Satellite images are, not surprisingly, captured by satellites that orbit the earth. The images can be real colour or show different spectrums like infrared. Most of the images you can see on Google Earth are captured from these satellites.
These images often form the base onto which geological maps are drawn. Geologists can never traverse the entire landscape in order to note the rock types occur there, so they rely on satellite images to help extrapolate the observations they do make. For example when a geologist is walking in the landscape and sees some limestone, she can look on a satellite image and see that this area appears a pale grey on the image. That pal grey area can then be inferred to be limestone for as far as it is recognised in the image. This is complicated by vegetation or soil cover. In these cases geophysics can be employed to assist in identifying trends in rock types.
The purpose of all this work in terms of gold exploration is it’s application to choosing the most suitable areas to explore and in particular in applying gold deposit model targeting.