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The isotopic composition of the lead minerals from the Balmat Area was determined by standard mass spectrographic methods. The results and sample descriptions are tabulated. The isotopic composition indicates a Precambraian age. According to the latest estimate of lead isotope evaluation in the earth's crust model, the age of deposition is 1050 the J-57 engine 100 million years.
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Brown et al. (1959) studied this question.
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