Acta Petrologica et Mineralogica

The Qingcaoshan mineralization area is located on the northwest side of the Duolong mining area, with a large area of magmatic rocks exposed on the surface and developed porphyry-type copper mineralization. However, the geochemical characteristics and origin and evolution of the magmatic rocks are not yet clear, which restricts further evaluation of the prospecting potential of this mineralization area. For this purpose, detailed zircon U-Pb geochronology, zircon trace elements, rock geochemistry, Sr-Nd isotopes, and hornblende electron microprobe analyses were conducted on the exposed magmatic rocks in the Qingcaoshan mineralization area to explore the source area and evolution process of the magmatic rocks, determine their temperature and pressure conditions, magma oxygen fugacity, and water content, and provide support for further evaluating the regional prospecting potential. The study shows that the ore-forming magmatic rocks in the Qingcaoshan mineralized area mainly consist of granodiorite porphyry, diorite porphyry, and monzonitic granite porphyry, with diagenetic ages concentrated between 120~118 Ma. The zircon U-Pb age of the postmineralization aplite is 114 Ma, all of which are products of Early Cretaceous magmatic activity. The average crystallization temperatures of zircons in granodiorite porphyry, diorite porphyry, and monzonitic granite porphyry during the mineralization period were calculated based on the Ti content in zircons, which were 604, 689 and 684℃, respectively. The average oxygen fugacity lg (f_O2) was -18.58, -15.77 and -14.18, respectively. The range of ΔFMQ variation was ΔFMQ-0.46~ΔFMQ+2.38, ΔFMQ-5.66~ΔFMQ+4.28 and ΔFMQ-1.32 ~ΔFMQ+6.24. The diorite porphyry and granodiorite porphyry belong to the high-potassium calcium alkaline-potassium basalt series, and quasi aluminum-weak peraluminous magmatic rocks, with arc magmatic rock properties; The (⁸⁷Sr/⁸⁶Sr)_i value ranges from 0.707 4 to 0.709 3, and the εNd(t) value ranges from -7.1 to -5.3, located in the region between the depleted mantle and the lower crust evolution line, showing the characteristics of crust-mantle mixed origin. The electron probe results of hornblende show that the average water content of diorite porphyry is 7.4%. The study proves that the Cretaceous magmatism of Qingcaoshan originated from the partial melting of mantle wedges caused by subducted slab, and was mixed by crustal materials, and shows the characteristics of high oxygen fugacity and high water content, indicating that the Qingcaoshan mineralized area has good potential for porphyry copper mineralization.

geochemistry; mineralogical characteristics; magmatic attribute; Qingcaoshan mineralization area; southern edge of Qiangtang terrane