Semi-empirically derived petrophysical and thermodynamical coefficients of permselective shales—Implications on ore mineralization

Phenomenological coefficients of shale–electrolyte systems may offer a glimpse into probable matrix-permeability and solute-exclusionary relationships. Shales from unexposed Upper Cretaceous Period Mancos Shale and from Permian Period Abo Formation were cut into thin wafers, placed in custom built osmometers and a chemical potential applied across them giving rise to induced osmotic flow. This in turn spawned matrix unique constants namely mechanical filtration coefficient LP (m3 N−1 s−1), diffusional mobility per unit osmotic pressure LPD (m3 N−1 s−1), osmotic flow coefficient; LD (m3 N−1 s−1), reflection coefficient σ (dimensionless) at zero gradients of temperature and hydrostatic pressure. Considering intrinsic relationships between these constants where image and LPD = −σLP, we have ascertained that the bentonitic fossiliferous Mancos shale had a lower LP and a higher σ compared to the kaolinitic and siliceous shale from Abo Formation indicating a higher degree of compaction post-diagenesis (lower porosity) and higher filtration efficiency. Mechanistic processes involved in solute transport and matrix morphology indicate key multi-scale transformations, ionic- and atomic-exchange competitions on high energy sites like cation-exchange sites, isomorphic substitution at argillaceous mineral edges, atomic-clipping within basal spacing, preferential pathway migration, dead-end pores that give rise to localized solute exclusionary processes and solute attenuation giving rise to anomalous osmotic gradients.