云南澜沧老厂铅锌多金属矿床闪锌矿微量元素组成

摘要

云南澜沧老厂是三江成矿带南段最重要铅锌多金属矿床之一,通过LA-ICPMS和ICP-MS微量元素组成分析结果表明,矿床中闪锌矿属于铁闪锌矿,形成于中温环境,以富Fe、Mn、Cd和In等元素为特征,其中Fe、Mn、Cd、In等元素以类质同象形式赋存于闪锌矿中,而Pb、Cu、Sn和Bi等元素含量变化范围较大,以显微包裹体(方铅矿和黄铜矿等)赋存于闪锌矿中.本矿床闪锌矿中Fe和Mn等微量元素组成与VMS矿床类似,但In和Cd的异常富集可能暗示其独特的成矿机制.总体而言,其闪锌矿微量元素组成特征和与燕山-喜山期花岗岩叠加改造作用有关的喷流沉积铅锌矿床(如云南白牛厂和广东大宝山)相似,而明显不同与矽卡岩型矿床(如核桃坪与鲁子园),更不同于MVT型铅锌矿床(牛角塘、会泽和勐兴)和金顶铅锌矿床.结合矿床产出地质特征,笔者认为云南澜沧老厂铅锌多金属矿区经历了古、中、新特提斯期不同程度的拉张与闭合发展演化,使矿床多期同住叠加成矿特征明显,其闪锌矿微量元素组成具喷流沉积成因特征,深部喜山期花岗斑岩与铅锌成矿作用关系不大,但在其侵入过程中叠加改造作用使闪锌矿等硫化物组合及其微量元素组成发生一定程度变化(如局部富集Sn和Sb等元素).此外,两种测试方法结果对比可以看出,在硫化物单矿物微量元素分析中,LA-ICPMS相对于ICP-MS分析具有更高精度,不仅可以进行硫化物原住分析,并能即时了解微量元素在硫化物中赋存状态,而且克服了ICP-MS分析中由于单矿物选样不纯致使测试误差大等弱点.%As one of the most important Pb-Zn poly metallic deposit, Laochang, Lancang, Yunnan Province is located on the southern end of Sanjiang metallogenic belt Researching on trace elements for sphalerite by LA-1CPMS and ICP-MS in the deposit, it show that the sphalerite belongs to marmatite, formed on medium temperature and be characterized by riching in Fe, Mn, Cd, In etc. , which are present isomorphously in sphalerite. There are wide variation ranges for Pb, Cu, Sn, Bi and other trace elements, which present as micro-inclusion (e. g. galena, chalcopyrite etc. ) in sphalerite. The character of rich in Fe and Mn is similar to that of VMS deposit in sphalerite, but the anomalous enrichment of In and Cd may imply that there is a particular metallogenic mechanism in the deposit Our research show that the trace elements composition of sphalerite is same as that of some Chinese volcanogenic massive sulfide Pb-Zn deposits which were overprinted by Himalayan-Yanshanian granite ( e. g. Bainiuchang, Yunnan Province and Dabaoshan, Guangdong Province) and quite different with that of skarn Pb-Zn deposits (e. g. Hetaoping and Luziyuan, Baoshan, Yunnan Province) , MVT Pb-Zn deposit (e. g. Niujiaotang, Huize and Mengxing) and Jinding Pb-Zn deposit Based on the geological feature of the deposit, it is suggested that, with the multi-stages opening and closing of Paleo Tethys Ocean, it formed a obvious multistage!! overprint metallization at same place in the deposit The trace elements composition is characterized by that of volcanogenic massive sulfide Pb-Zn deposits, and there are no any genetic relationship between Pb-Zn mineralization and concealed Himalayan granite-porphyry, but the sulfide assemblage and their trace elements composition were changed to some extent with the intrusion of the rock mass (e. g. enrichment of Sn and Sb partly). Furthermore, the contrast of two different analysis method for trace elements in sphalerite show that LA-ICPMS could provide more accurate results, it not only show the exist of different trace elements real-timely, but also avoid the error resulted in by impure sample in ICP-MS analysis.