滇西北兰坪盆地李子坪铅锌矿床微量元素地球化学特征

Trace element geochemistry of the Liziping Pb-Zn deposit,the Lanping Basin,Northwest Yunnan Province,China

闪锌矿中的稀土元素、微量元素蕴含着与成岩、成矿密切相关的地球化学信息。李子坪铅锌矿床位于兰坪盆地北部,矿体呈脉状、似层状产出于侏罗系花开佐组碎屑岩及碳酸盐岩夹泥质岩组合建造中。微量元素地球化学特征显示,该矿床闪锌矿形成于中低温环境,以富含Ga、Ge、Ag、Cd、Tl、Ni、Cu和As等微量元素,亏损Fe、In、Sn、Mn和Co等元素为特征。总体上,该矿床闪锌矿中Ag、Ga和Fe等微量元素组成明显不同于喷流沉积铅锌矿床(如白牛厂、老厂和大宝山),更不同于夕卡岩型矿床(如核桃坪与鲁子园),而与一般MVT型矿床(墨西哥Tre Marias、云南会泽和贵州牛角塘)和金顶铅锌矿床类似,但Cd含量明显低于MVT型矿床和云南金顶铅锌矿床,暗示其独特的成矿机制。稀土元素研究显示,闪锌矿与赋矿围岩的REE分布模式表现出相同的变化趋势,而不同于兰坪盆地富碱岩体,暗示该矿床闪锌矿的REE分布模式受围岩地层的影响。

Rare earth elements and trace elements in sphalerite reflect geochemical information of diagenesis and mineralization.The Liziping Pb-Zn polymetallic deposit is located in north Lanping basin.The orebodies at Liziping deposit are mainly hosted in the Jurassic Huakaizuozu Formation sandstone,siltstone,and mudstone,and occur as veins and stratified layers.According to trace element geochemistry of sphalerite in the deposit,it shows that the sphalerite is formed at low temperature and characterized by enrichments of Ga、Ge、Ag、Cd、Tl、Ni、 Cu and As and depletion of Fe、In、Sn、Mn and Co.In general,our research shows that the trace element composition of sphalerite is quite different from that of volcanogenic massive sulfide Pb-Zn deposits（e.g.Bainiuchang、Laochang and Dabaoshan）,and Skarn Pb-Zn deposits（e.g.Hetaoping and Luziyuan,Yunnan Province）,but are the same as that of some MVT Pb-Zn deposits（e.g.Tre Marias mine,Chihuahua,Mexico;Niujiaotang,Guizhou Province,Huize,Yunnan Province） and Jinding Pb-Zn deposit.Moreover,the sphalerite from the Liziping lead-zinc deposit has lower content of Cd than the MVT deposits and Jinding deposit,which may imply special metallogenic mechanism in the deposit.REE geochemistry of sphalerite in the deposit shows that sphalerite picked from different samples and wall-rocks have similar LREE enriched chondrite-normalied patterns,which are different from the that of alkali-rich rock in Lanping basin,suggesting that chondrite normalized REE patterns of sphalerite in the deposit were affected by the host rocks.