A Chelated mineral is basically just one that's broken down. I've never seen Chelated Zinc in as high as a 50 mg dose (it's normally in 30 mg at the most if it's Chelated)... who told you to take that high of a dose of specifically Chelated Zinc?
In general, the human body doesn't absorb pure minerals very efficiently (like pure Zinc), so it has to be bonded with another nutrient (like Gluconate, for example) that your body absorbs easier, then the mineral gets absorbed along with it. With Chelated minerals, they actually break down the pure mineral in a lab so that the mineral itself is easier for your system to absorb. That's the difference.
Does that help?