Abstract:

Carbonatite is a mantle-derived rock with minimal surface exposure. Carbonatite mantle metasomatism has received much attention, but the reaction between carbonate magma and the crust is little studied. Such reaction has been reported in China’s Caotan-Fengzhen regions, Germany’s Kaiserstuhl region, Russia’s Petyayan-Vara region, and Australia’s Nolans Bore deposit. The reaction is characterized by the formations of large quantities of iron-rich mica, pyroxene, sphene, hyalophane, and other silicate minerals, and disruptions to the C-O and Sr-Nd isotope systems. In the mantle, carbonatite magma reacts with peridotite to produce meta-exfoliated peridotite; in the middle and lower crust, such reaction produces antiskarn. The reaction between carbonatite magma and wall-rock can result in local Si enrichment, which encourages REE entry into apatite in the early magmatic stage and prevents REE mineralization. Carbonatite-silicate reactions in the deep crust are typically not exposed to the surface as shallow hydrothermal systems do under the same structural context, and reaction products are easily misidentified as skarn mineral assemblages. Therefore, it is critical to uncover the anti-skarn processes in the deep crust—particularly its associated mineralization, through high-temperature, high-pressure experimental research, along with re-evaluation of high-temperature skarn mineral assemblages whose sources of silicate fluids are unknown.

Key words: carbonatite, crustal metasomatism, metasomatic feature and mechanism, antiskarn, deep mineralization