The generator matrix

 1  0  1
 0  1 2a^2+3
 0  0  2

generates a code of length 3 over GR(64,4) who´s minimum homogenous weight is 8.

Homogenous weight enumerator: w(x)=1x^0+21x^8+1344x^14+147x^16+21504x^21+9408x^22+343x^24

The gray image is a code over GF(8) with n=24, k=5 and d=8.
This code was found by Heurico 1.16 in 0.00215 seconds.