中国东部火山岩型铍铀矿床成矿潜力与找矿远景

Metallogenic potential and prospecting prospect of volcanic-hosted beryllium-uranium deposits in eastern China

火山岩型铍铀矿床是铍金属矿床的主要成矿类型,它是指赋存于火山岩-次火山岩中,与高硅流纹岩和花岗斑岩有关的浅成低温交代和脉状矿床。1969年美国发现的Spor Mountain火山岩型铍铀矿床改变了世界金属铍的分布格局和供应态势。中国东部地区发育大量的中生代火山岩,该地区是否具备火山岩型铍铀矿床的成矿条件,成矿潜力如何?有没有找矿远景?这些科学问题尚未完全回答。本文在厘定火山岩型铍铀矿床的概念和基本成矿地质特征的基础上,对中国东部大兴安岭及其邻区和东南沿海地区已发现的火山岩型铍铀矿床的找矿线索进行了梳理,如:冀北窟窿山、内蒙古东山湾、江西密坑山、浙江青田、福建大湾、福里石等。中国东部地区已有的火山岩型铍铀矿床(矿化点)主要赋存于张家口组、南园组、鸡笼嶂组火山岩中;成矿年代学研究表明其主要形成于晚侏罗世、早白垩世早期和晚白垩世早期,其中早白垩世早期是主要的成矿期,与欧亚大陆中生代早期的伸展构造时限和中国东部构造体制大转折的时限基本一致,因此,该期火山岩型铍铀矿床又可称为“构造体制转折型”铍铀矿床。本文认为中国东部具有良好的火山岩型铍铀矿床的成矿潜力,找矿远景广阔。未来中国东部大兴安岭及其邻区的上白垩统张家口组、满克头鄂博组、玛尼吐组、白音高老组,东南沿海地区的上白垩统南园组、鸡笼嶂组、鹅湖岭组火山岩是火山岩型铍铀矿床的有利找矿层位。

Volcanic-hosted Be-U deposits generally refer to epithermal low-temperature metasomatic and vein deposits occurring in volcanic-subvolcanic rocks,and related to high silica rhyolite and granite porphyry.Volcanic-hosted Be-U deposit is the major sources for beryllium production in the world.The Spor Mountain volcanic-hosted Be-U deposits discovered in the United States in 1969 has changed the distribution pattern and supply trend of metal beryllium after then.A large number of Mesozoic volcanic-subvolcanic rocks occurred in eastern China,but the metallogenic conditions,metallogenic potential and the prospecting prospect of volcanic-hosted Be-U in the area is also unclear.Based on defining the concept and basic metallogenic geological characteristics of volcanic-hosted Be-U deposits in the world,this paper clarifies the prospecting clues of volcanic-hosted Be-U deposits discovered recently in Daxinganling and its adjacent areas and southeast coastal areas in eastern China,such as Kuolongshan in northern Hebei Province,Dongshanwan in Inner Mongolia,Mikengshan in Jiangxi Province,Qingtian in Zhejiang Province,Dawan and Fulishi in Fujian Province.The existing volcanic-hosted Be-U deposits(mineralization occurrences)in eastern China mainly hosted in the volcanic rocks of Zhangjiakou Formation,Nanyuan Formation and Jilongzhang Formation;The metallogenic chronology of volcanic-hosted Be-U deposits(mineralization occurrences)shows that they are mainly formed in the Late Jurassic,early Early-Cretaceous and early Late-Cretaceous.The early Early-Cretaceous is the main metallogenic period,which is basically consistent with the time of the extensional structure of Eurasia-Asia Continents in the Early Mesozoic,and the time limit of the tectonic regime transition in eastern China.This paper concludes that it preserves good metallogenic potential of volcanic-hosted Be-U deposits and a broad prospecting prospect in eastern China.The Upper Cretaceous Zhangjiakou Formation,ManketouObo Formation,Manitu Formation and Baiyingaolao Formation in Great Xing an Range and its adjacent areas,as well as the volcanic rocks of Upper Cretaceous Nanyuan Formation,Jilongzhang Formation and Ehuling Formation in the southeast coastal areas are the favorable for volcanic-hosted Be-U deposits(mineralization occurrences)prospecting in the future.