Constraints from volcanic and subvolcanic magmatism on low-sulfidation epithermal mineralization in the Yanbian area, NE China

Low-sulfidation (LS) epithermal gold deposits are a significant type of global gold resource, typically exhibiting a close spatial and temporal relationship with volcanic and subvolcanic (hypabyssal porphyry) rocks. LS systems have been widely investigated; however, the genetic relationship between gold mineralization and multi-phase volcanism remains insufficiently constrained. Here, we investigate their links through an integrated geochronological, geochemical, and petrological study of Early Cretaceous volcanic (multi-cycle) and subvolcanic (single-cycle) suites and their genetic association to LS epithermal Au deposits (Ciweigou, Ganhegou, and Wufeng-Wuxingshan) in the Yanbian area, NE China. New and published geochronological data constrain the mineralizing event to 105−102 Ma (sulfide Rb-Sr, 102.6 ± 2.2 Ma; hydrothermal apatite U-Pb, 103.7 ± 8.7 Ma; and quartz fluid inclusions Ar-Ar, 104.1−103.3 Ma), during the intervals of multi-cycle volcanic eruptions (Tuntianying-II [TTY-II], 124−112 Ma; Jingouling-I [JGL-I], 112−108 Ma; Jingouling-II [JGL-II], 108−106 Ma; and Ciweigou, 102−96 Ma). The ore bodies of the three deposits mainly consist of quartz ± calcite veins hosted in Jingouling-II andesite and granodiorite porphyry. Subvolcanic dikes (granodiorite porphyry and diorite porphyry) of JGL-II and its ore bodies are controlled by the same syn-volcanic faults. Volcanic suites of each cycle exhibit similar geochemical characteristics, including enrichment in large ion lithophile elements (e.g., Rb, Ba, K) and depletion in high field strength elements (e.g., Nb, Ta, P, Ti). Zircon εHf(t) values (+6.7 to +12.8) and whole-rock εNd(t) values (−2.1 to +3.5) for JGL-I, JGL-II, and TTY-II volcanics, together with two-stage zircon Hf model ages of 900−550 Ma, indicate derivation from a depleted mantle−dominated source, primarily via partial melting of Neoproterozoic lower-crustal material with minor ancient crustal contamination. Calculations of zircon oxygen fugacity and water content reveal that the JGL-II volcanic suite exhibits higher oxygen fugacity (fayalite-magnetite-quartz buffer [FMQ] +0.9, on average) and higher water contents (H2O = 6.35 wt%, on average) than those of the JGL-I volcanic suite (FMQ +0.40, H2O = 5.63, on average), which favored the retention of gold in the residual melt. The volcanic faults developed during the intervals between the multi-stage volcanic eruptions further facilitated the formation of economic LS gold deposits from ore-forming fluids.