Apollo 12 breccia 12013 is composed of two portions, one grey in colour, the other black. The grey portion of the brecciaconsists mainly of felsite thought to have formed during a single crystallisation event, while the black part is characterized bypresence of lithic fragments of noritic rocks and individual plagioclase crystals. In this study, U-Pb analyses of Ca-phosphateand zircon grains were conducted in both portions of the breccia. The zircon grains within the grey portion yielded a largerange of ages (4154 ± 7 to 4308 ± 6 Ma, 2r) and show decreasing U and Th concentrations within the younger grains. Moreover,some grains exhibit recrystallisation features and potentially formation of neoblasts. The latter process requires hightemperatures above 1600–1700 C leading to the decomposition of the primary zircon grain and subsequent formation ofnew zircon occurring as neoblasts. As a result of the high temperatures, the U-Pb system of the remaining original zircongrains was most likely open for Pb diffusion causing partial resetting and the observed range of 207Pb/206Pb ages. The eventthat led to the Pb loss in zircon could potentially be dated by the U-Pb system in Ca-phosphates, which have a weighted average207Pb/206Pb age across both lithologies of 3924 ± 3 Ma (95% conf.). This age is identical within error to the combinedaverage 207Pb/206Pb age of 3926 ± 2 Ma that was previously obtained from Ca-phosphates within Apollo 14 breccias, zircongrains in Apollo 12 impact melt breccias, and the lunar meteorite SaU 169. This age was interpreted to date the Imbriumimpact. The zircon grains located within the black portion of the breccia yielded a similar range of ages (4123 ± 13 to4328 ± 14 Ma, 2r) to those in the grey portion. Given the brecciated nature of this part of the sample, the interpretationof these ages as representing igneous crystallisation or resetting by impact events remains ambiguous since there is no directlink to their source rocks via textural relationships or crystal chemistry. Similarly, the currently available zircon data set for alllunar samples may be distorted by partial Pb loss, resulting in meaningless and misleading age distribution patterns. Therefore,it is crucial to fully understand and recognize the processes and conditions that may lead to partial resetting of the U-Pbsystem in zircon in order to better constrain the magmatic and impact history of the Moon.