Abstract:
The Baizhangzi gold deposit in western Liaoning is among the largest gold deposits within the Jidong−Liaoxi metallogenic belt, where Mesozoic magmatism has led to the formation of granitic rock mass closely associated with gold ore. On the basis of field investigation, we have identified that the Baizhangzi granite consists of biotite monzogranite, biotite−bearing monzogranite, monzogranite and granitic porphyry dykes, and studied petrology, petrogeochemistry, chronology and Hf isotopic characteristics. The zircon U−Pb ages of granitic porphyry dykes were determined to be 231.0 ± 1.3 Ma and 231.7 ± 2.7 Ma, indicating formation in the Late Triassic. The major elements of Baizhangzi granitic rock mass exhibit characteristics of a high−K calc−alkaline series, displaying quasi−aluminum to weakly peraluminous granite composition; while the trace elements show enrichment in Rb, Th, U, K, Hf and depletion in Nb, Ba, P, Ti without obvious Eu and Ce anomalies. Additionally, there is relative enrichment in light rare earth elements and depletion in heavy rare earth elements placing it within the Post−COLG on tectonic setting discrimination diagrams. The Harker diagram and rare element covariant relationship indicate fractional crystallization of biotite, potassium feldspar, apatite, ilmenite and spar from biotite monzogranite to granitic porphyry dykes. The zircon Hf isotope analysis of the granitic porphyry dykes reveals ε
Hf(
t) values ranging from −9.02 to −5.62 (average −7.43), with two−stage Hf model ages (
TMD2) ranging from 1592 Ma to 1810 Ma (average 1710 Ma), suggesting derivation of the magma through partial melting of Late Paleoproterozoic crust. The zircon rare elements in the granitic porphyry dykes show a △FMQ range from −1.23 to 4.65. The enrichment of alkali, high oxygen fugacity(
fO
2), and medium degree of evolution in granite porphyry dykes are favorable conditions for gold mineralization, indicating a strong potential for mineralization.