Constraints on the Universal CIV Mass Density at z~6 from Early IR
  Spectra Obtained with the Magellan FIRE Spectrograph
  We present a new determination of the intergalactic CIV mass density at 4.3 <
z < 6.3. Our constraints are derived from high signal-to-noise spectra of seven
quasars at z > 5.8 obtained with the newly commissioned FIRE spectrograph on
the Magellan Baade telescope, coupled with six observations of northern objects
taken from the literature. We confirm the presence of a downturn in the CIV
abundance at <z>=5.66 by a factor of 4.1 relative to its value at <z>=4.96, as
measured in the same sightlines. In the FIRE sample, a strong system previously
reported in the literature as CIV at z=5.82 is re-identified as MgII at z=2.78,
leading to a substantial downward revision in $\Omega_{CIV}$ for these prior
studies. Additionally we confirm the presence of at least two systems with
low-ionization CII, SiII, and OI absorption but relatively weak signal from
CIV. The latter systems systems may be of interest if the downward trend in
$\Omega_{CIV}$ at high redshift is driven in part by ionization effects.
