Fluorapatite solubility in H2O and H2O–NaCl at 700 to 900 °C and 0.7 to 2.0 GPa

摘要: Abstract The solubility of Durango fluorapatite was measured in H 2 O and O–NaCl at 700–900 °C 0.7–2.0 GPa a piston-cylinder apparatus. Solubility determined by weight loss using double-capsule method. At all conditions, dissolves incongruently to monazite + fluid, but residual monazite crystals were below weighing detection limits 0.6 μg. concentration dissolved pure is low investigated conditions (56 ± 8 288 ± 8 ppm weight), increases with temperature ( T ) pressure P ). data are well described the equation log c ap ° = − 3.56 + .00241  + 9.17 ρ , where ° apatite (in ppm), Kelvin, density g cm − 3 . Fluorapatite also fluids range Results indicate strong increase rising NaCl mole fraction X near halite saturation. fit  =  ° +  Ba 1/2 activity calculated from an ideal mixing model for O–NaCl, B  = (4.4 + 1.1 4 )exp(0.0070 ), GPa, Kelvin. results differ previous work that newly solubilities ≥ 10 times lower comparable constant show positive correlation discrepancy attributed unrecognized growth new run earlier study. Compared fluorite, calcite anhydrite, significantly O–NaCl; however, enhancement relative similar anhydrite much greater than fluorite. decreases undetectable requires significant light rare-earth elements (LREE), likely as chloride complexes, indicates metasomatic interaction brines apatite-bearing rocks high metamorphic grades can mobilize substantial LREE.