Gold is widespread in the earth's crust. While its concentration is low normally low (aprox 5 milligrams per tonne of rock) there are higher concentrations, normally called ore deposits. This area was thought to have an ore deposit.
Gold is transported through the earths crust in warm to hot salty water. These fluids are generated in large volumes in the Earth's crust as water-bearing minerals dehydrate during metamorphism.
The gold present in the rocks is heated, squeezed and sweated out and becomes a solution of complex ions. In this form the dissolved gold with other elements (such as silicon, iron, slphur etc) travels through fractures in the rock.
The gold generally travels upwards, to lower pressure and cooler regions near the Earth's surface. The gold eventually becomes insoluble and crystallises. This process frequently occurs with quartz (silicon dioxide), which results in quartz veins that contain Gold.
Quartz is almost always clear or white.
Gold deposits have formed at many different times during Earth’s history.
Based on your observations at the site, answer the following questions and message the CO with the answers:
- How long ago did the quartz and gold veins intrude into the sedimentary rock?
- At this site, what did the molten rock (which the gold intruded into) crystalise into?
- Looking at the rock near the mine entrance does it appear to be quartz?