渣尔泰山地区白垩纪酸性火山岩地质特征及成矿作用

渣尔泰山地区位于内蒙古中西部,大地构造位置处于华北地台北缘狼山-渣尔泰山裂陷槽的东段,根据近几年的找矿实践与研究,在白垩纪的酸性火山岩中已发现银金矿床、金银矿床,主要赋存于下白垩统白女羊盘组酸性火山岩中。该套火山岩具富硅富钾、相对贫钙镁的特点,属于铝过饱和的碱性系列;在球粒陨石标准化图解上岩石化学样品均显示为轻稀土(LREE)相对富集、重稀土(HREE)相对亏损的右倾型配分模式,轻重稀土分异较明显,显示较明显的负铕异常;微量元素显示明显的Rb、Pb正异常和Ba、Sr负异常,不相容元素比值Zr/Nb=2.47~4.87,Zr/Y=18.3~103。属大陆碰撞造山期后作用的产物,来源于地壳部分熔融。其岩石类型主要有:流纹质凝灰角砾岩、流纹质角砾凝灰岩、球粒状流纹岩、珍珠岩、显微嵌晶状流纹岩夹流纹斑岩等。银多金属矿的含矿层主要由复碎裂复硅化流纹质凝灰角砾岩、硅化复碎裂流纹岩、多期次硅化黄铁矿化角砾岩化流纹斑岩等组成。成矿元素Ag、Au、Sb、W显著富集于流纹质凝灰角砾岩、多期次硅化碎裂的流纹岩、流纹斑岩中,其平均含量高于中国流纹岩元素丰度10倍以上,说明该套火山岩提供了成矿物质来源;且元素含量的分异程度较大,指示明显受到后期成矿作用的叠加;有一定的找矿潜力。

Geological characteristics and mineralization of Cretaceous acid volcanic rock in the Zha'ertaishan area, Inner Mongolia

The Zha'ertaishan area, lied in middle-west area of Inner Mongolia, and is located in the east section of Langshan-Zha'ertaishan Mesoproterozoic rift zone of the northern margin of the North China Plate. In the course of prospecting and research, silver-gold and gold-silver deposits were discovered, which was occurred in acidic volcanic rocks of the Bainuyangpan Formation of the Lower Cretaceous which are peraluminous calc-alkaline series characterized by silicate-rich and potassium-rich, low iron and low magnesium. The rocks are enriched in LREE and relatively depleted in HREE, significant fraction between LREE and HREE, and with obvious negative Eu anomaly. The acidic volcanic rocks are characteristics of clearly positive anomalies of Rb and Pb, and negative anomalies of Ba and Sr. The ratios of incompatible element for Zr/Nb and Zr/Y are 2.47~4.87 and 18.3~103. They were the product of collision orogenics between North China Plate and Siberia Plate in Mesozoic era, which were formed by partial melting of the crust. The rocks are made of rhyolitic tuff breccia, rhyolitic tuff with breccia, spherulitic rhyolite, perlite, microaphanitic rhyolite with rhyolite porphyry, and the ore-bearing layer of silver polymetallic mine consists mainly of multiphase silicified rhyolitic tuff breccias with multiphase fragmentation, multiphase silicified rhyolite with multiphase fragmentation, multiphase brecciated rhyolite porphyry with pyritization and silicification etc. Ore-forming elements of Ag, Au, Sb and W are enriched significantly in rhyolitic tuff breccias, multiphase silicified rhyolite and rhyolite porphyry with multiphase fragmentation, and the average content of metallogenetic elements for Ag, Au, Sb and W in those are more ten times than abundance of chemical elements of the China rhyolite. It demonstrated that the volcanic rocks are the sources of orebodies. The variation of ore-forming elements is obvious, and it indicated that mineralization superposition is significant and is of potentials for prospecting Ag deposit in this region.