新疆包古图地区斑岩型铜矿化特征和成矿元素迁移规律初探

Mineralization and elements migration characteristics of porphyry copper deposits in Baogutu area,Xinjiang

新疆西准噶尔包古图地区斑岩型铜矿化发育,蚀变矿化特征随岩体不同存在显著差异。文章通过岩石学、矿相学和微量元素地球化学的方法,重点研究了Ⅲ号和Ⅴ号岩体的矿化特征和成矿元素迁移规律。结果表明:Ⅲ号岩体矿化中等,以黄铁矿、磁黄铁矿和黄铜矿为主,呈浸染状,硫化物脉少见;Ⅴ号岩体内部及其与围岩接触带产出大型铜矿床,金属矿物主要有黄铁矿、黄铜矿和辉钼矿,呈浸染状和细脉-网脉状分布。Ⅲ号岩体角闪石英闪长岩形成于岩浆-热液过渡阶段,与石英(花岗)闪长岩对比显示,挥发分出溶过程中,Cs、Rb、Ba、Th、U迁移进入挥发相,稀土元素稳定未迁移,Cu、Bi显著富集,Mo和Sb被流体迁移带走,形成热液矿化。Ⅴ号岩体钾化和硅化样品代表了不同的流体作用阶段,与未蚀变样品对比显示,在钾化阶段Nb、Ta、Zr、Hf性质稳定,轻稀土元素发生显著迁移,在硅化阶段轻稀土元素富集;重稀土元素在岩浆-热液演化过程保持稳定。Cu、Mo和Bi在钾化作用阶段富集成矿,Zn和Sb则主要在晚期石英脉中富集。

Porphyry copper deposits are well developed in Baogutu area, west Junggar, Xinjiang. Different intrusions show remarkable difference in alteration and mineralization features. The authors studied emphatically the min- eralization and ore-forming elements migration in intrusive body Ⅲ and V by means of petrology, ore mi- croscopy and trace element geochemistry. Intrusion Ⅲ has experienced a medium degree of mineralization, with plenty of disseminated pyrite, pyrrhotite and chalcopyrite and minor sulfide veins. Intrusion Ⅴ has large-size porphyry copper deposits within the rock body or along its contact zone with wall rocks, containing plenty of chalcopyrite, pyrite and molybdenite, with disseminated and veinlet structure. Amphibole-quartz diorite from in-trusion Ⅲ crystallized in the transition process from magma to hydrothermal solution, during which Cs, Rb, Ba, Th and U migrated into volatiles, REE was immobile, Cu and Bi were obviously concentrated, and Mo and Sb moved away with the fluid, producing hydrothermal mineralization. A comparative study of potassic altered samples, silicified samples and fresh samples from intrusion V indicates that Nb, Ta, Zr, Hf remained immobile during the potassic alteration while LREE moved until silicification. HREE remained stable during the whole magmatic-hydrothermal process. Cu, Mo and Bi precipitated during potassic alteration, whereas Zn and Sb were concentrated in the late stage quartz veins.