Stromatolites are the oldest recognized fossil recordings of life on Earth. Therefore, their study of them represents one of the most interesting topic that investigates the physio-chemical environmental conditions (formations and precipitations) at which the stromatolites formed. This work deals with the rare earth elements (REEs) geochemical characteristics and the redox-sensitive trace elements behavior of the stromatolites newly formed in Salda Lake, a closed system alkaline lake surrounded by serpentinite rocks in SW Turkey. The representative stromatolite samples collected from Salda Lake show higher contents of MgO (up to 41.5 wt.%), CO₂+OH (up to 56.6 wt.%), and MgO/CaO ratio (up to 42.2 wt.%) referring to the stromatolites had been controlled by microorganisms and deposited in subtidal areas having hydro-magnesite and aragonite mineralogy. The average trace element contents of the stromatolites are 8.4 ppm V, 0.09 ppm Cr, 3.50 ppm Co, 95.6 ppm Ni, 0.73 ppm Cu, 1.55 ppm Rb, 37.6 ppm Sr, 0.59 ppm Y, 17.7 ppm Zr, 3.60 ppm Nb, 21 ppm Ba, 0.05 ppm Hf, 3.5 ppm As, 0.02 ppm Cd, 0.05 ppm U, 0.05 ppm Th, 2.85 ppm Pb, and 6.60 ppm Zn. The Post-Archean Australian Shale (PAAS)-normalized REE patterns of the stromatolites reveal that the heavy REEs (HREEs) are enriched relative to the light REEs (LREEs) with highly negative Y and Ce-anomalies and positive Eu-anomalies. This refers to the stromatolites formed in predominantly oxidizing environmental conditions at partially warm lake waters. In addition, the hydromagnesite composition of the Salda Lake stromatolites indicates that they were precipitated from the waters influenced by Mg-rich meteoric waters fed from the serpentinite rocks around the Lake.

Gold-sulfide mineralization in the Abu Zawal (Fatira) mine area, North Eastern Desert of Egypt, is related to porphyritic felsite dikes and elongate silicification zones in granitic rocks. These felsite dikes and the host granitic rocks exhibit major and trace element geochemical features typical of calc-alkaline and metaluminous I-type granites, likely originated in a late-orogenic setting. Their geochemical characteristics along with their fractionated LREE relative to HREE patterns imply either formation in a subduction-related environment or generation from subduction-modified source materials. Partial melting of subduction-metasomatized lower crustal rocks during extension following the lithospheric thickening may account for the production of such fertile, high Sr/Y and La/Yb magmas. In the Abu Zawal (Fatira) area, NE-trending altered felsite dikes, hydrothermal breccias, quartz enclaves, and wall-rock replacements are characterized by disseminations of chalcopyrite, pyrite, and rare gold. Alteration mineralogy, dominated by sericite, drusy quartz, kaolinite, calcite, and specular hematite, combined with the available fluid inclusion data suggests moderate to low temperature and near neutral pH conditions. The geochemical data of the altered wallrocks and mass balance calculations indicate significant mass losses in the altered rocks consistent with fluid/wallrock ratios higher than unity and near neutral pH conditions. Considering that the silica-rich host rocks, hydrothermal alteration, and sulfide-bearing hydrothermal quartz breccia in Fatira mine area were intuitively related to sulfur-saturated, oxidized felsic magmatism and associated hydrothermal systems, they are most likely linked to the post-subduction felsite porphyries (post-Hammamat felsites ~ 607 Ma), or pertaining to the late phases of the subaerial high-K calc-alkaline volcanics (Dokhan Volcanics ≤ 620 Ma).

