Alteration of Mineral Phases via Ceres Analogue Ammonium Chloride Brine

Abstract

The dwarf planet Ceres is rich in phyllosilicates and ammoniated ice. It is theorized that a brine layer exists beneath the crust, which may interact with surface minerals following mobilization. In this study, we investigate the effects of ammonium chloride (NH4Cl) brine on various geologic materials to expand our understanding of weathering and diagenetic alteration on Ceres and other salty bodies in our solar system. One set of experiments was conducted at hydrothermal conditions (350 K) with near saturated brine, while two more were conducted at room temperature (295 K) using near saturated and 10x diluted brine. Most samples provided no distinct alteration. Siderite partially dissolved and precipitated hematite. The majority of clay samples were found to be highly altered, producing changes in Raman spectra, XRD patterns, EDS data, and VNIR spectra. These changes were caused by the exchange of the interlayer cation for NH4+ from the brine, strongly evidenced by the movement of the basal (001) plane and other significant peaks in XRD. Saponite SapCA-1 did not experience a shift of the basal (001) plane but produced otherwise highly distinct alterations. Partial dissolution of phases and interlayer cation exchange may have significant effects on the resulting mineral assemblage. The release of these ions may also influence the evolution of primitive lifeforms if such organisms are present beneath the surface of Ceres.