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I ain't being a smarta**, but portland is "made", not mined. Using cement kiln, they add lime, some metals and a bunch of other stuff, heat it under open flame to about 1800 F, and it comes out in round balls (clinkers) which are then milled into powder or cement. It doesn't take many people to run a kiln, but they can only make so much. There's no such thing as running slow or fast...they just run and continuously. Many now burn waste oils and hazardous wastes (solvents, paints, etc.) which is a really cheap fuel for them, and helps the waste disposal industry by making a home for stuff that otherwise would be pretty expensive to dispose of. I just toured a cement kiln in Ohio a few month ago, and it's quite an operation...huge!! We were looking to them as a resource to burn scrap tires (which are really beneficial to their process) but they tell me they hardly buy any coal or gas anymore, but instead others pay to have their wastes burned. Capacity hasn't changed, but their market has expanded dramatically overseas, and they've contracted a lot of their production for several months. Thus the "shortage" here...
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