If the geothermal well is two phase then after the separation plant you will get a small amount of the brine/or water phase in the steam. You will also get all the non condensable gases (H2S, CO2 etc) in the steam phase.
Carried over brine/water will contain all sorts of dissolved chemicals. See Joshs post above. But I would be supraised if there is Oxygen.
Dry steam wells can have the same cominates plus dust.