Diagrams with multiple metals in CHNOSZ
Jeffrey M. Dick
Abstract
CHNOSZ is an open-source R package that includes a thermodynamic database for thermodynamic calculations at 25 °C and higher temperatures and functions to make equilibrium chemical activity diagrams including Eh–pH diagrams and logf O2–pH diagrams. The main workflow supports the creation of basic diagrams where the reactions are balanced on a single element. Therefore, basic diagrams are limited to single-metal systems, but the ability to make diagrams for multiple metals is a common feature request. New functions have been added to the package to make diagrams for multiple metals. This paper describes the methods and demonstrates their use to reproduce published Eh–pH and chemical activity diagrams for oxide and sulfide minerals in two bimetallic systems (Fe–V–O–H and Cu–Fe–S–O–H). New logf O2–pH diagrams are presented to show dissolved species in the Cu–Fe–S–O–H–Cl system and the effects of Fe:Cu ratio on sulfide mineral assemblages. The functions greatly expand the thermodynamic systems that can be diagrammed in CHNOSZ and should be useful for researchers in different fields including hydrothermal geochemistry and materials science.