Distribution patterns and controlling factors of cave saltpeter around the Sichuan Basin, China

As one of the major karst geomorphic regions in China, the cave systems of Sichuan Province are renowned not only for their spectacular chemical depositional landscapes but also for their well-preserved clusters of ancient saltpeter mining sites. These sites represent invaluable records for studying the history of traditional mineral exploitation. This study aims to investigate the genesis of cave saltpeter. Through systematic calibration and quantitative analysis, we examined the distribution patterns of caves and saltpeter deposits around the periphery of the Sichuan Basin, along with their controlling factors. The results reveal that caves are primarily distributed along the margins of the basin, with saltpeter-bearing caves displaying a distinct clustered pattern, 63% of them are located in the northwestern and southeastern sectors of the basin. Stratigraphic and petrographic analyses indicate a significant correlation between saltpeter occurrence and carbonate formations, particularly the Triassic Jialingjiang Formation, which accounts for 30% of all saltpeter caves identified in the entire basin. Tectonic analysis further indicates that the distribution of these caves is strongly influenced by a deep and extensive fracture system trending northeast-southwest, with the Guixian-Jiangyou and Qianjiang faults playing crucial roles in their development. Elevation data reveal that saltpeter caves are predominantly located above 1,000 meters above sea level, whereas most non-saltpeter caves lie below 800 meters. Furthermore, historical records and vegetation analysis indicate significant differences in plant communities during the Ming and Qing dynasties. The northwestern region was dominated by high-potassium tree species such as pinus , vernicia fordii , quercus , toona sinensis , and alnus spp. , which contributed substantial potassium to support saltpeter mineralization. These findings not only provide a crucial foundation for understanding the material sources and genesis mechanisms of saltpeter but also offer new insights and a scientific basis for future resource exploration and conservation strategies.