Heavy mineral sands are usually fairly devoid of sufide minerals and therefore the potential for AMD generation is 'usually' minimal. However, if the deposit or part of the deposit has been in an anoxic environment with enough organic matter, then secondary sulfide minerals could form within the sands following deposition.

This is the kind of thing that you see in acid sulfate soils and there are examples of excavations in sand dune complexes that have resulted in acid release issues (the desalination plant near Bendigo, in Australia is a good example). I cannot think of any specific examples of this occurring in mineral sands but it is possible if conditions are right for it.

Do titanium dioxide mines not use a large quantity of sulphuric acid in their mining process? This is assuming they are going the sulfate route as opposed to the chloride process.

Looking at the sulfate process, http://www.rsc.org/learn-chemistry/resource/download/res00001267/cmp00002617/pdf this does rely on sulfuric acid.

We have recently run titanium dioxide mine produced water through our process with great success. We recovered 100% of the sulphuric used and converted the remaining salts into potassium nitrate, ammonium sulfate and sodium chloride. We also removed all radioactive salts and recovered 95% of the water. I would like very much to speak to someone who has experience with tio2 produced water.