Sedimentary environment and enrichment mineralization mechanism of the Lower Cambrian Meishucun Formation in the Yangchang phosphate deposit of Zhenxiong area, Northeastern Yunnan.

The Yangchang phosphate deposit is a large-buried shallow marine carbonate stratified phosphorite deposit discovered in the Meishucun Formation (∈₁ ms) of the Lower Cambrian recently. The understanding of its sedimentary environment and enrichment mechanism is still limited. Representative borehole cores were selected to carry out systematic sedimentary facies cataloguing. By means of sedimentary (microfacies) analysis, mineralogy acand mineral chemistry tracing, the characteristics of rock and mineral (assemblage), sedimentary (microfacies) types, sedimentary environment and spatial and temporal distribution of each lithologic section of the Meishucun Formation are analyzed. We also studied the sedimentary environment evolution, the source, migration and enrichment mechanism of phosphorus, and its metallogenic model. The comparative analysis shows that the ore-bearing strata exhibits the nearshore tidal flat facies sedimentary environment with transgression-regressive sequence vertically, 6 microfacies types in 3 subfacies namely supratidic flat, intertidal flat and subtidal flat are identified. Su-pratidic flat is divided into supratidic flat and supratidic carbonate flat. The intertidal flat is divided into intertidal carbonate flat, intertidal flat and storm current. The subtidal flat developed a low energy subtidal flat. The favorable phosphorus formation environment is the high energy intertidal flat in intertidal flat. Repeated action of tides and waves in the shallow water environment for a long time is conducive to the winnowing, enrichment and reconstruction of phosphorous rich particles, thus forming a phosphorous rock deposit with rich and thick beds in the northwest and poor and thin beds in the southeast of the mining area. To sum up, the ore forming process of the Yangchang phosphate deposit can be divided into three stages, namely: (1) initial accumulation and precipitation mineralization stage (phosphorus source carried by upwelling ocean current); (2) biochemical deposition and accretion mineralization stage (migration and enrichment driven by microbial decomposition, transformation and compound); (3) winnowing enrichment and re-enrichment mineralization stage (precipitation and enrichment driven by multi-stage wave and tidal action). This new points provides an important basis for prospecting and exploration in the mining area and peripheral areas. [ABSTRACT FROM AUTHOR]