滇中铅锌矿床地球化学与成因研究

滇中地层铅锌丰度高,成矿元素对于地层有继承性和一致性;硫同位素分散,富重硫;铅同位素稳定,多为单阶段演化正常铅,模式年龄与地层时代大体一致,矿质来自地层,矿床为层控型。同生沉积形成矿源层,后期改造(叠加)形成矿体。为中低温度的地下水热液成矿。

GEOCHEMICAL AND GENETIC STUDIES OF LEAD-ZINC DEPOSITS IN CENTRAL YUNNAN

There are nine predominant lead-zinc ore-controlling horizons from Proterozoic upper Triassic in Central Yunnan,The majority of the ore deposits (mineral occurences) are distributed along Luoci-Yimen fault,Puduhe-Dianchi fault and Xiaojiang fault,forming three north-south-trending fault-mineralization belts.According to various mineralizations,tile lead-zine deposits may be divided into four types,namely sedimentary-reworked deposits (type A),epigenetic deposits (type B),superimposedsed imentary-reworked-magmatic Lydrothermal deposits (type C) and sedimentary-reworked-superficial leaching enriched deposits (type D).The results of stratigraphical and geochemical studies (based on &; strato-geochemical profiles and trace elements analyses of 436 samples),indicate that the contents of Pb and Zn in the ore-controlling strata are higher metallogenetic elements are inherently and consistently related with the strata,metallogenetic metals were derived predominantly from the strata. Ph and Zn in source beds of sandstone and sandy dolomite are present in the form of ore elastics,those in source beds of mud-Carbonaceous dolomite are in the form of sulphides and ionic absorbers,and those in source beds of phosphorite-bearing dolomite are isomorphic.Sulphur isotopes analysis of 63samples shows that the δ³⁴S varies form - 39.1‰ to+20.6‰,and is 10‰-20‰ in51 samples of them.The enrichment in heavy sulphur and tower-shaped distribution pattern indicate that sulphur came predominantly from reductive sedimentary environment. This is proved by the fact that laminated pyrites in carbonaceous strata of the ore depsits are often seen.Pb isotopic composition analys is of 62 samples suggests that Ph isotopic composition in type A deposits is stable and belongs to normal lead in a single stage. The model ages roughly are consistent with the ore-bearing strata, indicating Ph came from the strata. For ore deposits of type B and C,the lead isotopic composition shows a polystage abnormal lead, implying the ores were formed in polystages and from polysources.Study of mineral inclusions of 53 samples shows that ore-forming fluids were derived from under-ground hydrothremal solutions,with temperature between 100-210℃ and their salinity (NaCl contents) between4%-16%. The temperature and salinity of type A deposits were lower than that of type B and type C.The ore deposits are stratabound,the source beds were formed in syndeposition and ore bodies were formed in later reworking and superimposing processes.