This paper describes a soil extraction method developed to investigate the different chemistries of Au in various soils in the Yilgarn Craton. The extraction solution is 1 M sodium bicarbonater0.1 M potassium iodide, saturated with CO2 and adjusted to pH 7.4 with hydrochloric acid. A soil : solution ratio of 1 : 2 Žg : ml. is used. Two different methods were used: Ž1. net iodide-extractable Au, with solutions analysed directly for Au; Ž2. gross iodide-soluble Au, where activated carbon is added to the mixture and the carbon analysed at the end of the extraction, thus providing a measure of all Au dissolved during the extraction Žincluding that readsorbed during the net extraction.. Depending on the extraction conditions, there may be appreciable readsorption of Au, particularly for organic-rich ŽG50%. and Fe-rich lateritic soils Ž)80%.. This readsorption is enhanced by pulverizing to -75 mm. Consequently, for simple extractions longer than 1 day, pulverized soils give lower apparent Au solubility than do unpulverized soils. Unpulverized carbonate-rich soils show high Au solubilities and little Žoften -20%. readsorption, and consequently show high net iodide-solubilities. These readsorption phenomena could affect other methods used in exploration and should be thoroughly investigated before incorrect conclusions are drawn. The readsorption problems are removed by adding activated carbon to the extraction mixtures; the carbon adsorbs Au as it is dissolved from the sample and is subsequently analysed. However, different soil types still show distinctly different Au solubilities, which should be recognized for interpretation of extraction results. Again, this effect should be tested for other extraction techniques. A more intractable problem may be that biological cycling of the Au through plants and other organisms appears to cause high Au solubilities in many soils. This effect may obscure any potential ‘mineralization signature’ that is being tested by selective extractions, and could cause problems for any extraction method, no matter how well designed

Mineralization, hydrocarbons and diagenesis
JOHNSTON, J. D., COLLER, D., MILLAR, G. & CRITCHLEY, M. F. Basement structural controls on Carboniferous-hosted base metal mineral deposits in Ireland
SHEARLEY, E., REDMOND, P., KING, M. & GOODMAN, R. Geological controls on mineralization and dolomitization of the Lisheen Zn-Pb-Ag Deposit, Co. Tipperary, Ireland
HOLLIS, C. & WALKDEN, G. The use of burial diagenetic calcite cements to determine the controls upon hydrocarbon emplacement and mineralization on a carbonate platform, Derbyshire, England
VEALE, C. & PARNELL, J. Metal-organic interactions in the Dinantian Solway Basin, UK: inferences for oil migration studies Carbonate buildups and Waulsortian mud-mounds
PICKARD, N. A. H. Evidence for microbial influence on the development of Lower Carboniferous buildups
AHR, W. M. & STANTON, R. J. JR. Constituent composition of Early Mississippian carbonate buildups and their level-bottom equivalents, Sacramento Mountains, New Mexico
KIRKBY, K. C. & HUNT, D. Episodic growth of a Waulsortian buildup: the Lower Carboniferous Muleshoe Mound, Sacramento Mountains, New Mexico, USA

It is increasingly apparent that faults are typically not discrete planes but zones of deformed rock with a complex internal structure and three-dimensional geometry. In the last decade this has led to renewed interest in the consequences of this complexity for modelling the impact of fault zones on fluid flow and mechanical behaviour of the Earth’s crust. A number of processes operate during the development of fault zones, both internally and in the surrounding host rock, which may encourage or inhibit continuing fault zone growth. The complexity of the evolution of a faulted system requires changes in the rheological properties of both the fault zone and the surrounding host rock volume, both of which impact on how the fault zone evolves with increasing displacement.

This volume brings together 36 of the manuscripts that were presented as oral or poster papers at the Third International Fluvial Sedimentology Conference hosted by Colorado State University in August, 1985. The conference was co-sponsored by the Society of Economic Paleontologists and Mineralogists and the U.S. Geological Survey with additional support and cooperation from Conoco, Inc., Rocky Mountain Energy, Mobil Corporation, the Rocky Mountain Section-SEPM, and the College of Forestry and Natural Resources and the Department of Earth Resources of Colorado State University.