Sedimentary evolution for the Wuling secondary rift of the western Nanhua Rift and exhalative-sedimentary mineralization cycles of “Datangpo-type” manganese ore deposits in South China

Abstract

The “Datangpo-type” manganese ore deposits, hosted within the Neoproterozoic Nanhua system (Pt₃³n) in the Tongren area of northeastern Guizhou Province (China), represents a newly identified deep-seated manganese-bearing fluid exhalative-sedimentary deposit. Using basic theories and methods of basin analysis and sedimentology, the main ore-bearing structural unit of the Songtao–Guzhang graben (level III) in the Nanhua Rift was analyzed to determine the metallogenic mechanism and distribution law governing Datangpo-type manganese ore deposits, with systematic focus on the sedimentary facies and depositional environments of the Nanhua system. Analysis revealed that the sedimentary characteristics of terrigenous clastic rocks and the vertical evolution of sedimentary facies in the Nanhua system reflect a complete rift-filling sequence, i.e., sections of initial, accelerated, rapid, decelerated, and ceased subsidence filling. The spatial distributions and vertical changes in rhodochrosite ore beds in terms of structure, thickness, and grade were obviously controlled by the rift stage and changes in the exhalative strength of the manganese-containing fluid, in addition to the sedimentary environment and sedimentary process. The strata hosting rhodochrosite ore beds are located mainly in the basal part of the first member of the Datangpo Formation, i.e., at the bottom of the section of rapid subsidence filling, which is a product of deep manganese-containing fluid exhalative-sedimentary processes from the early stage of maximum rifting. The exhalative-sedimentary processes of ore-forming materials exhibit five major macrocycles, and reveal spatiotemporal patterns in the mineralization of rhodochrosite ores across the study area.