Hematite Research Articles

Genesis of the Mamuniyeh copper deposit in the central Urumieh-Dokhtar Magmatic Arc, Iran: Constraints from geology, geochemistry, fluid inclusions, and H–O–S isotopes

The Mamuniyeh Cu deposit is located in the central part of the Urumieh-Dokhtar Magmatic Arc (UDMA), 10 km south of the city of Mamuniyeh, Iran. Mineralization is controlled by faults with a NW-SE trend and hosted within an Eocene volcanic sequence and Oligo-Miocene hypabyssal calc-alkaline monzonitic and gabbroic bodies. Quartz + chalcopyrite veins are most abundant and high-grade ore containing up to 5 wt% Cu, although quartz + pyrite veins have the most abundant sulphide content. In addition, quartz + chalcopyrite + specular hematite ± pyrite veins/veinlets are another common mineralized assemblage in the Mamuniyeh copper deposit, with pyrite, chalcopyrite, bornite, and oxide minerals (specular hematite, titanomagnetite, and magnetite) typical of the hypogene stage. Chalcocite, covellite, and dignite also formed at the margins of primary sulphides in the supergene (paleoweathering) stage. The mineralized veins exhibit colloform, crustiform, open space-fillings, replacements, and dissemination textural characteristics associated with mineralizing assemblages with silicification, argillization, chloritization, and sericitization assemblages. The salinity for L > V fluid inclusions is between 1.74 to 11.7 wt% NaCl and for (V > L) inclusions between 1.7 to 11.4 wt% NaCl. The average homogenization temperature and salinity for quartz + chalcopyrite + pyrite veins is 186 °C and 4.9 wt% NaCl. In the quartz + chalcopyrite assemblage an average of 185 °C and 4.5 wt% NaCl and for quartz + chalcopyrite + specularite ± pyrite (QCSP) an average of 195 °C and 5.59 wt% NaCl was determined. In these three vein types, the fluid density has almost identical values ranging from 0.8 to 1.0 g/cm3. The mineralizing system evolved in two-stages; the first metal precipitation occurred at less than 1 km of crustal depths and second metal deposition stage at shallower crustal levels (less than 500 m). Although it appears that the boiling process occurred within the fluids of the area, the primary factor contributing to Cu mineralization was influenced by fluidmixing processes. The δ18O and δD values of ore fluids computed vary from + 6.08 to −0.50 ‰ and −92 to −71 ‰, respectively, indicative of the blending of oxidizing and cooler meteoric waters with primary magmatic fluids. Calculated values of δ34S of H2S in equilibrium with chalcopyrite ranges from −7.6 to −1.9 ‰ and H2S in equilibrium with pyrite ranges from −7.1 to −3.8 ‰, respectively; this is consistent with monzodiorite to gabbro as the magmatic sulphur source for copper mineralizing fluids. Furthermore, the QCSP vein data align more closely with primary magmatic water compared to other veins, suggesting that precipitation occurred mainly from magmatic fluids, which experienced depletion in δ18O due to mixing with meteoric waters (shallow oxygenated ground waters), which caused sulphide deposition. The geochemical features for these magmas show that contamination with crustal materials occurred during the ascent of the parent magma, as well as the role of suprasubduction fluids released from the subducting plate in mantle metasomatism. Based on all evidence, Cu mineralization in the Mamuniyeh deposit has been categorized as a low-sulphidation epithermal-type system, which formed during active magmatism in the central part of UDMA.

Paragenetic and geological setting of the Starra iron oxide copper–gold deposits, Mount Isa Inlier, Queensland, Australia: constraints on IOCG deposit models

