Search Results (324)

The Dongwujiiazi deposit is a structurally controlled orogenic gold deposit situated in the eastern part of the Chifeng–Chaoyang gold belt along the northern boundary of the North China Craton. This study establishes a comprehensive metallogenic model for the Dongwujiiazi gold deposit by integrating whole-rock geochemistry (major and trace elements), in situ trace elements and REEs in zircon, multi-isotope systems (H, O, S, Pb), and precise zircon U–Pb geochronology. Five types of intrusive and associated rocks are identified within the main biotite-pyroxene gneiss host of the Dongwujiiazi gold deposit: mylonitized granitic pegmatite, mylonitized porphyritic monzogranite, propylitized fine-grained quartz monzodiorite, quartz monzonite, and porphyritic dolerite. The gold-bearing polymetallic sulfide ores are composed of pyrite, chalcopyrite, sphalerite, galena, digenite, and native gold. Zircon grains in the Dongwujiiazi gold ore (2502 ± 15 to 2539 ± 18 Ma) are inherited from surrounding Neoarchean gneiss, recording older crustal sources rather than forming contemporaneously with the gold mineralization. H–O isotopes indicate that the ore-forming fluids were mixed in origin, involving both magmatic and metamorphic components. S and Pb isotopes suggest that the mineralizing sulfur was mainly derived from a magmatic source, while lead originated predominantly from lower crustal materials associated with the surrounding high-grade metamorphic rocks. In this study, we present a new metallogenic model for the Dongwujiiazi gold deposit, in which slab-derived and lower-crustal metamorphic fluids interacted with ascending magmas, resulting in fluid mixing and gold precipitation within structurally controlled zones of gneissic host rocks. Combined geochemical and isotopic evidence (H–O, S, Pb) indicates contributions from both magmatic and metamorphic sources, supporting formation as an intracontinental orogenic gold system in an active continental margin. Full article

In this study, the characteristics of sulfide minerals during the acidic double reverse flotation of phosphate ore and the adsorption mechanisms of sodium oleate (NaOL) and dodecyl trimethyl ammonium bromide (DTAB) were investigated. Micro-flotation test results indicated that NaOL effectively collected galena, sphalerite, and pyrite at a concentration of 1 × 10⁻³ mol/L and pH 4–5.5, whereas DTAB exhibited selectivity for galena at 1 × 10⁻⁴ mol/L. Mixed mineral flotation revealed that NaOL induced a non-selective bulk flotation of sulfides with dolomite, resulting in a high froth yield of 93.23%, while the DTAB system showed superior selectivity with a froth yield of 54.91%. Surface analyses (Zeta potential, FTIR, and XPS) confirmed that NaOL chemisorbs onto sulfide surfaces via metal-oleate complexes, whereas DTAB adsorption is dominated by electrostatic attraction. Bench-scale tests validated the “double-rejection” flowsheet, significantly upgrading the P₂O₅ grade from 23.38% to 31.47% by sequentially partitioning Pb, Zn and Fe into the froth tailings. Size-by-assay analysis indicated that the sulfide separation was primarily controlled by the extent of mineral liberation. These findings provide a robust theoretical framework and practical guidance for the simultaneous management of sulfide minerals during phosphate beneficiation. Full article

The Beni Snassen belt (northeastern Morocco) hosts several Mississippi Valley-type Pb-Zn ± Cu occurrences localized along the Variscan basement/Lower Liassic carbonate interface within the Atlasic foreland system. This study integrates geological observations with organic petrography and C-O-S-Pb isotopic systematics to constrain the origin of mineralizing fluids, metal source, and ore-forming processes within a basin-scale metallogenic system. The host sequence consists of unmetamorphosed, dolomitized Pliensbachian carbonates with marl interbeds and organic-rich black shales. Mineralization is structurally focused along ENE-WSW and E-W faults and occurs as massive calcite-galena veins, “en échelon” tension gashes, vug fillings, and solution-collapse breccias. Ore-stage calcite exhibits restricted isotopic variability (δ¹³C = −4.7 to +1.2‰; δ¹⁸O = 14.9 to 19.7‰), consistent with rock-buffered basinal fluids and extensive fluid–carbonate interaction. Calculated δ¹⁸O_H2O values indicate precipitation from evolved saline brines variably mixed with meteoric waters. Galena δ³⁴S values (−20.9‰ to +10.3‰) reflect thermochemical sulfate reduction (TSR) under fluctuating redox conditions. Pb isotope compositions define a tight linear cluster between upper crust and orogene growth curves, indicating a predominantly upper crustal metal source, notably Triassic dolerite–diabase lithologies, with a possible contribution from organic-rich black shales. High-reflectance pyrobitumen (VR₀ up to 4%) indicates thermal conditions exceeding those predicted by local burial history, supporting long-distance migration of hydrocarbon-bearing metalliferous fluids from overpressured basin compartments, most plausibly the adjacent Neogene Guercif Basin. Fault reactivation during Late Miocene transtension fostered basin-scale fluid focusing and ore deposition. Hence, the Beni Snassen district represents a basin-integrated MVT system involving crustal metal leaching, organic-assisted metal transport, TSR-mediated sulfur reduction, and structurally focused fluid flow. These results refine metallogenic models for the Atlasic belts and highlight the exploration potential of structurally reactivated foreland basins hosting coupled hydrocarbon-hydrothermal systems. Full article

