内蒙古比利亚谷铅锌银矿床地质地球化学特征及成因

Geological and geochemical characteristics and genesis of the Biliyagu lead-zinc-silver deposit,Inner Mongolia

比利亚谷铅锌银矿位于海拉尔—根河中生代火山盆地北西缘地区。该矿床赋存于上侏罗统满克头鄂博组酸性火山岩中,受北西向断裂构造控制,主矿体呈脉状产出。赋矿围岩流纹质火山角砾熔岩LA-ICP-MS锆石U-Pb测年结果表明,其成岩时代为(159.2±1.8)Ma,并依据赋矿围岩与成矿的关系推测成矿时代为晚侏罗世。矿床赋矿围岩流纹质火山角砾熔岩和流纹岩的主量元素具有富硅(68.31%~77.18%)、富钾(3.39%~4.28%)、低钠(0.14%~0.18%)、高铝(11.74%~14.93%)的特征,属高钾钙碱性系列;岩石REE总量较低(93.65×10^(-6)98.94×10^(-6)),以轻稀土相对富集、轻稀土和重稀土分异明显、弱的Ce负异常和Eu负异常为特征;结合岩石具有亏损Sr、高度富集轻稀土等特征认为火山岩产于板内,与其有关的岩浆可能来源于上地幔,并混染了壳源物质。综合本次研究和区域构造演化特征,初步认为矿床形成于鄂霍次克板块剪刀式闭合时期的拉张伸展环境。

Located in the northwest of Hailar-Genhe Mesozoic volcanic basin, the Biliyagu lead-zinc-silver deposit occurs in the Upper Jurassic Manketouebo Formation acidic volcanic rocks and is controlled by the NW-trending faults, with the orebodies being mainly of vein type. LA-ICP-MS zircon U-Pb dating of rhyolitic volcanic breccia lava indicates that its age is （159.2 ± 1.8） Ma. Based on the relationship between the rock and the mineralization, the authors hold that the deposit was formed in late Jurassic. Major element geochemistry of rhyolitic volcanic breccia lava and rhyolite is characterized by high SiO2 （68.31%-77.18%）, potassium （3.39%-4.28%）, and aluminum （11.74%-14.93%） and low sodium （0.14%-0.18%）, suggesting high potassium calc-alkaline series. The REE content of rocks is low （93.65 × 10-6-98.94 × 10-6）, and has characteristics of high LREE and LREE/HREE ratios as well as weak Ce negative anomaly and Eu negative anomaly. Combined with the features of the rocks such as the loss of the Sr and the obvious enrichment of LREE, it is inferred that the volcanic rocks originated from the plate. The magma of rocks might have been derived from the upper mantle and mixed with crustal materials. Combining this study with regional tectonic evolution characteristics, the authors hold that the deposit was formed during the closure period of Okhotsk plate in a tensile extension environment.