Comparison of geochemical patterns from different sampling density geochemical mapping in Altay, Xinjiang Province, China

Abstract

With the continuous development of geochemical mapping, especially with the proposal of the “Chemical Earth” big science project, low-density geochemical mapping technology has received increasing attention due to “low cost and high efficiency”. Due to the special geochemical properties of Au, the distribution of Au in water sediments is so complicated that the differences of low-density and high-density Au geochemical mapping are not well known, which makes it difficult for researchers to accurately evaluate the Au anomalies from low-density geochemical mapping. This paper compares Au geochemical mapping data and geochemical patterns from ultra-low-density geochemical mapping (ULGM) (1 sample/1600 km2), super-low-density geochemical mapping (SLGM) (1 sample/180 km2) and high-density geochemical mapping (HGM) (sampling density 1 sample/km2) in Altay, Xinjiang province, China. We found that the standard deviation of Au increases with the mapping density. The median values of the HGM, SLGM and ULGM are 0.71 × 10−9, 0.77 × 10−9, and 0.94 × 10−9, respectively. Altay Au anomalous is mainly controlled by 3 factors and are consequently divided into 3 kinds of anomaly types: 1. regional-scale anomalies, caused by gold-rich stratum; 2. local Au anomalies, caused by gold mineralization; 3. anomalies around the catchment, caused by the supergene migration and enrichment of fine-grained Au. In general, as the mapping density decreases, the spatial correspondence between anomalies and geological factors become weaker. HGM can figure out the single gold deposit, SLGM can delineate Au deposits concentrated area; ULGM can delineate the Au metallogenic target area. So, the ultra-low density mapping is suitable for quickly obtaining the geochemical background of the Au region in the blank area, reflecting the large-scale enrichment behavior of Au in the supergene environment.