The nature of the aurophilic interaction is studied by applying local second-order Moller-Plesset perturbation theory (LMP2) on model dimers of [X-Au-PH3](2) (X=H, Cl) type. The possibility to decompose the correlation contribution of the interaction energy in the dimer (A-B) into different excitation classes reveals that the dispersion contribution (A-->A', B-->B') is accompanied by an almost equally important ionic component (A-->A', B-->A'), at shorter distances. Double excitations where at least one electron originates from the gold 5d orbitals account for almost 90% of the attraction. Relativistic effects amount to 28% of the binding energy and can be traced to arise almost exclusively from the relativistic expansion of gold d-shells.