Geochemistry and geochronology of zircons from granite-hosted gold mineralization in the Jiaodong Peninsula, North China: Implications for ore genesis

Abstract

Large-scale quart-vein and structurally-controlled gold mineralization is intensely developed in the Jiaodong Peninsula, North China Craton and is typified by the Linglong and Jiaojia deposits, respectively. In this work, zircons from typical gold-bearing ores of the Sanshandao Northern Sea (SNS), Jiuqu (JQ) and Canzhuang (CZ) gold deposits were compared in terms of texture, U–Pb age, trace element content and Hf isotopic signatures in order to discern whether zircon from ore samples can be used as an indicator of ore genesis and grade. Most studied zircons are magmatic in origin with a hydrothermal overprint (i.e., zircons with core-rim assemblages, fractured-dissolution textures and hydrothermal activity-related fluid/mineral inclusions). Three zircon age clusters were differentiated: ~120 Ma, ~150 Ma and >2000 Ma. The ~120 Ma zircons show evidence of hydrothermal alteration (dark in cathodoluminescent images with hydrothermal rim textures) and are characterized by high LREE, P, Ti and εHf(t) (−21 to −15) and young TDMC (2100–2500 Ma). This suggests an interaction between the mantle and crust at the magma source, and that a P/Ti-rich, Al-poor, high temperature, high fO2, wet late-stage residual granitic melt and intense hydrothermal alteration played an important role in the formation of gold mineralization. The ~150 Ma zircons have high Y, Nb, Ta and U contents, low εHf(t) (−26 to −20) and old TDMC (2300–3000 Ma) ages, and HREE-enriched patterns with pronounced Ce and Eu anomalies. These features indicate a reduced, cool and Al-rich magma which did not favor gold mineralization, even though it was highly evolved. This also implies that the degree of magma differentiation is not the key factor that led to gold mineralization in the Jiaodong gold province. The >2000 Ma zircons are primarily limited to gold ores with high Pb contents, HREE-enriched patterns and variable Ce and Eu anomalies, indicating that they were inherited from the Paleoproterozoic (2000–2200 Ma) basement. In addition, the SNS high-grade ores yielded zircon with the greatest U-Pb age range (mainly 110–180 Ma) and the most pronounced hydrothermal overprinting, indicating that large-scale mineralization resulted from multi-stage granitic intrusion, with intense fluid dissolution and metasomatism. This research highlights that correlations between zircon age populations, Hf isotope signatures, internal structures and trace element patterns can provide insights into ore genesis and fluid evolution in gold mineralization systems.