Schonfeld reported in early 1974 that The K-U, Th-U, and Th-Al systematics for lunar samples from the Apollo I t-17 missions
and the Luna 16 and 20 missions are summarized. With few exceptions (granitic portion of 12013 and
the Apollo 17 mare basalts) the Th/U ratio is 3.8 ::t: 0.2. The K/U ratio for lunar samples is about 2600
and is distinctly different from the K/U ratio found in terrestial samples and in the majority of
meteorites. The K-U systematics are similar to the K-La, K-Sm, K-Ba, and K-Zr systematics,
suggesting that the moon accreted approximately homogeneously. Based on a model the moon
contains an average abundance of about 80 ppb U, about 200 ppm K, and about 7 times chondritic
abundances for all the refractory elements such as Al, Ca, Ti, Zr, Ba, Sr, and REE. The Th-Al
systematics of many lunar highland rocks are dominated by the presence of the rock-type KREEP.
He concluded that:
1) The K/U ratio for lunar samples is about 2600 and distinctly different from the K/U ratio found in terrestrial samples (about 13000) and the majority of the meteorites.
2) The Th/U ratio in lunar samples is 3.8 ± 0.2. Exceptions are the granitic portion of rock 12013 and the Apollo 17 mare basalts.
3) The K-U systematics of lunar samples are similar to the K-La, K-Sm, K-Ba, and K-Zr systematics suggesting that the moon has accreted approximately homogeneously.
4) Based on a model presented in this paper, the average concentration of the Moon is about 80 ppb U, about 200 ppm K, and about 7 times chondritic abundances for all the refractory elements such as Al, Ca, Ti, Zr, Ba, Sr, REE, etc. A similar procedure for the earth gives concentrations of 31 ppb U and 400 ppm K for a core free of radioactive elements.
(5) In general, the relatively high concentrations of Th, K, and U found in lunar samples are associated with the lunar rock-type KREEP. In many highland rocks such as "low-K Fra Mauro basalt," "VHA," KREEPy 16, and KREEPy 17, the Th-AI systematics is dominated by the rock-type KREEP.
[All see a later review of K/U systematics by Campbell (1974)].
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