Ore fluid pathways at the giant Lannigou Carlin-type gold deposit, SW Guizhou, China

Abstract

Ore fluid pathways are essential for establishing metallogenic models at both the district and deposit scales and for guiding prospecting. The ore fluid pathways in fault-controlled Carlin-type gold deposits are poorly understood. The Lannigou deposit is a typical fault-controlled Carlin-type gold deposit in the Youjiang Basin, China. It consists of five ore blocks, that is, Huangchanggou, Rongban, Lintan, Shizhu, and Anbao. The Huangchanggou and Rongban ore bodies are hosted in fault F₃, Lintan is located in fault F₁₄, and Shizhu and Anbao are located in fault F₇₀. Petrographic observations, statistical analyses, and trace element distribution patterns across these five sections of the Lannigou deposit were used to delineate geochemical anomalies and trace the deposit scale ore fluid pathways.

The wall rocks and ores from the five ore blocks share a similar mineral composition, including quartz, illite, ankerite, pyrite, and muscovite. From the wall rocks to the ores, the quartz, pyrite, and arsenopyrite contents increased. Meanwhile, the ankerite content decreased. Gold, As, Sb, Hg, and Tl are mainly distributed along ore–controlling faults F₃, F_14, and F₇₀, suggesting that these faults are conduits for gold mineralisation. Fault F₃ is conduit for gold mineralisation for Huangchanggou and Rongban, F₁₄ for Lintan, and F₇₀ for Shizhu and Anbao. These ore-controlling faults converged at the Si-Ca interface. The distribution of trace element enrichment varies among the five ore blocks, with the highest concentrations of Au, As, Sb, Hg, and Tl observed in the Huangchanggou ore block.

Based on these results, a deposit scale metallogenic model of the Lannigou deposit was established. According to this model, deep-source ore fluids initially ascended along Lannigou–Weihuai fault to reach the Si-Ca interface. These fluids then migrated laterally along the interface and entered the connected secondary faults. As the ore fluids migrated into the secondary faults, they reacted with Fe-rich clastic rocks, causing the release of iron from the ankerite and the precipitation of Au-bearing pyrite and arsenopyrite, resulting in the formation of ore bodies. This model emphasises the Si-Ca interface and its linked thrust faults as the primary ore fluid channel framework. The intersection of multiple sets of faults plays a crucial role in the formation of thick ore bodies. Future exploration in the Lannigou district and surrounding areas should prioritise faults linked to the Si-Ca interface and areas in which multiple sets of faults intersect. This strategic focus will enhance the potential for discovering ore bodies similar to those found in the Lannigou deposit.