青海省都兰县双庆铁矿床磁铁矿地球化学特征及成因意义

Magnetite Geochemical Characteristics and Causes Significance of Shuangqing Iron Deposit in Dulan Area, Qinghai Province, China

青海省祁漫塔格-都兰成矿带是以铁铜多金属为主的成矿带,其矿产丰富但研究程度较低。双庆铁矿床是该成矿带上十分典型的矿床,目前尚未系统开展矿物地球化学研究。笔者采用电子探针、电感耦合等离子质谱仪(ICP-MS)等测试手段,对磁铁矿进行主(常)量元素、微量元素地球化学特征进行研究,辅以磁铁矿氧同位素数据,以期为矿床成因提供地球化学证据。磁铁矿主量元素的Ti O2-Al2O3-(Mg O+Mn O)三角成因图解揭示,形成双庆铁矿床的磁铁矿为接触交代作用的夕卡岩型磁铁矿。微量元素特征表明其成矿物质来源较深,Ni/Co比值揭示磁铁矿为火山热液交代的岩浆成因的来源特征,而Pb、Zn质量分数相对较高,表明有后期的热液叠加作用。稀土元素呈不对称的"V"字形配分模式,轻重稀土发生一定程度的分异作用,无明显δEu和δCe异常,稀土总量低;磁铁矿的氧同位素特征表明其成矿物质来源属于幔源,流体来源为花岗质岩浆水。

Qimantage-Dulan metallogenic belt is mainly of iron and copper polymetallic metallogenic belt of Qinghai province, with its mineral-rich but low research degree. Shuangqing Iron Deposit is very typical deposit located the metallogenic belt. There is currently no mineral geochemical study on that. In order to provide geochemical evidence for deposit genesis, this article studies geochemical characteristics of the major elements and trace elements in magnetite by using electron microprobe, inductively coupled plasma mass spectrometry（ICP-MS） and other testing methods, to supplement magnetite oxygen isotope data. The Ti O2-Al2O3-（Mg O＋Mn O）triangle formation diagram for magnetite major elements shows that the formation genesis of the magnetite in Shuangqing Iron Deposit is typical skarn magnetite of the contact metasomatic origin; geochemical characteristics of trace elements in magnetite indicate its deeper ore-forming material source, and the ratios of Ni/Co indicates that magnetite source is of volcanic hydrothermal metasomatic with magma genesis characteristics, while the contents of Pb and Zn are relatively high, indicating a late hydrothermal superimposition;REE is asymmetric ＂V＂-shaped distributed, and LREE and HREE occur to a certain extent differentiation process. REE have no obvious δEu and δCe anomaly characteristics with low ∑REE. Oxygen isotopic characteristics of magnetite shows that its ore-forming material belongs to mantle source and the fluid source belongs granitic magma water.