The announced sale price was $US300 million but the final price was $270 million after adjustments for working capital, mine capital and employee entitlements.
The agreement gave Gold Fields the option to pay for up to half the price in shares, which it elected to do.
Gold Fields has issued 28.7 million shares at $4.70 per share to Barrick and paid $135 million from existing cash reserves.
Barrick has no restriction on selling the shares and said it would use the proceeds from the sale to repay debt and general corporate purposes.
Gold Fields CEO Nick Holland said he was pleased to complete the acquisition, which comprised the Granny Smith, Lawlers and Darlot mines in Western Australia.
"Today we commenced integrating these assets with our existing operations in Western Australia where Gold Fields now has five active mines," he said.
The company expects to realise synergies, particularly between the contiguous Lawlers and Agnews operations.
The new mines will add around 400,000 ounces of gold to Gold Fields' annual production and makes Australia the South African company's largest region, accounting for 42% of annual output.
The three assets produced 452,000oz at all-in sustaining costs of $1137 per ounce last year and 196,000oz at $1145/oz in the first six months of this year.
The Yilgarn South assets have resources of 1.8 million ounces of gold.
Barrick maintained 2013 guidance of 7-7.4Moz of gold at $900-975/oz.
The Canadian gold giant offloaded the assets as part of its disciplined capital allocation framework.
The company also has plans to sell the Plutonic mine in WA, while media reports suggest it will also look to divest Kanowna.