COMPOSITIONAL CHARACTERISTICS OF PHOSPHORITES AND PRINCIPAL MINERALIZATION EPOCHS IN EASTERN CHINA

The composition of phosphorites from 25 Sinian, Cambrian and Devonian ore deposits in Eastern China were studied in this paper. We came to the conclusion that carbonate-f luorapatite is the main phosphatic mineral in the phosphorite of China. Hydroxyapatite can only be seen in recrystallised phosphorites occasionally. Principal associated minerals of the ore deposits are illite, dolomite and quartz (chalcedonite). According to the mineral associated relation, The phosphorites in China could be divided into five associated types. There are three important features in chemical composition of the phosphorites: First, the P₂O₅ contents change with types of ore, the sequence is the biogenic (35.04%), the micritic (34.88%-31.92%) the recrystallised (33.38%), the nodular (30.92%), the granular (29.01-28.14%) and the sandy (21.37%). Secondly, the P₂O₅ contents of ore change with mineralization areas, for example, the average P₂O₅ contents of the Cambrian ore in North China Platform and Yangtze Platform are 21.3% and 30.18% respectively. Thirdly, they change with mineralization epochs. With the squence of Sinian, Cambrian and Devonian, the CO₂/P₂O₅ ratios reduce from 0.15 to 0.04; MgO, CO₂, MnO and K₂O-contents are from higher to lower; however, the Al₂O₃ is in a converse case. Generally, the compositional differences of phosphorites in China are determined by the differences of mineralizational background, environments, facies characteristics and mineral paragenic types primarily.