Much as I approve of Australian analogues for martian environments I have to give a word of caution about using the acid lakes of South Australia. <br /><br />These lakes (Lock Claypan, Pinjarra Lakes etc.) and similar features in Western Australia (Lakes Glimore, Dundas) are typically thought to be acidic because of ferrolysis of iron silicate minerals (e.g. amphiboles, chlorite) in a deeply weathered environment. However all the examples I know in WA and SA (including the examples above) occur over thick successions of sulphide and organic rich sediment, and it is possible that the acid groundwater is from natural sulphide oxidation. What ever the cause the result is certainly impressive, acid (pH <3 waters covering areas of 100's of km2 and depositing alunbite and jarosite. Interestingly with respect to the carbonate issue, these lakes occur in depressions sunk into a calcreted landscape, so you have a carbonate rich soil elevated 1-5 m above and acidic watertable that crops out in the (mostly dry) lake beds.<br /><br />This is an area that needs a lot more research, not just from a Mars analogue perspective, but of what it can tell us about sedimentary diagenesis and because of the implications for land management (salinisation, acidification, inland acid sulphate soils) and mineral exploration (heavy metal ion mobilisation) in those areas.<br /><br />Jon <div class="Discussion_UserSignature"> <p><em>Whether we become a multi-planet species with unlimited horizons, or are forever confined to Earth will be decided in the twenty-first century amid the vast plains, rugged canyons and lofty mountains of Mars</em> Arthur Clarke</p> </div>