The 3D explicit simulation of mixed phase clouds is performed at the g-mesoscale using a new bulk microphysical scheme which attempts to incorporate the activation/nucleation properties of the aerosols. The scheme predicts the mixing ratios and the concentrations of the cloud water, the cloud ice and the raindrops while only the mixing ratios of the snowflakes and of the graupels are prognosed. The CCN activation is resolved analytically for lognormally distributed aerosols. The cloud ice formation is initiated by multiple homogeneous, heterogeneous (with IN) and secondary nucleation processes. A description of the scheme is first given with a special attention paid to the original treatment of some microphysical processes. A preliminary validation of the scheme is then presented in a 3D moderate convection case and the results are compared to those obtained with a very detailed bin scheme running on the same case. Finally the sensitivity of the precipitation formation pathways to the initial CCN and IN concentrations in a deep convective storm is explored.