太古宙绿岩带中铬铁矿床研究现状与展望

太古宙绿岩带中铬铁矿床不仅具有重要经济价值，而且是研究地球早期物质组成和地幔演化的重要对象。太古宙铬铁矿床形成时代久远，普遍经历了后期复杂的变质、变形和流体改造等一系列地质作用。相较于显生宙豆荚状铬铁矿和元古宙层状铬铁矿，对太古宙绿岩带内产出铬铁矿的研究还较为薄弱，尤其对铬铁矿体形成的地质背景和岩浆作用缺乏深入系统的研究。本文综述了格陵兰、印度、澳大利亚西部、加拿大以及津巴布韦等典型太古宙绿岩带中铬铁矿床的主要地质特征和研究现状，讨论了相关科学问题和研究展望。绿岩带中铬铁矿床主要产在古太古代-新太古代（3.3~2.7Ga）克拉通内的超基性岩石单元中，矿体常与蛇纹石化纯橄岩伴生。铬铁矿体产状复杂，既有层状和似层状，也有透镜状和不规则状，因此不能简单归于层状铬铁矿或豆荚状铬铁矿。铬铁矿岩以块状为主，其铬铁矿Cr^#相对较高（>60），属高铬型，Mg^#中等偏高（21~93）且与Cr^#呈负相关关系。研究认为，绿岩带中铬铁矿的成矿母岩浆来自深部亏损含水地幔分异所形成的科马提质岩浆，且受到了地壳物质混染。在开放的岩浆房内，含矿原始母岩浆与不断补给的科马提质岩浆相混合，并随着岩浆的重力分异和对流分层等作用形成堆晶状铬铁矿体。

A review and outlook on Archean greenstone belt-hosted chromite deposits

Archean greenstone belt-hosted chromite deposits are an important source of chromium and are also significant for understanding the characteristics and tectonic settings of the early Earth. Occurrences of chromitite have formed for a long time and have generally experienced metamorphism, deformation and fluid alteration. When compared with podiform chromitite and stratiform chromitite in more recent settings, there is a poor understanding and lack of systematic in-depth research for the Archean examples, especially the metallogenic and magmatic process. The main geological host rocks of typical Archean chromitites in Greenland, India, Australia, Canada, and Zimbabwe are described in this paper. Such chromitite deposits mainly formed in the Paleo- to Neoarchean (3.3~2.7Ga), and these ore bodies are either lentiform, stratiform or irregular and are generally hosted within serpentinized dunite. Therefore, it cannot be simply attributed to stratiform chromitite or podiform chromitite. The chrome-spinel of massive chromitite is characterized by having high Cr# (>60) values and medium-high Mg# value (21~93), which are negatively correlated. Such chrome-spinel contents are indicative of a parental magma of komatiitic affinity derived from high degrees of partial melting of a deep mantle reservoir, and subsequent modification by crustal contamination. Archean JP2]chromite deposits were emplaced within open magma chambers, where the primary parental magma mixed with continuously replenished komatiitic magma. This mixture underwent gravitational differentiation and convective layering within the magma chamber, leading to the formation of cumulate chromitite ore bodies.