Primero Announces Mid-Year Reserve and Resource Update

TORONTO, ONTARIO--(Marketwire - Sept. 4, 2012) - Primero Mining Corp.

is pleased to provide a mid-year update of estimated Mineral Resources and Mineral Reserves for its San Dimas mine as at June 30, 2012. The Company reported contained gold in Probable Mineral Reserves of 584,000 ounces - an increase over year-end 2011 of 79,000 ounces (126,000 ounces before depletion). The increase in contained gold in Indicated Mineral Resources (which include Probable Mineral Reserves) was 17% to 678,000 ounces; and in Inferred Mineral Resources it was 23% to 866,000 ounces. The Company also reported contained silver in Probable Mineral Reserves of 34.7 million ounces, Indicated Mineral Resources of 40.6 million ounces and Inferred Mineral Resources of 67.5 million ounces."Our exploration and delineation program has generated substantial results for the Company during the first half of 2012," stated Mr. Joseph F. Conway, President and Chief Executive Officer. "Primero has increased the contained gold ounces and grade in its Mineral Resources and Mineral Reserves, while making important strides in better defining the near-term potential of the San Dimas deposit. Our Mineral Reserves and Mineral Resources still only include 18 veins, of more than 120 known