According to the last I coud find the ballance of trade between india and iran

http://www.business-standard.com/india/news/change-in-payment-mechanism-to-impact-indo-iran-trade/420770/

Total export to Iran in 2009-10 was $178,751.4 million, while import was $288,372.9 mn and India’s trade balance was a negative $109,621.45 mn.

India would probably switch to other suppliers for non oil imports where they can pay in dollars to lessen the difference.

India has no other place to replace the oil they need so this deal would have them paying the difference of the adjusted tade balance in gold.