Thermodynamic analysis of the secondary minerals' stability in altered carbonatites of the Gldoinyo Lengai volcano, Northern Tanzania

Perova E. N., Zaitsev A. N.

Zapiski RMO (Proceedings of the Russian Mineralogical Society). 2016. V. 145. N 3. P. 1-13

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Language: Russian


Carbonatites from the Oldoinyo Lengai volcano, northern Tanzania, are unstable under normal atmospheric conditions. During carbonatite interaction with water the major minerals gregoryite Na2(CO3), nyerereite Na2Ca(CO3)2 and sylvite KCl are dissolved and replaced by secondary low-temperature minerals thermonatrite Na2(CO3)·H2O, trona Na3(CO3)(HCO3)·2H2O, nahcolite Na(HCO3), pirssonite Na2Ca(CO3)2·2H2O, calcite Ca(CO3) and shortite Na2Ca2(CO3)3. Thermodynamic calculations show that the formation of secondary minerals within Oldoinyo Lengai carbonatites are controlled by pH of pore solution, H2O and CO2 fugacity and the ratio of Ca and Na activities in the system Na2O—CaO—CO2—H2O.

Key words: gregoryite, nyerereite, pirssonite, calcite, carbonatites, low-temperature alteration, Oldoinyo Lengai volcano.