Geological Time Scale: News, Analysis and Market Coverage

The Archean eon (4 to 2.5 billion years ago) hosts some of the world's richest gold and iron ore deposits, including the Pilbara and Yilgarn cratons in Western Australia and the Witwatersrand Basin in South Africa. The Proterozoic eon hosts the Central African Copperbelt and uranium deposits in Canada. Mesozoic subduction along the Pacific Rim created porphyry copper deposit systems that host much of the world's copper and molybdenum. Carboniferous and Permian periods correspond to global coal formation from ancient swamp vegetation.

Eons are the longest divisions of geological time, spanning hundreds of millions to billions of years. The Hadean eon covers earth's earliest history from approximately 4.5 to 4.0 billion years ago. The Archean eon runs from 4.0 to 2.5 billion years ago. The Proterozoic eon runs from 2.5 billion to 541 million years ago. The Phanerozoic eon, covering 541 million years ago to the present, is subdivided into the Palaeozoic, Mesozoic, and Cenozoic eras, each defined by distinct geological and biological transitions.

Geological time is a core exploration tool because ore deposits are not randomly distributed through history: specific deposit types are concentrated in specific geological periods due to the conditions required to form them. Porphyry copper deposits cluster in Mesozoic and Cenozoic arc environments. Banded iron formations are almost exclusively Archean and early Proterozoic. High-grade gold provinces often occur in Archean greenstone belts. Knowing the geological age of a target terrane allows explorers to calibrate the probability of finding specific deposit types, improving the efficiency of exploration expenditure.

The Holocene is the current geological epoch, covering approximately the last 11,700 years of earth history. In mining, Holocene age sediments host many placer gold, mineral sand, and alluvial diamond deposits formed through recent weathering and fluvial redistribution of older ore sources. Holocene and late Pleistocene coastal environments are targeted for mineral sand mining in Australia, South Africa, and Mozambique, where beach and dune deposits contain concentrations of ilmenite, rutile, and zircon. The youth of Holocene deposits makes them typically shallow and amenable to surface extraction.

Most economically significant coal deposits formed during the Carboniferous and Permian periods, roughly 300 to 250 million years ago, when large areas of the earth were covered by dense tropical and temperate forests. Organic material from these ancient forests accumulated in swampy environments, was buried by sediment, and transformed over geological time into coal through heat and pressure. The quality of coal increases with depth of burial and thermal maturity: lignite is the youngest and least transformed, while anthracite represents the most deeply buried and thermally mature coal.