Experimental study of anisotropy of quartz dissolution and its role in fluid migration in rocks

Abstract

Quartz dissolution in hydrothermal-metasomatic processes is common feature in magmatic and metamorphic quartz rich rocks. This experimental work aims to compare the dissolution of individual quartz faces and to clarify the role of mechanical defects in quartz grain dissolution. Two types of experiments were made to define the dissolution anisotropy: hydrothermal experiments (quartz-distilled water) and chemical dissolution (quartz - 40 % hydrofluoric acid). Hydrothermal experiments using various types of quartz samples as well as chemical dissolution of quartz faces show that quartz dissolution is an anisotropic process. The solubility of rhombs is higher than that of prism faces. At lower temperatures the separated etch pits develop and with increasing temperature the etch pits start to link and the continuous striations (prisms) or overlapping arrows (rhombs) are observed. Such a surface structure may facilitate fluid migration through a solid rock. An experiment using a mechanically disrupted surface of the quartz crystal shows the decisive role of this defect on the dissolution. Fluid migration through rocks can then be strongly influenced for instance by brittle deformation, to which quartz with no cleavage is easily susceptible. Such defects additionally enhance fluid movement through rocks, which plays a decisive role during hydrothermal-metasomatic quartz dissolution.