Efficient recovery of critical metals from complex polymetallic ores relies on clarifying their mineralogical occurrence. A Cd-Ag-rich Pb-Zn ore from southwestern China was investigated via a multi-scale process mineralogy approach integrating reflected-light microscopy, TIMA and LA-ICP-MS. Systematic analysis was conducted on ore texture, mineral liberation characteristics, and the occurrence and distribution of Ag and Cd. The ore is a medium–low grade Pb-Zn deposit (Pb 0.81%, Zn 4.33%) with economically recoverable associated Cd (0.066%) and Ag (5.04 ppm), dominated by sphalerite (7.74%), galena (1.39%), pyrite (3.92%), quartz (47.80%) and calcite (18.66%). TIMA analysis revealed poor liberation of sphalerite and galena, with fully liberated particles accounting for <30%. LA-ICP-MS results showed that Cd is highly enriched in sphalerite (average 5982 ppm, 98%) mainly in isomorphous form, while Ag is dispersed in pyrite (average 178 ppm, 56%), galena (average 227 ppm, 25%) and sphalerite (average 31 ppm, 19%), also primarily as isomorphs; partial Cd in pyrite occurs as micro-inclusions. The multi-scale mineralogical data provide a scientific basis for resource utilization, indicating the necessity of fine grinding and differentiated recovery strategies: “zinc depression followed by lead flotation” for Pb-Zn recovery, the establishment of a comprehensive Ag recovery system with Pb-Zn-Fe as carriers for Ag recovery, and “Zn-carried Cd” flotation for Cd recovery. This study verifies the effectiveness of combined TIMA and LA-ICP-MS in elucidating critical metal occurrence, and provides a mineralogy-based process design for the sustainable processing of such complex ores. Full article

Hydrothermal cobalt (Co) deposits are a significant source of Co; however, the sources of Co and hydrothermal fluids for such deposits remain poorly understood. This study addresses this issue through an investigation of the geology, mineralogy, and in situ sulfur isotopes of the Qibaoshan Co-Pb-Zn-Cu deposit, a typical hydrothermal Co deposit in South China, to constrain the occurrence of Co and the sources of Co and hydrothermal fluids. Detailed scanning electron microscopy (SEM), TESCAN Integrated Mineral Analyzer (TIMA), and electron microprobe (EPMA) mapping analyses reveal that Co in the Qibaoshan deposit occurs predominantly as Co-bearing minerals in veinlet mineralization, mainly including cobaltite, skutterudite, and smaltite. EPMA elemental mappings reveal that cobaltite grains commonly show a compositional evolution from Ni-S-rich and As-Fe-poor cores to As-Fe-rich and Ni-S-poor rims. This evolution indicates a decrease in fluid temperature and Ni content, coupled with an increase in the As/S ratio during ore-forming processes. In situ S isotope analyses of various sulfides (pyrite, chalcopyrite, sphalerite, galena, and arsenopyrite) yield a wide range of δ³⁴S_V-CDT values from 0.24‰ to 19.08‰, with two dominant clusters at 2–5‰ and 15–17‰. This suggests two end-member sources for sulfur and hydrothermal fluids in the Qibaoshan deposit: magmatic and sedimentary sources. Arsenopyrite, which is closely associated with Co minerals, yields δ³⁴S_V-CDT values ranging from 2.17‰ to 5.99‰, pointing to a magmatic origin for Co in the Qibaoshan deposit. The Pb-Zn and Cu mineralization of the deposit was also likely mainly derived from magmatic sources, with the incorporation of sedimentary sulfur and fluids during the ore-forming processes. This study demonstrates that magmatic–hydrothermal fluids derived from depth can serve as sources of Co, even in hydrothermal deposits where no magmatic rock is exposed, which provides crucial implications for the metallogenic models and mineral exploration of hydrothermal Co deposits. Full article