The five Starra iron oxide copper–gold (IOCG) deposits, which are located in the Cloncurry district of the Mount Isa Inlier, NW Queensland, are hosted in a N-trending zone of deformed iron-rich metasedimentary rocks that are underlain by two mineralogically distinct mafic–intermediate meta-igneous rocks. Copper–Au mineralisation is subdivided into two stages—an early main stage that transitioned from a magnetite-dominated Cu substage comprising chalcopyrite, pyrite, biotite and chlorite, to a hematite–muscovite-bearing Cu–Au substage with chalcopyrite, bornite and rare chalcocite, as well as Au–Ag-tellurides and native Au. This second stage was followed by a subordinate but nonetheless important carbonate–quartz–barite vein stage with minor but locally high-grade Cu–Au mineralisation characterised by abundant chalcocite and bornite, minor native bismuth and wittichenite (Cu3BiS3), together with minor Au–Ag telluride minerals. Bornite in these carbonate–quartz–barite veins contains considerable amounts of Au (>10 ppm), which appears to be deported either as lattice substitution in the bornite crystal structure or as homogeneously distributed Au0 nanoparticles. An earlier, coarse-grained mafic intrusion was affected by early Na–Ca alteration, whereas a second mafic intrusion lacks evidence of Na–Ca alteration but was exposed to K–Fe alteration and subsequent mineralisation at Starra 222. Mushketovite (magnetite after specular hematite) is only observed in ironstone lodes proximal to the mafic–intermediate rocks. The close spatial and mineralogical associations of the mafic–intermediate bodies and the ironstone lodes point to a stronger link between magmatic activity and IOCG mineralisation than has previously been recognised at Starra. Remobilisation of gold by late-stage hydrothermal fluids aided by the relatively low fluid temperatures during the main pulse of Cu–Au mineralisation refined gold grades at Starra, making it a relatively gold-rich IOCG deposit. We show that the Cu–Au deposits of the Starra trend feature mineralogical and geochemical elements common to both Cloncurry IOCG deposits (e.g. abundant magnetite) and IOCG deposits of the Tennant Creek district (e.g. Au–Cu–Bi mineralisation; hematite–bornite–chalcocite assemblages), making them a unique and important member of this complex family of deposits.

Hematite Frictional Behavior and He Loss From Comminution During Deformation Experiments at Slow Slip Rates

AbstractDeformation experiments on hematite characterize its slip‐rate dependent frictional properties and deformation mechanisms. These data inform interpretations of slip behavior from exhumed hematite‐coated faults and present‐day deformation at depth. We used a rotary‐shear apparatus to conduct single‐velocity and velocity‐step experiments on polycrystalline specular hematite rock (∼17 μm average plate thickness) at slip rates of 0.85 μm/s to 320 mm/s, displacements of primarily 1–3 cm and up to 45 cm, and normal stresses of 5 and 8.5 MPa. The average coefficient of friction is 0.70; velocity‐step experiments indicate velocity‐strengthening to velocity‐neutral behavior at rates <1 mm/s. Scanning electron microscopy showed experimentally generated faults develop in a semi‐continuous, thin layer of red hematite gouge. Angular gouge particles have an average diameter of ∼0.7 μm, and grain size reduction during slip yields a factor of 10–100 increase in surface area. Hematite is amenable to (U‐Th)/He thermochronometry, which can quantify fault‐related thermal and mechanical processes. Comparison of hematite (U‐Th)/He dates from the undeformed material and experimentally produced gouge indicates He loss occurs during comminution at slow deformation rates without an associated temperature rise required for diffusive loss. Our results imply that, in natural fault rocks, deformation localizes within coarse‐grained hematite by stable sliding, and that hematite (U‐Th)/He dates acquired from ultracataclasite or highly comminuted gouge reflect minor He loss unrelated to thermal processes. Consequently, the magnitude of temperature rise and associated thermal resetting in hematite‐bearing fault rocks based on (U‐Th)/He thermochronometry may be overestimated if only diffusive loss of He is considered.

Sulfur and Carbon–Oxygen Isotopic Geochemistry and Fluid Inclusion Characteristics of the Yolindi Cu-Fe Skarn Mineralization, Biga Peninsula, NW Turkey: Implications for the Source and Evolution of Hydrothermal Fluids

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.

Ochre use at Olieboomspoort, South Africa: insights into specular hematite use and collection during the Middle Stone Age

