Hydrothermal alteration and mineralization of Baiyun gold deposit in Liaodong Peninsula, North China Craton

Abstract

Baiyun deposit is a large gold deposit in the Liaodong Peninsula (North China Craton), containing over 31.7 t of gold. Silicic alteration, K-feldspar alteration, and pyritization are well developed and closely related with mineralization in Baiyun deposit. Based on field and optical microscopic observations, the alteration styles include quartz + K-feldspar zone, pyrite + sericite +quartz zone, and chlorite zone from orebody outward. In this study, the quartz, K-feldspar, and pyrite of pre-ore, syn-ore stages 1 and 2 were selected for LA-ICP-MS trace element analysis and electron probe microanalysis (EPMA) to reveal the alteration-mineralization link. Results show that the albite was altered to mainly K-feldspar and minor secondary quartz at syn-ore stage 1. Fluid-rock reaction of the silicic-potassic alteration may have decreased the fluid oxygen fugacity (fO 2 ), which triggered the gold precipitation. Most of invisible gold occurred in the form of solid solution. At syn-ore stage 2, albite altered to mainly quartz and minor K-feldspar. The syn-ore stage 1 K-feldspar also altered to minor secondary quartz at syn-ore stage 2. In addition, the release of sulphur from the syn-ore stage 1 pyrite was likely another trigger for the gold precipitation. Most of syn-ore stage 2 invisible gold occurred as nano-particles. The ore-forming fluids consist mainly of primary magmatic fluids mixed with minor metamorphic fluids. The ore metals may have sourced mainly from the magmatic fluid and the sillimanite-mica schist of the Gaixian Formation.

Petrogenesis of the Early Paleoproterozoic Felsic Metavolcanic Rocks from the Liaodong Peninsula, NE China: Implications for the Tectonic Evolution of the Jiao-Liao-Ji Belt, North China Craton

“…2160-2100 Ma) (Figure 9). The meta-volcanic sequences are mainly outcropped in the North and South Liaohe Groups and characterized by bimodal volcanic rocks [21,40,77,78]. They display various lithologies, mainly composed of meta-rhyolite, meta-dacite, finegrained gneiss, amphibolite, and meta-basalt.…”

“…2.2-2.1 Ga mafic intrusions were identified in southern Jilin Province and on the Liaodong Peninsula [31,38,44,46,79]. Thirdly, the metavolcanic sequences in the JLJB are mainly composed of bimodal volcanic rocks [21,40,77,78], which indicates that the JLJB experienced an intra-continental rift rather than magmatic arc during the early Paleoproterozoic. Fourthly, a large number of Liaoji granites with an affinity of A-type granite also suggest an intra-continental rift setting [21,22,43,45,80].…”

“…Firstly, the differentiation process of basaltic magmas will produce a complete set of magmatic evolutionary sequences, including basaltic, andesitic and rhyolitic magmatisms. However, the early Paleoproterozoic meta-volcanic sequences in the JLJB are characterized by bimodal volcanic rocks [21,40,77,78]. Secondly, multiple positive correlations between La contents and La/Sm, La/Yb, La/Hf ratios strongly suggest that the petrogenesis of the felsic metavolcanic rocks is mainly controlled by the partial melting process rather than fractional crystallization (Figure 11a-c), which is also supported by the positive correlation between Ce contents and Ce/Zr ratios (Figure 11d).…”

“…However, many studies revealed that the JLJB went through an intra-continental rift system during the early Paleoproterozoic. Firstly, the Longgang and Nangrim blocks on both sides of the JLJB have similar Archean basement rocks geochemically geochronologically [3,40], which indicates that the two blocks previously belonged to a unified continent. Secondly, the existence of regional large-scale mafic dykes generally represents a crustal extension tectonic regime.…”

“…Although numerous geochronological, geochemical, metamorphic, and structural studies have been carried out in the JLJB [13,19,22,[24][25][26][27][28][29][30][31][32], its tectonic evolution during the Paleoproterozoic remains highly controversial [21,22,24,32,33]. Currently, there are three main tectonic models: (1) the first model involves oceanic subduction and arc/continent-continent collision between the Longgang and Nangrim blocks [27,30,[34][35][36][37][38][39]; (2) the second model suggests the opening and closure of an intra-continental rift for the tectonic evolution of the JLJB [13,14,25,[40][41][42]; (3) the third model proposes that the JLJB experienced early intracontinental rift and subsequent oceanic subduction and collision [3,17,[21][22][23]. In recent years, increasingly studies suggest an extension tectonic regime for the JLJB during the early Paleoproterozoic (ca.…”