Deep magma evolution and gold mineralization in Wulong area, Liaodong Peninsula: Evidence from the Wulong 3000 m scientific drilling

Abstract

The Wulong area is located in the Liaodong gold-polymetallic mineralization belt on the northeastern margin of the North China Craton. The area is characterized by intense tectonic-magmatic activity and the widespread distribution of Yanshanian intrusive rocks. The intrusive dikes are spatially, temporally, and genetically related to gold mineralization. A 3000 m scientific drill core (project number WLSZ001) was recently obtained in the area under the auspices of the National Key Research and Development Program, providing valuable samples for investigating deep magmatic evolution and gold metallogeny in the Liaodong region. This study presents petrogeochemistry, zircon U-Pb geochronological, and Hf isotopic characteristics of intrusive rocks (including dikes) samples from WLSZ001. Field observations indicate that the drill core intersected substantial intrusive dikes of the Wulong pluton, predominantly comprising biotite monzonite granite, diorite, lamprophyre, and diabase. Simultaneously, multiple levels of gold polymetallic ore bodies (including mineralized zones) were identified, consisting of four gold ore bodies, three gold mineralized zones, two zinc ore bodies, and one zinc mineralized zone. Zircon U-Pb dating reveals two distinct intrusive episodes: the first spanning between 153.8 to 166.3 Ma (Middle to Late Jurassic), and the second between 123.9 and 136.1 Ma (Early Cretaceous), consistent with the regional pluton emplacement age. Geochemically, the deep intrusive rocks are characterized by high-Al, high-K, low-Mg and low-Ca contents, classifying them as calc-alkaline to high-K calc-alkaline. They display enrichment in light rare earth elements (LREE) and large ion lithophile elements (LILE; e.g., Ba, K, La, Pb) and depletion in heavy rare earth elements (HREE) and high field strength elements (HFSE; e.g., Nb, Ta, Pb, P, Ti). Notably, the granitic dikes exhibit features characteristic of peraluminous S-type granites. Zircon εHf(t) values for the deep intrusive rocks range from –32.0 to −2.3 (average –22.8), yielding two-stage Hf model ages (T_DM2) averaging 2661 Ma (ranging from 1565 and 3176 Ma). These data suggest that the deep intrusive rocks originated from partial melting of Paleoproterozoic ancient crustal materials in a volcanic arc and co-collision environment related to the oblique subduction of the ancient Pacific Plate. Integrating field geological observations, geochronological and geochemical data, and previous research, it is considered that the two phases of intrusive rocks in the deep Wulong area represent pre-mineralization intrusions. While not directly involved in the genesis of the Wulong gold deposit, the pervasive vein network creates pathways for ore-forming hydrothermal fluids, and areas with dense vein development are prospective targets for gold exploration in the region.