Phosphorite generative processes around the Precambrian-Cambrian boundary in South China: An integrated study of Mo and phosphate O isotopic compositions  

作　　者：Haiying Yang Jiafei Xiao Yong Xia Zhuojun Xie Qinping Tan Jianbin Xu Shan He Shengwei Wu Xiqiang Liu Xingxiang Gong 

机构地区：[1]State Key Laboratory of Ore Deposit Geochemistry,Institute of Geochemistry,Chinese Academy of Sciences,Guiyang 550081,China [2]School of Earth Sciences,Yunnan University,Kunming,650500,China [3]School of Qilu Transportation,Shandong University,Jinan 250061,China [4]University of Chinese Academy of Sciences,Beijing 101408,China [5]Reserve Bureau of Land and Mineral Resources of Guizhou Province,Guiyang 550081,China

出　　处：《Geoscience Frontiers》2021年第5期237-263,共27页地学前缘（英文版）

基　　金：supported by the United Foundation of National Natural Science Foundation of China(Grant Numbers:41972095,U181240004,9206220039);the Public Beneficial,Basic Geological Project of Department of Land and Resources of Guizhou Province(Grant Number:2016-09-1).

摘　　要：Large phosphorite deposits in Central Guizhou,China,were formed around the Precambrian/Cambrian boundary(PC/C),including the Ediacaran(Doushantuo stage)and early Cambrian(Gezhongwu stage).Among them,Gezhongwu phosphorite from Zhijin are enriched in rare earth elements(REE)plus yttrium(REY),reaching 3.503 million tons.Although phosphorites have attracted great attention,the specific sources P and REY remained unclear.To determine the P and REY sources and establish a phosphogenic model of PC/C phosphorite,we present an integrated dataset of Mo and phosphate O isotopes for the first time,along with carbonate C and O isotopes,geology,petrology,and geochemistry.In all samples,d18Op,Y/Ho,and Zr/Hf decreased from the Ediacaran to the early Cambrian,indicating increased terrigenous weathering fluxes while decreased upwelling water input.Furthermore,terrigenous weathering delivery significantly elevated marine REY concentrations in the Cambrian in Zhijin.The Ceanom and d98/95Mo suggest that seawater was oxidized in the later Ediacaran and became entirely oxic in the early Cambrian.The positive feedback between oxygen levels in atmosphere and primary productivity caused progressive oxygenation in ocean-atmosphere system and enable phosphorites to be formed by different mechanisms.Results show that the Lower Doushantuo consist of abiotic intraclasts and exhibited“seawaterlike”REY types,indicating abiological and mechanical reworking phosphogenesis.The Upper Doushantuo and Gezhongwu Formation contained mainly microbial debris and abiogenic intraclasts,and exhibit “hat-shaped”REY plots,suggesting microbially mediated phosphogenesis.Based on this data set,we developed a phosphogenic model illustrating formation of these two phosphorite deposits,wherein the Lower Doushantuo phosphorite formed through the reworking of pre-existing phosphatic sediments in anoxic and abiotic ocean,whereas the Upper Doushantuo and Gezhongwu phosphorite formed via microbial metabolisms in oxic and biotic conditions.Our study has implication

关 键 词：Doushantuo formation Gezhongwu formation PHOSPHORITE Ore-forming material origin Phosphate O isotope Mo isotope 

分 类 号：P619.2[天文地球—矿床学]