岩浆成矿系统的尺度效应

小岩体成大矿理论强调了岩浆侵入体的几何尺度与内生金属成矿作用的有机联系,但这种联系的实质尚理解甚少。简要分析了岩浆成矿系统的基本问题,聚焦于侵入体几何尺度与几种关键控矿因素的内在联系。利用前人提出的固相线前锋迁移距离与冷却时间之间的函数关系估算了岩浆侵入体固结的时间尺度,发现小岩体的存活时间尺度与超大型矿床的形成时间尺度一致。基于斯托克定律的估算,含有暗色微粒包体的小岩体以岩浆快速上升为特征,符合流体中成矿金属溶解度与压力(P)、温度(T)正相关的实验结果。分析了岩浆产量与源区减压速率和所产生岩浆中挥发分含量之间的关系,提出大规模岩浆活动之后岩浆产量必然逐渐减少,因而流体-熔体比值逐渐增加。据此认为,超大型矿床可形成于紧接着大规模岩浆活动之后,并以长英质岩浆成矿系统为例将其称为岩基后成矿作用。因此,岩浆成矿系统的尺度效应是一种重要的地质效应,尺度效应分析支持小岩体成大矿理论。

Scale Effects of the Magma-related Metallogenic Systems

The theory of large orebodies hosted in small intrusion emphasizes the relation between the geometrical scale of a magmatic intrusion and the efficiency of endogenic metallic mineralization.However,the essence of this relation is poorly understood till now.The basic problems related to the magma metallogenic system were briefly analyzed,and the intrinsic relations between the geometrical scale of an intrusion and several key factors controlling mineralization were focused.The published functional relation between the cooling duration and the migrating distance of solidus front in a magmatic intrusion was used to estimate the solidification time-scale of a magmatic intrusion.It is found that the living time-scale of the small intrusion is consistent with the time-scale required for forming a super-giant deposit.Based on Stock＇s Law,the simulation suggests that the small intrusions containing melano-microgranular enclaves are characterized by rapid ascending of magma,which is consistent with the experimental observations showing positive relation of the fluid solubility of ore-forming metal to its pressure （P）and temperature （T）.The relations of the magma production to the source decompression rate and the volatile concentration in the produced magma were analyzed.Accordingly,it is proposed＆amp;nbsp;that the magma production followed a huge volume of magmatism must decrease,and hence the ratio of fluid and melt increases gradually.Therefore,it is believed that a super-giant deposit can form immediately behind the extensive magmatism,and such a metallogenic process can be called as the post-batholith metallogenesis,taking the felsic magma metallogenic system as an example. In general,it is concluded that the scale effect of the magma metallogenic system is an important geological effect,and the analysis of scale effect supports the theory of giant deposit mineralized by the small intrusion.