Potassium-argon and neutron activation analysis studies of polyhalites near the WIPP site
Samples of the purest available polyhalite (K/sub 2/Ca/sub 2/Mg(SO/sub 4/)/sub 4/.2H/sub 2/O) were selected from various drill cores or other available specimens. The selected material was very gently crushed by hand to -40/+200 mesh under dehumidified conditions. Radiogenic argon analyses were performed in duplicate on separate aliquots of each sample using conventional K-Ar dating techniques. The argon analyses were performed statically using an AEI MS-10 mass spectrometer. Potassium analyses were done by flame photometry after fusion of the samples with LiBO/sub 3/. The data obtained are of interest for several reasons: (1) the determined polyhalite K-Ar ages agree well with the Rb-Sr isochron age suggesting that the actual last crystallization of the potash ore may have taken place in the Triassic (210 m.y.) rather than in the Latest Permian; (2) polyhalite associated with a lamprophyre dike is reasonably close in age (21.4 m.y.) to the dike itself (31 m.y.) and confirms the age of intrusion of the dike. The nearby melt halite and post-polyhalite sylvite are probably also close to 20 m.y. in age; (3) the polyhalite data refute the old statements made by several authors that this mineral is not suitable for K-Ar dating; (4) polyhalite is apparently a very useful mineral for dating by the K-Ar method. Polyhalites can and should be used for purposes of tracing diagenetic and post-formational events at the WIPP site and in other evaporites.
- Research Organization:
- New Mexico Univ., Albuquerque (USA). Dept. of Geology
- DOE Contract Number:
- AC04-76DP00789
- OSTI ID:
- 6537702
- Report Number(s):
- SAND-81-7071
- Country of Publication:
- United States
- Language:
- English
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HADRON REACTIONS
HYDRATES
ISOTOPE DATING
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NEUTRON REACTIONS
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NUCLEAR REACTIONS
NUCLEON REACTIONS
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