how are gold and coal mines responsible for large amounts of acid rain in water?

Answer 1

Acid rain is not caused by mining. Acid rain is caused by pollutants from smokestacks from factories, refineries, etc.. The chemical pollutants in the smoke combine with moisture in the atmosphere to percipitate an acidic (low pH) rain. A byproduct from mining operations can cause acidic waters however, EPA regulations mandate these operations use holding ponds and chemical treatments to minimize the impact of their operations on the environment.
The biggest source of acid rain is factories and powerplants that subvert EPA mandates by manipulating the "allowable" output of their pollutants and by companies outside the United States where environmental laws are less stringent.

Answer 2

http://sharept63.fwhn.com/H7/g55/anthony.aspx

Mines, especially gold and coal mines, are responsible for large quatities of acid water. Agricultural pesticides, fertilisers and herbicides may wash into rivers and stagnant water bodies.