The enigmatic role of cratons in Zn-Pb deposit formation during continental rifting

The growing global demand for metal resources requires new discoveries of high-grade ore deposits. Known sediment-hosted clastic-dominated base metal deposits are found in failed continental rifts and the passive margins of successful rifts. Recent studies indicate that the majority of these Zn-Pb deposits are located near steps in lithospheric thickness (e.g., Hoggard et al., 2020), but a potential causal link between ore formation and craton edges remains elusive. However, numerical models have shown that a craton edge close enough to an incipient rift controls the direction of asymmetry of the rift system (Raghuram et al., 2023) and that asymmetric rifts are more favorable to deposit formation (Glerum et al., 2024). Understanding the large-scale controls of cratons on rift-related mineralizing processes, occurring on much smaller spatial and temporal scales, can thus help identify new areas for exploration.

To this end, we use the geodynamic code ASPECT (Kronbichler et al., 2012; Heister et al., 2017) coupled to the landscape evolution model FastScape (Braun and Willett, 2013; Neuharth et al., 2022) to model 2D rift systems from inception to break-up in the presence of a craton. We investigate the relationship between craton distance and favorable conditions for ore formation, i.e., those conditions where potential source rock, host rock, and fluid pathways co-occur. Our results show that cratons have a negative effect on ore formation in narrow asymmetric rifts, but a positive effect in wide rifts.

In a second step, we further investigate the hydrothermal ore-forming mechanisms by using potentially favorable geodynamic configurations from the ASPECT simulations as input for fluid flow modelling with CSMP++ (Weis et al., 2014; Rodríguez et al., 2021). This input comprises basin geometry, temperature, boundary heat flow and a permeability structure dependent on strain and strain rate. With a temperature- and salinity-dependent proxy of metal solubility in the basinal brines, we track the leaching, transport, and precipitation of metals. This cross-scale workflow allows us to identify those rifting scenarios with the highest metal enrichment potential.

 

References:
Braun and Willett, 2013. Geomorphology 180–181: 170–79. DOI: 10.1016/j.geomorph.2012.10.008.
Glerum et al., 2024. Solid Earth 15: 921-944. DOI: 10.5194/se-15-921-2024.
Heister et al., 2017. Geophys. J. Int. 210 (2): 833–51. DOI: 10.1093/gji/ggx195.
Hoggard et al., 2020. Nat. Geosci. 13 (7): 504–10. DOI: 10.1038/s41561-020-0593-2.
Kronbichler et al., 2012. Geophys. J. Int. 191 (1): 12–29. DOI: 10.1111/j.1365-246X.2012.05609.x.
Neuharth et al., 2022. Tectonics 41 (3): e2021TC007166. DOI: 10.1029/2021TC007166.
Raghuram et al., 2023. Geology 51:1077–1082. DOI: 10.1130/G51370.1.
Rodríguez et al., 2021. GCubed 22 (6). DOI: 10.1029/2020GC009453.
Weis et al., 2014. Geofluids 14, 347-371. DOI: 10.1111/gfl.12080.