Study on three-dimensional enrichment regularities of Au, As, and S and their indicative significance in the giant Nibao gold deposit, Southwestern Guizhou, China

Abstract

The Nibao gold deposit is one of the typical Carlin-type gold deposits in the Youjiang Basin. In these areas, the presence of As and S is closely involved in Au mineralisation. However, considering that excessive amounts of As and S can be harmful to human health and to the environment, studying the three-dimensional (3D) enrichment regularities of Au, As, and S can help acknowledge the details of the gold mineralisation process, and guide processes such as mineralisation prediction, prospecting exploration, and mine construction. Here, 3Dmine software is used to create a 3D visual geological modelling of the Nibao gold deposit. The models show that the concentration of Au, As, and S is abundant in the area and have similar enrichment regularities. Results have pointed out that the main enrichment strata are P₃l¹ and P₃l², and the main enrichment locations are F1, the Sbt, and the Erlongqiangbao anticline. The areas with high contents of Au, As, and S are formed with the occurrence of strata and fault. Combining the results here presented with the outcomes of previous studies on the material and fluid sources of Au in the Nibao gold deposit, we have concluded that the mineralisation process relies on the migration of over pressure fluids that are rich in Au, As, S, and poor in Fe. Because of the lithological changes and tectonic influences, they emerge from depth along the deep large faults, and then flow into F1, resulting in the flow of fluids into the parts with good permeability, and water–rock reaction with Fe-rich rocks, especially sulfidation occurs, generating arsenic-bearing pyrite which provides a carrier for Au enrichment into the deposit. The 3D distribution characteristics and correlation of among Au, As, and S are qualitatively and quantitatively analysed, and our results revealed that the three elements are positively correlated in the overall. This correlation was further divided into two sections. In the first section, the Au content ranged from 0 to 2 × 10⁻⁶; there is a good positive correlation among Au, As, and S. In the second section, the content of Au content was > 2 × 10⁻⁶, and higher amounts of Au would imply higher amounts of As and S as well. Considering the above outcomes, the enrichment regularities and correlation among Au, As, and S can be used as a reference index in the metallogenic prediction and prospecting exploration of the Nibao gold deposit and similar deposits. These are valid especially areas with higher concentration of As and S, which are the prospecting target. Furthermore, there will be a large number of As and S in the process of mining, smelting, slag treatment, and green restoration of the mine, so measures need to be taken to avoid excessive As and S from causing health hazards to workers and environmental pollution.