新疆巴楚小海子岩体铁钛成矿特征及资源利用前景

Iron-titanium metallogenic characteristics and resource utilization prospect of Xiaohaizi intrusion in Bachu area,Xinjiang

新疆巴楚小海子是近年来在塔里木大火成岩省探获的一个低品位-大吨位岩浆型钒钛磁铁矿床,其成岩成矿机制以及资源利用前景尚不清楚。文章针对小海子岩体2种含矿岩相橄榄辉长岩和橄榄辉石岩开展了地质地球化学研究。橄榄辉长岩相和橄榄辉石岩相虽然在空间上关系不明,但岩相学观察表明它们矿物组成的差异与矿物堆晶作用有关,且二者具有相似的稀土元素球粒陨石标准化和微量元素原始地幔标准化配分曲线,说明是同源岩浆演化的产物,橄榄石较低的Fo值(67.9~72.5)指示幔源母岩浆在深部岩浆房中发生了分异。小海子岩体和与相距约45 km的瓦吉里塔格相比,岩石组成和地球化学组成相似,表明为同源岩浆成因,但后者矿物组成变化范围更大,指示瓦吉里塔格岩体在形成过程中经历了更高程度的分离结晶作用,这可能是造成瓦吉里塔格岩体比小海子岩体的w(TiO_(2))更高的原因。小海子岩体虽然w(TiO_(2))较低(3%~4%),但铁钛氧化物固溶体分离结构不发育,且矿物颗粒粗大,使得铁和钛选矿解离比中国其他地区的钒钛磁铁矿更为容易,因此钛资源利用前景巨大,笔者建议出台地方性的勘查技术规范,为这类铁钛资源的开发利用提供技术标准。

The Xiaohaizi is a low-grade but large-tonnage magmatic Fe-Ti deposit that newly discovered in the Tarim Large Igneous Province.The sequence of magma evolution,the genetic relationship with other deposits in the same area,as well as the resource utilization prospect of the Xiaohaizi deposit remain unclear.This study carried out geological and geochemical studies of two types of ore bearing rock facies of olivine gabbro and olivine pyroxenite.Although the facies of olivine gabbro and olivine pyroxenite are not spatially in contact,petrographic observations indicate that the differences in their mineral assemblages are related to mineral accumulation.These two facies show similar chondrite-normalized REE patterns and primitive mantle-normalized patterns,suggesting a comagmatic feature.The low Fo values(67.9~72.5) of olivine indicate significant differentiation of mantle-derived magma in the deep magma chamber.The Xiaohaizi and Wajilitage intrusion show similar petrographic and geochemical characteristics,indicating that they are comagmatic.However,the latter has a larger range of mineral composition,which implies that the Wajilitage intrusion experienced a higher degree of fractional crystallization during magma evolution,and this may be the reason why the Wajilitage intrusion having higher w(TiO_(2)) contents than the Xiaohaizi intrusion.Although the w(TiO_(2)) contents(3%~4%) of the Xiaohaizi intrusion is relatively low,the features of nondevelopment of solid solution separation structure and coarse grain size are in favor of iron and titanium separation in the beneficiation process.Thus,it is recommended to establish a regional exploration technical specification for the low-grade but large-tonnage Fe-Ti resources in South Xinjiang.