Abstract:

The Songjiachong skarn Au,Cu-Mo deposit is located in the southwestern part of Jiujiang-Ruichang metallogenic district in the Middle-Lower Reaches of the Yangtze River. The Songjiachong porphyritic granodiorite is the ore-related granitic intrusion. Zircon LA-ICP-MS dating of the intrusion suggests its emplacement age of (142.8±0.6) Ma. Whole-rock samples from the Songjiachong intrusion are metaluminous, low content of MgO(1.29%-2.58%), high content of Al₂O₃(15.52%-16.88%) and Na₂O(K₂O/Na₂O=0.57-1.04). They are enriched in large ion lithophile elements (eg. Rb, Ba, Th and La) and depleted in high field strength elements (eg. Nb, Ta and Zr). These rocks are of geochemical features of typical adakites, such as high content of Sr(＞618×10^-6), low content of Y(＜17.1×10^-6), high Sr/Y(39-61), and low content of Yb(＜1.45×10^-6) and La/Yb(＞30). They show a narrow range (⁸⁷Sr/⁸⁶Sr)_i of 0.705 8-0.706 7, ε_Nd(t) of －6.4-－4.9 and ε_Hf(t) of －10.1-－5.1. Based on integration of the geological characteristics of the studied area, we suggest that the Songjiachong granitic intrusion was derived from partial melting of an enriched mantle source. The petrogenetic-metallogenic event probably occurred in a transitional environment from an early compressional stage to the late intraplate extensional environment.

Key words: zircon U-Pb dating, geochemistry, Sr-Nd-Hf isotope, Jiujiang-Ruichang metallogenic district, Jiangxi