What are the consequences of an early a6 in the Sicilian? Once I encountered an opponent who used a very early a6 in his Sicilian Opening. 

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1. e4 c5 2. Nf3 a6


What could have been his objective with this move and how should I have have countered it?
This is called the O'Kelly variation of the Sicilian.

If white plays normally (i.e. 3.d4 cxd4 4.Nxd4 Nf6 5.Nc3), then black can eventually kick the d4 knight with ...e5 when the knight doesn't have any great squares.  In this case, 2... a6 keeps the knight from moving to the natural b5 square (as in the Sveshnikov Sicilian).  This will allow black to quickly play ...d5 with equality.

White's best plan is to play either c3 or c4 trying to prove that black's move 2... a6 is not a good developing move.  When white plays c3, the natural plan is to follow up with d4, and then if black plays ...cxd4, white will respond with cxd4, gaining a classical pawn center.  When white plays c4 instead, white's plan is to set up a Maroczy bind.

An unambitious plan for white would be to play into a closed Sicilian - in the closed Sicilian, black frequently plays a6-b5 in order to get counterplay on the queenside.  Furthermore, in the closed Sicilian, tempi matter a lot less because the position will not change radically from one move to the next.