Well... I have a whole bunch of issues with this plan, but let me throw in my couple of cents.
Have you thought about sectioning the mass with fault lines and deliberate failure locations. Basically, you create a lattice of drilled holes in the object and mine them with explosives. When the object approaches the moon, the explosives are ignited shattering the object into many smaller pieces and distributing the impact over a significantly wider area. The larger pieces would be mined with the intention of shatter zones in order to absorb significant amounts of the energy of impact and allow for easier collection of the material (like a crumple zone on a car).
The object that is required to be "shipped" would be place in one of the larger pieces with the deliberate shatter zones and suspended within some form of energy absorbing material/foam. The object itself would be made of an incredibly hard/resilient object. I would also recommend lacing it with some form of radioactive tracer element deliberately designed to have a specific energy yield and there being SEVERAL of them within protected crumple zones. Because honestly, if they were going through all this work they'd never leave this up to chance/just having one of them.
Basic assumptions are that the minerals are an ore rather than a processed material, because otherwise the shattering idea wouldn't work very well.
How, if I may be so bold, do you expect there to be a barrel of appropriate strength to contain the force of the explosion to launch this? ( Even the Saturn V rockets were only 3200 tons and they were mostly fuel )
Would not a more efficient method (and subsequently just as impressive) be multiple launches from a variety of locations with multistage rockets ( a la Saturn V rockets )?
