The study focuses on how gold formed and moved within the Sawayaerdun gold deposit in northwest China, a large orogenic system shaped by long periods of burial, deformation and heating. Before any visible gold veins existed, the host sedimentary rocks already contained microscopic pyrite formed during early burial. This earliest pyrite, referred to as Py0, developed within carbon rich layers and was unusually rich in gold, even though that gold was invisible to the naked eye. It was locked inside the crystal structure of the mineral rather than forming nuggets or veins. Along with gold, this pyrite also concentrated elements such as arsenic, cobalt and nickel. These early conditions are important because they show that gold was present from the beginning, stored quietly within common sedimentary minerals long before mountain building began.
