Geology

austone-banner

austone-geologyTHE NAMBUCCA OPERATION

Geological Origin of the pebble deposit.

Conglomerate beds – a cemented mixture of sand and pebbles – occur both onshore and offshore along the central coast of NSW. Marine erosion of these beds exposed on the sea floor results in the freed pebbles and sands moving to the land by the constant northwest set of the ocean current.

Attrition through tide changes and wave action further rounded the pebbles and destroyed weak particles. Later changes in sea levels through the latest Ice Ages caused these deposits and their host sand dunes to be abandoned in what is now an inland position well removed from the present beach. Extraction rights were granted to Austone Pty Ltd by the NSW Department of Lands as the pebble reserve lies under Crown land. The product is marketed under the name ‘Nambucca Gold.’

THE CUMBORAH OPERATION

 

Geological Origin of the pebble deposit

Pebbles produced in northwestern NSW have a very different history to those at Nambucca. During the period of erosion, which created that great plains of western NSW and Queensland, vast areas had relatively soft sedimentary rock outcrop at or near the surface (?) The limited coarse rock fragments became concentrated in the low profile drainage systems of that time. In places these river gravels became cemented so that as erosion continued the gravel beds became the durable caps to ridges (or ‘inverted’ river beds). Many of these thin ridge capping have since been eroded away; some exist merely as remnants; and very few remain that are of commercial consequence. The Cumborah deposit, though of limited thickness, is quite extensive. Here again the land belongs to the Crown and extraction rights were granted by the NSW Department of Lands to our sister company Hatexiu Pty Ltd. The product is marketed under the name ‘Cumborah Bronze’ after the local village.

footer