  We investigate the energy spectrum of the biaxial spin systems with magnetic
field along the hard anisotropy axis by using the complex periodic orbit
theory. All important features of the system appearing in whole energy range,
such as oscillations of level splittings due to Wess-Zumino effect and their
absence at higher magnetic field etc., can be completely understood within this
semiclassical scheme. We find out that the fields at which the tunnelling
quenches do not shift at higher energy levels and the absences of the quenching
at higher magnetic field have their origin in an exact coincidence of the
quenching field with the field of resonant tunnelling. Based on the result, we
propose that the complete cancellation of quenching with resonant tunnelling
would be a general property of Wess-Zumino tunnelling systems.
