One is an almost 2000 feet deep rock salt mine, which extends 5 square miles under the Lake Huron and produces over 7 million tons of highway deicing salt annually. Today's "room and pillar" mining begins with a shaft sunk through the overlaying rock to the salt deposit. The salt is removed leaving large square caverns alternating with pillars of salt which serve as support for the rock and earth above. The size of the rooms and pillars is determined by the depth and thickness of the deposit. Blasting breaks the salt into manageable pieces which are conveyed to cryushers. After crushing, the salt is screened to various sizes. Purity depends upon the type of salt deposit, but is usually between 92% and 98%.
The other is an evaporator plant that extract brine and uses it to produce a variety of products for industrial, agriculture and other commercial use.
(OT.Ljøstad information, taken from the caption of his photo of halite. See also the messageboard at )
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