Pyrite oxidising makes sulphuric acid; carbonate neutralises it. Acid-base accounting weighs the two against each other in the same unit — kilograms of calcium carbonate per tonne of rock — and the whole calculation follows from the chemistry, not from a table.
Sulphate sulphur is acid that has already been generated and gone — gypsum, jarosite, a weathered rind. Including it in the acid potential counts the same acid twice and makes a sample look far worse than it is. Sulphide sulphur is what has yet to react, and it is the only sulphur that matters.
Acid-base accounting is a balance sheet; it does not say who wins the race. The net acid generation test settles it directly — hydrogen peroxide oxidises all the sulphide at once, the carbonate neutralises what it can, and the pH at the end is the answer.
Where the two methods disagree, believe the one that says acid and test again. Disagreement usually means slow-reacting carbonate, or sulphide locked in silicate that the peroxide reached and the weather never will — or the reverse, which is worse.
A static test says whether, never when. A dump can sit for years looking clean while the carbonate is used up, and turn in a single season. The lag time is the whole management problem, and it is measured by leaching a column, not by calculation.
Once the pH falls below about 3.5, iron-oxidising bacteria take over and the reaction accelerates by orders of magnitude. Before that the rate is chemical and slow; after it, the same rock behaves like a different material. A prediction made from the slow phase and applied to the fast one is not conservative — it is wrong by a factor nobody can afford.
Before any laboratory, the ground tells you. Colour, coating and the pH of a puddle place a seep on the scale better than most people expect, and they cost nothing.
| what you see | what it means |
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The chemistry of the water itself — hardness, saturation indices, whether it can be drunk or irrigated with — is Water chemistry; the ochre minerals that colour it are in What is this rock?; and the sulphur assay behind all of this has to have survived QA/QC first.