The minimum requirement of 12V 24Amps is for the WHOLE system...not just the video card.
And that Corsair HX520 has plenty of power for your whole system. In total it has 40Amps of +12V. (max combined +12V = 480 watts divided by 12 volts gives you
errr .. 40Amps).
Your GTX 460 has a peak demand of around 181watts (15Amps) with a typical full load of around 137watts (11.4Amps).Palit GeForce GTX 460 Sonic Platinum