The score to Black Gold is a great score. Horner is a most incredible composer for understanding the emotion of the characters, which is most effective in film scoring. I did however catch some snippets of Horner's previous score, Enemy of the Gates. If you listen to the score, you may hear it. However, it is not as obvious as some of the other themes he's reused in other score.
I really don't care what the man uses or reuses, he is truly talented in telling stories musically, and I will continue to buy score from Horner as long as he keeps writing music. There is an interview of him talking about Black Gold, and the way he sees things musically is almost like how John Nash sees things mathematically.