The Diavik dimond mine and A154S pit in the Lac de Gras kimberlite field were certainly the highlight of the kimberlite fieldtrip that I organized in 2004 for our students. On this photograph, the black ground our group is standing on is resedimented volcaniclastic (i.e. erupted and reworked) kimberlite loaded with diamond-indicator minerals (chromian diopside, pyrope, etc.) and... well, yes, diamonds. At nearly 5 carats per tonne (= 1 part per million), the A154S pipe has one of the highest grades among all diamond deposits currently in production. Another interesting detail: Before any mining could begin, a series of dikes with thermosyphons (ground-freezing equipment) had to be constructed to enclose the site of future mining operations, and preclude waters of Lac de Gras from seeping into the mine. On the photograph, we are standing well below the lake level. See next photo.