REE geochemistry of No.1 ore body group of Guoluolongwa Au deposit, East Kunlun Orogenic belt, Qinghai Province, China

Guoluolongwa Au deposit,a large prospective and typical orogenic Au deposit of Gouli Au metallogenic district,is located in the Kunzhong fault of East Kunlun Orogenic belt.In this paper,the geological characteristics of No.1 ore body group were investigated by field geological survey and detected under microscope systematically.Based on detailed observation,the ore types are divided into four groups: quartz vein type,altered rocks type(strongly silicification),phyllite type(weakly silicification) and oxidized type,the main of which are the quartz vein and altered rock types.The distribution,mineral assemblage,texture and structure,wall-rock alteration of the four types were systematically described,of which the REE contents were analyzed by inductively coupled plasma mass spectrometry(ICP-MS).The results show that all samples have light rare earth element(LREE) contents higher than heavy rare earth elements(HREE)(LREE/HREE = 4.52–16.82),whereas no obvious fractionation in the internal LREE and HREE.All samples have negative Eu anomaly(Eu/Eu * = 0.56–1.00) and positive Ce anomaly(Ce/Ce * = 0.95–1.61),indicating that the ore-forming fluids are Eu depleted and/or originated from a Eudepleted source.The mineralization formed under a reducing condition.Comparision of the ores,host rocks and Au-enriched pyrite,suggests that the REE in the ore-forming fluids is inherited form the host rocks,and the evolution is from quartz vein to altered rock,then to phyllite types.