广东河台金矿床矿物特征对成矿环境的制约

Metallogenic conditions of Hetai gold deposit in Guangdong Province, South China: Constraint from mineralogical characteristics

位于高要市境内的河台金矿床是目前广东省最大的金矿床,被普遍认为是韧性剪切带型金矿床。为了进一步认识金矿床的成矿环境,对采自河台矿区高村矿段的矿石进行了详细的研究,利用电子探针(EPMA)分析了矿石中毒砂、绿泥石和闪锌矿等矿物的成分。通过矿物温度计计算,毒砂的形成温度在330℃左右,绿泥石的形成温度集中在230~250℃之间,闪锌矿的形成温度在205~230℃之间,可能分别代表成矿早、中、晚期的温度;结合前人包裹体测试结果,推测河台金矿床成矿温度可能在205~250℃之间,属于中低温热液矿床。而糜棱岩的形成温度可能在300~500℃之间,明显高于金矿床的形成温度,因此,河台金矿床可能是动力变质期形成的糜棱岩带在热液期又发生脆性变形,并伴随含矿热液活动,最终导致成矿。在成矿过程中,绿泥石和闪锌矿是随着温度降低而相继连续产出的。在此过程中硫逸度也在不断降低,表现出比较宽泛的特征,lgf(S2)可能介于-20^-1,lgf(O2)可能介于-50^-30。

The Hetai gold deposit in Gaoyao area is the biggest gold deposit in Guangdong Province. Because the orebodies are hosted by ductile shear zones strictly, the deposit has been regarded as a ductile shear zone related gold deposit. In order to constrain the ore_forming conditions, the authors investigated mineral chemistry of the indicative ore and gangue minerals（ chlorite, sphalerite, arsenopyrite） from Gaocun ore block of the Hetai gold orefield by EMPA based on the observation of ores and thin sections. The calculated temperature of arsenopyrite is ca. 330℃,that of chlorite is ca. 250～230℃ and that of sphalerite is ca. 230～205℃, which correspond to the early, medium and late mineralization stage, respectively. Combined with the published homogeneous temperature of liquid inclusions, the ore_forming temperature should be ca. 205 ~ 250℃. This indicates that the Hetai gold deposit is amesothermal_epithermal gold deposit. However, the mylonitization temperature in the Hetai gold deposit is ca. 300~ 500℃, considerably higher than the ore_forming temperature. Therefore, the formation of the Hetai gold deposit was principally related to the hydrothermal fluid associated with the brittle deformation superimposed upon the shear zones. The crystallization of chlorite and sphalerite is consecutive with the temperature declining. At the same time, the sulfur fugacity lgf（ S2） is gradually reduced as well, showing a broad width ranging from-20 to-1.The oxygen fugacity lgf（ O2） ranges from-50 to-30.