However month-on-month figures show production has started to climb in the months since restrictions have eased following the nationwide lockdown to stem the spread of COVID-19.
Stats SA said the gold and iron ore sectors were the largest negative contributors for the 12-month period, down 14.8% and 18.1% respectively.
Platinum group metals miners were the largest contributor, up 12.7%.
Gold's drop contributed -1.9 percentage points to the change in production volume, while PGMs' gain added 2.6 percentage points.
Seasonally adjusted mining production rose 27.5% for the three months ended August 2020, compared with a year earlier.
The month-on-month seasonally adjusted figures have risen from -0.7% in June, to 20.3% in July and a further 6.8% increase in August.
Mining production had plunged 47.3% year-on-year in April, the first month following the lockdown which began on March 27.
Mineral sales were up 20.9% year-on-year in August, Stats SA said.
PGMs were up 63%, contributing 15.8 percentage points, ahead of iron ore, up 39.3% and contributing 5.1 percentage points.
The government department noted it was the first publication using weights based on national accounts value added data for 2016-2018, rather than 2015-2017.
Under the reweighting, the coal sector represented 25%, followed by PGMs with 22.43% then gold with 16.81%.