广西金牙金矿床百逢组沉积特征及其与金矿的关系

SEDIMENTARY CHARACTERISTICS OF THE BAIFENG FORMATION AND THEIR RELATIONS WITH JINYA GOLD DEPOSITS,GUANGXI

广西金牙金矿产于中三叠统百逢组中 ,矿区的百逢组为一套陆源碎屑浊积岩 ,既有阵发性高密度浊流引起的浊积扇体系 ,又有稳定低密度浊流引起的鲍马序列。百逢组下段为浊积扇体系 ,中段及上段为鲍马序列 ,一般不全 ,其中d、e段最发育 ,其次为c、b段。金矿化出现在砂泥混积的百逢组中段。矿体位于鲍马序列段 ,尤其是de和cde组合段 ,岩石为富含有机质的泥质与粉砂的混积岩 ,属远端浊积岩。其中 ,钙质泥岩和粉砂质泥岩是最有利的矿化围岩。主要载金矿物毒砂和黄铁矿呈自形晶出现。矿体的有机碳含量高于相邻围岩的有机碳含量 ,与运移烃类的叠加有关。金品位随有机碳含量的增加而增加 ,有机质也是有用的金的载体。富含有机质的浊积岩是浊积岩型金矿床形成的有利条件。

Jinya gold deposits in Guangxi occur in the middle Triassic Baifeng Formation.The Baifeng Formation in the area belongs to a set of terrigenous clast turbidite,including turbidite fan systems caused by the moment high-density turbidite current and the Bouma sequence caused by the stable low-density turbidite current.The lower member of the Baifeng Formation is suggested to be turbidite fan systems.The middle and upper members are suggested to be the Bouma sequences,which are usually not complete and consist of divisions mainly d,e and subsidiarily c,b.Gold mineralization took place in the silt-mud-mixed middle member of the Baifeng Formation.Ore bodies occur in the Bouma sequence,especially in divisions de and cde,of which rocks are organic-rich pelitic- and silty- mixed ones,belonging to the distal turbidite.The calcareous mud stone and the silty stone are the most favorable mineralized lithology.The major Au-carriers of arsenopyrite and pyrite are automorphic crystals.The content of organic carbon is higher in ore bodies than in country rocks,which is suggested to be related to the migrated hydrocarbon.The Au assay is increased with the increase of organic carbon content.The organic matter is suggested to be a useful Au-carrier and one of the contributor to the formation of the gold deposits.The organic-rich turbidite is the favorable condition for the formation of the turbidte-type of gold deposits.