen and trace element data from apatite. Zircon U–Pb dating shows that the Langdu intrusions were emplaced at ca. 216 Ma in a continental arc setting associated with the westward subduction of the Garzê–Litang oceanic crust during the Late Triassic. Geochemical and mineralogical features indicate that the Langdu intrusions are I-type granite. They originated from partial melting of the mantle wedge metasomatized by subduction fluids. During their ascent, these magmas experienced fractional crystallization dominated by amphibole, titanite, rutile, and monazite. Geochemical records from zircon and apatite further reveal that the ore-forming magma of the Langdu intrusions exhibited high oxygen fugacity (ΔFMQ = +1.53), elevated H₂O content (avg. 7.63 wt.%), and enrichment in S (avg. 560 ppm) and Cl (avg. 2141 ppm). This Cl-rich magma experienced fluid exsolution during its early evolutionary stage. This provided the necessary conditions for metal extraction and transport. In summary, the key factors controlling the formation of the Langdu porphyry–skarn Cu deposit are high-oxygen-fugacity magma enriched in water and volatiles (S and Cl), coupled with efficient fluid exsolution. This understanding is important for better understanding regional metallogeny and for guiding mineral exploration.

The Huangliangou Nb-Ta-Be deposit in the Baoshan Block of western Yunnan hosts two distinct generations of columbite–tantalite group minerals (CGMs) and tapiolite, which record the evolution of a highly fractionated rare metal pegmatite. To investigate the relationship between Huangliangou pegmatite differentiation and Nb-Ta mineralization, we conducted an integrated study combining petrography with mineral chemistry and geochronology. Electron probe microanalysis (EPMA) was used to determine the compositions of two CGMs and tapiolite. LA-ICP-MS U-Pb dating of these Nb-Ta oxides yields weighted mean ages of 60.25 ± 0.75 Ma for CGM-1 and 59.4 ± 1.1 Ma for CGM-2, indicating their synchronous formation in the early Paleocene. LA-ICP-MS trace element analysis of muscovite reveals a trend of decreasing Nb/Ta and K/Rb ratios with increasing Cs content from two-mica to garnet-bearing pegmatites. This chemical evolution in muscovite parallels the mineralogical transition from magmatic CGM-1 to metasomatic CGM-2 and tapiolite, confirming that late-stage hydrothermal fluids were characterized by volatile enrichment and Ta accumulation. The textural and chemical evolution reflects a late-stage, fluid-assisted autometasomatism within a highly fractionated melt. These results identify the northern garnet-bearing pegmatite dikes as a high-priority target for Ta exploration and provide a chrono-lithological framework for prospecting Paleocene pegmatite-type Nb-Ta deposits in western Yunnan and comparable Tethyan settings.

The Geza island‐arc is a well‐known mineralization concentration area, part of the Sanjiang Domain at the east margin of the Tibetan Plateau. In recent years, several Late Yanshanian granitic intrusions and associated deposits have been found in this region, the largest one of which in the Shangri‐La region is the Laba molybdenum deposit. Previous studies suggested that the timing of the Laba mineralization is 85 ± 2 Ma. However, the ages of the granodioritic porphyry remain unknown. In this study, LA‐ICP‐MS U‐Pb dating of zircons from three samples of the molybdenite‐bearing granodioritic porphyry has been conducted with resulting dates of 85.00 ± 0.23 Ma (MSWD = 0.58), 85.28 ± 0.28 Ma (MSWD = 1.12), and 84.83 ± 0.26 Ma (MSWD = 0.79), respectively, indicating that these granodioritic porphyries formed in the Late Yanshanian around ∼85 Ma. Combined with the geological features of the mineralization, the Laba deposit is spatially, temporally, and probably genetically associated with the granodioritic porphyries. In addition, the ages of the Laba deposits are consistent with the other Late Yanshanian intrusions and mineralization, suggesting that the mineralization was probably generated under an intra‐plate extensional environment during the Late Cretaceous.