You can use a soil pH meter or just buy a pH meter, for you to know the acidity of the ore it self.

You most likely are more concerned about how much base it will take to neutralize the ore rather than just pH. There are standard laboratory procedures for this. In general, you take a split-down sample, ground/pulverized to a specified fineness, like minus 100 mesh, and add water to form a dilute slurry. Then a base is slowly added, commonly dilute NaOH, and the pH monitored. By keeping track of the amount of NaOH needed to titrate to a target pH (such as pH 5), the acid consumption of the ore can be calculated. Although the measurements are generally made as mmol/gram, the results are often converted to kg lime per ton.

Dave is correct; however, the most accurate procedural would be to perform a Leco C & S for organic/inorganic C & elemental/sulfide/sulfate S; very simplistically, the neutralization rxn may be represented as:

S2- + 3/2O2 + H2O = H2SO4

H2SO4 + CO32- = SO42- + CO2 + H2O

A S2-/CO32- ratio hence represents the ore acidity.