International audiencehosted in a folded and low to medium grade sedimentary and volcanic rocks, unconformably overlaid by Permo-Triassic to Cretaceous red beds and limestones. Intrusion of the hydrothermally altered multiphase ca. similar to 330-319 Ma Aouli granite batholith has contact metamorphosed the host rocks to a metamorphic assemblage of cordierite, andalusite, chlorite, muscovite, and biotite +/- sillimanite +/- garnet. The mineralized structures that consist mostly of quartz, fluorite, and barite occur principally as ENE-WSW, WNW-ESE, and E-W-trending trans-tensional steeply dipping veins, veinlets and en echelon tension gash fillings. Irrespective of colour, location, paragenesis and textural position within the mineralized vein structure, the fluorite is characterized by high total REY contents ranging from 250 to 662 ppm, distinctive positive Eu and Y anomalies, and middle rare-earth element enrichment. Fluid inclusion data indicate that the ore-forming fluids correspond to evolved NaCl-CaCl2 + other cations sedimentary (94-174 degrees C), saline (14-24 wt% NaCl equiv.) brines. The strontium isotopic compositions of fluorite (Sr-87/Sr-86 = 0.710155-0.712293) and barite (0.710215-0.701401), along with the Liassic dolomitized limestones (0.707867-0.708140) are more radiogenic than the Cambro-Ordovician and Triassic-Early Jurassic seawater values, with the Aouli Late Variscan granite (0.70814 +/- 12) and the Triassic arkoses (0.709839-0.712313) displaying the highest Sr-87/Sr-86 ratios. Barite separates show uniform delta S-34 ratios of +11% to +13.4% consistent with Permian-Triassic seawater sulphate. The calculated REY fluid compositions along with fluid inclusion, strontium and sulphur isotope data point to the role of hot sedimentary brines with fluid-rock interaction at high fluid/rock ratios. The fluid system is likely related to the Pangea rifting and subsequent Central Atlantic opening during Permian-Triassic time. The fluorite-barite mineralization is likely due to mixing at the basement-cover interface of an ascending deep-seated fluid that equilibrated with Variscan crystalline basement rocks and cooler more dilute formation water

The Arapuçandere Pb–Zn–Cu ore body is a typical vein-type lead–zinc deposit of the Biga Peninsula, and is currently being mined for lead and zinc. In the study area, Permian–Triassic metamorphic rocks, Triassic metaclastic and metabasic rocks, Oligocene–Miocene granitoids, Miocene volcanic rocks, and Quaternary terrigenous sediments crop out. The ore deposits developed as Pb–Zn–Cu-bearing veins along faults in Triassic metasandstone and metadiabase. Microscopic studies reveal that the veins contain galena, sphalerite, chalcopyrite, pyrite, marcasite, covellite, and specular hematite as ore minerals, and quartz, calcite, and barite as gangue minerals. Analysed sulphur-isotope compositions (δ³⁴S_VCDT) of galena, sphalerite, and chalcopyrite range from − 5.9 to − 1.9‰ (average − 3.4‰), from − 5.5 to − 1.7‰ (average − 4.2 ‰), and from − 3.5 to − 0.9‰ (average − 2.6‰), respectively; that of H₂S in the hydrothermal fluid was in the calculated range of − 5.8 to +0.1‰ (average − 2.5‰). These isotopic values suggest that magmatic sulphur dominates in sulphides, mixed with minor, isotopically light sulphur. Because no contemporaneous magmatic activity is associated with mineralization, it may be assumed that sulphur was leached from the surrounding Triassic units, mainly from metabasic, partly from metaclastic rocks. Lead-isotope studies indicate a model age of 114–63 Ma for the lead reservoir, in accord with possible sulphur-bearing local source rocks. Thus, the sulphur and lead deposited in the studied ore veins were probably leached from Triassic metabasic and metaclastic rocks some time during the Early Cretaceous to the Palaeocene.

The Arapuçandere Pb-Zn-Cu ores are typical examples of vein-type lead-zinc deposits in the Biga Peninsula. Permian—Triassic metamorphic, Triassic metaclastic and metabasic rocks, Oligocene—Miocene granitoids, Miocene volcanic rocks, and Quaternary terrestrial sediments crop out in the study area. The veins occupy fault zones in Triassic metasandstone (meta-arkose and subarkose) and metadiabase, and contain galena, sphalerite, chalcopyrite, pyrite, marcasite, covellite and specular hematite as ore minerals, with quartz, calcite, and barite as gangue minerals. Based on macro- and micro-petrographic investigations, sulfide minerals formed in the earliest stage of mineralization, and were followed by quartz and calcite crystallization. Fluid inclusion studies showed that salinity (avg. 18.3%) was low, but that temperature was relatively high (avg. 301.4°C) during stages of sulfide precipitation. In contrast, the salinity (avg. 27.1% NaCl equiv.) increased and the temperature (avg. 240.2°C) decreased during crystallization of the quartz. Finally, the salinity and temperature of the fluid gradually declined through the later episode of mineralization when the primary and secondary inclusions in calcite formed. Isotopic compositions of the aqueous fluid (δ18O = -7.5 to -1.7%, and δD = -90 to -55%) indicate the presence of meteoric water modified slightly by fluid-rock interaction. A geologic and genetic relation between ore veins and Oligo-Miocene granitoids and Miocene volcanic rocks appears to be lacking. The ore and host-rock relations suggest only a post-Triassic age for the mineralization. Pb-isotope model ages suggest a pre-Eocene age for the mineralization, which predated Oligo-Miocene granitoid emplacement and Miocene volcanic activity. We conclude that the Pb-Zn-Cu veins in the study area formed by deeply circulating meteoric water. The metals and sulfur were leached from the surrounding pre-Eocene units and deposited along fault zones.