黔东八克金矿毒砂标型特征研究

Typomorphic Characteristics of Arsenopyrite in the Bake Gold Deposit,Eastern Guizhou Province

黔东八克金矿床以金高度富集矿体和围岩中广泛出现毒砂而与该区其他金矿有明显区别。以成因矿物学和找矿矿物学的理论和方法为指导,在前人对该矿床的地质背景、成矿条件、矿床地球化学等方面进行分析的基础上,利用现代测试技术和手段对该矿区中产出的毒砂进行了标型特征研究,从另一个角度取得了矿床成因方面的重要信息。研究表明,矿体含金毒砂粒度小,结晶程度差,晶胞参数接近理论值,热电性为N导型且热电系数均值为-195.6μV/℃,明显低于毒砂热电系数均值在近矿围岩中的-185.1μV/℃和在远矿围岩中的-174.6μV/℃。化学成分中S/As大于1,Fe/(As+S)小于0.5。电子探针形貌观察发现其颗粒较为破碎,裂隙发育,并有伴生矿物方铅矿填充。稀土元素和微量元素研究结果表明,矿体内毒砂REE含量明显低于围岩中毒砂的REE含量,铕呈现强烈的负异常。成矿流体中富集亲硫元素和LREE,亏损HFSE,为具有弱还原性的富C l型体系。通过对Y/Ho、Zr/H f、Nb/Ta和Co/N i比值的研究,推断八克金矿是一种岩浆热液型的中温矿床。

The Bake gold deposit is characterized by high richness in gold in ore body and widely distributed arsenopyrite in surrounding rocks,which make a clear distinction with other gold deposits of this area.Based on the analysis of the geological background,regional geological conditions of mineralization,ore-forming mechanism,by applying theories and methods of minerageny and prospecting mineralogy,using the modern testing technology,the typomorphic characteristics of arsenpyrite in the Bake gold deposit were studied in this paper,achieving important information on the genesis of ore deposits from the view of another point.The results show that gold-bearing arsenopyrite in ore bodies have the features of small size,poor crystallinity,unit cell parameters close to the theoretical value,N-type thermoelectricity,and the mean value of-195.6 μV/℃ for pyroelectric coefficient which is significantly lower than that of arsenopyrites adjacent to the surrounding rocks （-185.1μV/℃） and that far away from the surrounding rocks（-174.6μV/℃）.For the chemical compositions,S/As is more than 1,and Fe /（As＋S） is less than 0.5.From the morphology by electron probe observation,arsenopyrite particles are relatively broken,fractures develop,and galenas are filling being associated minerals.The results of rare earth elements and trace elements indicate that,REE contents in arsenopyrite of ore body are obviously lower than those of surrounding rock,and show strong Eu negative anomaly.Ore forming fluids are rich in chalcophile elements and LREEs,lose HFSEs,belong to a fluid system with weak deoxidation and rich Cl.Through the study on Y/Ho,Zr/Hf,Nb/Ta and Co/Ni ratio,Bake gold deposit is inferred to be a magmatic hydrothermal type deposit with medium temperature.