Study on clues for gold prospecting in the Maizijing-Shulonggou area, Ningxia Hui autonomous region, China, using ALI, ASTER and WorldView-2 imagery

Abstract

Several gold occurrences have been discovered in the Maizijing-Shulonggou area, Ningxia Hui autonomous region, China. The clues for gold prospecting in this area may relate to fractures and hydrothermal alterations, but it is very difficult to conduct a field investigation on the clues because of the alpine valleys. To explore the clues for gold prospecting, this study extracted geological information related to fracture zones and hydrothermal alterations using ALI, ASTER, and WorldView-2 data, and subsequently, explored potential relationships between extracted geological characteristics and gold mineralization. The WorldView-2 image in the study area was used for fracture interpretation. The azimuth and density of linear fractures were investigated, and the results showed that linear fractures with NE direction were most common, the gold occurrences except Au2 were all located in NE fracture zones, and all gold occurrences located in high fracture density areas (level 1–3 areas) where NE and NW fractures were the most common observations. This suggests that the high fracture density and NE and NW fractures are important indicators of potential gold mineralization. Hydrothermal alteration minerals in exposed bedrocks were mapped using ALI and ASTER imagery. Based on the spectral analysis, ASTER image in the study area were used to map quartz, illite and chlorite, while ALI image were used to map limonite. The spatial distribution of alteration minerals revealed regional specific alteration mineral in gold mineralization. In the northern Maizijing region, the composition of alteration mineral in the surrounding of Au1 was overwhelmed by quartz, while the alteration minerals in the surrounding of Au2-4 were dominated by limonite in the southern Shulonggou region, which showed different indicator minerals for gold prospecting in the two regions. As a result, the key areas for prospecting are the NE and NW fracture zones with quartz veins in the Maizijing region and the NE and NW fracture zones with limonitization in the Shulonggou region. In the Shulonggou region, pyrite in buried quartz-pyritization belt and illitization-pyritization belt is likely to be the precursor of limonite. Heavy mineral assemblages were analyzed for native gold content, and the results suggested high native gold content in the illitization-pyritization belt, followed by quartz-pyritization belt, which was consistent with the strong association of limonite and gold mineralization, thus the two belts shall be prioritized for gold prospecting in the Shulonggou region.