I've been looking for a good explanation on the origin of the turkish word bakır, but I can't find much on it. Is it a loan or is it really a Turkic word for copper?
There is no evidence that bakır comes from any other living language family, and cognates of it are present in many other Turkic languages.
Yakut uses the Turkic root for gold, many major Turkic languages use the Iranic word مس (mis) and a few others жез, джез (compare Mongolian зэс).
bakır was borrowed into Balkan languages from Ottoman Turkish. In any case, although the etymology is opaque, it has been in Turkic for a very long time.
Incidentally, the city now known by some as Diyarbakır had nothing to do with bakır. It was explicitly renamed to as part of 20th century Turkification policies, from Ottoman Diyâr-ı Bekr itself from Arabic Diyaru Bakr, after the occupying Bakr tribe. The actual Aramaic and Greek name is Amida, Kurdish Amed, in Armenian Tigranakert.
The root is not known. But for etymology I would recommend Misalli Büyük Türkçe Sözlük (It is online on kubbealtilugati.com .
According to it, bakır has been used since the old Turkic, but there are some claims that it can be loan word from an Iranian Language (Sogdian maybe?)