Reductive deposition of heavy metals arsenic antimony and antimony-silver alloys has been observed in acidic groethrmal waters; two-phase and brine solutions. These waters may be corrosive to carbon steel but observed corrosion rates appear to be accelerated by the presence of reductively depsoited heavy metals. Electrochemical testing has proved difficult because of the formation of gases on these metals under cathodic polarisation.This work is focussed on laboratory coupon exposures that aimto characterise contrbuting factors that influence the rate of corrosion of carbon steel under ion beam coatings of heavy metalsin pressurised simulated geothermal brines.