岩浆系统演化对巨型斑岩铜矿形成的制约：以智利Chuquicamata矿为例

The formation of porphyry copper deposits (PCDs) has a close relationship with magmatic processes, which is generally associated with high Sr/Y, hydrous, oxidized magmas at shallow crustal levels. These shallow porphyry intrusions are believed to originate from larger magmatic systems at depths, which are recognized as the main source of hydrothermal fluids, sulfur and metals. However, the genetic links between the genesis of PCDs and magmatic evolution are not yet well understood due to the lack of economic PCDs in which the deeper protions of the magmatic systems are exposed. The proposal is based on the excellent exposures of the magmatic complexes, which represent both the deep magmatic systems and the shallow mineralized porphyries, in the second world-calss PCD-the Chuquicamata deposit of northern Chile. We plan to conduct systematic geochronogical, whole-rock geochemical study and detailed textural and compositional investigations of hornblende and plagioclase to provide constraints on the lifetime and magma source of the magmatic systems and to reconstruct the evolution of the intensive parameters (P-T-H2O-fO2) as well as the behavior of the ore-forming metals. Ultimately, we aim to have a better understanding of the impact of magmatic evolution on the genesis of the porphyry copper mineralization.

斑岩铜矿的形成与岩浆作用密切相关，通常与高Sr/Y、高含水量、高氧逸度的浅成斑岩体共生，而这些小型斑岩体被认为来源于深部的大型岩浆房，该岩浆房同时提供成矿所需的热液流体、硫和金属元素。现有研究成果多侧重成矿斑岩体的研究，而对深部岩浆房，因鲜有出露，研究较匮乏，使得目前对岩浆系统演化和斑岩铜矿形成的关系尚未得到很好的理解。本项目以智利北部的全球第二大斑岩铜矿Chuquicamata矿为解剖对象，该矿独具特色，同时出露代表深部岩浆系统和浅部成矿斑岩的岩浆演化序列，拟对不同岩石单元开展系统的同位素年代学、岩石地球化学，以及角闪石和斜长石的精细结构和元素地球化学分析，限定该岩浆演化序列的岩浆活动时限和岩浆源区特征，反演岩浆演化过程中岩浆性质(P-T-H2O-fO2)的变化和成矿金属元素的分配行为，从而探讨岩浆系统演化对巨型斑岩铜矿形成的控制作用。

斑岩铜矿是一类非常重要的岩浆热液矿床，提供了全球约75%的铜，其形成与高Sr/Y、富水、高氧逸度的浅成斑岩体密切相关，而浅成斑岩体来源于深部的大型岩浆房。因此，理解浅成斑岩体的岩浆起源和演化过程对认识斑岩铜矿的形成机制具有重要的科学意义。本项目通过对智利北部的Chuquicamata超大型斑岩铜矿同时出露的成矿前深部岩浆系统和浅部成矿斑岩系统通过开展详细的岩石学、年代学、矿物学和地球化学研究，准确限定了成矿母岩浆的活动时限和岩浆源区特征，并探讨了岩浆性质的变化。锆石U-Pb年代学研究显示与成矿相关的岩浆演化序列的岩浆活动时限长达12个百万年，表现出岩浆活动的长期性和成矿作用的瞬时性。该岩浆演化序列具有典型的弧岩浆岩的地球化学特征，且显示非常一致的Sr-Nd同位素和锆石Hf-O同位素，限定其岩浆源区为受俯冲物质交代的地幔楔。锆石微量元素特征显示随时间演化该岩浆演化序列经历了角闪石、榍石和磷灰石等矿物的分离结晶以及氧逸度的逐渐升高，表明浅成斑岩体的高氧逸度是岩浆结晶分异的结果。本项目提出长期的岩浆演化和充足的岩浆体量是巨型斑岩铜矿形成的先决条件。