ABSTRACT A model for a reduced chimney above ore deposits is presented that complements the existing electrical charge model. This new model emphasizes the role of reduced gases in the formation of the chimney. A computer model for the transport of reduced gases in the unsaturated zone and subsequent microbial oxidation is applied to a hydrocarbon gas chimney. The role of nitrogen soil gases is demonstrated for active epithermal systems. The formation of gaseous As(CH3)3 and its transport and oxidation in the unsaturated zone is postulated for the formation of near-surface extractable As, and possibly other elements. The transport of Hg and its flux into the atmosphere is demonstrated to have a significant seasonal variation. This in turn results in variation in seasonal soil gas Hg concentrations. The unsaturated zone model is applied to the vertical transport of ultrafine particulates with application to Au. Barometric pumping causes pressure gradients in the unsaturated zone that are capable of moving sub-micron Au particulate to the surface. A variety of exploration methods are suggested by the data and modelling of transport processes.
- Received August 15, 2007.
- Accepted May 23, 2008.
- © 2009 AAG/Geological Society of London