Estimation of Dolomite Formation: Dolomite Precipitation and Dolomitization

Reactive-transport models are developed here that produce dolomite via two scenarios: primary dolomite (no CaCO3 dissolution involved) versus secondary dolomite (dolomitization, involving CaCO3 dissolution). Using the available dolomite precipitation rate kinetics, calculations suggest that tens of meters of thick dolomite deposits cannot form at near room temperature (25-35 degrees C) by inorganic precipitation mechanism, though this mechanism will provide dolomite aggregates that can act as the nuclei for dolomite crystallization during later dolomitization stage. Increase in supersaturation, Mg+2/Ca+2 ratio and CO3-2 on the formation of dolomite at near room temperature are subtle except for temperature. This study suggests that microbial mediation is needed for appreciable amount of primary dolomite formation. On the other hand, reactive-transport models depicting dolomitization (temperature range of 40 to 200 degrees C) predicts the formation of two adjacent moving coupled reaction zones (calcite dissolution and dolomite precipitation) with sharp dolomitization front, and generation of > 20% of secondary porosity. Due to elevated temperature of formation, dolomitization mechanism is efficient in converting existing calcite into dolomite at a much faster rate compared to primary dolomite formation.