深部韧性剪切变形与金矿成矿作用

DEEP DUCTILE SHEAR DEFORMATION AND GOLD METALLOGENESIS

金元素不对称的原子结构决定了它在剪切带中容易被活化， 活化条件除需要较高的氧逸度外， 温压条件与低绿片岩变质相的范围相近： Ｐ＝ ０２５～１０ Ｇ Ｐａ， Ｔ＝ ３５０～５００℃， 也与石英、白云石、方解石和云母等造岩矿物出现韧性形变的温压条件吻合。金矿质在韧性剪切带中与氧化硅和硫化物形成配合物在深部流体中沿着化学位梯度方向迁移和富集。岩石在强应力作用下产生屈服 （韧性形变）， 微观上表现为位错。位错处于高能态， 能自动发生动态重结晶形成亚晶粒和微裂隙， 使韧性剪切带具有可渗透性，有利于成矿流体的运移和萃取金矿质。剪切带由韧性到脆性的转化阶段， 常与退变质作用相伴随， 并发生钾化、硅化、碳酸盐化、黄铁矿化蚀变， 导致成矿流体中金配合物分解和金元素沉淀成矿。

The unsymmetric atomic configuration of gold determined that it is easy to mobilize in ductile shear zone. The conditions for gold mobilizing need not only high oxygen fugacity, but also the similar temperature pressure conditions of low green schist metamorphic facies ( P =0 25~1 0 GPa, T =350~500℃). T he mobilizing conditions also tally with the temperature pressure condition that ductile deformation appears in rock forming minerals, such as quartz, dolomite, calcite and mica etc. In ductile shear zone,the gold is migrated and enriched in deep fluid with silica and sulfide in forms of the complex driven by the chemical potential. When rock suffers from strong stress, it produces ductile deformation which microcosmically appears dislocation. The dislocation is in high energy environment, which can be automatically recrystallized to produce subgrains and micro fissures. Meanwhile, the ductile shear zone becomes permeable, which is favorable for mineralizing fluid to migrate and extrat gold matter from its source rock. When shear zone transforms from ductile to brittle, it always accompanies with retrograde metamorphism, as well as potassic, silicated, carbonated and pyritic alterations, causing the decomposition of Au complex and precipitation of Au in mineralizing fluid.