The generator matrix

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

generates a code of length 4 over GR(64,4) who´s minimum homogenous weight is 8.

Homogenous weight enumerator: w(x)=1x^0+28x^8+448x^14+294x^16+7168x^21+6272x^22+1372x^24+172032x^28+50176x^29+21952x^30+2401x^32

The gray image is a code over GF(8) with n=32, k=6 and d=8.
This code was found by Heurico 1.16 in 0.135 seconds.