Argyle diamond mine at the Ekati mine, both in Canada. However, Argyle has two to four times the concentration of diamonds (ore grade) of these mines. This makes extraction economically feasible, as mine costs are mostly related to the amount of ore processed, not the amount of diamond extracted. In 2005, Rio Tinto was given the go-ahead to a future expansion project, moving it from an open pit to an underground mine. This plan was postponed; in September 2010 Rio Tinto announced fresh plans to develop an underground mine beneath the existing pit, increasing annual production to 9 million tonnes of ore. The
Permafrost down to . Discontinuous permafrost is often further divided into "extensive discontinuous permafrost", where permafrost covers between 50 and 90 percent of the landscape and is usually found in areas with mean annual temperatures between , and "sporadic permafrost", where permafrost cover is less than 50 percent of the landscape and typically occurs at mean annual temperatures between . In soil science, the sporadic permafrost zone is abbreviated SPZ and the extensive discontinuous permafrost zone DPZ. Exceptions occur in "un-glaciated" Siberia and Alaska where the present depth of permafrost is a relic of climatic conditions during glacial ages where winters