Geology
Biga Peninsula is distinguished under the Sakarya Zone which is an east-west-oriented continental fragment between the Anatolide - Tauride Block to the south and İstanbul - Strandja zones to the north.
The basement in Kazdağ Mountains consists of Paleozoic high grade metamorphic rocks such as gneisses, amphibolites, marbles and meta-ophiolites. Around Kazdağ Mountains, younger rocks called the Karakaya Complex outcrop over wide areas. These rocks are believed to represent subduction - accretion units and composed of Permo - Triassic metabasites - marble - phyllite series, overlain by chaotically deformed but unmetamorphosed clastic and basic volcanic rocks of Triassic age including older exotic blocks. The Karakaya complex is uncomfortably overlain by Jurassic-Cretaceous terrigeneous to shallow marine clastic and carbonate rocks.
İzmir-Ankara-Erzincan suture representing the the scar of the main Tethys ocean between Laurasia and Gondwana during the Mesozoic and Early Tertiary is situated between the Sakarya Zone and Anatolide-Toride Blocks. The suture zone is generally composed of mafic and ultramafic rocks together with pelagic limestones, clastics and radiolarite. Similar kinds of rocks are also seen western parts of the Kazdağ Mountains called Çetmi and Denizgören Ophiolites.
Eocene intrusive and volcanic rocks occur at the northern parts of the Biga Peninsula and show a rough east-west trend. The Neogene intrusive and volcanic rocks are generally at the south and more widespread. Calc-alkaline volcanic activity commenced in the Late Oligocene-Early Miocene followed by alkali basaltic volcanism from Late Miocene to Late Pliocene.
Ore Mineralisation
The Biga Peninsula is historically known as a "Gold Country". Gold and other metals' mining was common in ancient times and many old mining relicts can be seen in various localities (Kartal Dağ, Maden Dağ, Balya, Papazlık, Kısacık, Bahçedere etc…). Although there is no working gold mine at present, many new gold deposits have been discovered and announced recently (Ağı dağı with 1.2 Moz Au, Kirazlı with 0.8 Moz Au, Kısacık with 1.0 Moz possible gold reserve, Halilaga with large porphyry Cu-Au mineralisation, Havran-Tepeoba stock work Cu-Mo deposit).
The Biga Peninsula is shown as one of the best prospecting region for gold in international scientific media. So many domestic and foreign companies have been exploring the area in detail at present.
The young (Neogen) calc-alkali volcanic rocks create the most favorable environment for the epithermal and vein type of ore mineralisation. Beside Au the Biga Peninsula is also rich in metallic ores and generally known as a Pb-Zn provens. Many Pb-Zn mine containing some Cu have been operating for a long time. Balya Pb-Zn mine is the biggest and maybe the oldest mine in the region containing more than 1.5 Mton metallic Pb-Zn. Other deposits, Lapseki - Koru, Yenice - Arapuçan, Kaklım - Handeresi Pb-Zn mines contain a few million tons of reserve with 10 % Pb-Zn-Cu in approximate. Other Pb-Zn deposits are smaller and generally distributed around the bigger known deposits.
Occurrences of the Pb-Zn deposits are not homogeneous. It has been originally defined as skarn or vein type of mineralisations. The role of the magmatic activity is usually not clear. The ore deposits do not all seem to be epigenetic, some could be syngenetic, because of the conformity between the mineralisation and the country rocks. In Papazlık and Handeresi mines, the mineralisation is concordant with the amphibolites and schists and there is no magmatic rocks around which could be responsible for the mineralisation. On the other hand, the Pb-Zn mineralisations in Lapseki - Koru mine being in rhyolites are directly related to the magmatic activity, defined by some as VMS type of mineralisation.
Similar problems also exist in the mode of occurrences of gold mineralisations. Gold, as it is commonly known, is related to young volcanic rocks and described as high and low sulphidication systems, but some deposits, such as Bahçedere gold deposit, are not directly related to any young volcanic activity, and these features should be carefully considered during the ore explorations.
