| 其他摘要 | The southeastern area of Yunnan province is separated from Yangtze platform by the Mile-Shizong fault in the northwest, abuts on the Ailaoshan block in the southwest, links with the North Vietnam ancient land in the south and is in line with the Nanling fold system at the Wenma fault in the east, which is an important mine base of Sn, Ag, Pb, Zn, and so on, and from east to west, the three superlarge Sn deposits are Gejiu, Laojunshan and Bainiuchang, each of which is embayed by a granitic pluton. Gejiu and Laojunshan pluton have been deeply studied other than Bozhushan pluton and its related deposits. In this paper, we mainly investigate Bozhushan pluton from petrology and geochemistry, and then analyse the source of ore-forming materials of contact ore deposits and Bainiuchang ore deposit by dint of lead isotope aiming to illuminate the relationship between the ore deposits and Bozhushan pluton.
Bozhushan granite is comprised by two intrusions. The first one is dominated by medium grained biotite monzogranite, belonging to peraluminous(average A/CNK＝1.14) S-type granite and generated in a syn-collisional setting, and the second is mainly consists of fine grained monzogranite, which is formed in an extensional setting. Comparing with the first intrusion, the second has a characteristic of positive Rb、Ta、Tb、Y and negative Ba、Sr、La、Ce. Based on the Sr-Nd isotope, both of them have a higher 87Sr/86Sr and lower εNd, but the model age tell us they are derived from the different magmatic source, mesoproterozoic crust and archaeozioc basement, separately.
Bozhushan pluton showing a narrow lead isotope from the feldspar, consist with the ore deposits in Bozhushan contact zone, is the source of the Bozhushan contact mines. As for the Bainiuchang ore deposit, the baiyang ore blocks and the southeastern ore blocks share the similar lead isotope except of some peculiar samples, indicating the single lead origin of ore deposits in Bainiuchang and Bozhushan contact zone. All of these imply the ore-forming materials resulting from Bozhushan granite. The lead isotopic ratios of the ore-hosted strata (Cambrian sedimentary rocks) are completely different with the ore body, showing the Cambrian sedimentary rocks making a little or no contribution to the Bainiuchang ore deposits.
By comparing the lead isotopic composition of granite, ores and sedimentary rocks, we recognize that the lead of ore deposits in Bainiuchang is not derived from the ore-hosted strata but largely from the Yanshanian magmatic pluton. So the ore-forming materials are probably supplied by the concealed pluton under the mine body. In the early stage, the Bainiuchang ore deposit may go through exhalative sedimentary process without bringing much ore-forming materials. With the intruding of Yanshanian granite, lots of ore-forming materials come and form the Bainiuchang ore deposit. |
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