内蒙白云鄂博矿区H_9中火山岩岩石特征及其意义

PETROLOGICAL FEATURES OF VOLCANIC ROCKS INH_9 FORMATION OF THE BAYAN OBO ORE DISTRICT,INNER MONGOLIA,AND THEIR SIGNIFICANCE

白云鄂博矿区Ｈ＿９地层岩石被中外学者长期看作是板岩或页岩，经近期研究发现岩性极为复杂。Ｈ＿９地层岩石是一套呈互层产出的粗面岩、流纹岩、流纹英安岩、变辉绿岩、白云岩、石英岩、黑云母岩、钠闪石－长石岩、钠辉石－长石岩、红柱石－黑云母角岩及碳质绢云板岩等。文中详细论述了这些火山岩石的结构构造、矿物成分和岩石化学成分，以及微量元素。对Ｈ＿９地层中火山岩，尤其是粗面质火山碎屑岩的确定，对了解白云鄂博矿床的成因和白云鄂博群形成的地质背景有重要意义。

Owing to their cryptocrystalline texture and platy structure , rock of H_9 formation in theBayan Obo ore district were referred to as sfate or shale by geologists both in China and abroad;nevertheless,recent researches show that lithology of the H_9 formation is extremely complex,con-sisting of an interbedded sequence of trachyte,rhyolite,rhyedacite,metadiabase,dolomite,quartzite,biotitite,riebeckite-feldspatite,aegirine-feldspatite,andalusite-biotite hornfels and car-bonaceous sericite slate, Of these rocks,the first four are volcanic or volcanogenic rocks,whereasthe last five are altered or metamorphosed volcanic and volcanogenic rocks or argillite. The pre-sent paper deals in detail with these volcanic rocks in such aspects as their texture,structure,mine-ral composition,petrochemical composition,and minor element geochemistry.Both H_8 and H_9 formations in the Bayan Obo ore district are host rocks,and within H_9 for-mation independent niobium and REE orebodies can be delineated. Fairly detailed investigationhas been conducted in H_8 formation,with lots of papers published.In contrast,many geological,petrological and geochemical problems of H_9 formation remain unsolved.The identification of vol-canic rocks in H_9,especially trachytic pyroclastic rock,is of great significance in finding out thegenesis of the Bayan Obo ore deposit and the geological setting for the formation of Bayan OboGroup. it is conceivable that mineralization was related to volcanism and ore-forming materialswere derived from the depth.