  The cross section for coherent $\mathrm{J/}\psi$ photoproduction in Pb-Pb
collisions is the sum of two contributions, one from low-, the other from
high-energy photon-nucleus interactions. A novel method to disentangle both
contributions allowing one to extract the coherent photo-nuclear cross section
for coherent $\mathrm{J/}\psi$ production, $\sigma_{\gamma \rm Pb}$, is
presented. The utility of the method is demonstrated using measurements from
peripheral and ultra-peripheral Pb-Pb collisions at the LHC. Applying the
proposed method to the available data it is possible to obtain $\sigma_{\gamma
\rm Pb}$ up to a photon-lead centre-of-mass energy of 470 GeV, which
corresponds to $x$ of 4.4x10$^{-5}$. To illustrate a possible use of the
extracted photo-nuclear cross sections, the corresponding nuclear suppression
factors are computed and they are compared to predictions of gluon shadowing
calculated in the leading-twist approximation approach.
