  NGC5824 is a massive Galactic globular cluster suspected to have an intrinsic
spread in its iron content, according to the strength of the calcium triplet
lines. We present chemical abundances of 117 cluster giant stars using
high-resolution spectra acquired with the multi-object spectrograph FLAMES. The
metallicity distribution of 87 red giant branch stars is peaked at
[Fe/H]=-2.11+-0.01 dex, while that derived from 30 asymptotic giant branch
stars is peaked at [Fe/H]=-2.20+-0.01 dex. Both the distributions are
compatible with a null spread, pointing out that this cluster did not retain
the ejecta of supernovae. The small iron abundance offset between the two
groups of stars is similar to those already observed among red and asymptotic
giant branch stars in other clusters. The lack of intrinsic iron spread rules
out the possibility that NGC5824 is the remnant of a disrupted dwarf galaxy, as
previously suggested. We also find evidence of the chemical anomalies usually
observed in globular clusters, namely the Na-O and the Mg-Al anticorrelations.
In particular, NGC5824 exhibits a huge range of [Mg/Fe] abundance, observed
only in a few metal-poor and/or massive clusters. We conclude that NGC5824 is a
normal globular cluster, without spread in [Fe/H] but with an unusually large
spread in [Mg/Fe], possibly due to an efficient self-enrichment driven by
massive asymptotic giant branch stars.
