$^{64}$Zn is produced in complete Si-burning (cf. Umeda & Nomoto 2003, 2005). In addition, hypernovae, defined as supernovae with high explosion energies (E$_{51}$ $\simgreat$ 2 for M$\sim$13 M$_{\odot}$ and E$_{51}$ $\simgreat$ 20 for M $\simgreat$ 20 M$_{\odot}$), give rise to ejecta with \[Zn/Fe\] as high as $\sim$0.5 (Umeda & Nomoto 2002; Nomoto et al. 2013). Therefore, Kobayashi et al. (2006) have invoked hypernovae to explain the high \[Zn/Fe\] ratios in metal-poor stars.

The majority of the Fe-peak elements show solar abundance ratios in most objects for all metallicities. The elements Sc, Mn, Cu, and Zn, however, show different trends (e.g. Sneden et al. 1991; Nissen et al. 2000; Ishigaki et al. 2013; Barbuy et al. 2013). Nissen & Schuster (2011) find that Zn behaves like alpha elements, with high-alpha halo stars and thick disk stars displaying also high Zn abundances, whereas the low-alpha halo stars show a lower Zn enhancement that decreases with metallicity. This distinct behaviour is explained if both these elements (Zn and alphas) are produced by core-collapse supernovae. The \[Zn/Fe\] decrease with metallicity in low-alpha stars is then expected, characterizing a system with slower chemical enrichment.

A useful means of better understanding the nucleosynthesis processes yielding iron-peak 