The Geological Backbone of the Gold Coast and its Quarry Industry

1. The Geological Backbone of the Gold Coast and its Quarry Industry

2. A fortunate location • The Gold Coast is fortunate in its geological setting for the supply of quarry rock – • - although not so much for sand

3. One convenient geological unit can provide much of the rock – theNeranleigh –Fernvale beds

4. What are the Neranleigh-Fernvale beds?- and why are they so special ? • they are sedimentary rocks, but ones with a particular history • they occur in thick beds • are steeply inclined • and have been hardened and slightly recrystallised internally (meta-sediments)

5. To understand them we need to go back in time to look at their origins 360 to 310 million years ago the geography around here was a little different -

6. Volcanic mountains being eroded Sediments deposited in deep ocean trench Gold Coast region

7. Sediments slumped into trench • Coarse ‘dirty’ sands with rock fragments • Fine silts and muds • Some basalt lavas erupted onto ocean floor • Siliceous ooze from accumulations of skeletons of microscopic ‘radiolaria’

8. 310-300 million years ago- compression Rocks crumpled, hardened, stood on end

9. Resulting rocks • Greywacke, or meta-greywacke, from ‘dirty’ sands -

10. Argillite, from silts and muds -

11. Greenstone from submarine basalt lavas -

12. and Chert, or Quartzite, from siliceous ooze

13. Greywacke forms the mainstay of the quarrying industry

14. Great masses form thick beds, particularly on the west • but much is in inaccessible terrain

15. In quarry site selection or expansion- • important to minimise interbeds of argillite, as this gives flaky particles • in exploration drilling, angled holes required as beds are vertical or steeply inclined Inclined beds of argillite

16. Quartzite also quarried – • Mainly for pavement gravels as gives dusty aggregates Stapylton quarries

17. Greenstone also quarried – • One quarry in Albert Valley • Gives a heavy aggregate

18. Do other parts of the backbone provide potential sources of quarry rock? • Younger rhyolite lavas occur west of the Neranleigh-Fernvale Beds- the Chillingham Volcanics

19. Similar to rhyolite lavas quarried on the Sunshine Coast • However, in steep terrain entirely within Canungra Army training area, or national park

20. Extensive basalt lavas from the later Tweed & Focal Peak Volcanoes cap the high ranges to the west

22. Basalt is normally a good quarry rock • but here it is in steep, scenic terrain, deeply weathered, and with interbedded soft flows and old soil horizons • only a few sites found suitable

23. Sand situation • Gold Coast is not well endowed • Medium to coarse sand previously obtained from Coomera River channel and flats, but now virtually exhausted • Now obtained from finely crushed greywacke in the rock quarries, • and -

24. Two quarries scraping and crushing quartz sandstone of the Woogaroo Subgroup at Tamborine Village

25. Sandstone of Woogaroo Subgroup occurs in thick beds • Other sandstone to west (Marburg Subgroup) unsuitable as feldspathic and soft

26. Fine sand once obtained from creeks and rivers west of Beaudesert, but now exhausted • Now obtained from one pit on Logan River near Beenleigh, and – • Several pits in poorly graded estuarine and dune sands in old estuarine areas at Jacobs Well and Woongoolba east of Beenleigh

27. The Future Supplies are adequate for the present, but longer-term problems are looming • The area of outcrop of the Neranleigh-Fernvale Beds is rapidly urbanising, or forms steep inaccessible terrain in Water Reserves or National Parks – new quarries will be difficult if not impossible to site • The Chillingham Volcanics are entirely within steep country in the Army training area or national park

28. The basalt lavas to the west are problematical • they are at high levels, commonly in scenic terrain, and are deeply weathered with interbedded softer flows and old soil horizons • production of a consistent product is difficult • road routes from the west are few and tortuous • possibly Tweed Shire in NSW, and low country around Beaudesert merit investigation

29. It will be difficult to site new sand quarries in the eastern part of the Woogaroo Subgroup because of increasing urban and broad acre development. • However other such material west of Beaudesert merits investigation. • The sandstone of the Marburg Subgroup is unlikely to be suitable • The fine sand pits of the estuarine areas east of Beenleigh are constrained by surrounding land uses such as sugar cane

30. Maximum use of existing quarries and immediate surrounds will be required