Copper leaching, transport and deposition in sedimentary basins: Insights from 3-D numerical modelling

We report three-dimensional (3-D) numerical simulations of groundwater flow driven by temperature and salinity to investigate processes that control copper leaching, transport and precipitation in sedimentary basins. We simulate flow in two different models representing syn- and post-rift stages of basin evolution. Our simulations capture leaching of copper from red-bed sandstones and basement source rocks, transport by groundwater, and precipitation at a redox boundary.

Results suggest that groundwater convection plays an important role in mineralisation. Convective flows are complex and time varying, and occur at different length-scales. The presence and permeability of basin-scale faults is a key control on convection, which (i) redistributes heat, increasing source rock temperature; (ii) transports saline brines from where they form by halite dissolution or evaporite precipitation, to both intra- and extra-basinal source rocks, and (iii) transports leached Cu in enriched brine from source rocks to sink. Basins likely contain numerous convection cells operating at different length-scales.

Mineralisation occurs over a long period of groundwater circulation comprising multiple cycles of enrichment and deposition, rather than a single pass of enriched groundwater, unless Cu is efficiently leached by groundwater resident in source rocks. The location of upwelling limbs of convection cells that supply Cu-enriched brine is an important control on the spatial distribution of mineralisation. Intra-basinal red-bed deposits are a viable source so long as grain coatings contain in the order of 10’s ppm Cu that can be efficiently leached. The relatively larger volume of potential basement source rocks may deliver higher grade mineralisation.