\begin{table}%t5
%\centering
\par
\caption{\label{dust}Iron to zinc or silicon ratio and extinction estimate for 4 strong Mg~{\sc ii} systems.}
\begin{tabular}{lcccccccc}
\hline\hline\noalign{\smallskip}
& $z$ & $N$(FeII) & $N$(ZnII) & $N$(SiII) & [Fe/Zn] & [Fe/Si] & $N_{\rm Fe}^{\rm dust}$ & $ A_{\rm V}$ \\  
&     &(cm$^{-2}$) & (cm$^{-2}$) &(cm$^{-2}$) &     &        & (cm$^{-2}$) & \\
\hline
GRB021004&1.3800&$15.09\pm0.05$&&$15.19\pm0.09$&&$-0.05\pm0.10$&$14.18\pm0.23$&$\sim$0\\
GRB021004&1.6026&$14.60\pm0.03$&$12.78\pm0.02$&&$-1.03\pm0.04$&&$15.59\pm0.02$&$<$$0.2$\\
GRB060418&1.1070&$14.69\pm0.01$&$12.87\pm0.03$&&$-1.05\pm0.03$&&$15.68\pm0.03$&$<$$0.2$\\
GRB060607A&1.8033&$14.07\pm0.03$&&$14.36\pm0.10$&&$-0.24\pm0.10$&$13.94\pm0.17$&$\sim$0\\
\hline
\end{tabular}
\end{table}