I found some pictures from 2003 that I took at the Museum of Oriental Antiquities, a part of the Archaeological Museum complex. I was informed this is a Sumerian limestone plaque showing a king (the large figure on the left) carrying a basket of earth on his head--which would be used to make the first mud-bricks to lay the foundation of a very important building--possibly a temple. This was probably the foundation plaque for that temple. There is an inscription on the tablet (in front of the king).

Thanks for letting us know.