  Recent {\it Hubble Space Telescope} photometry in the nearby elliptical
galaxy NGC 5128 shows that its halo field star population is dominated by
moderately metal-rich stars, with a peak at [m/H] $\simeq$ -0.4 and with a very
small fraction of metal-poor ([m/H] $<$ -1.0) stars. In order to investigate
the physical processes which may have produced this metallicity distribution
function (MDF), we consider a model in which NGC 5128 is formed by merging of
two major spiral galaxies. We find that the halo of an elliptical formed this
way is predominantly populated by moderately metal-rich stars with [m/H] $\sim$
-0.4 which were initially within the outer parts of the two merging discs and
were tidally stripped during the merger. To match the NGC 5128 data, we find
that the progenitor spiral discs must have rather steep metallicity gradients
similar to the one defined by the Milky Way open clusters, as well as sparse
metal-poor haloes (5% or less of the disc mass). Very few stars from the
central bulges of the spiral galaxies end up in the halo, so the results are
not sensitive to the relative sizes (bulge-to-disc ratios) or metallicities of
the initial bulges. Finally, we discuss the effects on the globular cluster
system (GCS). The emergent elliptical will end up with metal-poor halo clusters
from the original spiral haloes, but with moderately metal-rich halo stars from
the progenitor discs, thus creating a mean offset between the MDFs of the halo
stars and the GCS.
