Mixing models using major and trace elements show that the bulk composition of lithology A (xenocryst-bearing magnesian basalt) of EETA79001 can be reasonably approximated as a simple mixture of ~44% EETA79001 lithology B (ferroan basalt) and ~56% of ALHA77005 light lithology (incompatible element-poor lherzolite). Micro-INAA data on xenocryst-free groundmass samples of lithology A show that about 20-25% of the melt phase could be dissolved lherzolite. The bulk and groundmass samples of lithology A have excesses in Au, indicating either meteoritic contamination or addition by some unknown martian geochemical process. Previous workers have suggested that lithology A was formed by either assimilation of cumulates like ALHA77005 by a basalt like lithology B, or by mixing of basaltic and lherzolitic magmas. The former scenario is energetically improbable and unlikely to explain the normal Fe/Mg zonation in lithology A groundmass pyroxenes, while the latter is unlikely to satisfy the constraints of the mixing model indicating the ultramafic component is poor in incompatible elements. We suggest rather that EETA79001 lithology A is an impact melt composed dominantly of basalt like lithology B and lherzolitic cumulates like the trace element poor fraction of ALHA77005 or Y-793605. This model can satisfy the energetic, petrologic and geochemical constraints imposed by the samples. If EETA79001 lithology A is an impact melt, this would have considerable consequences for current models of martian petrologic evolution. It would call into question the generally accepted age of magmatism of martian basalts, and preclude the use of lithology A groundmass as a primary martian basalt composition in experimental studies. Regardless, the latter is required because lithology A groundmass is a hybrid composition.