内蒙古黑鹰山富铁矿床磷灰石钐-钕同位素年龄及其地质意义  

Sm-Nd isotopic dating of apatite separates from Heiyingshan high-grade iron deposit, Inner Mongolia

作　　者：聂凤军[1] 江思宏[1] 刘妍[1] 胡朋[1] 

机构地区：[1]中国地质科学院矿产资源研究所,北京10037

出　　处：《矿床地质》2005年第2期134-140,共7页Mineral Deposits

基　　金：国家自然科学基金项目 (编号 :40 0 73 0 15 );国家地质调查项目 (编号 :K1.3 .3 2 )资助

摘　　要：黑鹰山富铁矿床地处北山造山带西伯利亚板块与哈萨克斯坦_北山板块汇聚地带,是中国西北地区规模最大和品位最高的富铁矿床之一,其独特的产出环境和地质特征为国内外地质学界所关注。为了查明该矿床的形成过程,笔者首次对致密块状铁矿体中的6件磷灰石样品和脉状铁矿体中的2件磷灰石样品进行了钐_钕同位素测定。块状矿体的6件样品所获等时线年龄为(32 2 .0±4 .3)Ma,MSWD值为0 .0 9,14 3 Nd/14 4 Nd初始比值为(0 .5 12 30 8±0 .0 0 0 0 0 3) ,εNd(t)为(1.6 6±0 .0 1)。脉状矿体中2件样品的εNd(t)值分别为7.2 0和7.2 6 ,明显高于块状矿体磷灰石样品。依据上述同位素分析数据和特征比值,结合容矿围岩和矿体地质特征,推测黑鹰山富铁矿床的形成与海西早期富碱岩浆流体多期次活动有关,成矿物质主要来自地幔物质占优势比例的壳_幔混源岩浆房。Located in the northeastern part of Hongshishan-Heiyingshan terrane within Kazakhstanian- Beishan plate, the Heiyingshan deposit is one of the most important high-grade iron deposits in northwest China. Iron mineralization occurs within the Early Carboniferous dacite, rhyolite, dacitic lava and brecica of Baishan Formation as massive blocks, stratoid layers, lens and veins. The iron-bearing intermediate-acid volcanic sequences are cut by a number of Hercynian mafic and granitoid dykes and controlled by a number of NE- and EW-trending fractural or faulted zones. Individual iron orebodies, from 4 to 12 m in thickness, can be traced along the strike for 115～200 m, and down the dip for 100～200 m. Moreover, several independent yttrium orebodies were recognized within the iron deposit. Although apatite predominates over iron-bearing minerals, no difference has been observed between iron and yttrium orebodies in such aspects as geological setting, wall rock, mineral assemblage and attitude. Mineralogical composition of both iron and yttrium ores is relative simple, composed of magnetite, hematite and trace amounts of pyrite. Gangue minerals include apatite, quartz, chlorite, and hornblende. Eight apatite separates from the massive and vein type iron ores respectively were selected for Sm-Nd isotopic analysis. Six apatite separates from massive iron ores of Heiyingshan deposits give a Sm-Nd isochron age of (322.0±4.3) Ma with ε Nd (t) value of 1.66±0.01 (2σ). As the Sm-Nd isochron age is in agreement with field geological evidence, and apatite has co-existing relations with magnetite, it is suggested that the Sm-Nd isochron age represents the ore-forming time of the Heiyingshan high-grade deposit. The ore-forming material might have been derived from a mixed source of depleted mantle- and crust-derived magma or fluids. In contrast, the ε Nd (322 Ma) values of two apatite separates from the vein-type iron ores range from 7.20 to 7.26, much higher than the values of massive iron ores. Combined with other

关 键 词：地球化学 富铁矿床 磷灰石 钐-钕同位素 矿床成因 黑鹰山 内蒙古 

分 类 号：P618.31[天文地球—矿床学] P597.3[天文地球—地质学]