Fractal Characteristics of Particle Size Distributions in Shewushan Lateritic Gold Deposit, Hubei, China: Implication for Ore Genesis

摘要

Shewushan gold deposit, Hubei is the first found lateritic gold deposit in China. It is hosted in red soil that weathered from basement carbonates. Previous studies show that gold enrichment of the deposit is closely related to the soil formation during weathering. However, the relationship between ore-forming processes and soil changes both in compositions and particle sizes is still an open question. The purpose of this study is to investigate the soil particle size distributions (PSDs) in the lateritic profile and its constraints on water-soil reaction and gold accumulation. The PSDs analysis of ore-hosting soils from two sub-sections was carried out by the laser diffraction method using Mastersizer2000.Results show that the average volume sizes of the upper sub-section (USS) and lower sub-section (LSS) are respectively 3.52, 5.57, 15.11μm and 7.18, 12.82,12.24μm from the top to the bottom of each sub-section. Fractal characteristics of the PSDs have been analyzed by power-law functions relating accumulative volume of panicles to diameter between 1.71 μm and 19.46μm. Study shows that associated fractal dimensions (D) are respective 2.22, 2.40, 2.46 and 2.34, 2.56, 2.86. Moreover, the D values increase with clay content while decrease with sill content. Combined with mineralogical analysis, these imply that the fractal dimensions of PSDs might increase with the development of water-soil reaction and corresponding soil size reduction during chemical weathering. The increment of Fine grade size aggregates is of great significance to absorb Au particles and to form the economic ore bodies. Furthermore, the two sub-sections structure might be formed by tectonic thrust on newly stage of weathering and ore-forming processes, which results in the formation of multi-layer ore bodies in the lateritic profile.