The generator matrix

 1  1  1  1  1  1  1  1  1  1  1  1  1  1  1  1  1  1
 0  2  0  2 2a+2 2a+2  0  2 2a+2  0  2 2a+2 2a 2a 2a 2a  0  0
 0  0  2 2a+2 2a+2  2 2a 2a  0 2a+2  2 2a  0  2 2a 2a+2  0  0

generates a code of length 18 over GR(16,4) who´s minimum homogenous weight is 48.

Homogenous weight enumerator: w(x)=1x^0+15x^48+192x^54+45x^56+3x^72

The gray image is a code over GF(4) with n=72, k=4 and d=48.
This code was found by Heurico 1.16 in -3.24e-008 seconds.