Than you should change it to incorporate more types of blocks..
Right now the array is filled with 0's and 1's, maybe adding 2's and 3's and 4's could be used to add more materials?
And if diamond is only found in a deep level you might want to add a condition
"If level is deep add diamonds"
So only if level is deep ( I guess you know when a level is deep and are able to tell the computer when that is) add the number 5 to the array (assuming number 5 is diamond)
If this all is a bit too much, you might want to opt for creating the levels yourself inside the tilemap-object and or array..