Mineralization and petrogenesis of the Qiongheba porphyry copper deposit in Mengxi district, East Junggar, China.

• Sulfide-rich fibrous veins and miarolitic cavities represent the magmatic–hydrothermal transition in porphyry systems. • Fractional crystallization process could induce the exsolving of sulfur from magma to porphyry systems. • Color cathodoluminescence can be used to unravel the paragenesis of ore-bearing in porphyry deposit. The Qiongheba porphyry Cu deposit is characterized by geochemical features of island arc and adakitic intrusions with fractional crystallization playing a key role in the formation of the ore-bearing rocks. Calculated sulfur concentrations in silicate melts at sulfide saturation show that two-thirds of the sulfur was exsolved during the fractional crystallization process to contribute to the formation of sulfides. The ore-bearing rocks in the Qiongheba area yielded U-Pb zircon ages of 414–412 Ma coeval with the 412 Ma Re-Os age of molybdenite indicating that sulfide mineralization is broadly coeval with magmatic crystallization. The color cathodoluminescence of quartz (purple) and K-feldspar (pink) in the fibrous veins and miarolitic cavities (Qtz-2 and Kfs-2) are the same as those (Qtz-1 and Kfs-1) in the granitic porphyry whereas the hydrothermal quartz (Qtz-3) and K-feldspar (Kfs-3) are black and green, suggesting that the color cathodoluminescence can be used to unravel the paragenesis of PCD. The oxygen isotopic values of Qtz-1 and Qtz-2 range from 9.15 to 10.1‰ and 8.93 to 10.4‰ with calculated equilibrium fluid compositions of 9.86 to 11.7‰ and 10.5 to 12.0‰, respectively, indicating a magma-dominated fluid composition, whereas Qtz-3 veins have very low oxygen isotopic values from −4.60 to −1.25‰ with corresponding fluid compositions of −3.51 to −0.17‰, implying that the fluid formed via the mixing of magmatic and meteoric water. Titanium-in-quartz thermometry constrains the magmatic crystallization to 580–627 °C, whereas the magmatic to hydrothermal transition occurred at 523–613 °C. [ABSTRACT FROM AUTHOR]