A rep for the City of Indio tells TMZ ... Goldenvoice was fined $51,000 for curfew violations racked up during Weekend 2. That might sound like a lot, but pales in comparison to the $117k they shelled out last week for the lengthy final sets that crept into the wee hours of the morning.

Here's the breakdown ... we're told Friday night's festivities went 2 minutes past the 1 AM curfew -- amounting to a $20,000 fine. Saturday, which also had a 1 AM curfew in place, didn't go over the line at all ... so no ding there. Sunday, however, went well past the slightly earlier 12 AM curfew ... at 16 minutes, and costing Goldenvoice $31k.

You'll recall -- the contract festival organizers have with the City calls for a daily fine of $20k for the first 5 minutes past curfew, with another $1,000 added for every minute thereafter.

Like we said ... $51k is nothing to sneeze at, but considering they got the fines down a significant amount compared to Weekend 1 ($66,000 in savings) -- it's not half bad.

The lineup changed a bit this week ... including the notable replacement of Frank Ocean, who had to bow out after injuring himself. Blink-182 stepped in to handle main stage duties at 9:20 PM, and then Skrillex and other EDM DJs filled the void later at 10:25 PM.