The metamorphic rocks that comprise the majority of the Barrier Ranges represent a sequence of heated and deformed sedimentary rocks that were deposited 1710-1715 million years ago. These sedimentary rocks were intruded shortly after they formed by basaltic magmas (similar to the stuff that comes out of the Hawaiian volcanoes). This package of rocks were then cooked (metamorphosed) around about 1600 million years ago at temperatures of about 600 degrees, under pressure of about 4500x that at the surface of the Earth (at about 12-15 km depth).
The grey-brown rocks seen in the hills are the metamorphosed sedimentary rocks, whereas the black rocks seen up Eldee Creek are the metamorphosed intrusive rocks, known as amphibolite. During the hottest part of the metamorphic process, a different batch of molten magma intruded the rocks again, this time producing the white pegmatite rocks that comprise a large proportion of the hills. Overlying rock was gradually eroded off the top during the subsequent 1590 million years to expose the hills as we see them today.