STUDY ON THE SEDIMENTARY ENVIRONMENTS OF THE SINIAN AND CAMBRIAN PHOSPHORITE IN SOUTH CHINA

Phosphorite ore deposits are widely distributed in South China. They have been found in almost every system through the geological ages. But about 70% of the industrial phosphate deposits are accumulated in the Sinian and Cambrian strata in Yunnan, Guizhou, Sichuan, Hunan, Hubei and other provinces in South China. Sinian is one of the most important mineralization periods of phosphorite in China. More than half of the industrial phosphate deposits were formed in the epicontinental sea of South China Platform during this time. The Sinian phosphorite is mainly distributed around archipelagos or islands and the submarine highlands, forming a mineral zone or group of phosphorite beds controlled by the palaeotectonics and palaeogeomorphy of the platform. Several phosphorite horizones have been found in Cambrian strata of China, but the most important one in South China is lying in the bottom of Cambrian. During Early-Cambrian, thick marine phosphate deposite, consisting of mudy or siliceous phosphorites, were formed in the epicontinental sea of the South China Platform, distributed chiefly along the eastside of the "Hubei-Sichuan-Yunnan Island Arc" , in the west, and along the westside of the "South Yangzi Archipelago" in the east, The former is much important than the latter, and the industrial ore deposits are chiefly confined in the former. Going further to the southeast, the phosphorite ore deposite are hardly found in the bottom of the Cambrian flysch-like deposite in the South China Trough. During Late Sinian and Early Cambrian, the cold deep water rich in phosphorus might be flowing into the South China marine basin from the Arctic Region in the southeast, and then many large and small phosphorite ore deposits were generated around the basin in favourable terrains such as: archipelagos, islands and submarine highlands, by the processes of mechanical, chemical and organic concentration and deposition. The depositional environments of phosphorite are briefly discussed in this paper as follows: 1) the character of rock assemblage of phosphate-bearing series;2)the relationship between the phosphorite ore deposits and the transgression and regression due to the tectonic movement;3) the latitudinal distribution of phosphorite and palaeoclimate conditions;4) the palaeogeomorphic features of phosphrite deposition) 5) the geochemical conditions of phosphorite deposition;6) the organic effects on phosphorite deposition;7) the hydrodynamic conditions of phosphorite deposition;and 8) the phosphorus sources.