  We investigate effects of non-zero Dirac and Majorana CP violating phases on
neutrino-antineutrino oscillations in a magnetic field of astrophysical
environments. It is shown that in the presence of strong magnetic fields and
dense matter, non-zero CP phases can induce new resonances in the oscillations
channels $\nu_e \leftrightarrow \bar{\nu}_e$, $\nu_e \leftrightarrow
\bar{\nu}_\mu$ and $\nu_e \leftrightarrow \bar{\nu}_{\tau}$. We also consider
all other possible oscillation channels with $\nu_\mu$ and $\nu_\tau$ in the
initial state. The resonances can potentially lead to significant phenomena in
neutrino oscillations accessible for observation in experiments. In particular,
we show that neutrino-antineutrino oscillations combined with Majorana-type CP
violation can affect the $\bar{\nu}_e$/$\nu_e$ ratio for neutrinos coming from
the supernovae explosion. This effect is more prominent for the normal neutrino
mass ordering. The detection of supernovae neutrino fluxes in the future
experiments, such as JUNO, DUNE and Hyper-Kamiokande, can give an insight into
the nature of CP violation and, consequently, provides a tool for
distinguishing the Dirac or Majorana nature of neutrinos.
