Thermodynamic Analysis of Secondary Minerals Stability in Altered Carbonatites of the Oldoinyo Lengai Volcano, Northern Tanzania

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1 Scopus citations

Abstract

Carbonatites from the Oldoinyo Lengai volcano, northern Tanzania, are unstable under normal atmospheric conditions. Owing to carbonatite interaction with water, the major minerals—gregoryite Na2(CO3), nyerereite Na2Ca(CO3)2, and sylvite KCl—are dissolved and replaced with 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 in Oldoinyo Lengai carbonatites are controlled by the pH of the pore solution, H2O and CO2 fugacity, and the ratio of Ca and Na activity in the Na2O–CaO–CO2–H2O system.

Original languageEnglish
Pages (from-to)584-591
Number of pages8
JournalGeology of Ore Deposits
Volume59
Issue number7
DOIs
StatePublished - 1 Dec 2017

Scopus subject areas

  • Geology
  • Geochemistry and Petrology

Keywords

  • calcite
  • carbonatite
  • gregoryite
  • low-temperature alteration
  • nyerereite
  • Oldoinyo Lengai volcano
  • pirssonite

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