Characteristics and metallogenic significance of granite porphyry dykes from Baizhangzi gold deposit in western Liaoning

The Baizhangzi gold deposit in western Liaoning is one of the largest gold deposit in the Jidong-Liaoxi metallogenic belt, Mesozoic magmatism played a key role in gold mineralization, where granitic dykes are closely related to gold ore. On the basis of field investigation, we found the Baizhangzi granite comprises biotite monzogranite, biotite-bearing monzogranite, monzogranite and granitic porphyry dykes, and studied petrology, petrogeochemistry, chronology and Hf isotopic characteristics. The study showed zircon U-Pb age of granitic porphyry dykes was 231.0 ± 1.3 Ma and 231.7 ± 2.7 Ma, formed in the late Triassic, which is similar to the time when the Baizhangzi granite pluton emplaced. The major elements of Baizhangzi granite and granitic porphyry dykes showed the characteristics of high-K calc-alkaline series, quasi-aluminum to weakly peraluminum I-type granite, the trace elements showed the characteristics of Rb, Th, U, K, Hf enriched while Nb, Ba, P, Ti depleted, without obvious Eu and Ce anomalies, and relatively enriched in light rare earth elments and depleted in heavy rare earth elments, fall into the Post-COLG in the tectonic setting discrimination diagrams. The zircon Hf isotope of the granitic porphyry dykes showed that the ε_Hf(t) value varies from -9.02 to -5.62 (average -7.43), and the two-stage Hf model age (T_MD2) range from 1592Ma to 1810 Ma (average 1710 Ma), which indicates that the magma was likely derived from partial melting of the late Paleoproterozoic crust. Harker diagram and rare element covariant relationship showed there were fractional crystallization of biotite, potassium feldspar, apatite, ilmenite and spar from biotite monzogranite to granitic porphyry dykes. According to the zircon rare elements of granitic porphyry dykes, logfO₂ range from -16.7 to -10.1, △FMQ range from -1.23 to 4.65, △NNO range from -1.79 to 4.09. The richness of alkali, high fO₂ and low evolution degree of granite porphyry dykes was conducive to gold mineralization and has a good mineralization potential.