An extract from the Minerals Council of Australia webpage
Victorian geology gives a technical account of how the forest rocks were formed over 450 million years ago and how the gold came to be there:
“Sedimentary rocks continued to be deposited during the Ordovician (500 to 420 million years ago) in a deep marine basin that extended northward into New South Wales and southward into Tasmania. To the east there was a line of volcanic islands that occur intermittently in a belt north of Victoria with the edge extending into north-eastern Victoria near Benambra. There, dacites and andesites occur within a narrow stretch of rocks. Nearly all the Ordovician rocks in Victoria are of deep water sedimentary origin. Most are interbedded sandstones, mudstones and minor shales of turbidite origin or thick sequences of deep water, black shales. The source material for these sediments is from the west as discerned from scour and ripple marks in the turbidite sequences.
During the Late Ordovician to Early Silurian (420 to 440 million years ago), Victoria was effected by large area deformation. Regions in both western and eastern Victoria were uplifted to form dry land. This orogeny caused the Ordovician sediments across Victoria to be folded and faulted. Another major period of deformation affected most of Victoria around 385 to 395 million years ago, probably due to a continent-continent collision. This was the final stage in the formation of what is now the south-eastern part of the Australian continent. It was probably the most dramatic geological event ever to occur to Victoria and caused major changes in the patterns of sedimentation. Uplift caused sedimentation to cease and a major mountain range was formed in eastern Australia. Associated with this orogeny was extensive granitic intrusion and intrusion of large numbers of parallel quartz to olivine rich dykes. Fractures within the dykes are filled with quartz which carries gold; historically Victoria’s most economic mineral resource.”