* Smith set to win 70th cap four years after previous test
* One of three changes in forwards after 13-6 win in Pretoria (Adds detail, quotes)
BUENOS AIRES, Aug 20 (Reuters) - South Africa flanker Juan Smith has been given the chance to win his 70th Springboks cap nearly four years after his last test when they face Argentina in The Rugby Championship in Salta on Saturday.
Smith, who spent the better part of two years fighting to recover from an Achilles tendon injury he suffered in February 2011, is one of three changes, all in the forwards, announced by coach Heyneke Meyer.
"We have a couple of options at blindside flank, but we've decided that this will be a great opportunity to give Juan a chance," Meyer said of the 33-year-old, who last played for South Africa against England at Twickenham nearly four years ago.
In the other changes to the side that narrowly beat Argentina 13-6 in their tournament opener in Pretoria last weekend, Gurthro Steenkamp comes in at openside prop for Tendai Mtawarira and Eben Etzebeth replaces Bakkies Botha in the second row.
Meyer made four changes to the replacements, including Mtawarira and Botha. Marcell Coetzee, a last minute substitute for injured flanker Willem Alberts in the starting XV last Saturday, starts on the bench along with wing Lwazi Mvovo.
Smith, a member of South Africa's 2007 World Cup-winning team, had a string of operations on his tendon before rebuilding his career after more than two years out of rugby and helped Toulon win the French Top 14 title and Europe's Heineken Cup last season.
"Apart from experience and leadership, Juan is a superb ball-carrier and also brilliant at the back of the lineouts, where we missed Willem Alberts last week," Meyer told reporters in Buenos Aires before the team trip northwest to Salta.
"Our lineouts are an important attacking platform and we need to improve this week - I'm sure Juan will add another dimension," added Mayer after the Pumas posed South Africa problems in that area of Saturday's match in Pretoria.
Meyer said that because of the short time between the two tests against Argentina, he had decided to alternate players in the front five bringing in Etzebeth, who has come back from injury, and Steenkamp.
South Africa will play in Salta for the first time after they faced the Pumas in Mendoza on their two previous visits to Argentina in the Championship.
15-Willie le Roux; 14-Cornal Hendricks, 13-Damian de Allende, 12-Jean de Villiers (captain), 11-Bryan Habana, 10-Handre Pollard, 9-Ruan Pienaar, 8-Duane Vermeulen, 7-Juan Smith, 6-Francois Louw, 5-Lood de Jager, 4-Eben Etzebeth, 3-Jannie du Plessis, 2-Bismarck du Plessis, 1-Gurthro Steenkamp Replacements: 16-Adriaan Strauss, 17-Tendai Mtawarira, 18-Frans Malherbe, 19-Bakkies Botha, 20-Marcell Coetzee, 21-Francois Hougaard, 22-Morne Steyn, 23-Lwazi Mvovo (Writing by Rex Gowar, editing by Pritha Sarkar)