1939 GGIE 'Tower of the Sun' medallion

Any interest in this medallion?





Bigger than a so-called dollar, the diameter measures 63mm. I only see smaller tokens with the tower on eBay, and the only of the same size I found is this one that's sold:

https://www.vcoins.com/en/stores/praefectus_coins/130/product/1939_golden_gate_exposition_san_francisco_ca_63_mm_91_gm_medallion/825366/Default.aspx

What is it made of ? Whats the story behind it?

Metal. Which metallic elements, I don't know. It's a commemorative souvenir piece from the Golden Gate International Exhibition held in San Francisco in 1939.