LA-ICP-MS Dating and Geological Significance of the Dagugongka Ore-bearing Porphyry in Qinghai Province

The Dagugongka porphyry copper-molybdenum deposit is located in the northern section of Sanjiang, south of Qinghai Province, and it is the important porphyry copper-molybdenum metallogenic belt in Qinghai Province. The formation age of Dagugongka ore-bearing granite porphyry is 240.1±0.89Ma. The SiO₂ content of ore-bearing porphyry ranges from 65.18-70.43%, K₂O from 3.05%-6.76%, Na₂O 1.99%-3.47%, characterized by rich SiO₂, K₂O and Na₂O, relatively poor in Fe, Mg, Ca. Ritmann index is 1.09-4.29, and aluminum saturation index (ASI) is 1.01-1.23. Overall, it is a series of rocks from weak peraluminous to strong peraluminous high potassium calc-alkaline. The partition curves of the microelement are generally right-dipping, with the enrichment of large ion lithophile elements (LILE), the deficiency of high field strength elements (HFSE) and weak negative Eu anomaly. The geological, petrological and geochemical characteristics of the rock mass combined with the characteristics of regional tectonic evolution preliminarily determined that the Middle Triassic granite porphyry in Dagugongka was formed in the subduction stage. It indicates that the Indo-Chinese porphyry deposit is related to the subduction environment in the Sanjiang belt.