云南省勐满金矿硅质岩地球化学特征及沉积环境分析

Geochemical Characteristics and Sedimentary Environment of Cherts from the Mengman Gold Deposit in Yunnan Province

通过对勐满金矿野外地质调查及岩石化学、主量元素、微量元素及稀土元素等研究,以对其硅质岩的成因类型及沉积环境进行探讨.结果表明,硅质岩SiO_2质量分数94.57%~98.04%,均属纯硅质岩范围,Al/(Al+Fe+Mn)均值0.135,Al-Fe-Mn和(wAl/wAl+Fe+Mn)-(wFe/wTi)成因判别图解反映了研究区硅质岩为热液成因.根据δCe、δEu、(La/Ce)N以及100*Al_2O_3/SiO_2-100*Fe_2O_3/Si O、Al_2O_3/(100-SiO_2)-Fe_2O_3/(100-SiO_2)和Al_2O_3/(Al_2O_3+Fe_2O_3)-LaN/CeN等地球化学参数及环境判别图解,初步判定勐满金矿硅质岩沉积环境位于洋中脊和大陆边缘过渡位置,但总体上更靠近大陆边缘.对硅质岩的微量元素应用Ni/Co比值及Zr-Cr判别图解,显示为现代热水沉积物的环境特征.

The genetic types and sedimentary environment of cherts are explored based on field and petrological studies as well as the geochemical characteristics including major elements,trace elements and rare earth elements in the gathered samples. Research results show that the major element is SiO2,which makes up 94. 57%—98. 04% of the mass,within the range of pure cherts. The average value of Al/（ Al ＋ Fe ＋ Mn） is 0. 135,and the causal diagrams of Al-Fe-Mn and（ wAl/wAl ＋ Fe ＋ Mn）-（ wFe/wTi） shows the siliceous rocks in this region are of hydrothermal origin. On the basis of δCe,δEu,（ La/Ce）N,100＊ Al2O3/SiO2-100＊ Fe2O3/Si O,Al2O3/（ 100-SiO2）-Fe2O3/（ 100-SiO2）and Al2O3/（ Al2O3＋ Fe2O3）-LaN/CeNgeochemical parameters and environmental discrimination diagram of siliceous rocks,we tend to determine that the sedimentary environment of cherts from the Mengman gold deposit is located in mid ocean ridges and continental margins,but overall it is closer to the continental margins. Ni/Co and Zr-Cr diagram of trace element of cherts show the sedimentary environment is modern water deposits.