The Kocayayla Pb–Zn ± Cu vein-type mineralization is located in the Biga Peninsula, northwestern Türkiye. This study aims to constrain the geological, geochemical, and isotopic characteristics of the mineralization and to clarify its genetic classification. The deposit is hosted mainly by andesitic and basaltic andesitic rocks as well as schists and is structurally controlled by E–W-trending strike-slip faults. Mineralogical and petrographic identifications, XRD analyses, whole-rock geochemistry, and sulfur isotope data were integrated to evaluate ore-forming processes. Mineralization is temporally and spatially associated with propylitic and phyllic to argillic alteration and is concentrated within zones of intense silicification and chloritization, accompanied by quartz, sericite, kaolinite/nacrite, chlorite, and carbonate assemblages. The ore assemblage is dominated by galena, sphalerite, and subordinate chalcopyrite, with minor fahlore-group minerals. Rare earth element patterns of ore samples (whole rock) overlap with those of the wall rocks, whereas Pb–Zn enrichment reflects selective hydrothermal metal transport. Sulfur isotope compositions show limited internal variation and indicate sulfur derived predominantly from H₂S-dominated magmatic–hydrothermal fluids. Regional comparison of δ³⁴S datasets and reported Au contents across the Biga Peninsula indicates that Au-rich intermediate-sulfidation epithermal systems exhibit broader and more variable sulfur isotope ranges, whereas Au-poor intermediate-sulfidation epithermal systems show relatively restricted and near-zero δ³⁴S values. These features collectively support the classification of the Kocayayla mineralization as an Au-poor intermediate-sulfidation epithermal Pb–Zn system. Full article

Xylaria karsticola NBIMCC 9097 is a recently described and rare fungicolous species originating from Bulgaria. Understanding its growth behavior and bioactive potential is essential for evaluating its biotechnological and pharmaceutical relevance. In the presented study, we model the in vitro growth kinetics of X. karsticola mycelium under submerged cultivation and assess its antimicrobial activity. Optimization of MCM and MYB media markedly increased biomass yields to 20.11 and 23.25 g/dm³, respectively, compared with non-optimized media (9.9 ± 0.21 and 10.8 ± 0.28 g/dm³). The maximum specific growth rate was higher in the MCM (0.803 ± 0.004 h⁻¹) in comparison with the MYB medium (0.711 ± 0.003 h⁻¹); however, the MYB medium supported greater biomass accumulation and more efficient substrate utilization, reflected by a higher utilization coefficient (0.9900 ± 0.001 versus 0.9644 ± 0.005). The antimicrobial activity was evaluated using agar disk diffusion and minimum inhibitory concentration assays against Gram-positive and Gram-negative bacteria and yeasts. Hexane and ethyl acetate extracts were most effective against Pseudomonas aeruginosa ATCC 9027 (MIC 0.067 and 0.059 mg/cm³), while notable anti-yeast activity was observed, particularly against Wickerhamomyces anomalus, Saccharomycodes ludwigii, and Pichia membranifaciens. The lowest MIC (0.02 mg/cm³) was recorded for the water biomass extract against S. ludwigii indicating potent antimicrobial activity against the tested microorganism. These findings identify X. karsticola as a potential source of antimicrobial metabolites and provide a strong motivation for comprehensive metabolomic profiling and systematic optimization of its cultivation. Full article

