Answer:
Ores mined from shields.
Step-by-step explanation:
The Precambrian supereon is an informal division of the geological time scale, it is the first and longest stage in the history of the Earth - more than 88% -, which includes the Hádic, Archaic and Proterozoic eons. This supereon began when the Earth formed, between 4567.9 and 4570.1 million years ago and ended 542.0 (± 1.0) million years ago. It lasted approximately 4027 million years and gave way to the Phanerozoic Aeon / Paleozoic Era / Cambrian Period. The study of the Precambrian is very complex, because in general the rocks formed during this time are very transformed by different orogenic cycles (tectonic deformation, metamorphism, etc.) and fossils are very scarce.
Precambrian rocks are mainly igneous and metamorphic. In South Africa, the Kaapvaal Craton, in Western Australia, the Pilbara Craton and in Greenland are the oldest terrestrial rocks dating back approximately 3800 million years.