【摘要】 落雪组作为云南易门狮子山铜矿区最主要的赋矿层位，前人对该地层沉积时代研究程度较低，缺乏确切的地层形成时代资料。本文对狮子山铜矿区落雪组一段的凝灰质白云岩进行锆石U-Pb定年，获得3组有效²⁰⁷Pb/²⁰⁶Pb年龄值，分别为：（1）1.7 Ga—2.0 Ga;（2）2.11 Ga—2.43 Ga;（3）2.5 Ga—3.02 Ga。其中，第一组锆石年龄代表成岩期后构造热液事件；第二组锆石自形程度较好，棱角分明，发育韵律环带，为岩浆结晶锆石，其加权平均年龄为2299 Ma±29 Ma（n=27, MSWD=8.1）,指示落雪组一段凝灰质白云岩的沉积时代为古元古代；第三组锆石年龄为捕获的古老继承锆石年龄，锆石的微量元素w（Y）—w（U）、w（Y）—w（Ce）/w（Ce）^*、w（Y）—w（Yb）/w（Sm）岩性判别图解显示，该组锆石主要来自陆壳花岗质岩石中的S型花岗岩，暗示扬子板块西南缘古元古代—新太古代存在近源出露的花岗岩类岩石，存在较早的酸性成分的大陆地壳。通过区域地层岩性特征和地层沉积时代对比分析，研究认为狮子山铜矿区出露的落雪组应为滇中易门群罗洼垤组的延伸，同属古元古代的沉积建造。更多还原

【Abstract】 Luoxue formation is the main Cu ore-bearing horizon in Shizishan mining area with little study on the sedimentary chronology and without definite data of formation of the strata. This paper deals with zircon U-Pb dating of tuffaceous dolomite of the first member of Luoxue formation. The data obtained are 1.7 Ga-2.0 Ga, 2.11 Ga-2.43 Ga and 2.5 Ga-3.02 Ga. 1.7 Ga-2 0 Ga represents post diagenesis tectonic hydrothermal event. 2.11 Ga-2.43 Ga the sedimentary time of the tuffaceous dolomite corresponding to Proterozoic Era(zircon from which the data are obtained is euhedral grain crystallized from magma with clear edges and corners and rhythmic rings. The average weighted age 2299 Ma ± 29 Ma(n=27, MSWD=8.1). 2.5 Ga-3.02 Ga is the age of that captured ancient inherited zircon. Trace element(w(Y)-w(U), w(Y)-w(Ce)/w(Ce)~*, w(Y)-w(Yb)/w(Sm)) discrimination diagram of the zircon from which 2.5 Ga-3.02 Ga is obtained shows that it comes from S-type granite of continental crust implying that proximal outcrops of granitic rocks occured at southwest margin of Yangtze plate during Early Proterozoic-Late Archean period, i.e. occured earlier acidic continental crust. Comparative analysis of lithologic characteristics of regional strata and sedimentary time of the strata draws a conclusion that Luoxue formation out cropped in Shizishan copper mining area is likely to be the extension of Luowadie formation of Yimen group, which is also Proterozoic sedimentary formation outcropped in the central Yunnan province.更多还原