G'day all
I would also say that it is probably from a smelting site and maybe not even a legal one. when I was working around Kalgoorlie I would often come across such sites from small bush smelting operations using rich gold stolen from the major mines.
I also remember a story from an Ion Idriess book about how he got a good start by finding smelter sites (old and legal ones of a significant size). He would take everything around the site including soil, old crucibles and bricks - crush it all up and pan off. he said that the amount of smelting spills were high.
Araluen