Abstract The Biga Peninsula in northwestern Turkey hosts a large number of high- and low-sulfidation epithermal gold-silver-(copper) and associated copper-gold porphyry deposits and prospects, associated with voluminous, Eocene-Miocene calc-alkaline volcanism and plutonism. In this area, 50 to 20 Ma intermediate to felsic volcanic and volcaniclastic strata overlie metamorphosed basement rocks of the Camlica Group. The volcanic sequence is variably altered over an area covering several hundreds of square kilometers, including argillic, advanced argillic, and massive to vuggy residual quartz alteration, the latter present at the tops of many of the higher elevation peaks in the area. Moderate- and high-angle normal and oblique faults are common in the area and influenced the distribution of mineralization. While gold mineralization associated with these high-sulfidation epithermal systems and flanking low-sulfidation epithermal systems has long been recognized, the existence of porphyry roots to these systems was not fully appreciated until the discovery of the Halilaga porphyry in 2008. In the southern part of the TV Tower property, low relief areas consist of schist and serpentinite intruded by the Kuşçayir pluton, a composite, ~40 Ma intrusion that averages granodiorite in composition. Intermediate volcanic and volcaniclastic rocks are exposed in the highest elevation areas. The northern edge of the pluton, at low to intermediate elevations, consists of at least six intrusions of similar age and composition that differ primarily in degree of porphyritic texture and phenocryst quartz content. The intrusions are parsed into pre- syn- and late mineralization phases with respect to hydrothermal alteration and mineralization related to at least two Au-Cu porphyry centers, Valley and Hilltop. The porphyry systems occur below and are to some degree overprinted by high-sulfidation alteration and mineralization. The porphyry/high-sulfidation system was subjected to weathering and oxidation, giving rise to a supergene copper enrichment blanket that lies near the transition from the high sulfidation into the porphyry environment. Alteration associated with the porphyry systems includes chlorite-magnetite-actinolite, K-feldspar-biotite-quartz-magnetite-hematite (“potassic”), and, at higher elevations, overprinting quartz-muscovite (“phyllic”) alteration. Quartz stockwork veining is ubiquitous in the phyllic and potassic assemblages, and includes quartz-K-feldspar “A” veins, quartz sulfide “B” veins, pyrite-quartz “D” veins, and quartz-magnetite “M” veins. Copper mineral assemblages range from bornite-chalcopyrite to chalcopyrite-pyrite, and chalcopyrite-chalcocite or chalcocite-covellite-digenite in the supergene zones. High-sulfidation epithermal mineralization is dominantly oxidized, and consists of residual vuggy and massive quartz, alunite, pyrophyllite, and iron oxides. New U-Pb dates for the Kuşçayir pluton and Hilltop and Valley intrusions range from 38 to 40 Ma, consistent with other Cu-Au porphyry systems in the region, whereas most dated high-sulfidation epithermal deposits in the region formed at roughly 29 Ma, coeval with an Oligocene suite of intrusions. It is possible that the epithermal-porphyry relationship at Karaayi is one of overprinting of two unrelated hydrothermal systems.

Abstract Epithermal Au-(Ag) and porphyry Cu-Au-(Mo) mineralization of the Biga Peninsula in northwestern Turkey occurs in a district comprised of NE- to ENE-trending metamorphic horst blocks separated by half-graben volcano-sedimentary basins. These developed as a result of rollback of the northward-subducting African slab during the Eocene, Oligocene, and Miocene. We propose that epithermal and porphyry systems occupy distinct, favorable positions within the overall extensional architecture and fault/fracture array. High- and low-sulfidation epithermal alteration systems, along with related quartz veins, preferentially occupy half-graben basins and border faults. These epithermal systems are found above a core complex detachment fault system, forming major strata-bound silicified zones fed by steeply dipping extensional faults and associated fractures above inferred intrusions. At greater depths and higher pressure and temperature conditions, porphyry-style alteration systems are spatially associated with porphyritic stocks that occur in close association with plutonic bodies. These plutons have intruded the footwall of ductile to brittle extensional faults and spatially and temporally link to metamorphic core complex exhumation. Episodic changes in the tectonic stress resulted in pulses of crustal extension that favored porphyry-type and high-sulfidation-style mineralization during mid to late stages of Eocene and Oligocene extensional tectonic phases. On the other hand, the early stages of each extensional phase promoted higher structural permeability, enabling the development of vein systems and low-sulfidation epithermal-style mineralization. Postemplacement crustal extension resulted in “domino-style” block rotations and half-graben formation throughout the Miocene and Pliocene. Since the early Pliocene, the westward propagation of the North Anatolian fault has resulted in dextral transtension in the Biga Peninsula and, as a result, postmineralization structural dismemberment of deposits and alteration systems is common.

Abstract In the Central Sakarya area of Turkey there are two main Alpine continental units, separated by a south verging ophiolitic complex which represents the root zone of the İzmir-Ankara Suture Belt. The Central Sakarya Terrane in the north includes two ‘Variscan’ tectonic units in its basement. The Söğüt Metamorphic rocks represent a Variscan ensimatic arc complex and the Tepeköy Metamorphic rocks are characteristically a forearc-trench complex. The unconformably overlying Triassic Soğukkuyu Metamorphic rocks correspond to a part of the Karakaya Formation and are interpreted as a Triassic rift basin assemblage. These units are unconformably overlain by a transgressive sequence of Liassic-Late Cretaceous age that represents the northeastward deepening carbonate platform of the Sakarya Composite Terrane. The middle tectonic unit (the Central Sakarya Ophiolitic Complex) comprises blocks and slices of dismembered ophiolites, blueschists and basic volcanic rocks with uppermost Jurassic-Lower Cretaceous radiolarite-limestone interlayers. Geochemical data from basalt blocks suggest mid-ocean ridge basalt (MORB)- and suprasubduction-type tectonic settings within the Neotethyan İzmir-Ankara Ocean. The southern tectonic unit includes basal polyphase metamorphosed clastic rocks (Sömdiken Metamorphics), intruded by felsic and basic dykes and overlain by thick-bedded marbles. This assemblage is unconformably overlain by continental clastic rocks gradually giving way to thick-bedded recrystallized limestones, cherty limestones and pelagic limestones intercalated with radiolarites, and finally by a thick high pressure-low temperature (HP-LT) metamorphic synorogenic flysch sequence. This succession is identical to the passive continental margin sequences of the Tauride Platform. It is suggested that this passive margin was subducted during the Late Cretaceous in an intraoceanic subduction zone and affected by HP-LT metamorphism. The emplacement of the allochthonous oceanic assemblages and the collision with the Central Sakarya Terrane was complete by the end of the Cretaceous.