“... The Oxley River is a part of the Tweed River system in the state of New South Wales, -just south of the Queensland border- Australia. It drains the area formed by the Mt Warning shield volcano. Most of the material found in the river has travelled a long way, so many broken and waterworn pieces of agate are often found.
Agates are found in the gravel beds of the river system. However, the availability of agate is confined to post flood situations when the gravel beds are "turned over" to reveal gemstone material. It is not uncommon to find "Iris Agate" in all the streams of the Tweed River system.
Tyalgum creek is a tributary of the Oxley River so material found here is similar to Tyalgum creek agates and chalcedony etc....”
according to personal communication with John Nedwich