How does North Dakota potash compare to Arizonas?

I was disbelieving when I read the article saying that North Dakota has 50 billion tons of potash. 50 Billion!

We calculated Arizona's Holbrook basin, which is drawing a lot of exploration interest, has up to 2.25 billion tons and that's big.

So, I checked with Ed Murphy, ND State Geologist. Ed confirmed the number. He told me that the are using an estimate that Sid Anderson in his office and Burlington Northern’s chief geologist came up with in 1980. They are hiring a new geologist this summer and one of that person’s duties will be to go back through the oil wells penetrating the Devonian and reassess the potash amount – Ed thinks it could be bigger!

Mark Cocker, minerals geologist with the USGS here in Tucson is completing a global assessment of potash with colleague Greta Orris. Mark shared that the big potash companies seem reluctant to explore the ND deposit because of its roughly 3 km and greater (~10,000-12,000 ft) depth. The Chinese reportedly have done some experimental work on other deposits down to 2.5 km. The Prairie Evaporite Formation also tends to be thinner than potash deposits in Saskatchewan. Mark says there are no grades or mineralogy of the potash that far south - most of the information is from the Regina area to the north and east. Whether the primary mineralogy is carnallite or sylvite makes a big difference. [right, isopach of Prairie Fm, Canada and ND. Credit, North Dakota Geological Survey]

So, for now, Arizona's potash looks pretty competitive. It's shallow, near major rail and highways, and we have some solid info on its mineralogy. There are 4 core rigs drilling for 3 companies, with additional seismic lines being shot. And while a few thousand acres have been leased in ND, it looks like at least 150,000 acres and perhaps over 200,000 acres are tied up in the Arizona play.