8. Producing gold

8.1  Overview

The process emissions from gold manufacture arise from limestone and/or dolomite used to control the acidity of stockpile leachate. The carbonates react with sulphuric acid in the leachate, to form calcium and magnesium sulphates, carbon dioxide and water. In addition, there may be smaller amounts of CO₂ emissions from limestone used in other gold processing activities. Not all of the calcium and magnesium carbonate used for acidity control is likely to be reacted.

8.2  Information you are required to collect

The total tonnes of uncalcined limestone or dolomite used over the reporting period would normally be determined by direct weighing with sampling and analysis to determine the carbonate content. ISO17025 accreditation is recommended.

8.3  Example calculation

Goldrush Goldmine Ltd is a gold producer. During the reporting period, 5000 tonnes of uncalcined limestone and 4000 tonnes of uncalcined dolomite were used to control the acidity of stockpile leachate. Additional limestone and burnt lime were used for on-site roading purposes, but are not reported. Goldrush Goldmine Ltd has undertaken laboratory testing to determine the purity of the limestone and dolomite used, and the results came back as 75 per cent and 85 per cent purity, respectively. There is no data to indicate that any of this limestone remains unreacted in use, so Goldrush Goldmine Ltd will assume that it is all reacted for the purposes of reporting its emissions.

Using the formula provided in the regulations:
E = (3750 × 0.4397) + (3400 x 0.4773)
E = 3272 tonnes CO₂-e