Hydrothermal Alteration And Mineralization Of Baiyun Gold Deposit In Liaodong Peninsula, North China Craton

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.