云南东川雪岭矿区浅部铜多金属矿化地质地球化学特征及成矿规律研究

GEOLOGICAL AND GEOCHEMICAL FEATURES AND METALLOGENIC REGULARITY OF SHALLOW CU-POLYMETALLIC MINERALIZATION IN XUELING MINING AREA OF DONGCHUAN,YUNNAN,CHINA

雪岭矿区位于扬子板块西缘,浅部赋存的铜多金属矿化受落因断裂系南延断裂及其次级断裂和辉绿岩脉所控制产出于灯影组白云岩中。对矿区浅部铜多金属矿化的岩矿石地球化学和同位素地球化学分析显示:围岩与矿石的稀土元素特征相似,且围岩富集Cu,Ag,Pb,Zn等成矿元素,故围岩应该为成矿提供了部分成矿物质;与之共生的石英样品δD_(V-SMOW)值介于-85.7‰^-102.2‰,δ^(18) O水值介于0.9‰~2.4‰,表明成矿流体以层间封存水为主,混合了部分天水和原生岩浆水;3件来自铁矿化带中的黄铁矿δ34 SV-CDT值为+9.9‰^+27.4‰,1件来自铜银(铅锌)矿化带中裂隙脉状矿体的黄铁矿δ34 SV-CDT值为-37.5‰,暗示本区硫来源复杂,硫可能主要来源于沉积地层的海相硫酸盐,部分混染幔源硫和生物硫,或者与其成矿过程中fO2和pH值发生急剧变化有关;3件来自铁矿化带的黄铁矿^(206)Pb/^(204)Pb=18.279~18.372,^(207)Pb/^(204)Pb=15.653~15.673,208Pb/^(204)Pb=38.272~38.462,1件来自铜银(铅锌)矿化带裂隙脉状矿体的黄铁矿^(206)Pb/^(204)Pb=19.310,^(207)Pb/^(204)Pb=15.771,208Pb/^(204)Pb=38.792,显示本区铅来源复杂,具壳幔混合铅的特征;具正确铅特征的硫铁矿模式年龄为260 Ma^350 Ma,与峨眉山玄武岩的成岩时代相近。经综合分析,本区浅部铜多金属矿化应是晚二叠世时,受峨眉山玄武岩喷溢作用热动力影响导致热液萃取深部陡山沱组成矿物质,并沿途淋滤围岩中部分成矿物质,沿断裂带向上运移至浅部灯影组白云岩中沉淀富集所致。

The shallow Cu-polymetallic mineralization in Xueling mining area occurs in the dolomite of Dengying Formation, and is controlled by south trending faults and secondary faults of Luoyin fracture system and diabase vein. The primary minerals mainly are tetrahedrite, chalcocite, chalcopyrite, pyrite and galena, and the secondary minerals mainly are malachite, limonite and azurite, with dolomite, calcite, barite and quartz as gangue minerals. The research of rock and ore geochemistry and isotope geochemistry shows that the REE of the ore is similar to the surrounding rock,and the surrounding rock contain more Cu, Ag, Pb, Zn. δDv-sMow and δ18 O, values of quartz varies in a range of -85.7‰ to -102.2‰ and 0. 9‰ to 2.4‰,indicating that interlayer water in the sedimentary rock makes up a large part of metallogenic fluid, combined with some meteoric water and magmatic water. δ34 SvcDr values of three pieces of pyrite in Fe-mineralization belt and one pieces of pyrite in fracture vein ores are ＋9.9‰ to ＋27.4‰ and -37.5‰,suggesting that the source of sulfur is complicated,it might come from seawater sulfates,mixed with some mantle sulfur and biogenie sulfur, or related to the drastic change of fo2 and PH during metallogenic process. The ^206Pb/204Pb,^207Pb/204Pb and ^208Pb/^204Pb ratios of three pieces of pyrite are 18. 279- 18. 372,15. 653-15. 673 and 38. 272-38. 462 ,and the corresponding ratios of one pieces of pyrite in fracture vein ores is 19. 310,15. 771 and 38. 792,revealing that the source of lead is complicated,and it may be from crust-mantle mixed lead. The model age of the pyrite ranges from 260 Ma to 350 Ma, close to the age of Emeishan basalt. By synthetic analysis,the shallow Cu-polymetallic mineralization is caused by influence of Emeishan basalt acted in Late Permian. The hydrothermal fluid extracts the metallogenic material from deep Doushantuo Formation,leaches the metallogenic material from the surrounding rock, then migrates and precipitates in dolomite of Dengying Formation along the faults.