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shafts at the Wills-Weaver mine. The potash operations of Duval are now Western
Ag-Minerals. Southwest Potash, now controlled by Horizon Potash, began operation in
1952. The shaft of National Potash (now Mississippi Chemical) in Lea County, New
Mexico, was completed in 1956, and production started in 1957. The Kerr-McGee
facility, completed in 1957, delayed operation until 1965 and is now New Mexico Potash.
Minable potash was discovered in Saskatchewan, Canada, in 1952, but many
factors prevented major production until the late 1950's with exports to the United States
commencing in 1962. In 1964, U.S. domestic consumption permanently exceeded
domestic production . The highest production year for New Mexico potash was 5.7
million st KCl or 3.3 million st KlO in 1966. Production has decreased steadily as
lower-eost Canadian potash has supplied an increasing share of U.S. potash consumption.
The cross-over years were 1970 and 1971, when imports fIrst exceeded domestic
production. A low of 1.3 million st of KlO was produced in 1986 in the United States.
Overall U.S. potash capacity utilization declined from 83% (1984) to 61 % (1985), made
more signifIcant because total capacity also declined during this period.
A dumping fmding against Canadian producers by the International Trade
Commission in 1987 and the 1988 antidumping agreement between the U.S. Department
of Commerce and Canadian producers reversed the downward trend in output and
utilization and revitalized the industry in New Mexico. Mississippi Chemical was
reactivated in 1988 after several years on standby. Price increased after a 1988 anti-dumping
agreement with Canada allowed AMAX to continue operation until its mine was
purchased by Horizon in 1992 (closed in 1994) and has increased reserves at other
properties in the Carlsbad Potash District. Large exports by the former USSR again
depressed prices and demand in 1992-93. The impact of Canadian, Russian, and other
competition, declining reserves and grades, and increased mining costs, led to many
changes in ownership since 1985. Of the older companies, only Mississippi Chemical
and IMC remain active (Table 5).
III-3
ECONOMIC GEOLOGY
Potash-bearing evaporites occur in Ochoan (Upper Permian) marine rocks in the
Delaware basin portion of the Permian basin of west Texas and southeast New Mexico.
Ochoan rocks, which are about 240 million years old, overlie Guadalupian carbonates and
sandstones within the basin and overlie dominantly reefal carbonates along the basin
flanks (many sources including King, 1948; Hayes, 1964; Pray, 1988; and Ulmer-Scholle
et al., 1993). The Ochoan is divided into four formations (Fig. 3; Lowenstein, 1988):
(1) the Castile Formation (oldest)-halite and banded anhydrite/limestone, (2) the Salado
Formation--potash (ore mainly in the McNutt Member), halite, muddy halite, anhydrite,
polyhalite, dolomite, and mudstone, (3) the Rustler Formation-halite, gypsum, anhydrite,
siliclastic rocks, dolostone, and limestone, and (4) the Dewey Lake Redbeds (youngest)--siliclastic
mudstone and sandstone. The Castile and basal portions of the Salado
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