Is possession of 1 ounce of marijuana or less in a drug free zone, a permanent bar to reenter the US after being deported?

Your question requires an attorney consultation. It is not a simple question that can be answered on this type of forum. There are many factors that would need to be considered and evaluated. The possession of marijuana alone, without the enhancement, is enough to keep you out of the U.S. after being deported. It may be possible to qualify under the Minor First Offense exception if the charges and conviction can be changed and the enhancement set aside. I strongly suggest that you contact an experienced immigration and criminal defense attorney for a face-to-face consultation and give him/her all of the facts surrounding your situation. The would then be in a better position to analyze your case and advise you of your options.