Excess Lead in "Rusty Rock" 66095 and Implications for an Early Lunar Differentiation

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Science  30 Nov 1973:
Vol. 182, Issue 4115, pp. 916-920
DOI: 10.1126/science.182.4115.916


Apollo 16 breccia 66095 contains a remarkably high amount of lead (15 parts per million), 85 percent of which is not supported by uranium and thorium in the rock. An acid leach experiment coupled with separate analyses of the whole rock and mineral fractions for uranium, thorium, and lead indicate that the excess lead has a lunar source and was apparently introduced about 4.0 x 109 years ago. The data also suggest that a major lunar crustal differentiation occurred about 4.47 x 109 years ago.