The current study sought to investigate the physiochemical conditions and fluid evolution within the Yolindi Cu-Fe skarn mineralization located in the Biga Peninsula, NW Turkey. This was accomplished through a comprehensive investigation of geological and mineralogical data, along with isotopic analyses of sulfur (δ³⁴S), carbon (δ¹³C), and oxygen (δ¹⁸O) of sulfide and calcite minerals, respectively, as well as fluid inclusion data pertaining to various minerals (e.g., andradite, quartz, and calcite). The Yolindi area features a complex geological framework, including the Paleozoic Kalabak Group (which includes the Torasan, Yolindi, and Sazak formations) and the Triassic Karakaya Complex. These formations were subsequently intruded via Early Miocene Şaroluk granitoids and Hallaçlar volcanics. Skarn formation is zoned into endoskarn and exoskarn types (being categorized into proximal, intermediate, and distal zones), with distinct mineral assemblages indicating concentric and contact metamorphic alteration patterns around the western part of Şaroluk granitoid intrusion in contact with the Torasan formation. The ore mineralogy and paragenesis suggest three distinct stages of evolution: an initial phase of prograde metasomatism characterized by the formation of magnetite and pyrite alongside anhydrous calc-silicate minerals; a subsequent phase of retrograde alteration marked by the formation of epidote, actinolite, and scapolite, accompanied by the occurrence of chalcopyrite and specular hematite; and finally, a post-metasomatic stage involving oxidation processes that led to the development of secondary mineral assemblages containing cerussite, covellite, and malachite. Sulfur isotopes (δ³⁴S) of sulfides from endoskarn (from +0.27 to +0.57‰_VCDT) to intermediate exoskarn (from −9.44 to −5.46‰_VCDT) zones indicate a diverse sulfur source, including magmatic, sedimentary, and possibly organic matter. δ³⁴S values in hydrothermal fluids suggest a magmatic–hydrothermal origin, with endoskarn and proximal zone fluids showing a slight negative signature and intermediate zone fluids indicating a strong influence from organic-rich or metamorphic sulfur reservoirs. Carbon and oxygen isotopic compositions (δ¹³C and δ¹⁸O) of calcite revealed a progression from marine carbonate signatures in marble samples (from +1.89 to +2.23‰_VPDB; from +21.61 to +21.73‰_VSMOW) to depleted values in prograde (from −6.0 to +0.09‰_VPDB; from +6.22 to +18.14‰_VSMOW) and retrograde skarns (from −3.8 to −2.25‰_VPDB; from +0.94 to +3.62‰_VSMOW), reflecting interactions with high-temperature magmatic fluids and meteoric water mixing. The fluid inclusions in prograde minerals generated under the conditions of fluid boiling exhibited high temperatures, reaching up to 412 °C, and salinities up to 26 wt.% NaCl equivalent. Conversely, the fluid inclusions in retrograde minerals, which were generated due to fluid mixing, exhibited lower temperatures (with an average of 318 °C) and salinities with an average of 4.9 wt.% NaCl equivalent. This indicated that the cooler and more diluted fluids mix with meteoric waters and interact with organic materials in the host rocks. This suggests a multifaceted origin involving various sources and processes. Therefore, this study concluded that the skarn mineralization in the Yolindi area resulted from complex interactions between magmatic, metamorphic, and meteoric fluids, reflecting a dynamic ore-forming environment with implications for the regional metallogeny of Cu-Fe skarn deposits.

The current work investigates the impact of magmatic fluids and metasomatic processes on the Yolindi Cu-Fe skarn deposit in the Biga Peninsula, Turkey. It traces the stages of skarn evolution, from prograde to retrograde alterations, and investigates findings within a broader geological, mineralogical, and geochemical framework. Additionally, it assesses the evolutionary history of the Yolindi deposit in relation to calc-alkaline magmatic activity in an island-arc environment and compares its mineral compositions and genesis with other global and regional Cu-Fe skarn deposits. The Yolindi Cu-Fe skarn deposit in the Biga Peninsula was formed by the intrusion of Şaroluk quartz monzonite pluton into Upper Paleozoic Torasan Formation rocks such as phyllite, schists, hornfels, marble, and serpentinites. During skarnification, reactions between the magmatic fluids from the Şaroluk quartz monzonite pluton and the Torasan Formation produced skarn minerals associated with metals such as Fe and Cu. Initially, these reactions formed prograde skarn minerals such as augite-rich pyroxenes and andradite garnets with magnetite and pyrite. As the system cooled, these initial minerals underwent retrograde alteration, leading to the formation of minerals such as epidote, actinolite, and chlorite, as well as other copper and iron minerals including chalcopyrite, bornite, secondary magnetite, and specular hematite. Therefore, four main stages influenced the formation of the Yolindi Cu-Fe deposit: metamorphic bimetasomatic, prograde metasomatic, and retrograde metasomatic stages. Later, oxidation and weathering resulted in supergene minerals such as cerussite, malachite, and goethite, which serve as examples of the post-metamorphic stage. The mineralogical shifts, such as the andradite–grossular transition, reflect changing hydrothermal fluid compositions and characteristics due to the addition of meteoric fluids. Importantly, the formation of magnetite after garnet and clinopyroxene during the retrograde stage is evidenced by magnetite crystals within garnet. The mineral associations of the Yolindi Cu-Fe skarn deposit align with the global skarn deposits and specific Turkish skarns (e.g., Ayazmant Fe-Cu and Evciler Cu-Au skarn deposits). The Yolindi Cu-Fe skarn deposit, in association with ore-bearing solutions having magmatic origins, developed in an island-arc setting.