Recently-discovered Bahçecik Au±Ag mineralization in the Eastern Pontides, Gümüşhane-NE Türkiye: geological and geochemical implications on the intermediate sulfidation epithermal deposit

Intermediate sulfidation epithermal deposits represent significant reservoirs of precious metals, playing a crucial role in global mining operations. The Anatolian Peninsula, predominantly characterized by relatively young (Tertiary) lithologies, hosts numerous occurrences of epithermal base and precious metal mineralization. Within the realm of research in Northeastern Anatolia, several hydrothermal alteration zones have emerged as indicators of concealed epithermal mineralization, with the Bahçecik mineralization standing out as a recent focal point. The Bahçecik mineralization represents an intermediate sulfidation epithermal Au-Ag system, hosted by Late Cretaceous andesitic rocks, as well as Eocene dacitic lava and tuffs. Employing U-Pb LA-ICP-MS zircon dating of the dacitic host rocks, the mineralization is estimated to have occurred during the Lutetian epoch (43.61 ± 0.35 Ma) or later. The genesis of the Bahçecik deposit is believed to be linked to postcollisional regional extensional tectonics, primarily controlling its structural arrangement. Comprising pyrite, chalcopyrite, low-Fe sphalerite, galena, tetrahedrite/tennantite, enargite-luzonite, and gold-silver minerals, the deposit is accompanied by prominent gangue minerals such as Mn- and Ca-carbonates, quartz, and barite. Microprobe measurements have identified a majority of Au-Ag minerals (krennerite, buckhornite, and nagyagite) closely associated with sulphide minerals. Fluid inclusion data reveal that mineralization and fluid transportation occurred at temperatures ranging from 153 to 327°C, with solutions exhibiting salinity levels consistent with those of intermediate sulfidation deposits (1.7–7.3 wt.% NaCl). This study unequivocally classifies the Bahçecik mineralization as an intermediate sulfidation deposit, contrary to the conclusions drawn in previous research. Moreover, our investigation has unveiled the presence of a substantial ore resource, totalling 7.84 million tons, featuring 1.76 g/t Au and 2.24 g/t Ag. As an intermediate-type deposit, it shares characteristics with other subtypes within the epithermal class, bridging the realms of both high and low sulfidation systems.

中硫化型浅成低温热液矿床（Intermediate sulfidation epithermal deposits）是重要的贵金属储库，在全球矿业作业中发挥着关键作用。安纳托利亚半岛（Anatolian Peninsula）以相对年轻的第三纪岩性为主要地质特征，发育众多浅成低温热液贱金属与贵金属矿化点。在安纳托利亚东北部（Northeastern Anatolia）的相关研究中，多个热液蚀变带已成为隐伏浅成低温热液矿化的找矿标志，其中巴赫杰吉克矿化（Bahçecik mineralization）成为近期的研究焦点。

巴赫杰吉克矿化属于中硫化型浅成低温热液Au-Ag系统，赋存于晚白垩世安山岩以及始新世英安岩熔岩和凝灰岩中。通过对赋矿英安岩开展U-Pb LA-ICP-MS锆石定年，估算该矿化形成于吕特期（Lutetian epoch，43.61±0.35 Ma）或更晚时段。研究认为，巴赫杰吉克矿床的成因与碰撞后区域伸展构造紧密相关，该构造主要控制了矿床的空间结构展布。

该矿床的金属矿物包括黄铁矿（pyrite）、黄铜矿（chalcopyrite）、低铁闪锌矿（low-Fe sphalerite）、方铅矿（galena）、黝铜矿/砷黝铜矿（tetrahedrite/tennantite）、硫砷铜矿-吕宋矿（enargite-luzonite）以及金银矿物，伴生的主要脉石矿物为锰-钙碳酸盐、石英（quartz）和重晶石（barite）。电子探针测试（Microprobe measurements）显示，多数金银矿物（碲金银矿krennerite、碲银金矿buckhornite和碲铅金矿nagyagite）与硫化物矿物紧密共生。

流体包裹体数据表明，矿化作用与流体运移发生于153~327℃的温度区间，成矿流体的盐度特征与中硫化型矿床一致（1.7~7.3 wt.% NaCl）。本研究明确将巴赫杰吉克矿化归为中硫化型矿床，这与以往研究的结论相悖。此外，本次调查还探明了可观的矿石资源，总矿石量达784万吨，金品位为1.76 g/t，银品位为2.24 g/t。作为中硫化型矿床，其兼具浅成低温热液矿床其他亚类的特征，衔接了高硫化型与低硫化型矿化系统的研究范畴。