Zircon U-Pb Age, Geochemical Characteristics and Geological Significance of Diabase in the Yanlinsi Gold Deposit, Northeastern Hunan Province

The Yanlinsi gold deposit, located in the middle section of the Jiangnan Orogenic Belt, is one of the typical gold deposits in northeastern Hunan Province. Diabase dikes are exposed by underground workings and drill holes in the mining area. The dikes strike NW and cut the NE-trending gold ore body. To investigate the petrogenetic age, characteristics of the magmatic source area, and tectonic setting of the diabase dikes in the Yanlinsi gold mining area, northeastern Hunan, and to determine the mineralization age of the deposit, in this paper, diabase dike LA-ICP-MS zircon U-Pb dating, whole-rock geochemistry, and gold-bearing quartz vein LA-ICP-MS zircon U-Pb dating were studied. The results of LA-ICP-MS zircon U-Pb dating indicate that the diabase was emplaced at an age of 219.5 Ma, belonging to the late Indosinian. The investigated diabase dikes are characterized by low SiO2 (43.68%–46.55%), high MgO (7.78%–9.84%), and high Mg# (65.0–68.7) values, belonging to the alkaline basalt series with high potassium. The chondrite-normalized REEs patterns show highly fractionated LREEs and HREEs ((La/Yb)N = 11.21–14.82), and the primitive mantle-normalized spider patterns show enrichment in large ion lithophile elements (e.g., Rb, Ba, K and Sr) and relative depletion in high field strength elements (e.g., Nb, Ta, and P), similar to those of ocean island-like basalt (OIB). Rock geochemical characteristics indicate that the magma of the Yanlinsi diabase was formed by partial melting of the enriched mantle (EM II), with the source region being spinel-garnet lherzolite. The degree of partial melting was approximately 10%–15%, and the assimilation and contamination with continental crustal materials were weak. Meanwhile, weak fractional crystallization of olivine, clinopyroxene, and apatite occurred during the magma evolution process. On the basis of a synthesis of previous research results, it is concluded that the Yanlinsi diabase formed in an extensional tectonic setting after intracontinental collisional orogeny. The LA-ICP-MS U-Pb age of hydrothermal zircons from quartz veins in the main mineralization stage of the Yanlinsi gold deposit is 421.9 ± 1.5 Ma. Combined with the cross-cutting relationships between mafic dikes and gold veins (ore bodies), it is determined that the main mineralization stage of the deposit formed during the Caledonian Period.