A comparative study on formation mechanisms of phosphorites of the Lower Cambrian P-bearing rock series in the Zhijin and Kunyang deposits in South China
A comparative study on formation mechanisms of phosphorites of the Lower Cambrian P-bearing rock series in the Zhijin and Kunyang deposits in South China
Large-scale phosphogenesis occurred globally during the early Cambrian Epoch,meanwhile large phosphorite deposits,represented by the Zhijin deposit in Guizhou and Kunyang deposit in Yunnan,were formed in South China.In order to explore similarities and differences of mineralization mechanisms and constraining factors of the Zhijin and Kunyang deposits,mineralogical and geochemical analyses of P-bearing rock series in the Xinhua oreblock of the Zhijin deposit and the Wangjiawan oreblock of the Kunyang deposit have been carried out in this paper.The results show that grain sizes of both collophane and apatite minerals in the P-bearing rock series of the Kunyang deposit are significantly larger than those of the Zhijin deposit,implying that the P-bearing rock series in the Kunyang area were formed in a relatively shallow seawater with strong hydrodynamic condition;There are significantly-weakly positive relationships between P2O5 and A12O3,SiO2,Zr/Hf and Sr contents in P-bearing rock series of both Zhijin and Kunyang deposits,indicating that terrestrial weathering input provided the material sources of phosphorous in Cambrian Ocean;The variation ranges of redox-sensitive elements(V,Ni,Cr,Mo,U)contents and Ce/Ce*values of P-bearing rock series in the Zhijin area are larger than those of P-bearing rock series in the Kunyang area,showing that there was a relative strongly fluctuated oxic-suboxic deposition condition in the zhijin area comparing to the Kunyang area;The P-bearing rock series of the Zhijin and Kunyang deposits have"hat-shaped"PAAS-normalized REE distribution patterns,with characteristics of negative Ce anomalies,significantly positive Y anomalies,and negative or weak-positive Eu anomalies Eu anomalies,indicating that their phosphogenetic processes were controlled by biological/organic matters and/or Fe-Mn(oxyhydr)oxides.It is concluded that the formation mechanisms of P-bearing rock series in the Zhijin and Kunyang deposits are highly similar,but differences of lithofacies paleogeographical locations and redox conditions were important reasons for the differences between P-bearing rock series of the Zhijin deposit and those of the Kunyang deposit.
关键词
华南/早寒武世/磷块岩/成矿机制/织金新华磷矿/昆阳王家湾磷矿
Key words
South China/Early Cambrian/phosphorite/formation mechanisms/Xinhua oreblock of the Zhijin deposit/Wangjiawan oreblock of the Kunyang deposit
维普
万方数据