Recent excavations at Olieboomspoort (OBP) in the Waterberg Mountains of South Africa confirmed previous research at the site that highlighted an abundance of ochre in the Middle Stone Age (MSA) deposits. Here, we report on the results of an analysis of the ochre from the MSA deposits excavated in 2018–2019. Fossilised equid teeth from these deposits were recently dated to approximately 150 ka, an early date for such a sizeable ochre assemblage in southern Africa. Calcium carbonate concretions were removed from ochre pieces using hydrochloric acid. Macro- and microscopic analyses were undertaken to identify raw material types and to investigate utilisation strategies. There are 438 pieces in the assemblage and only 14 of them show definite use-traces. The predominant raw material is a micaceous, hard specular hematite, which is rare at MSA sites elsewhere in southern Africa. A preliminary investigation into the geological nature of the ochreous materials in the archaeological sample and those available in the area was performed using semi-quantitative portable X-ray fluorescence (pXRF), XRF, and inductively coupled plasma mass spectrometry (ICP-MS). Together with site formation processes, we suggest possible, primarily local sources of the ochre found in the deposits. The data do not support previous suggestions that OBP was used as an ochre caching site that may have formed part of an exchange network during the MSA. Instead, the local abundance of nodules of specular hematite within the Waterberg sandstone, the limited number of used pieces in the assemblage, and the stratigraphic context indicate a more natural, less anthropogenic explanation for the abundance of ochre at the site.

Migration of nanocolloid-carrying antibiotics in paddy red soil during the organic fertilization process

Soil nanocolloids are highly mobile and can act as carriers for the transport of antibiotics to a wider and deeper range of soils; however, the inherent behavior and mechanism of nanocolloid-carrying antibiotics in soil remain unclear. In this study, we conducted a comprehensive investigation of the migration of antibiotics in paddy red soil during the organic fertilization process using four common soil nanocolloids: kaolin (KL), montmorillonite (MT), hematite (HT), and humic acid (HA). The results showed that nanocolloid carriers promoted the intra-medium (from soil surface to the bottom) and inter-medium transfer (from organic fertilizers to soil) of antibiotics. The migration mechanisms of antibiotics carried by the nanocolloids differed: the phenolic hydroxyl and carboxyl groups of HA esterified with the carboxyl groups of quinolones and phenolic hydroxyl groups of tetracyclines, respectively, while the oxygen atoms of HT formed stabilizing complexes with the soil, which could further adsorb antibiotics using their functional group-rich complexes. Smaller antibiotic compounds were adsorbed in the metal oxide interlayer of MT via cation exchange, whereas KL adsorbed antibiotics on its metal oxide surface layer in the same way but were susceptible to desorption. Additionally, nanocolloids changed the adsorption capacity of soil for antibiotics and influenced the enrichment of dominant/functional bacteria (e.g., Burkholderiaceae) and thus varied the vertical distribution of antibiotics in soil. These findings enhance our understanding of the migration behavior and mechanism of nanocolloid-carrying antibiotics in red paddy soil and provide a theoretical foundation for preventing and controlling antibiotic pollution in arable systems.

Genesis and Evolution of the Yolindi Cu-Fe Skarn Deposit in the Biga Peninsula (NW Turkey): Insights from Genetic Relationships with Calc-Alkaline Magmatic Activity

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.

Large-scale mining and smelting of specularite ores in the Altai mountains during the 1st millennium AD

According to past historical documents and archaeological evidence, the Altai, rich in iron ore deposits, was a major iron production region in Eurasia during the 1st millennium AD. The present article focuses on the investigation of the large specularite (specular hematite) deposit Rudny Log in the Southeastern Altai (Russian part), long time regarded as a potential mine for the 1st millennium AD iron smelters. To test this hypothesis, we use complex approaches combining: 1) spatial analyses and field recording of traces of workings found at the mine; 2) radiocarbon dating; 3) microstructural (by OM and SEM); 4) geochemical (by XRF and ICP-MS) and 5) multivariate statistical investigation of iron ore and slag samples found at the mine and seven major ancient iron smelting sites in the Southeastern Altai.The results of spatial analysis and fieldwork carried out at the mine reveal the presence of c. 350 pit workings from ancient exploitation, which can be estimated as c. 2500 tons of extracted ore. The radiocarbon analyses indicate the 1st-2nd c. AD timeframe to the start of the exploitation of the mine and the earliest iron smelting in the Southeastern Altai, which is likely linked to the Xiongnu expansion. The materials and statistical analyses allow us to preliminary identify Rudny Log, or, alternatively, another major deposit in the region, as the main source for five major iron production sites operated during the 1st millennium AD. Apart from that, the analyses suggest the exploitation of two currently unknown ore sources at three of the smelting sites. The significant scatter and remoteness of metallurgical centers from the mine can be associated with the nomadic subsistence of smelters who integrated seasonal metallurgical production with the search for new pastures and fuel resources.

