辽宁八家子铅—锌矿床的铅同位素研究

笔者对八家子矿床矿石铅、岩体长石铅和高于庄组沉积地层铅同位素的详细研究表明,矿石铅是由下地壳基底岩石铅、上地壳高于庄组沉积地层铅和高于庄组沉积矿石铅三端元混合的产物。与矿化关系密切的黑云母石英闪长岩浆来自一个铀亏损区,推测岩浆房在下地壳,岩浆上侵过程中同化了部分围岩。矿床成因类型应为沉积—岩浆热液活化型交代充填铅—锌矿床。

LEAD ISOTOPIC COMPOSITIONS OF THE BAJIAZI LEAD-ZINC DEPOSIT,LIAONING PROVINCE

The lead isotopic compositions of ore, feldspar from biotite--quartz diorite andsedimentary rocks from ore--bearing strata in the Bajiazi ore deposit are studied indetail. The ~(206)Pb/~(204)Pb, ~(207)Pb/~(204)Pb and ~(208)Pb/~(204)Pb ratios of sedimentary rocks are16. 452--17. 871, 15. 216--15. 348 and 36. 584--37. 102 respectively. The Pb--Pb isochronage calculated from those data is 1548 Ma. The feldspar leads of biotite--quartzdiorite are depleted in U--Pb(~(206Pb/~(204)Pb 16. 308--16. 870 and ~(207)Pb/~(204)Pb 14. 990-15. 255)as compared to the Stacey two--stage model, but had a normal Th--Pb(~(208)Pb/~(204)Pb 35.565--36.695). The calculated single--stage modle age is much olderthan tbe true age of intrusion. From those characteristics, it may be inferred thatthe magma originated from the lower crust and mixed with some of the uppercrustal rocks in its way of intrusion. The ore leads show a wide variation. The ~(206)Pb/~(204)Pb, ~(207)Pb/~(204)Pb and ~(208)Pb/~(204)Pbratios of pyrite are 16. 162--17. 904, 15. 149--15. 482 and 36. 340--37. 710 respectively, which show a wider variation range than those of galena(~(206)Pb/~(204)Pb 16.123-16. 560,~(207)Pb/~(204)Pb 15. 149--15. 550 and ~(208)Pb/~(204)Pb 36. 075-37. 580). According to thethree--end member mixing model, the formula of the mixing model of ore leads isobtained. The coefficient of regression of this formula is very high (r=0.984 8).indicating that the ore leads had three end components. It is concluded that theore leads are composed of a mixture of the leads of the lower crustal rocks. theupper crustal rocks and sedimentary sulfides. Based on the lead isotopic compositions and the geological features of thedeposit, it is proposed that the deposit is genetically a sedimentary --magmatichydrothermal metasomatic and filling lead--zinc deposit.