| Abstract: | Current evidence suggests that most of Victoria is underlain by a relatively thick (20 km +) basement of sialic composition of assumed Proterozoic age. This basement is nowhere exposed and its structural relationship with exposed Palaeozoic rocks is conjectural. This uncertainty has resulted in both ensimatic and ensialic tectonic models being proposed for Victoria during the Cambrian.Mineralization associated with Cambrian igneous activity shows a variety of styles from minor orthomagmatic chromite deposits, through Au and Cu deposits of syngenetic or epigenetic origin, to Fe---Mn, Ba occurrences of exhalative volcanogenic affiliation.Cambrian volcanism and associated sedimentation was followed by the deposition of dominantly quartz-rich turbidites with interbedded shale and siliceous units. Subsequent to the epi-Ordovician Benambran Orogeny, late Silurian crustal extension caused several rifts to open along roughly orthogonal NW and NE aligned fractures. Within these fault-bounded depressions, thick acid volcanic sequences were deposited in close association with shallow-marine sediments. Mineralization in these Upper Silurian rocks comprises polymetallic base-metal sulphide lenses and minor disseminations, at least some of which are of exhalative volcanogenic affiliation.The Silurian rifts were obliterated and their rocks strongly deformed during the Bindian (Bowning) deformation during late Silurian to early Devonian time. This in turn was followed by another episode of crustal extension and rifting, during which the formation of a broad meridional trough marks the Buchan Rift. A very thick sequence of largely subaerial bimodal volcanics is overlain by shelf limestone and mudstone. A variety of minor base metal, barite, manganese, and iron mineralization is hosted by these volcanics and shelf sediments.The mid-Devonian Tabberabberan Orogeny was followed in the Late Devonian by bimodal volcanism and granite intrusion, and “red-bed”-type non-marine sedimentation. In Central Victoria, thick bimodal volcanics were erupted into a series of cauldron subsidences and intruded by comagmatic granites. Bimodal volcanism also occurred in the Mount Howitt Province farther east, but was followed by deposition of extensive fluviatile and lacustrine sediments (mainly mudstone, sandstone, and minor conglomerate). In the Mansfield Basin, these contain minor sedimentary copper occurrences.There are four distinct episodes of granite emplacement in Victoria, namely Late Cambrian -Early Ordovician (Delamerian) in the Glenelg Zone; Early Silurian (Benambran) in the Highlands Zone; Early Devonian (Bindian) in the Grampians, Ararat-Bendigo, Highlands, and Mallacoota Zones; and Middle Devonian-Carboniferous (post Tabberabberan) in the Ararat- Bendigo, Melbourne, Howqua, and Highlands Zones. Data for the Delamerian granitoids are sketchy, but in the remaining groups S-type granitoids predominate with the exception of eastern Victoria, east of the Yalmy Fault (I-S line), where only I- and A-type granitoids occur. A variety of Sn, Mo, W deposits and prospects are associated with the Benambran and younger intrusive phases.Victoria is a major gold province which has produced nearly 2.5 × 106 kg gold. Primary gold occurs in a number of geological settings including veins and disseminations spatially associated with mafic Cambrian volcanism, vein deposits in turbiditic sequences of central and eastern Victoria, veins associated with mafic and intermediate intrusives of Mid to Late Devonian age, and minor amounts associated with a variety of granitoids and porphyry dykes. |
