Placer Gold Puzzles starts with the Witwatersrand, South Africa and  the long debate over the model for gold formation. After that, we head to Brazil to see how quality geochemical data analysis assisted by machine learning helped decipher a Proterozoic paleo placer. Lastly we consider changing mindsets about legacy mining through a new model that aims to create net benefit from the mining of placer gold.  Professor Hartwig Frimmel (University of Wuerzburg) takes us through the history and the science of ore deposit models for the Witwatersrand, providing insights into what makes our work relevant and how do we can do our best work.  From the Archaean in South Africa we go to Tristar Gold's Castelo de Sonhos Project to find out how Britt Bluemel (Goldspot Discoveries) used geochemical analysis of large data sets helped create a geologic model for exploration. We finish up with Stephen D'Esposito (President and CEO of Resolve NGO). Steve  spearheaded, Salmon Gold, a new venture that works with placer gold miners to rehabilitate streams in Alaska, the Yukon and British Columbia. Can we do more than just the minimum and create net-benefit for biodiversity? He suggests a change in mindset, where we start looking at legacy of mining as an opportunity.Theme music is Confluence by Eastwindseastwindsmusic.com