Structure, Isotopes, and 40Ar/39Ar Dating of the Pengjiakuang Gold Deposit, Mesozoic Jiaolai Basin, Eastern China

Abstract

The Pengjiakuang gold deposit, located on the northeastern margin of the Mesozoic Jiaolai basin, eastern Shandong Province, China, is controlled by a low-angle detachment fault. Three economic ore bodies and more than 10 mineralized bodies have been proved in recent years. The main ore bodies are made up of gold-bearing breccia, cataclastic rocks, and sulfide-quartz veins in lenses and veins. Gold ores are typically brecciated, veinlet, and disseminated. Lamprophyre dikes are spatially and temporally associated with the gold ore bodies. The isotopic analysis indicates that the δ34S range (6.5-12.89‰) of sulfides in the Pengjiakuang gold deposit is consistent approximately with that of metamorphic rocks, Mesozoic granites, and the Jiaojia and Linglong gold deposits in eastern Shandong. However, there are wide ranges of compositions of δ34S and lead isotopes in the Pengjiakuang ore except for lower 206Pb/204Pb ratios. Analyses of sulfur and lead isotopic compositions suggest that the ores have a multiple origin. Unlike the Jiaojia and Linglong deposits, the oxygen and hydrogen isotopic compositions of fluid inclusions in the Pengjiakuang deposit show a mixed source: dominant meteoric water, and subordinate magmatic water. The Ar-Ar method was adopted to date the Au-bearing quartz. Brecciated ore yields a 40Ar/39Ar age of 118.42 ± 0.25 Ma and an isochron age of about 117.03 ± 0.13 Ma. Veinlet ore yields a 40Ar/39Ar age of 118.70 ± 1.40 Ma and an isochron age of 117.33 ± 0.15 Ma. The results indicate that the Pengjiakuang gold deposit was formed at ∼117.3-118.4 Ma. Biotite from a lamprophyre dike gives an age of 117.49 ± 0.25 Ma and an isochron age of 116.83 ± 0.36 Ma. Clearly, the formation of both lamprophyre dikes and gold mineralization are coeval products of tectonic-magmatic activity. The consistency in metallogenic age between the Pengjiakuang gold deposit, located on the margin of a Mesozoic pull-apart basin, and gold deposits of the northern uplift area in eastern Shandong suggests that both can be ascribed to the same the metallogenic event.