Geochemistry and zircon U-Pb-Hf isotopes of igneous rocks associated with the Dongnam Fe-Mo skarn deposit, Taebaeksan Basin, South Korea

摘要

The Dongnam Fe-Mo skarn deposit is located at the northern part of the Taebaeksan Basin, an important mineralized province in South Korea. The age of Fe-Mo mineralization is Late Cretaceous (79.1-75.9 Ma), and the orebodies are distributed along the contact between age-unknown igneous complex (quartz monzodiorite, granodiorite, and granite) and Pungchon Formation (limestone). Previous study suggested that the Dongnam Fe-Mo skarn deposit was mainly formed by the hydrothermal replacement of quartz monzodiorite. However, Fe-Mo mineralization and skarn are also commonly observed along the contact between granite and limestone, and the hydrothermal replacement of quartz monzodiorite began at the contact with granite. In this study, we conducted whole-rock geochemistry and zircon U-Pb-Hf isotope analyses to examine the characteristics of the ore-associated igneous rocks from the Dongnam deposit. Whole-rock chemistry and zircon Hf isotopes indicate that the granite was formed from crust-derived magma in a volcanic arc setting and exhibits geochemical characteristics (highly fractionated, oxidized, peraluminous, and high-K calc-alkaline etc.) similar to those from the Shinyemi and Wondong magnetite-associated igneous rocks in the Taebaeksan Basin. According to the zircon U-Pb age dating, quartz monzodiorite and granodiorite were emplaced in the Early Cretaceous (113.7-109.4 Ma) and granite was emplaced in the Late Cretaceous (80.3 Ma). Combined with geological observations, the geochemical and zircon U-Pb-Hf isotope data of the igneous rocks suggest that the Dongnam skarn Fe-Mo deposit was formed in association with Late Cretaceous granite derived from highly fractionated and oxidized magma, which is consistent with the mineralization age estimated by previous K-Ar and Re-Os dating.