The Neoproterozoic Paraguay Belt (western Brazil), formed by the Brasiliano/Pan-African Orogenic Cycle during Western Gondwana amalgamation, hosts tens of gold occurrences and deposits. This review provides new insights into the metallogeny and tectonics of the Paraguay Belt Gold Province, based on previous and new data on stratigraphy, structural geology, metamorphism, hydrothermal alteration, and gold grades. The mineralizations correspond to turbidite-hosted orogenic gold systems, with quartz veins cutting metasedimentary rocks with minor metavolcanics. A six-phase tectonic–metallogenic evolution model is proposed. The early stages correspond to glaciolacustrine deposition in a rift that evolved into a passive margin and then into a foreland basin, with glaciomarine sediments. Late sedimentation corresponds to glacial-to-post-glacial shallow marine units in the foreland. The orogeny progressed with cratonic collisions, resulting in three deformation (two compressional and one extensional) and three metamorphic (regional, dynamic, and contact) phases. The Au mineralization results from metamorphic fluids that transported metals from the metasedimentary pile and deposited them in reactive rocks (rich in magnetite or organic carbon). Gold occurs in sulfide-rich (pyrite and galena) veins and hydrothermal alteration zones. The metallotects and structural controls highlighted here are useful tools for prospecting gold in the Paraguay Belt and similar geological terranes. Full article

Kutná Hora ore district, one of the largest historical silver deposits in Central Europe, consists of nine major lodes with Pb-Zn-Ag mineralization hosted by high-grade basement rocks of the Kutná Hora Crystalline Complex in central part of the Bohemian Massif. We conducted a detailed electron-microprobe study of a previously unknown ore mineralization from the uppermost level of the Muzejní důl mine, which is a medieval mine located within the Ag-richest Oselské pásmo Lode, in the southern part of the ore district. An unusual nature of this ore mineralization, which originated during three respective stages, was found. The early stage comprises the hypogene mineralization commonly occurring in the southern part of the district, composed of pyrite, arsenopyrite, Fe,Mn-enriched sphalerite, galena, and (keno)argentotetrahedrite-(Fe) hosted in quartz and siderite-rhodochrosite gangue. The second stage was characterized by the corrosion of early vein fill followed by the crystallization of a specific suite of ore minerals anomalously enriched in Ag, Cu, Zn, Cd, As, and Sb, including galena, Cd-enriched and Fe-poor sphalerite, greenockite, bornite, Ag,As,Sb,Mn-bearing chalcopyrite, silver, gold, stephanite, As,Cu-bearing pyrargyrite, Ag-Cu- and Sb-As-bearing polybasite-pearceite group minerals and a suite of tetrahedrite-group minerals, the latter showing wide variations in Ag-Cu, Sb-As, and Fe-Zn-Cd contents. The origin of the second-stage mineralization is interpreted in hydrothermal remobilization of ore metals and metaloids from the early ore mineralization, which was mediated by surficial fluids characterized by elevated redox potential. The third stage comprises acanthite and probably also Ag-Cu minerals (stromeyerite, jalpaite, and mckinstryite), Cu-S phases (covellite, spionkopite, geerite), and an Ag-Cu-Hg mineralization. This late mineralization was likely related to the pre-Cretaceous weathering of the apical part of the ore deposit and to the associated supergene enrichment of deeper parts of the ore zone by descending Ag,Cu-bearing waters. Full article

This study evaluates the role of groundwater in the dynamics of the Slano blato landslide using hydrogeochemical and stable isotope data. Results show that deep groundwater inflow significantly affected the landslide behavior, as demonstrated by pronounced hydrogeochemical and isotopic differences among springs. Springs within the landslide differ markedly from those in similar geological settings of the Vipava Valley, indicating a distinct local groundwater system. Groundwater is present within the landslide body even during dry periods. Waters originate mainly from a higher karstic recharge area and flow through deep flysch strata, particularly fractured sandstones, where they become enriched in dissolved ions, especially K⁺ and SO₄²⁻, and show increased mineralization in the lower parts of the landslide. Saturation indices indicate slight oversaturation with calcite and dolomite and equilibrium with quartz for most samples, reflecting interaction with carbonates and flysch sandstones. Elevated sulphate concentrations and near-equilibrium conditions for mirabilite and thenardite suggest salt-related deterioration of landslide material, enhanced by evaporation. Stable isotope data (δ¹³C_DIC, δ¹⁸O, δ²H) indicate dominant carbonate recharge, meteoric origin, evaporation effects, and long-term water–rock interaction. This study highlights the need for additional isotope tracers, groundwater age indicators, seasonal monitoring, and on-site meteorological measurements to improve interpretation. Full article

