Baker et al (1993) (p236)

"Species such as Mn, Fe, Cu, Zn, and many others, may exhibit depressed 
element/heat ratios in diffusely venting fluids as a consequence of the 
precipitation of sulfide minerals due to cooling, and increased pH, oxygen 
concentration, and residence time that occurs when souce fluids are diluted 
with seawater within the interstices of the basalt seafloor."

Good intro prose in Butterfield et al (1990) p.1

-- p.12,898b --
	Assumption of zero magnesium based on experimental water-rock results