永平铜矿海底火山热液沉积成矿作用的依据

EVIDENCES OF SUBMARINE VOLCANIC HYDROTHERMAL SEDIMENTMINERALIZATION YN YONGPING COPPER DEPOSIT

永平铜矿产于钱塘江～信江拗陷带中 ,主要受中石炭统叶家湾组沉积 -火山沉积岩所控制。矿体主要呈层状 ,与围岩呈整合接触 ,少数呈脉状 ,并穿切层状矿体。层状矿体见胶状、草莓状结构 ,层状、层纹状和条纹状构造 ;原生层状矿体的包裹体温度较低 ,为 10 0℃～ 2 17℃ ,改造矿体包裹体温度较高 ,为 2 0 0℃～ 340℃ ;层状矿体中的Co/Ni比值较小 ,为 1.38～ 1.4 6 ,改造矿体较大 ,为 2 .76～ - 32 .4 6 ;层状矿体的σ3 4 S‰为 - 0 .3～ +2 1.6 ,改造矿体的σ3 4 S‰为 +0 .4～ +4.3;铅同位素主要属正常铅 ,其模式年龄明显分为三个区间 ,分别对应于基底、原生层状矿体和印支 -燕山期岩浆活动的年龄 ,氢氧同位素与沉积 -火山热液沉积矿床类似。各种特征说明永平铜矿是沉积-火山热液沉积经后期构造、岩浆改造和叠加矿化的块状硫化物矿床。同类矿床的找矿方向是沿华力西断裂拗陷带并循石炭系地层找矿 ,同生断层、火山岩、硅质岩、层状矽卡岩、花岗岩等是重要的找矿标志。

Yongping copper deposit occurs in the Yejiaman Formation,middle-Carboniferous Period. It is controlled by Qiantang River-Xin River Variscan facture depression belt. It has been ascertained that there a lot of marine volcanic rock in ore area. They occur in the formations and the bedded ores as many continuous bed that show the marine volcanism lasted a long time and with cyclic activity. The primary ores have typical bedded, stripped, laminated colloform and frambidal fabric. Their forming temperature is lower, 100～217℃, Co/Ni is 1.38～1.46, σ 34 S‰ is -0.3 ～+21.6. The reformed ores have massive and granular fabric, Their forming temperature is higher,200～340℃, Co/Ni is 2.96 ～32.46, σ 34 S‰ is +0.4～ +4.3. The model ages of Pb isotope can been divided into three parts that they respectively match ages of based rocks, bedded ores and magmatic rocks. All characteristics show that Yongping copper deposit is a submarine volcanic hydrothermal sedimentary massive sulfide deposit and reformed by the late tectonism and magmatic intrusion. It is a major principle looking for similar mineral deposit to find along Variscan facture depression belt and Carboniferous formation. The most important clues are ancient deep fracture, narrow and deep basin, marine volcanic rocks, bedded skarn, iron hot and unusual characters in geophysics and geochemistry.