攀西地区道坪子铁矿床地球化学特征及成因分析

Geochemical Characteristics and Genesis of Daopingzi Iron Deposit in Panzhihua-Xichang Region

道坪子铁矿床位于上扬子地台西缘盐源—丽江逆冲带,矿体呈脉状赋存于大板山岩体辉长岩与志留系碳酸盐岩接触带。为查明矿床成因机制,开展了磁铁矿主量、微量元素及方解石碳、氧同位素分析。结果显示,磁铁矿在TiO_(2)-Al_(2)O_(3)-MgO图解、(Ca+Al+Mn)-(Ti+V)图解、V/Ti-Fe图解中落入热液磁铁矿区域,Ni/Cr比值为2.08~3.33,指示其为热液交代成因;磁铁矿相对富集Th、Ta、Zr、Hf,∑REE含量低(1.5×10^(-6)~1.9×10^(-6)),具弱正Eu异常,与辉长岩中的磁铁矿具有近似的微量元素组成特征,表明铁可能主要源自于辉长岩磁铁矿;成矿热液为高温(300~400℃)富气热液,与形成矿山梁子铁矿床的铁矿浆同源,可能由低钛玄武质岩浆分离形成的富铁质岩浆演化而来。研究认为,道坪子铁矿床是源于低钛玄武质岩浆的高温富气热液与辉长岩相互作用的结果,为接触交代型铁矿床。

The Daopingzi iron deposit is located in Yanyuan-Lijiang Thrust Belt on the western margin of Yangtze Platform,and its vein orebodys occurs in the contact zone between gabbro of Dabanshan intrusion and Silurian carbonate rocks.In order to find out the genesis of the deposit,this paper analyses the main elements,trace elements,C-O isotopes of calcite.The magnetite samples falls into hydrothermal magnetite area of TiO_(2)-Al_(2)O_(3)-MgO diagram,(Ca+Al+Mn)-(Ti+V)diagram and V/Ti-Fe diagram,Ni/Cr ratio is 2.08~3.33,it indicates that the magnetite of Daopingzi iron deposit is hydrothermal origin.The magnetite is relatively enriched in Th,Ta,Zr,Hf and low inΣREE(1.5×10^(-6)~1.9×10^(-6)),and has weak Eu negative anomaly,which is similar to magnetite of gabbro,it indicates that the Fe of Daopingzi iron deposit may be mainly derived from gabbro magnetite.The metallogenic hydrothermal solution is gas rich hydrothermal solution with high temperature(300~400℃),which is homologous with the iron slurry that formed Liangzi iron deposit and may have evolved from iron rich magma separated from low-Ti basaltic magma.It is considered that Daopingzi iron deposit is a contact metasomatic iron deposit,which is the result of the interaction between the high temperature and gas rich hydrothermal solution derived from low-Ti basaltic magma and the gabbro.