The top right piece in the second photo looks on the money for me - almost a conglomerate in places of quartz in ironstone. The quartz indicates that hydrothermal mineral solutions were in motion (in Vic), whilst the red/brown iron stains in the quartz show that other etched materials are precipitating - such as gold. I believe that iron and gold have an affinity, as many of my coarser nuggets have been in/with ironstone.
Sometimes, iron laterites have formed around gold nuggets that have been in the ground a long time (viz surface iron being dissolved from the ironstones by Carbonic acid in the rain, and concentrating around gold particles), whilst on others, it was evident that gold and ironstone formed together, as when the ironstone was etched out, the interior of the nuggets showed fine fingers (ie: not elluvial or alluvial) and were highly crystalline.
This concept is just my understanding, - if I am off target, will someone more knowledgeable please speak out.