Further discussion on the genesis of the podiform chromite deposits in the ophiolites—questioning about the rock/melt interaction metallogeny

The author has emphatically discussed the genesis of the podiform chromite deposits in the ophiolites and thus questions the widespread rock/melt interaction metallogeny. The mantle peridotites-bearing chromite deposits in the world also exhibit a vertical zoning of melting, with more basic material in the upper part and more acid material in the lower part, being opposite to vertical zoning of magmatic differentiation with more acid material in the upper part and more basic material in the lower part. The podiform chromite deposits are closely associated with the dunite or dunite-harzburgite complex belts in the upper part of melting profile. The podiform chromite deposits are products formed by highly partial melting and reconstitution of primary peridotites. The Cr-rich chromite deposits belong to PPG ophiolite series and form in island arc (or fore-arc basin) and Al-rich one are associated with PTG ophiolite series and form in MOR or(back-arc basin). A residue depleted mantle was left after the formation of Cr-rich podiform chromite deposit, which is needed to form the boninite. So, there is no genetic relationship between the chromte and boninite. The Al-rich podiform chromite deposits are products formed by re-equilibrium between the Cr-rich ore magma and basic melt and are not formed by interaction between the tholeiitic melt and peridotite. The occurrence of the UHP mineral inclusions in the chromite ores suggests a deeper mantle genesis for the podiform chromite deposits, but the boninite is segregated in the lower pressure (<10km). The podiform chromite deposits are rich in strong compatible elements IPGE (Os, Ir, Ru) alloys during partial melting, in contrast the boninites are rich in incompatible elements PPGE (Pt, Pd) surfide (arsenite) representing a later magmatic segregation. Obviously, there is no any genetic relationship between the boninite and Cr-rich podiform chromite deposit, and they are also controlled by island arc (or fore-arc) tectonic environment and thus only occur together spatially.