Late Paleocene orogenic gold formation in the Upper Triassic Nilüfer Unit (Lower Karakaya Complex), So¨güt Gold Deposit, Sakarya Zone, Bilecik, NW Türkiye: An integrated fluid inclusion, isotope and geochronological study
JOURNAL OF GEOCHEMICAL EXPLORATION, cilt.292, 2027 (SCI-Expanded, Scopus)
- Yayın Türü: Makale / Tam Makale
- Cilt numarası: 292
- Basım Tarihi: 2027
- Doi Numarası: 10.1016/j.gexplo.2026.108243
- Dergi Adı: JOURNAL OF GEOCHEMICAL EXPLORATION
- Derginin Tarandığı İndeksler: Science Citation Index Expanded (SCI-EXPANDED), Scopus, Artic & Antarctic Regions, Chemical Abstracts Core, Compendex, Geobase, INSPEC, Academic Search Ultimate (EBSCO), Engineering Source (EBSCO)
- İstanbul Üniversitesi-Cerrahpaşa Adresli: Evet
Özet
The So & uml;g & uuml;t gold deposit in northwestern Anatolia represents one of T & uuml;rkiye's significant recent gold discoveries. It is hosted by the Upper Triassic, high-pressure-low-temperature (HP-LT) metamorphosed Nil & uuml;fer Unit of the Lower Karakaya Complex (LKC). The deposit is structurally controlled by E-W-trending, south-vergent shear zones and is characterised by gold-bearing mineral assemblages, including native gold, native tellurium, coloradoite, calaverite, stibnite, and scheelite. Mineralisation is associated with pervasive Mg-Fe-rich alteration dominated by carbonate minerals, particularly dolomite, ankerite, and siderite. Despite its economic significance and distinctive mineral assemblage, the timing, physicochemical conditions, and mechanisms responsible for gold mineralisation at So & uml;g & uuml;t have remained poorly constrained. Here, we investigate the genetic evolution of the So & uml;g & uuml;t deposit by integrating ore mineralogy, carbonate alteration, sulphur isotope compositions of pyrite, fluid-inclusion microthermometry, and geochronological constraints. The results indicate that mineralisation formed at approximately 375 degrees C and 1.6 kbar from low-salinity, COQ-bearing metamorphic fluids. We propose that episodic reactivation of the controlling shear zones caused transient pressure fluctuations and promoted fluid immiscibility, which together with wall-rock sulphidation and carbonatization, destabilised aqueous gold-bisulphide complexes and facilitated gold precipitation. Systematic variations in in-situ delta 34S values of pyrite, ranging from negative values in the early mineralising stage (-8.64 to-3.65%o) to positive values in late-stage barren pyrite (+11.39 to +13.93%o), reflect an evolving metamorphic fluid system that acquired sulphur from metasedimentary protoliths and subsequently underwent progressive sulphur depletion and fluid mixing. We further link the timing and genesis of the So & uml;g & uuml;t mineralisation to Paleocene continental collision in northwestern Anatolia. The ca. 58 Ma mineralisation broadly overlaps Barrovian metamorphism (ca. 64-57 Ma) of the Tavs & cedil;anl & imath; Zone during its underthrusting beneath the Sakarya margin, providing a temporal and tectonic framework for metamorphic fluid generation and hydrothermal activity in the overriding plate. We propose that metamorphic devolatilisation of underthrust and/or tectonically accreted material contributed HQO-COQ-bearing fluids that migrated upward along crustal-scale structures and were focused into structurally prepared lithologies of the Nil & uuml;fer Unit. Slab break-off and associated asthenospheric upwelling may have enhanced the regional thermal regime but are not required as the direct trigger for mineralisation. The integrated geological, geochemical, and geochronological evidence supports a collision-related orogenic gold model for the So & uml;g & uuml;t deposit and provides new insight into the coupling between collisional tectonics, metamorphic fluid generation, and hydrothermal gold mineralisation in northwestern Anatolia and comparable collisional orogens.