Mexico 950+ silver belt buckle, with gold, from a coin?,! I bought 40 years ago in Mexico, but how old?

I did not think that this was silver because it just says MEXICO on back of buckle. I bought around 1973 in Mexico. The gold looks like from a coin as there is writing in Spanish on it. I gave it to my father and he wore it. He died in 1993 and I got it back. It is going to my son, who already has worn it. I bought a silver and gold test kit and it tested dark red which is 950 or more. I took tiny scrape of gold and tested with 10K and it passed. I never looked real close at it. But now I have and it is really well made. I wonder who and when it was made?