The Yawan gold deposit, located in the Western Qinling Orogen, contains gold mineralisation that is predominantly controlled by approximately east-west-trending fault systems. This study integrates field geology, petrography, cathodoluminescence imaging, electron probe microanalysis of gold-bearing minerals (pyrite and arsenopyrite), and in situ laser ablation U-Pb dating of calcite to constrain the timing of mineralisation and to elucidate the mechanisms of gold enrichment. This study reveals that the deposit is significantly structurally controlled and comprises two discrete mineralisation stages: a quartz-pyrite (Py1)-arsenopyrite (Apy1)-chalcopyrite assemblage (Stage 1), and a quartz-calcite-pyrite (Py2)-arsenopyrite (Apy2)-stibnite-sphalerite-galena assemblage (Stage 2). Py1 displays distinct zonation, with rim As contents notably higher than core values, while Co and Ni contents gradually decrease from core to rim. Py2 is characterised by high As (0.00%–4.72%), low Fe/S ratios, and a porous texture, containing gold and arsenopyrite inclusions. Invisible gold occurs in lattice-bound form in both Py1 and Py2. The As-Fe-S ternary diagram of pyrite indicates that Au⁺ likely entered the crystal lattice as a solid solution. Arsenopyrite geothermometry yields a mineralisation temperature of 389 ± 44 °C, and sulfur fugacity (ƒS₂) decreased markedly from Stage 1 to Stage 2. Combined with the S and Fe characteristics of pyrite, these features support a medium-temperature metamorphic hydrothermal environment. U-Pb dating of calcite from Stage 2 yields an age of 215.6 ± 7.1 Ma. In summary, the Yawan gold deposit belongs to the orogenic gold system, with its gold precipitation and enrichment controlled by sulfidation triggered by Late Triassic tectono-fluid activity. Full article

The Chaijiagou Mo deposit (0.11 Mt Mo @ 0.07%) is located along the northern margin of the North China Craton. This study integrates ore geology, S–Pb–He–Ar–H–O isotopes, and fluid inclusion (FI) analyses to constrain the sources of ore-forming fluids and metals, as well as mineralization mechanisms. Three principal inclusion types were identified: liquid-rich, vapor-rich, and saline FIs. Microthermometry documents a progressive decline in homogenization temperatures and salinities from early to late mineralization stages: Stage 1 (360–450 °C; 5.3–11.3 and 35.4–51.5 wt.% NaCl equation), Stages 2.1–2.2 (320–380 °C and 260–340 °C; 5.4–11.8 and 33.8–44.5 wt.% NaCl equation), and Stage 4 (140–200 °C; 0.4–3.9 wt.% NaCl equation). Noble gas and stable isotope data reveal that the ore-forming fluids were initially dominated by crustally derived magmatic–hydrothermal components with a minor mantle contribution, subsequently experiencing significant meteoric water input. S–Pb isotopic compositions demonstrate a genetic relationship between mineralization and the ore-bearing granite porphyry, indicating a magmatic origin for both sulfur and lead. Fluid–rock interactions and fluid boiling were the dominant controls on molybdenite and chalcopyrite deposition during Stage 2, whereas mixing with meteoric waters triggered galena and sphalerite precipitation in Stage 3. Full article

The Qingshan lead–zinc (Pb–Zn) deposit in northwestern Guizhou Province is a structurally controlled, carbonate-hosted system formed from basin-derived hydrothermal processes. Geology, fluid inclusion, and isotopic data reveal a multi-stage hydrothermal circulation after Emeishan Large Igneous Province (ELIP, ~260 Ma) tectono-thermal reactivation within the Sichuan–Yunnan–Guizhu triangle (SYGT) area. Fluid inclusion microthermometry indicates that ore-forming fluids were derived from deep sources influenced by enhanced crustal heat flow linked with possible thermal input from Indo-Caledonian tectonic activity after ELIP. Ore-stage calcite records mixed carbon derived from marine carbonates with additional inputs from organic matter and deep-sourced fluids, reflecting carbonate dissolution and fluid–rock interaction. Sulfide, together with fluid inclusion temperatures > 120 °C, indicates sulfur derived from evaporitic sulfate reduced by thermochemical sulfate reduction (TSR); the heavy sulfur signature and partial isotopic disequilibrium among coexisting sulfides reflect dynamic fluid mixing during ore deposition. Lead isotopes indicate metallogenic metals were leached mainly from Devonian–Permian carbonates with subordinate basement input. Ore precipitated by cooling, depressurization, and mixing of metal-rich, H₂S-bearing fluids in structurally confined zones where the carbonate–clastic interface effectively trapped ore-forming fluids, producing high-grade sphalerite–galena mineralization. Collectively, these data support a Huize-type (HZT) carbonate-hosted Pb–Zn genetic model for the Qingshan deposit. Full article

