A model for the formation of carbonatite-phoscorite assemblages based on the compositional variations of mica and apatite from the Palabora Carbonatite Complex, South Africa

Summary First results in the phlogopite + magnesite (KMASH-CO2) system demonstrate that a potassiumbearing fluid will be the metasomatic agent at sub-continental-lithospheric-mantle conditions with a continental geotherm of 40 mWm -2 . In this case, phlogopite can be stable to a depth of 200 km in the presence of carbonate, and will coexist with potassic fluids. Assuming a hotter geotherm of 44 mWm -2 , these fluids can be present to a depth of about 180 km. Beyond this depth, at the base of a thick sub-continental lithospheric mantle, a hydrous, potassium- and CO2-rich silicate melt would be the metasomatic agent. In this system, garnet is present above solidus as a residual phase, which implies that a K-CO2-H2O-enriched metasomatic fluid or melt could react with garnet peridotite to form phlogopite.

Phlogopite

Metasomatism

Peridotite

Solidus

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Citations (1)

Implications of experimental petrology to the evolution of ultrapotassic rocks

Lithos (1992)

A. D. Edgar D. Vukadinovic

Phlogopite

Metasomatism

Amphibole

10.1016/0024-4937(92)90007-l

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Citations (48)

Inside front cover (Editorial Board)

Journal of Asian Earth Sciences (2004)

Phlogopite

Carbonatite

Metasomatism

10.1016/s1367-9120(04)00199-3

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Citations (0)

Major- and trace-element compositional variation of phlogopite from kimberlites and carbonatites as a petrogenetic indicator

Lithos (2009)

Ekaterina P. Reguir Anton R. Chakhmouradian N. M. Halden V. G. Malkovets Panseok Yang

Phlogopite

Carbonatite

Trace element

Phenocryst

10.1016/j.lithos.2009.05.023

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Citations (80)

The origin and composition of carbonatite-derived carbonate-bearing fluorapatite deposits

Mineralium Deposita (2020)

Sam Broom-Fendley Pete R. Siegfried Frances Wall Mary O’Neill Richard A. Brooker

Abstract Carbonate-bearing fluorapatite rocks occur at over 30 globally distributed carbonatite complexes and represent a substantial potential supply of phosphorus for the fertiliser industry. However, the process(es) involved in forming carbonate-bearing fluorapatite at some carbonatites remain equivocal, with both hydrothermal and weathering mechanisms inferred. In this contribution, we compare the paragenesis and trace element contents of carbonate-bearing fluorapatite rocks from the Kovdor, Sokli, Bukusu, Catalão I and Glenover carbonatites in order to further understand their origin, as well as to comment upon the concentration of elements that may be deleterious to fertiliser production. The paragenesis of apatite from each deposit is broadly equivalent, comprising residual magmatic grains overgrown by several different stages of carbonate-bearing fluorapatite. The first forms epitactic overgrowths on residual magmatic grains, followed by the formation of massive apatite which, in turn, is cross-cut by late euhedral and colloform apatite generations. Compositionally, the paragenetic sequence corresponds to a substantial decrease in the concentration of rare earth elements (REE), Sr, Na and Th, with an increase in U and Cd. The carbonate-bearing fluorapatite exhibits a negative Ce anomaly, attributed to oxic conditions in a surficial environment and, in combination with the textural and compositional commonality, supports a weathering origin for these rocks. Carbonate-bearing fluorapatite has Th contents which are several orders of magnitude lower than magmatic apatite grains, potentially making such apatite a more environmentally attractive feedstock for the fertiliser industry. Uranium and cadmium contents are higher in carbonate-bearing fluorapatite than magmatic carbonatite apatite, but are much lower than most marine phosphorites.

Carbonatite

Fluorapatite

Paragenesis

10.1007/s00126-020-01010-7

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Citations (28)

Metasomatic processes in the lithospheric mantle beneath the V. Grib kimberlite pipe (Arkhangelsk diamondiferous province, Russia)

Russian Geology and Geophysics (2015)

Elena Shchukina A. M. Agashev S. I. Kostrovitsky N. P. Pokhilenko

Phlogopite

Metasomatism

Peridotite