Actual Weathering Research Articles

Mechanism of gold transfer and deposition in a supergene environment

The possibility of gold mobility in supergene environments is suggested by numerous indirect observations of gold particles. However, presently there are no dissolution or transport data based on the chemistry of actual weathering solutions. We have investigated models of gold transport by studying the water chemistry of a stream where weathering of auriferous minerals is occurring under supergene conditions in a temperate climate. Dissolved gold concentrations in the auriferous zone are forty times higher (200 pmolL −1) than in non-auriferous zones (5 pmolL −1). We have examined the potential gold ligands: thiosulfate, hydroxide, and chloride. Speciation calculations using the field data show that gold solubility is controlled by a gold thiosulfate complex: Au(S 2O 3) 2 3−. The oxidation of the thiosulfate ligand induces the destabilization of the aurothiosulfate complex. Gold is then reduced to the metallic state as submicronsized suspended particles. This conclusion is supported by the measured increase in gold content of suspended particulates. Mass balance calculations performed with both dissolved and paniculate gold data permit the quantification of gold deposition along the stream.

A review of experimental weathering of basic igneous rocks

Summary Attempts to reproduce and accelerate in the laboratory the effects of weathering on minerals are reviewed, together with some observational evidence of actual weathering effects. Laboratory experiments confirm the importance of water as the main agent of chemical weathering and that the progress of weathering is controlled by drainage, oxidation and pH. Some practical applications of accelerated weathering to engineering problems are briefly described, including a short description of the authors’ own work. The relative importance of chemical and physical weathering processes is considered briefly.

THE CLAY MINERALOGY AND SOME TRACE ELEMENT CONTENTS OF THE SPEETON CLAY

Summary Pronounced time-related trends are evident in the clay mineralogy of the Speeton Clay (Lower Cretaceous): the kaolinite/illite ratio decreases consistently as the sediments get younger, and the other main mineral, probably an illitesmectite, becomes progressively more illitic. It is suggested that these changes reflect weathering conditions at the source rather than differences in actual source-rock type or weathering of the Speeton Clay itself. This conclusion is supported by the relative consistency in trace element contents, which might be expected to reflect major changes in source material.