Look around you at the bright white rocks scattered across this landscape. These are remnants of quartz veins and were regarded as good news by early gold prospectors. They believed that where there is quartz there is gold.
Until this point we believed that as well. In reality it is not quite that simple.
Gold and other minerals mined in the Murchsion are found in a type of rock known as greenstone. Here you are standing at the southern tip of a greenstone belt that stretches all the way from Meekatharra.
Greenstone belts can be found in association with cratons - the older, stable part of continents that have survived many cycles of merging and rifting. The craton is generally found towards the interior of tectonic plates. Greenstone belts can be hundreds of kilometres long and tens of kilometres wide.
This belt lies in the northwest corner of the Achaean age Yilgarn Craton which is a huge geological region. It is Australia’s premier mineral province and includes the goldfields of Kalgoorlie. It is bounded by a mixture of sedimentary basins and Proterozoic fold and thrust belts.
Generally speaking, greenstone belts are composed of volcanic rocks that also have small amounts of sedimentary rocks interwoven with the various volcanic rocks. Basalt, a volcanic rock, and gabbro are the most common types of rocks found in this greenstone belt. The minerals in these metamorphic rocks are typically dark green in colour hence the name of the belt.
However, the belts also contain other rock types such as banded iron-formation. All these rocks were deposited under water in an ancient ocean which once covered the area. All the greenstone rocks in the Murchison are older than 2,700 million years with some being dated as more than 3,000 million years old.
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1. Other than gold name two other minerals found in the greenstone belt.
2. What type of rock separates the greenstone belts from one another?
3. How far across is the Yilgarn Craton?
4. What type of rock is gabbro?
We hope you enjoy learning about greenstone belts in the Murchison at this Earthcache.