Homevale National Park Mackay

Nature, culture and history

Natural Environment

Geology

Cliffs, peaks and spires prominent on the eastern horizon of Homevale National Park are remnants of the Nebo Volcanoes, which erupted here about 34 to 32 million years ago. The Nebo Volcanoes were the second in a line of volcanoes that erupted down the eastern side of Australia from 34 to 6 million years ago, as the Australian crustal plate drifted northwards over a stationary ‘hot-spot’ in the Earth’s mantle below. The first eruptions were at Cape Hillsborough north of Mackay.

The initial lavas were of basalt, but later rhyolite lavas, breccias and tuffs (fragmental rocks) were ejected in violent eruptions. The Diamond Cliffs, Sydney Heads and the peak of Mount Britton are formed of these rocks, while the Marling Spikes are plugs of rhyolite probably intruded into a subsidiary vent. These peaks are prominent in the landscapes because their rocks are more resistant to erosion than the surrounds.

The volcanoes erupted over earlier rocks of the Bowen Basin, a major depression that sank behind eastern Australia in Permian times about 290 million years ago. The first rocks of this basin, the Lizzie Creek Volcanics, underlie the eastern part of the national park but they weather deeply and are poorly exposed. Gold-bearing quartz veins in these rocks have been worked in the old Mount Britton mine, and have shed alluvial gold into the nearby Oaky Creek.

The next phase of the Bowen Basin saw the sea invade and deposit marine sediments, which are now exposed in the western section of the national park. Important marine shellfish fossils have been found there. Later the sea retreated, and extensive swamps accumulated decomposing vegetation which consolidated to coal deposits. The Hail Creek coal mine is working some of these deposits just west of the national park boundary.

Geology content courtesy of Warwick Willmott.

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