Increased solubility of quartz following ferrous–ferric iron reactions
A knowledge of the solubility of quartz and silicates in natural waters is important to the understanding of many gelogical processes. Here we provide experimental data to support an earlier hypothesis1, that during the supergene enrichment of banded iron-formations, redox reactions involving iron result in a much more rapid dissolution of quartz than would be predicted from its known solubility in water. The process is relevant not only to iron ore genesis but also to the much wider field of chemical weathering— for example, to the genesis of laterites and soils from quartz-bearing rocks. In addition, the reactions may offer a mechanism by which quartz is pseudomorphed by iron oxides.
Silicon isotopes and the origin of the Archaean cherts
The first detailed investigation of silicon isotope systematics in Archaean cherts shows that silicon isotope variability in 3.0-3.5 Ga cherts of the Pilbara craton is significant on sub-centimetre to kilometre scales. A total delta30Si range of -2.4 to +1.3‰ was established. The silicon isotope compositions were determined with high precision (
Supergene alteration of sulphides, I. A chemical model based on massive nickel sulphide deposits at Kambalda, Western Australia
Abstract An electrochemical model for the weathering of massive sulphide deposits that have undergone conditions similar to those affecting the Kambalda nickel deposits is presented. Galvanic corrosion due to aeration of the top of the ore body near the water table results in a deep anodic reaction whereby primary sulphides undergo an oxidative transition to sulphur-rich violarite—pyrite ore and also a shallow oxidative anodic reaction where the violarite—pyrite ore is oxidised to sulphate and gossanous oxides. Electrons are conducted through the ore from the anodes to the cathode where dissolved oxygen radicals are reduced and the corrosion cells are completed by ionic transport through the groundwaters to the anodic regions that can be some 200 m deep in the case of deep weathering processes. The kinetics of the weathering are described in terms of resistance to the flow of corrosion currents in the electrochemical cells. The effect on the model of physical perturbations such as rising and falling water table, faulting, etc. is discussed.