粤北大宝山矿区中南部斑岩型铜矿成矿热液特征

Characteristics of Ore-forming Hydrothermal Fluid of Porphyry Copper Deposit in South-central Dabaoshan Deposit,Northern Guangdong Province

粤北大宝山矿床是南岭成矿带独具特色的铜多金属矿床之一,矿区中南部斑岩型铜矿的找矿突破表明南岭成矿带具有斑岩型铜矿的成矿条件。英安斑岩中硫化物石英脉类型有A脉、B脉、D脉、H脉、闪锌矿石英脉(S脉)和含少量硫化物的石英脉(Q脉)。为解析大宝山斑岩型铜矿的热液形成过程,开展了流体包裹体、温度测试以及蚀变围岩地球化学组分平衡计算等研究。结果表明,这些脉中发育的流体包裹体以富液相为主,少量为富气相,个别包裹体中含有子晶。包裹体长为3~25μm,宽为2~14μm,长宽比多数为1.0~1.5。斑岩型铜矿成矿初始热液是富含K^(+)、Cu^(2+)、Zn^(2+)、Pb^(2+)、SiO_(4)^(2-)的氧化性流体,其进入容矿空间时为高温(平均371℃)、低盐(平均7.55%NaCl_(eqv))、低密度(平均0.67 g/cm^(3))流体。该流体与矿区辉钼矿成矿流体特征迥异,这表明其与花岗闪长斑岩之间没有成因联系,而与英安斑岩相关。水岩反应是粤北大宝山矿区中南部斑岩型铜矿热液的主要沉淀机制,而辉钼矿的成矿作用受水岩反应和流体混合双重机制的影响。

The Dabaoshan deposit in northern Guangdong is a unique polymetallic deposit in the Nanling metallogenic belt.It indicates that there are metallogenic conditions for porphyry copper deposits while there made breakthrough for porphyry copper prospecting in the south-central Dabaoshan deposit.The sulfide quartz veinlets in dacite porphyry are A vein,B vein,D vein,H vein,sphalerite quartz vein(S vein)and quartz vein(Q vein)containing a small amount of sulfide.In order to analyze the hydrothermal process of Dabaoshan porphyry copper deposit,fluid inclusion study,temperature measurement and geochemical composition balance calculation of altered wall rocks were carried out.The results show that the fluid inclusions are two-phase inclusions with mainly of liquid in the last five kinds of veins,and the scales of inclusions are 3~25μm in length and 2~14μm in width.The ratio of length to width is usually 1.0~1.5.Porphyry copper ore forming hydrothermal fluid is an oxidized and enriches in K^(+),Cu^(2+),Zn^(2+),Pb^(2+)and SiO_(4)^(2-).When the fluid moves into the ore forming space,it is of high temperature(371℃in average),low salt(7.55%NaCl_(eqv)in average)and low density(0.67 g/cm^(3)in average).The characteristics of ore forming hydrothermal fluids are quite different from that of molybdenite mineralization.It indicates that the porphyry copper deposit is not generated from granodiorite porphyry,but from the dacite porphyry.The main precipitation mechanism of porphyry copper fluids is water-rock reaction in the south-central Dabaoshan deposit in northern Guangdong province,while the mineralization of molybdenite are affected by the double mechanisms of water-rock reaction and fluid mixing.