Silicification in Wongfu Phosphorus Deposits in Guizhou,China
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摘要: 贵州瓮福磷矿中广泛伴生着硅化作用,硅化岩类型以其交代程度可分成弱硅化岩、强硅化岩及结晶硅化岩三类,三类间相互过渡,在空间上有一定的配置关系。硅化岩的U、Th和稀土元素显示了热水沉积产物的特点,石英δ18O值,结晶硅化岩为18.83‰,强硅化岩为20.80～23.67‰,,依氧同位素分馏平衡计算的形成温度为:结晶硅化岩101～115℃,强硅化岩66～98℃。Abstract: Wongfu phosphorus deposits is a kind of sedimentary phosphorus deposits formed in Doushantou formation with era of Sinian,widely associated with silicified rocks which were formed by means of replacing original rock(such as phosphorate,dolomite.etc. )below sedimentary level during the period of penecontemporaneous sedimentation. The characteristics of the silicified rocks in fields are : (1)Spreaded widely .they could be seen in almost all the mined columns. (2)Formed in many formations and along them, the silicified rocks mainly distributed on the top and bottom of the phospharate formation,and a little less in the phosphorate formation. ( 3) Silicification had the characteristics of selected replacement. which were showed by both of selecting formation and lithology. The former means that the top and bottom formations of phosphorate were firstly silicified. The later indicates that some type of rocks were silicified easily. The lithologic sequence in order of silicification is as follows:stromatolithic dolomite-dolomite-stromatolithic phosphorate-clastic phosphorate-black banded laminated phosphorate with colloform structure. (4) The silicified clasts in clastic phosphorate showed that the silicification took place during the period of penecontem-poraneous sedimentation. Under microscope, the silicified rocks mainly consist of coarse, fine,micro-,muddy crystal quartz and chalcedony. However,they were not a diagenetic series. The silicified rocks were divided into slight,strong and crystalized silicified rocks respectively, according to the level of replacement and their texture and structure. The three groups of rocks varied transitionally in space,which shows the characteristics from strong to weak silicification. U/Th is 4. 6-102. 5,∑REE is ranged from 6. 12 to 18. 537ppm.in the silicified rocks LREE/HREE is 7. 283-94. 5,δCe = 0. 251 - 0. 413. There were both positive and negative Eu abnormality (δEu=1. 36 in silicified rocks, δEu = 0. 37 in intense ones). δ18 O of 18. 83 and 20. 80-23. 67 in crystalized and strong silicified rocks respectively. The forming temperature of crystalized and intense silicified rocks is 101 - 105℃ and 66-98℃ respectively .through the isotopic equilibrium fractionation temperature function of quatz-wa-ter.
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