In my opinion hydrogeochemistry is the one of the most powerful tool of subsurface resource exploration for geologists. Because as a geologist we are searching for geochemical signatures as anomalies. Every mineral deposits (ore minerals) occurs with other minerals, with mobility of minerals, which includes to the groundwaters. for example uranium ions and EC in waters is being used for uranium explorations or arsenic and Au is used for gold explorations. fossil waters have more iodine amounts and iodine is related to organic matter. so iodine in water is a useful tool for hydrocarbon explorations. On the other hand Iran and Turkmenistan produces iodine from oilfield brines. Lithium is a raw material for battery technologies as you know lithium also produced in geothermal brines.. If I will have a research chance at an institution, I want to study chemistry of lacustrine waters for industrial raw material potential for production posibilities. Some explorationists uses benzene in formation brines at dry wells to reach reservoir and using benzene to guess reservoir distance to the dry wells.
In conclusion you can use hydrochemistry for many purpose If your brain works as exploration geologist, you can find whatever you want to use hydrogeochemistry. Some environmental scientists are studying Hg in waters but I have no any idea why are they doing it..
Hydrochemistry is the best dicipline in geology I think :D
I agree with Orkun Turgay in the importance of hydrogeochemistry in ore metal exploration, but it is not the only uses of hydrogeochmistry.
Hydrogeochemistry has a wide range of applications in different disciplines including hydrogeological characterizations, environmental hydrogeology, hazard assessment, water-rock interactions, water pollution ....etc.
whatever you have, hydrogeochmistry can greatly help to describe and assess the studied problem..