山东邹平碑楼斑岩铜矿床流体包裹体及H、O、S、Pb同位素研究

Fluid Inclusion and H,O,S,and Pb Isotope Studies on Beilou Porphyry Copper Deposit in Zouping County,Shandong Province,China

碑楼铜矿床矿化石英脉中流体包裹体均一温度介于158-385℃之间,均值为270℃;盐度介于2.74%-62.51%(NaCl)之间,均值为15.2%(NaCl);均一温度峰值分别为210-240℃和270-300℃,盐度峰值分别为5%-10%(NaCl)和55%-60%(NaCl)。成矿流体在250-380℃区间发生沸腾作用,分离出了富液相和富气相的中一高温低盐度的两相流体和含子晶的中一高温高盐度的三相流体;在250℃左右时,高盐度的三相流体基本消失,成矿流体逐渐均一成以富液相为主的中一低温低盐度流体。流体的气体组分主要是H2O,个别包裹体的气相中含有少量的CO2。矿化石英脉中的δ18OH2O介于1.26‰-7.24‰之间,均值为4.63‰;δD介于-89‰--69‰之间,均值为-76.67‰,表明碑楼铜矿床的成矿流体主要来源于岩浆,后期混入了大气降水。矿石矿物中黄铁矿的δ34S介于-2.8‰～-1.3‰之间,均值为-1.75‰;黄铜矿的δ34S介于1.02‰～2.12‰之间,均值为1.46‰。矿石矿物的206Pb/204Pb介于18.295-18.402之间,均值为18.349;207Pb/204Pb介于15.555-15.573之间,均值为15.564;208Pb/204Pb介于38.215-38.331之间,均值为38.273;说明矿石中的硫、铅可能主要来自于深源,后期受到上地壳物质和大气降水的混染。以上研究证明,碑楼铜矿床属于中一高温浅成斑岩型铜矿床。

On the basis of field geological investigation, the authors discuss the genesis of Beilou copper deposit with the methods of fluid geochemistry and isotopic geochemistry. The homogenization temperature of primary fluid inclusions, in the mineralized quartz veins of Beilou copper deposit, ranges from 158℃ to 385 ℃ with an average of 270 ℃, while their salinity ranges from 2.74% to 62.51% NaC1 with an average value of 15.2% NaCI. Peak homogenization temperatures are 210 - 240 ℃ and 270 - 300 ℃, with the peak salinity of 5% - 10% and 55% - 60% NaC1, respectively. Ore-forming fluid boiling occurred at 250 ℃ to 380 ℃, resulting the formation of three-phase fluid of liquid-rich and gaseous-rich fluid at medium-high temperature and low salinity, containing daughter minerals with medium-high temperature and high salinity. At 250℃, the high salinity three-phase fluid disappeared, and ore-forming fluid changed into liquid-rich fluid at medium-low temperature and low salinity. Raman analysis of the fluid inclusions indicates that, in the gaseous phase, water vapor is dominant with small amount of CO2. The 818OH20 and 5D values of quartz range from 1.26‰ to 7.24‰ （average value being 4.63‰） and from -89‰ to -69%0 （average value being -76.67‰）, respectively, implicating that the ore-forming fluids are mainly derived from magma and mixed with meteoric water. Values of 834S in pyrite and chalcopyrite range from -2.8%0 to -1.3‰ （average value being -1.75‰） and from 1.02‰ to 2.12‰ （average value being 1.46‰）, respectively. Values of 206pb/204npb range from 18.295 to 18.402 with an average of 18.349; 207pb/204pb from 15.555 to 15.573 with an average of 15.564; 208pb/204pb from 38.215 to 38.331 with an average of 38.273. This indicates that sulfur and lead are originated from lower crust or mantle and are influenced by the mixture of the upper crust rocks and meteoric water in the late ore-forming stage. This research confirms that this Beiku copper deposit is a shallow medium-high temperature porphyritic copper deposit.