Damn... "thanks a bunch" = a sarcastic/ironic version of saying thank you. 
Oh boy, and I often used it to thanks people here on twitter for their comments. 
Sorry!! english is not my first language
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...Not entirely true. If used with an exclamation, like "Thanks a bunch!" then it seems genuine. Or with some kind of emoji. "Thanks a bunch" on it's own can be interpreted either way. But if it's with a period, it's likely to be seen as passive aggressive or sarcastic.
