北武夷梨子坑火山盆地流纹斑岩与铅锌矿的成因关系

梨子坑火山盆地位于北武夷中生代月凤山—梨子坑火山岩带东段,已知铅锌(铜、银)矿体或矿化呈细脉-浸染型、脉状,产于流纹斑岩脉的内外接触带及其外侧围岩中,发育钾化、绿泥石化、硅化、绿帘石化等围岩蚀变。地球化学特征显示流纹斑岩为钙碱性系列,岩石具有高SiO2、富碱、高K2O、高钙铁、低镁、K2O/Na2O值偏高的特点,为强过铝质岩石。w(ΣREE)值为76.28×10-6～222.54×10-6,ω(ΣLREE/ΣHREE)比值较大,为4.08～12.30,属于轻稀土元素富集型。成矿流纹斑岩形成于137±2.1Ma(SHRIMP锆石U-Pb法)～138.8±1.4Ma(LA-MC-ICPMS锆石U-Pb法),属早白垩世。铅锌矿属于次火山斑岩脉型铅锌(银铜)成矿系列,划分为次火山斑岩脉型和次火山热液破碎带型两种矿床成因类型。

Genetic relationship between rhyolite porphyries and lead-zinc mineralization in Lizikeng volcanic basin,northern Wuyishan

Lizikeng volcanic basin is located in the east section of the Mesozoic Yuefengshan-Lizikeng volcanic rock belt,northern Wuyishan.The known lead-zinc(copper, sliver) ore-bodies or mineralizations which are shown as veinlet-disseminated and vein ores are mainly occurred in internal or external contact zones and wall rocks of rhyolite porphyries,where wall-rock alterations such as potassic alteration,chloritization,silicification and epidotization are well developed.The results of geochemical analyses show that the rhyolite porphyries belong to strongly peraluminous calc-alkaline series rocks with high contents of alkali,SiO2,K2O,Ca,Fe,high ratios of K2O/Na2O and low contents of Mg,w(ΣREE)values vary from 76.28×10-6 to 222.54×10-6,w(ΣLREE/ΣHREE) values are relatively high(4.08～12.30),suggesting a strongly right-inclined LREE enrichment type.Ore-forming rhyolite poyphyries are occurred in 137±2.1 Ma(SHRIMP zircon U-Pb)～138.8±1.4 Ma(LA-MC-ICPMS zircon U-Pb),belong to the Early Cretaceous.The lead-zinc deposit can be genetically divided into subvolcanic porphyry vein type and subvolcanic hydrothermal fracture zone type,belonging to subvolcanic porphyry vein type lead-zinc(copper,sliver) metallogenic series.