Via jpoysti on reddit, there is a new code for the Citigold 50k AAdvantage miles bonus, valid until 3/31/2016. The code is WD3QFS2Y4C.
For a step by step guide to applying for the Citigold account and funding it with a credit card, see Doctor of Credit.
I’ve personally done the Citigold signup bonus myself and am waiting for the miles to post to my account!