* Due to the varied uses of the Oval GZ is only a suggested point, anywhere on or close to the main oval is fine to visit for this EC.
The geology of Tasmania is complex, with the world's biggest exposure of dolerite. The rock record contains representatives of each period of Neoproterozoic, Paleozoic, Mesozoic and Cenozoic eras. It is one of the few southern hemisphere areas that were glaciated during the Pleistocene with glacial landforms in the higher parts. The west coast region hosts significant mineralisation, which brings us to Queenstown.
Queenstown is uniquely beautiful and an environmental disaster all in one. Reminders of the impacts of mining’s past, present and future are prevalent from nearly every viewpoint in Queenstown, whether it’s the stark baron hills around town, the messy mullock heaps, the ‘pumpkin soup’ constantly flowing down the Queen river or the grassless football oval ‘The Gravel’ in town.
‘The Gravel’ as it is affectionately known, is the best and only example of Siliceous rocks left in Queenstown, naturally occurring in the area silica was present before the construction of the oval. The silica here is a result of the dolomite being dissolved away and wash down over millions of years, leaving layers silica. Since 1969 scrap silica from the surrounding mines have been placed into of the already existing silica layer to enhance the conditions and form a flat playable surface, grass was initially tried but as is the case in most of Queenstown, grass would not grow because of the environmental damage associated with mining of Copper and other minerals in the area.
Siliceous rocks are sedimentary rocks that have silica (SiO2) as the principal constituent. The most common siliceous rock is chert; other types include diatomite. They commonly form from silica-secreting organisms such as radiolarians, diatoms, or some types of sponges.
Smelters Quarry in Queenstown is a disused quarry where the Siliceous rocks were also able to be seen, much of the gravel from this quarry when it was closed ended up supplementing the oval in town. We have inserted a passage from Department of Infrastructure, Energy and Resources report Tasmanian Geological Survey Record 2009/03.
SMELTERS QUARRY, QUEENSTOWN Limestone in this disused quarry [380400/5340900] dips steeply and youngs southwards, as indicated by stromatoporoids in growth position and geopetal vug fillings. The quarry exposes an interbedded sequence of fine-grained, dark grey limestone, in places with dolomitised burrows; thinly interbedded limestone/dolomite; fine-grained dolomite; and laminated pale grey limestone. Within the dark grey limestone there are rare, unusual stromatactis-like vugs that are irregularly hemispherical to tubular in shape and 50–200 mm in diameter. These are filled with coarse calcite spar and a later mineral, probably saddle dolomite; a few are floored with laminated internal sediment. There are common, coarsely calcified stromatoporoids, gastropods (Lophospira, Lesueritella), calcareous algae, and silicified Tetradium. Hill (1955) and Hill and Edwards (1941) recorded several species of Tetradium and other corals from this locality. Corals and cephalopods here suggest correlation with the upper part of the Lower Limestone Member (Banks and Baillie, 1989).
It should also be noted that Siliceous rocks were used as a flux by many of the local mines. By definition (in metallurgy) Flux, any substance introduced in the smelting of ores to promote fluidity and to remove objectionable impurities in the form of slag. Limestone is commonly used for this purpose in smelting iron ores. Other materials used as fluxes are silica, dolomite, lime, borax, and fluorite.
To log this Earth Cache, we require you to visit GZ to make some observations, consider the information given, then message us with the following answers to the best of your ability.
1. Visit the Oval, touch the surface, pick some of the gravel up, does it feel soft or harsh and sharp? Explain why you think it feels like this?
2. Describe the colours in the pieces, are they all the same or are the pieces made up of various colours. Explain why you think this is the case?
3. Why do you think the oval is gravel?
4. A photo of you or a personal item at the Oval (no close ups of the gravel please)
You are welcome to log your find straight away to keep your TB's and Stats in order but please message us with your answers within a couple of days. Cachers who do not fulfil this Earth Cache requirement will have their logs deleted without notice.
Source: Britanica.com, https://www.mrt.tas.gov.au/, Wikipedia.