This cache has been placed with the permission of the Yolongu people through the Dhimurru Aboriginal Corporation. A Dhimurru permit will be required to access this area. We acknowledge the traditional owners and ask that you respect this very sensitive area, taking only photographs and leaving only footprints.
Information relating to Permit acquisition can be found here.
Laterite is both a soil and a rock type rich in iron and aluminium and is commonly considered to have formed in hot and wet tropical areas. Nearly all laterites are of rusty-red coloration, because of a high iron oxide content. They develop by intensive and prolonged weathering of the underlying parent rock, usually when there are conditions of high temperatures and heavy rainfall with alternate wet and dry periods. Tropical weathering (laterization) is a prolonged process of chemical weathering which produces a wide variety in the thickness, grade, chemistry and ore mineralogy of the resulting soils. The majority of the land area containing laterites is between the tropics of Cancer and Capricorn.
Lateritic Bauxite or Bauxite as its more commonly referred to is the most important aluminium ore in the mining industry. It consists mostly of the minerals gibbsite Al(OH)3, boehmite γ-AlO(OH), and diaspore α-AlO(OH), in a mixture that usually includes the two iron oxides goethite and hematite, and may include the clay mineral kaolinite (see our nearby Earthcache GC9Z5A9), and small amounts of the titanium minerals anatase TiO2, Ilmenite, FeTi 03, and FeO Ti02.
Bauxite is sedimentary and forms just from the weathering of rocks. Weathering is what happens when rocks are left out in the rain, and comes in three forms: physical, chemical and biological. Physical weathering is when bits of rock are attacked by wind, or water, or sometimes just gravity during rock falls. Chemical weathering is when rocks slowly dissolve – rainwater is naturally ever so slightly acidic, and that acid will slowly dissolve the rocks. The third sort of weathering is biological, where rocks are attacked (chemically or physically) by living things.
For bauxite to form, the important factor is chemical weathering (when rocks slowly dissolve) under very specific conditions. Aluminium is the third most abundant element in the Earth’s crust (after oxygen and silicon) and, at 8.4%, the most abundant metal. Aluminium is usually combined very tightly with other elements in some very common minerals. When chemically weathered, Feldspar (found in lots of igneous and metamorphic rocks), forms kaolinite, a clay mineral. This process increases the amount of aluminium oxide in the rock. The essential thing in the formation of bauxite is that all of the other elements dissolved in the process which aren’t wanted such as silica or quartz as you may know it, can, in tropical conditions, stay dissolved in the rainwater and be carried away, leaving the aluminium in place.
To log this EarthCache we require you to visit GZ and WP2, consider the information given and make some observations, then message us with the following answers to the best of your ability.
1. Observe the rocks around GZ, note their colour, particle size and visual composition. What characteristics of the location and the rocks you see suggest you are in fact looking at Bauxite?
Now we would like you to walk through the Wurrwurrwuy stone arrangements, the entrance is near the parking coordinates, please stick to the path and do not remove any rocks. A part of the way through the walk you will arrive at WP2.
2 At WP2 there are several medium rocks embedded in the ground on the paths edge. Compare their particle size and colour to those at the posted cords, in your answer suggest what the differences are and suggest what has happened to the particles at both locations before their formation into bauxite.
3. A photo of you or something relating to you and/or your team at/near GZ
You are welcome to log your find straight away to keep your TBs and Stats in order, but please message us with your answers within a few days. Cachers who do not fulfil the Earth Cache requirement will have their logs deleted.
Source: www.open.edu/openlearn/mod/oucontent, Geology.com. Wikipedia.