I found a water leak in a copper pipe that is coming from an area of dark, black corrosion. I've seen the blue/green pipe corrosion but I'm not sure why I have sections of copper pipe (some of which don't seem old) with this black corrosive build up. Any ideas?? I have to fix the leak but also need to figure out if I need to start replacing other areas of black corrosion.

Thanks in advance!