Geology
Balıkesir region is between the Sakarya Zone and the Toride-Anatolide Block and generally represented by the İzmir-Ankara-Erzincan suture zone which consists of a metamorphic and nonmetamorphic ophiolitic melange association and a peridotite nappe. Therefore the suture is regarded as the remnant of an oceanic realm that was consumed between the two continents.
The Sakarya Zone at the north, around Ayvatlar and Kepsut properties is made up of the metabasite-marble-phyllite sequence of the Karakaya Complex tectonically overlain by Triassic greywackes with exotic Permian and Carboniferous limestone blocks. Towards to the south, the Sakarya Zone is in contact of with a regional blueschist belt (the Tavşanlı Zone), of the Anatolide-Tauride Block, a belt of deformed volcanosedimentary rocks affected by high pressure/low temperature metamorphism during the Campanian, Cretaceous.
On the east the Alaçam mountains formed by Paleozoic chlorite-sericite schist, phyllites, interclated by carbonates, metamorphosed by low to medium grade, are thought to be cover units of the Menderes Masif of the Torid-Anatolid Block.
The Neogene granitic rocks composed mainly of granodiorite, granite with some leucogranite and quartz-diorite are closely distributed together with the basement rocks in Alaçam near Dursunbey, in Çataldağ near Susurluk and in Solarya dağ near Şamlı.
The Miocene andesite dome, lav and pyroclastic rocks are common at the north and south part of Balıkesir, while the dacitic volcanic rocks are at the eastern part of the region, around Bigadiç. The youngest volcanic activity is in alkali character, represented by trachitic domes and alkali bazaltic daykes and lavas at northern part of Bigadiç.
Ore Mineralisation
The Balıkesir region is famous for borate deposits, near Bigadiç, Susurluk and Mustafakemalpaşa. The borate mineralisation developed within the Neogene lacustrine volcanosedimentary rocks.
Pb- Zn deposits containing a few million tons with 8-10 % grade in the Alaçam Mountains defined as skarn type of deposit, but seem to follow the carbonate zones and show a conformable structure in the Paleozoic schists. Şamlı Fe deposit, on the other hand, is at the contact of a granodiorite-quartz diorite pluton and is a skarn type of mineralisation.
The silicified zones developed in Tertiary volcanic rocks around Pb-Zn rich Alaçam Mountains are enriched in some low temperature minerals containing Au, Ag, sometimes with Mn and Fe.
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