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Do you know your Gneiss from your Schist?
Since 1968 Arkaroola has been a privately operated 60,000 hectare wildlife sanctuary developed in harmony with the environment. Arkaroola is truly a geological wonderland. The Arkaroola area is well known for its remarkable mineralization and complex geology. The rugged bedrock exposures of the Adelaide fold belt at Arkaroola range in age from Palaeo-Proterozoic to Cambrian, and include marine and nonmarine sediments, basalts, and felsic intrusives. Copper was mined and smelted around 1910 Uranium mining reached a peak during World War 2. Gold and other precious minerals have also been found in the area.
The mineral groups found on Arkaroola include:
• Precious Minerals - gold, sapphire, ruby, amethyst, jasper
• Ore Minerals - malachite, azurite, chrysocolla, covellite, hematite, titanite
• Radioactive Minerals - uraninite, pitchblende, torbenite, autunite
• Rock-forming Minerals - quartz, feldspar, muscovite, biotite, tourmaline, actinolite, granite, basalt, dolomite, limestone
In specific geolocial terms the area around Arkaroola consists of two Mesoproterozoic inliers, the Mount Painter and Mount Babbage Inlier, overlain by Neoproterozoic sediments. The Mt. Painter Inlier consists of deformed and metamorphosed metasediments and 1575 Ma granites. The Mesoproterozoic, rocks are unconformably overlain by the Adelaidean Sequence, which consists mostly of clastic sediments and stromatolitic carbonates. Altered rift basalts near the base of the sequence, the Wooltana Volcanics, are 800 Ma. The metamorphic basement is exposed as the Mt. Painter Inlier in the core of a large anticlinorium, which formed during the 500 Ma Delamerian Orogeny. That orogeny was followed at 440 Ma by a major hydrothermal event, which also produced a large granite intrusion in the middle of the Inlier: the British Empire Granite. The hydrothermal activity resulted in widespread quartz, magnetite-haematite, and actinolite-tremolite-scapolite alteration. It also caused the concentration of uranium in haematite breccia bodies.
The Arkaroola Sanctuary is a paradise for geologists that draws students and scientists from all round the world. The geological monuments of Mt Gee, Mt Painter and The Armchair are all rare geological peculiarities listed on the National Estate. According to the SA Museum the three dimensional exposure of rare crystalline rock formations in the Arkaroola landscape has no global parallel as a natural museum of geology. To the east of Arkaroola Village is a recently discovered fossil 'fringing reef' built at the end of Snow-ball Earth approximately 700 million years ago. It is estimated to be 800m thick compared to the Great Barrier Reef (100m), and contains the calcified remains of organisms that probably represent the oldest animals on Earth. The reef complexes themselves are also of great importance as there have been no other comparable reefs of that age yet discovered anywhere on Earth.
The Earthcache brings you to ArkHenge, a display of geological rock types found in the Arkaroola region. An examination of the samples will provide answers to the following questions. You are encouraged to explore Arkaroola and learn more about the local geology from the owners of Arkaroola, Doug and Marg Sprigg, son and daughter of Reg Sprigg, famed South Australian geologist and founder of Arkaroola, who described the area as 'one great open-air museum of geological history'.
Your earthscience tasks to log this Earthcache are as follows.
Ark Q1: Describe the size and shape of the fossils in the Fossil Limestone? What is the average fossil length that you can see? What do you think these fossils were?
Ark Q2: Compare the feel or texture of Marble surface with the surface of Sandstone?
Ark Q3: How many sides does the Basalt column have? Is the shape regular?
Ark Q4: Measure the size of the cobbles in the Tillite boulder. Are the cobbles smaller or larger than your GPSr?
Ark Q5: (Optional) Submit a photo of yourself between the Gneiss and Schist boulders.
STOP PRESS: Arkaroola Saved from Mining Forever!
Arkaroola Sanctuary has been granted permanent wilderness status by the South Australian government. The revised status means that proposed mining and mineral exploration within the pastoral lease will not progress. Mining will be banned forever in Arkaroola with the aim of national and World Heritage listing.
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