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 similar to 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 similar to 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.