  In preparation to the experimental results which will be available in the
future, we consider geo-neutrino production in greater detail than in [F.
Mantovani et al., arXiv:hep-ph/0309013], putting the basis for a more refined
model. We study geo-neutrino production for different models of matter
circulation and composition in the mantle. By using global mass balance for the
Bulk Silicate Earth, the predicted flux contribution from distant sources in
the crust and in the mantle is fixed within +-15% (full range). A detailed
geological and geochemical investigation of the region near the detector has to
be performed, for reducing the flux uncertainty from fluctuations of the local
abundances to the level of the global geochemical error. A five-kton detector
operating over four years at a site relatively far from nuclear power plants
can measure the geo-neutrino signal with 5% accuracy (1 sigma). It will provide
a crucial test of the Bulk Silicate Earth and a direct estimate of the
radiogenic contribution to terrestrial heat.
