Argyle diamond mine of tunnelling, the Argyle underground block cave development was officially completed. In 2013, Argyle is estimated to produce 10.2 million carats with an average per carat price of $25/carat. The Argyle diamond mine is also notable for being the first successful commercial diamond mine exploiting a volcanic pipe of lamproite, rather than the more usual kimberlite pipe; much earlier attempts to mine diamonds from a lamproite pipe in Arkansas, USA were commercially unsuccessful. The Argyle mine is owned by the Rio Tinto Group, a diversified mining company which also owns the Diavik Diamond Mine in Canada and the Murowa Diamond
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