GEOLOGICAL HISTORY
(www.northeastvictoria.online)
The history of North-east Victoria began with a vast inland sea/lagoon which occupied most of Eastern Australia about 500 million years ago. Over time this lagoon filled with sediments (mud, silt, sand and organic waste) which became compressed, heated and cemented into rock (shale, mudstone, sandstone and coal).
This era of weathering and erosion continued until about 400 million years ago when volcanic activity caused the intrusion of volcanic rock (such as granite) and the deposition of thick layers of volcanic ash. Mount Buffalo is an example of intrusive volcanic rock which has subsequently been exposed by erosion.
After this volcanic era the landscape was again modified by the gradual erosion of sedimentary and volcanic rocks from the higher peaks and deposition of this material on the floodplain.
Further volcanic activity occurred and many parts of Victoria were inundated by extensive basalt lava flows. These lava flows formed the Dargo and Bogong High Plains.
In more recent times, materials generated by chemical and physical weathering and erosion were washed out of the High Country and deposited on the floodplains of the Ovens, King, Kiewa, Goulburn and Murray Rivers.
This geological history sets the scene for much of what can be seen today; the rolling hills are largely folded and faulted sedimentary rocks, such as sandstones, with granitic intrusions exposed in many localities.
The vast amount of gold found in the North-east owes its existence to this geological history. Gold ores were probably transported close to the surface by highly mineralised ground water brought up with volcanic magmas.
These ores found their way into ancient stream beds (the so-called ’deep leads’), long since dried out as the surface topography changed. Weathering and erosion has since carried gold bearing ores into the alluvium along the banks and beds of present day streams.
These alluvial deposits were often the site of the first gold rushes in the area, as they were easy to get at, requiring little or no specialised mining equipment, and were often very visible.
The geologic history of the area is expressed in many of the historic buildings in the North-east. For example, fine, durable sandstones became a sought-after building material for the early settlers, and many of Beechworth’s notable buildings made use of this material.
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