甘肃公婆泉铜矿化集中区火山岩的地球化学特征

Geochemical characteristics in Gongpoquan copper mineralized province,Gansu

公婆泉铜矿化集中区产出中性—基性和中酸性两大类型火山岩.前者稀土元素总量低,轻度富集轻稀土,弱铕亏损,轻、重稀土分馏均不明显,亲石元素的强不相容元素及Ce,Sm富集,而Nb,Ta亏损,Th/Yb,Hf/Th,La/Ta,Ti/Zr和K 分别为0 7～1 4,1 3～1 6,33～50,34～83和14～20;后者稀土元素轻稀土富集,弱—强铕亏损,轻稀土分馏较明显而重稀土分馏不明显,强不相容元素富集,而Nb,P,Ti等亏损,Ti/Zr,Hf/Nb和K 值分别为38～50,1 1～2 5和4 5～26.它们属于岛弧型钙碱性玄武岩—安山岩—流纹岩产出的构造环境,由地幔楔形源区玄武岩浆结晶分异演化形成.各类火山岩特别是钾质中酸性火山岩中成矿元素Cu及其主要伴生元素Au,Ag,Pb,Zn和As等富集,说明其受到了成岩后火山或次火山热液的叠加作用.

There are two types of rock series of neutralbasic and neutralacidic volcanic rock in Gongpoquan copper areas.The neutralacidic volcanic rocks are divided into three subtypes of sodal,nomal and kalic volcanic rock. In the neutralbasic volcanic rocks, the rareearth elements are characterized by lower gross,little rich in light rareearth elements,while light loss Eu,near plainness distribute curve and light and heavy rareearth elements are all not evident to fractionation.The lithophile elements are characterized by in rich strong not consistent elements of Ce,Sm but loss Nb,Ta at cobweb diagram, and Th/Yb,Hf/Th,La/Ta,Ti/Zr and K* are separately 07～14,13～16,33～50,34～83 and 14～20. In the neutralacidic volcanic rocks the rareearth elements are characterized by rich light rareearth, light-strong loss Eu, right incline distribute curve,and light rareearth elements are evident but heavy rareearth elements not evident to fractionation.The lithophile elements are characterized by rich strong not consistent elements(except Sr) but loss Nb,P,Ti at cobweb diagram,and Ti/Zr,Hf/Nb and K* are separately 38～50,11～25?45～26.The formation of two types of volcanic rock in this province may be considered to be a result of crystallzationdifferentiation and evolution for basaltmagma which comes from mantle cuneiform section and is regarded as an island curve construction circumstance producing calcalkaline basaltandesiteliparite.The distribution pattern of REE and the cobweb diagram of lithophile elements of kalic neutralacidic volcanic rock are very similar to those of hypodaciteporphyry and granodioriteporphyry.All volcanic rocks,especially kalic neutralacidic volcanic rock,show an obviously rich in metallogenetic element of Cu and associated Au,Ag,Pb,Zn and As etc. as compared with sedimentaryvolcano series of regional Silurian system.Their contents are characteristic of leaning lognormal or bimodal probability distribution.This explaines that the volcanic rocks get these elements from volcanic or subvolcanic hydrothermal superposition after they have been formed.