关键词: 花岗斑岩, 地球化学, 年代学, 阳山金矿带, 碧口群, 下草地村, 西秦岭

Abstract:

The gold bearing granite porphyry in Xiacaodi Village, Jiuzhaigou County is located in the western extension of  Yangshan gold deposit belt in the West Qinling. In order to explore the relationship between magmatic activity and gold mineralization in this metallogenic extension zone, as well as characterize the parent rock of the ore bearing granite porphyry, petrographic, geochemical, and LA–ICP–MS zircon U–Pb dating studies were conducted on the gold bearing granite porphyry. The results indicate that the granite porphyry belongs to the calcium alkaline series, characterized by rich silicon aluminum and poor iron magnesium calcium; The trace elements are characterized by enrichment of K, Rb, Cs, U, Pb, while the mass fractions of Nb, Ta, Zr, Hf, Ti and other elements are low, while Ba, Sr, Nb, Ti and other elements are deficient. The δCe is 0.91 to 0.98, which is similar to the distribution pattern of volcanic arc granite, indicating genetic association with subduction collision environments; The total amount of rare earth elements is 74.78% to 90.28%, with characteristics of light rare earth element enrichment and heavy rare earth element depletion; The δEu value ranges from 0.62 to 0.79, indicating weak loss of europium and belonging to peraluminous granite. Zircon U-Pb dating yielded four distinct age populations: (217.7±2.2), (222.3±5.2), (216.5±5.5), and (758±11) Ma. Combined with previous comparative analysis of geochemical, isotopic, and other data from intermediate acidic intrusive rocks (veins) in  Yangshan gold belt, it is believed that the gold mineralization in  Yangshan gold belt is closely related to the Late Indosinian magmatic activity, and the granite originates from partial melting of the basement rocks (Bikou Group) in a collision environment. The granite porphyry in Xiacaodi Village is a typical post magmatic hydrothermal gold deposit type within  Yangshan gold belt. This type of granite porphyry rich in silicon and aluminum is a horizontal metallogenic indicator for gold prospecting, while vertically it may overlie gold-bearing bodies genetically related to early-stage intermediate-acidic veins in its lower part.

Key words: granite porphyry, geochemistry, geochronology, Yangshan gold belt, Bikou Group, Xiacaodi Village, West Qinling