SULFIDE TEXTURES AND ORE GRADES IN MINERALIZED CARBONATES DEPEND ON PÉCLET AND DAMKÖHLER NUMBERS

Abstract

Clastic-dominated (CD-type) deposits contain a significant proportion of the global resources of Zn, Pb, and Ag, and include some of the largest deposits that formed through subseafloor replacement. Mineralization textures in these deposits can be highly variable, and the physical properties that control these textures are poorly defined. The style of dissolution in carbonate units can be described by dimensionless parameters (Péclet and Damköhler numbers) that represent fundamental properties of reacting flow systems. Using reaction transport modeling of a CD-type deposit, this work investigates the relationships between Péclet and Damköhler numbers with textures and ore grades. In 1-D and 2-D simulations, a metalliferous brine was reacted with a host rock at variable rates of fluid flow and dolomite dissolution, resulting in different mineralization textures depending on the spatial relationship of the inflowing brine to the reaction front and the flow and dolomite dissolution rate. Ahead of the front, disseminated textures developed at low Damköhler numbers. At, or behind, the front where the Damköhler number was higher, massive or interfingered textures formed, depending on the Péclet number. The shift between massive (higher-grade) to interfingering to disseminated (lower-grade) mineralization led to a correlation between Damköhler and Péclet numbers with ore grade. The models presented here demonstrate the association between mineral kinetics and flow rate with mineralization textures. Therefore, understanding the implications of Damköhler and Péclet numbers can help in interpreting textures on a hand-sample to outcrop scale and patterns of grade and ore geometry.