摘要:
内蒙古赤峰市白音诺尔铅锌矿床是大兴安岭地区储量最大的铅锌矿床。该矿床位于白音乌拉火山机构的北部,矿区范围内出露二长花岗岩和花岗闪长(斑)岩侵入体,与黄岗梁组大理岩或结晶灰岩接触带附近发育系列矽卡岩,铅锌矿体主要产于透辉石矽卡岩中,属于矽卡岩型矿床。二长花岗岩地球化学显示富硅(SiO2=68.98%~75.44%),高铝(Al2O3=12.49%~15.62%)、低镁(Mg=0.1%~1.25%),富碱(Na2O+K2O=7.73%~8.80%,Na2O/ K2O=0.96~1.33)的特点,属于高钾钙碱性系列的准铝质花岗岩。稀土配分呈轻稀土富集型分布模式,稀土总量变化于127.4×10-6~145.95×10-6之间,存在较弱的正Ce异常和明显的Eu负异常,微量元素表现为Rb、Th、K等大离子亲石元素富集,而Nb、Ta、P、Ti等高场强元素亏损的特征。在Rb-(Y+Nb)、Rb-(Yb+Ta)构造环境判别图解中,所有样品均落入火山弧花岗岩构造环境中。两件二长花岗岩锆石LA-ICP-MS法U-Pb年龄为254.8±1.6 Ma和245.6±3.5 Ma,将岩浆岩侵入及相关的成矿作用限定为古生代末期,推测在晚古生代末期古亚洲洋局部残留洋盆的俯冲是形成白音诺尔二长花岗岩及成矿的动力学机制。
Abstract:
The Baiyinnuoer ore deposit in Inner Mongolia is the largest Pb-Zn deposit in Da Hinggan Mountains metallogenic belt. It located in the northern part of Baiyinwula volcanic agencies, Pb-Zn orebodies mainly occur along the contact zone between the gradiorite and the carbonate rock. The authors dated the zircons of two sam-ples from the granodiorites using the LA-MC-ICP-MS method. Two reliable weighted mean 206Pb/238U ages are (254.8±1.6)Ma(MSWD=3.0,n=29)and(245.6±3.5)Ma(MSWD=5.9,n=13). Lead-zinc mineralization was spa-tio-temporal correlation with granodiorites, suggesting that Baiyinnuoer Lead-zinc Deposit was the product of late Hercynian to early Indosinian tectonic magmatic activity. The granodiorites have a SiO2 range of 68.98 to 75.44wt%,with relatively high Al2O3 (15.52%~15.26 wt%) and low MaO (0.1~1.25wt%) content, and charac-terized by extremely rich alkali(Na2O=4.04%~4.36%,K2O=3.98%~4.05wt%,Na2O+K2O=7.73%~8.80wt%, Na2O/ K2O=0.96~1.33). All samples fall into the high K calk-alkali series region and have metaluminous charac-teristics. The distribution of REE characterized by enrichment in LREE, and total amount of rare earth varied from 127.4~145.95 ppm. The REE are weak positive Ce anomalies (δCe=1.11~1.34) and significant negative Eu anomalies (δEu=0.08~0.58), trace elements characterized enrichment Rb, Th, K, LILE, loss Nb, Ta, P, Ti and other high field strength element (HFSE). In the Rb- (Y+Nb) and Rb- (Yb+Ta) tectonic environment discrimina-tion diagrams, all samples fall into the tectonic setting of volcanic arc, suggesting that local remnant basin subduc-tion in the late stage of the Late Paleozoic to Early Indosinian formed the high-K calc alkaline and metaluminous granodiorite in Baiyinnuoer.
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