Abstract:
Although calcite is a common vein-filling mineral in rocks, there has been little understanding of the kinetics of vein-filling that gives a quantitative estimation of the fluid volume and time needed for calcite vein formation in subsurface fracture systems. A new experimental system capable of simulating calcite precipitation in veins was used to determine the influences of flow velocity and initial solution saturation state on the quantitative precipitation pattern of calcite in synthetic veins. Results are in relatively good agreement with the model predictions. Use of a Mn2+ tracer indicated that even at low concentrations manganese can have a substantial effect on the morphology of the calcite precipitate. Our model predicts that an extremely large volume of fluid is required to produce calcite veins in nature; typically 105 to 106 for a fluid/calcite volume ratio for formation of thin short veins. The model also predicts the time necessary for vein filling is thousands to millions of years, and is highly variable depending on factors such as fluid saturation state, flow velocity, vein dimension, and the precipitation kinetics that can differ under subsurface conditions.