Geology and mineralization of quartz vein-type and altered rock-type gold deposits in the Linglong gold orefield (916 t), Jiaodong Peninsula, China: A review

Abstract

The Jiaodong Peninsula in North China Craton as the world’s third largest gold metallogenic region, holding gold deposits primarily of the altered rock type and the quartz vein type. The Linglong gold orefield, with 916 t of proven gold resources presently, is a typical birthplace of quartz vein-type gold deposits in the Jiaodong Peninsula and develops altered rock type gold deposits. This study elaborated on the characteristics of deposits and the spatial distributions of orebodies in the Linglong gold orefield, analyzing control factors, geochemical characteristics, mineralization era, and mineralization mechanism. Comprehensive research has found that: The altered rock-type gold deposits have gentle dip angle and large scale, fine grain size of the gold ore, low average ore grades, low metal sulfide content, which is about 1/3 compared to the quartz vein-type gold deposits. Their gold minerals primarily occur as intercrystalline gold. In contrast, the quartz vein-type gold deposits occur in the steeply dipping tensile fissures in the footwall of main faults. Their orebodies exhibit steep dip angles and small scales but high average ore grades and metal sulfide content, with gold minerals primarily occurring as inclusion gold. The Linglong gold orefield experienced gold mineralization at about 120 Ma, with ore-forming fluids belonging to a moderate- to high-temperature, low-salinity, and reducing H₂O-CO₂-NaCl±CH₄ system. The ore-forming fluid mainly comes from the mixture of magmatic water and meteoric water. The ore- forming materials primarily originated from the lower crust, supplemented by some mantle-derived components. The comprehensive analysis leads to the following conclusions: Extensive crust-mantle mixing provided thermodynamic conditions, migration pathways, and partial fluid sources for ore-forming fluid activity in the Jiaodong region. The rapid magma ascent led to the formation of detachment faults and associated tensile structures in the shallow crust, which create favorable space for fluid migration and the enrichment and precipitation of ore-forming elements. The pressure fluctuation of fluids arising from changes in the dip angles of faults is the main cause of the stepped metallogenic pattern. The quartz vein- and altered rock-type gold deposits are the product of the same metallogenic event under different metallogenic modes and tectonic locations. Based on the deep metallogenic regularity, this study established a geological-geophysical prospecting model for altered rock-type gold deposits, of which the critical factors include ore-hosting faults, high-precision geophysical exploration, and a stepped metallogenic pattern.