This is just of the top of my head so dont take it as gospel but i believe there would be a chemical change in the water if the temperature decreased. It will be dependent on the magnitude of temperature change.

I think the answer lies on the site http://www.lsbu.ac.uk

Good luck...

Bane V.

Hello! Geothermal water chemistry is dependent upon several factors – including dissolved chemical species leached from the surrounding lithology, temperature and kinetics. Therefore, geothermal water chemistry will change upon cooling; as the drop in temperature will directly affect the chemical equilibrium within the considered system. As high temperature water has an increased saturation state, upon cooling, precipitation of specific mineral phases will result depending upon redox conditions; as it (redox) becomes the controlling geochemical parameter with regards to dissolved ion speciation, at steady pH.

Perhaps the following articles might also be of some interest to you:

1) Fluorite Solubility Equilibria in Selected Geothermal Waters (NORDSTROM and JENNE, 1977)

http://www.rcn.montana.edu/pubs/pdf/1977/Nordstrom_Jenne_GCA_1977_v41.pdf

2) Feldspar Saturation State in Natural Waters (STEFÁNSSON and ARNÓRSSON, 2000)

http://144.206.159.178/FT/402/20158/13681820.pdf

The equalibrium conditions of thermal water depend on temperature and preassure. Therefore the chemical composition of the thermal water will change with decrease the temperature or preasure. And actually, in petrology there are many stages of the hydrothermal diffrencial and each stage associated with deposition of different metal groups. So the composition of hydrothermal water will chang

Definitely there will be a change in composition in content as well as speciation. What actually happens depends on several factors as mentioned already above. You can model the change with the following program made available by the USGS:

http://wwwbrr.cr.usgs.gov/projects/GWC_coupled/phreeqc/

Good luck!

I agree with all the previous answers. Please note too that depending on the temperatures and water compositions involved, bacterial mediation may affect water chemistry. Extremeophiles are everywhere.

Also, I always put in a plug for stable isotope analyses becusse the data are so powerful and, at equilibrium, are great geothermometers.

Indeed, I agree with all the above. Stable isotopes would be my go to approach. I would add that microbial mediation would deplete your C13 values of sediments. It is worth looking at.

You have to take into account two situations : the water is in contact with a rock, or not, when it is cooling down. Depending on them, the evolution of composition won't be the same. Generally speaking, the composition will evolve.

Do not forget pH change if degassing is possible. And little amounts of oxygen entering the system will most often lead to precipitation, also temperature change.

As already mentioned the physico-chemical characteristics of the aqueous solution will change with dropping T. Considering a closed system with no allowance for degassing or water-rock-interactions, his may lead to supersaturation with respect to solid phases (or vice-versa). Depending on the salt content of your solution, I suggest to use EQ3/EQ6 fpr modeling purposes or other code that allows for the inclusions Helgeson´s data sets.

Thanks for answer: Yes, water chemistry change, with different temperature.