广东长坑-富湾超大型独立银矿床Rb-Sr定年及形成分析  

Rb-Sr DATING AND GENESIS OF CHANGKENG-FUWAN SUPERLARGE SILVER DEPOSIT IN WEST GUANGDONG

作　　者：梁华英[1] 王秀璋[1] 程景平[1] 夏萍[1] 张湖[1] 单强[1] 张国恒 

机构地区：[1]中国科学院广州地球化学研究所,广州510640 [2]广东省地质矿产局757地质大队,江门529040

出　　处：《地质科学》2000年第1期47-54,共8页Chinese Journal of Geology(Scientia Geologica Sinica)

基　　金："九五"攀登计划;国家自然科学基金

摘　　要：长坑－ 富湾超大型银矿床主要产在下石炭统灰岩与上三叠统页岩断层不整合面下的硅质岩及灰岩中，矿化多为脉状，主要由石英、方解石、方铅矿、闪锌矿及银矿物组成。成矿流体Ｒｂ－ Ｓｒ 等时线年龄为６８±８．５Ｍａ，表明成矿发生在５９．５—７６．５ Ｍａ 之间。（８７Ｓｒ／８６Ｓｒ）Ｉ＝ ０．７１６４。成矿流体δ１８Ｏ 在－ ０．８６‰—４．１‰之间，δＤ 在－ ３９．８‰—－ ５９‰之间，表明成矿流体为循环大气降水或建造水。银矿床铅同位素组成和产于中新元古代地层中茶洞银矿床方铅矿的铅同位素组成基本一致。据成矿年龄、成矿流体氢氧同位素组成及铅同位素组成特点，认为长坑－ 富湾超大型独立银矿床是晚白垩世至第三纪火山及次火山活动加热循环大气降水及建造水溶解深部矿源岩中经过早期成矿富集的成矿物质，迁移至灰岩与硅质岩及硅质岩与页岩界面时沉淀析出形成的。Fuwan large silver deposit occured in silicolites and limestone directly under the unconformity between the lower Carboniferous limestone and the upper Triassic carbonaceous shale Silver vein composed of quartz, calcite, galena, sphalerite and different kinds of silver minerals occurs in limestone and siliceous rocks. Rb-Sr isochron age of fluid inclusion in quartz of silver vein is 69±8 5Ma, with strontium isotope initial ratio ( 87 Sr/ 86 Sr) I=0 7164. δ 18 O and δ D of ore-forming fluid of silver mineralization are in ranges of -0 864‰—4 1‰ and -39 8‰— -59‰, respectively, suggesting that the ore-forming fluid come from circulating meteoric water or formational water. Lead isotope of Changkeng-Fuwan silver ore body, which differs from that of ore-bearing strata, falls in the same region in 207 Pb/ 204 Pb- 206 Pb/ 204 Pb diagram as those of the Chadong silver orebody occured in Proterozic formation Based on the characteristics of lead isotope and Rb-Sr age, it is concluded that the Changkeng-Fuwan superlarge silver ore is the product of reworking processes. The first reworking process results in enrichment of silver in the source rock. The second reworking process leads the enriched silver to move out of the source rock to the boundaries between the limestone and silicolites as well as silicolites and carbonaceous shale and precipitate due to the sudden change of physico-chemical environment.

关 键 词：银矿床 成矿时代 粤西富湾 钕口-锶 定年 

分 类 号：P618.520.2[天文地球—矿床学] P618.520.5[天文地球—地质学]