The Wunuer deposit is an important hydrothermal Zn-Pb-Ag-Mo polymetallic deposit in the central Great Xing’an Range, NE China. The zinc–lead polymetal mineralization is closely hosted by the volcanic rocks of the Manketouebo formation (rhyolite and lithic crystal tuff) and related to the Mesozoic granite porphyry. Field evidence and petrographic observations have identified three mineralization stages within this deposit from deep to shallow: (1) late magmatic stage with vein-type Mo mineralization characteristics and mainly related to the deep granite porphyry; (2) magmatic–hydrothermal transition stage characterized by breccia-type Zn mineralization, which occurred within a steep cryptoexplosive breccia; and (3) hydrothermal stage featured by vein-type Zn-Pb-Ag mineralization hosted by the ore-bearing fractured zone. In this contribution, we present the mineralogy, zircon U-Pb age, sphalerite Rb-Sr dating, whole-rock geochemistry, and Hf-S-Pb isotopes of the Wunuer deposit. LA-ICP-MS zircon U-Pb dating of the ore-related granite porphyry, rhyolite, and lithic crystal tuff suggests that the Mo mineralization from the late magmatic stage occurred between 144.8 Ma and 145.8 Ma. The Rb-Sr isochron dating of sphalerite indicates that the hydrothermal stage Zn mineralization age is 121 ± 2.3 Ma, which is related to the volcanism of Baiyin’gaolao Formation in the Wunuer area. The concentrated and positive δ³⁴S_V-CDT values (0.17‰~5.40‰) of sulfides, as well as uniform Pb isotope compositions of granite porphyry intrusion and galena, jointly imply a magmatic source of metallogenic materials for Pb-Zn mineralization. Whole-rock geochemistry and Hf-Pb isotopes reveal that the granite porphyry and rhyolite both originated from a mantle-derived juvenile component and assimilated by minor ancient crustal material in an extensional setting. Our study demonstrates the prospect of further exploration for two mineralization events in the hydrothermal polymetallic deposits of the central Great Xing’an Range. Full article

Samples of flotation tailings generated during the exploitation and processing of Zn–Pb–Cu–Ag ore from the Rudnik mine (Serbia) were investigated for their mineralogical, geochemical, and magnetic susceptibility properties. The flotation tailings consist of a complex mineral assemblage, including silicates, carbonates, sulfides, phosphates, sulfates, oxides, hydroxides, and native elements. Quartz, calcite, and orthoclase dominate the coarse fraction (>400 µm), accompanied by epidote, Ca-garnet, and Ca-clinopyroxene. Sulfide minerals are concentrated in finer fractions (<400 µm), with pyrite and arsenopyrite being the most abundant, followed by pyrrhotite, sphalerite, galena, and chalcopyrite. These sulfides occur as dispersed grains within a silicate–carbonate matrix. Post-depositional oxidative alteration is moderately developed, with pyrite replaced by hematite, galena by cerussite, and chalcopyrite by malachite. Geochemical analyses reveal that SiO₂ (avg. 38.98 wt%), Fe₂O₃ (avg. 23.68 wt%), Al₂O₃ (avg. 8.95 wt%), CaO (avg. 9.03 wt%) and MgO (avg. 1.50 wt%) dominate the composition. Economically significant metals include Zn (avg. 0.47 wt%), Pb (avg. 0.20 wt%), Cu (avg. 0.11 wt%), Ag (max. 19 µg/g), and Bi (max. 130 µg/g). Mass magnetic susceptibility shows a strong correlation with S (r = 0.92), Co (r = 0.90), and Bi (r = 0.87); moderate correlation with Fe₂O₃, Al₂O₃, and As; and negative correlation with Mn, TiO₂, Zn, and Pb. The ferromagnetic phase most likely originates from pyrrhotite, as well as hematite formed during pyrite alteration and goethite. Full article