Effects of Metasomatism on Granite-Related Mineral Systems: A Boron-Rich Open Greisen System in the Highiş Granitoids (Apuseni Mountains, Romania)

Greisenization is typically linked with highly fractionated granites and is often associated with hydrothermal vein systems. Late to postmagmatic metasomatic processes involve the enrichment of volatile components such as boron and halogens as well as several metallic elements. The purpose of this study is to reveal the main metasomatic effects and paragenetic sequences of the related mineralizations in Highiş granitoids, Romania. In a natural outcrop, more than 30 samples were collected from granitoids, felsic veins, and country rocks. We carried out a detailed mineralogical and petrological characterization of carefully selected samples using X-ray powder diffractometry, electron microprobe analysis, and microscopic methods together with K–Ar ages of whole rocks and K-bearing minerals. Several characteristic features of albitization, sericitization, tourmalinization, epidotization, and hematitization were recognized in the studied samples. Crystallization of quartz, K-feldspar, and magnetite represents the first stage during the magmatic-hydrothermal transition. The mineral assemblage of albite, sericite, schorl, and quartz originates from the early and main stages of greisenization. While the subsequent mineral assemblages, which predominantly include dravite, specular hematite, and epidote, are closely related to the late vein-depositing stage. We propose that the study area could belong to a boron-rich open greisen system in the apical portion of Guadalupian A-type granite. Based on a new hypothesis, the previously published Permian crystallization ages (between ~272 Ma and ~259 Ma) could be homogenized and/or partially rejuvenated during the hydrothermal mineralization processes due to uraniferous vein minerals. Additionally, the Highiș granite-related system suffered a Cretaceous thermal overprint (between ~100 Ma and ~96 Ma). The results may help to understand the evolution of highly evolved granite intrusions worldwide and improve our knowledge of the effect of hydrothermal mineralization processes on the emplacement ages.

The Bahariyeh iron oxide copper–gold deposit, Khaf-Khashmar-Bardaskan magmatic belt, NE Iran: Constraints from geochemical, fluid inclusions, and O-S isotope studies

The Bahariyeh deposit is located in the central segment of the Khaf-Kashmar-Bardaskan magmatic belt (KKBMB), northeast Iran. Previous U-Pb data on zircon revealed an age of 38–41 Ma for the felsic-intermediate intrusions. The stockwork like vein orebodies are hosted in Eocene monzodiorite porphyry rocks which have strong structural controls imposed by the Great Dorouneh Fault System. Hydrothermal alteration is dominated by silicification, propylitic (chloritization), argillic, and sericitic zones. The mineralized veins in the Bahariyeh deposit can be divided into seven types: 1) quartz ± pyrite; 2) quartz + specular hematite + pyrite ± gold; 3) quartz + chalcopyrite + pyrite; 4) quartz + specular hematite + chalcopyrite + pyrite ± sphalerite ± galena ± gold; 5) chalcopyrite + specular hematite + pyrite ± gold; 6) specular hematite ± pyrite; and 7) chalcopyrite + pyrite. The various vein-style orebodies contain high concentrations of Cu, Au, Pb, Zn, and Ag. Microthermometric measurements of fluid inclusions in mineralized veins demonstrate homogenization temperatures in the range of 271–500 °C (mode of 300 °C), and corresponding salinities in the range of 7.9–26.3 wt% NaCl equivalent. The δ18OWater values calculated from δ18O of quartz, and the δ34S values of chalcopyrite reveal a dominantly magmatic origin for the ore-forming fluids. The fluid inclusions indicate that mixing between magmatic fluids and meteoric water, together with cooling, are the dominant mechanisms for metal deposition in the Bahariyeh district. The combination of ore deposit geology, alteration type, fluid evolution processes, and O–S isotope data suggest that the Bahariyeh deposit be classified as a Cu ± Au-rich iron oxide-copper–gold (IOCG) system.

Post-Subduction Granite Magmatism and Gold-Sulfide Mineralization in the Abu Zawal (Fatira) Area, Eastern Desert, Egypt

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).

Tectonic Rotation Pattern at the Northern End of the Red River Fault System in SE Tibet: New Paleomagnetic Evidence From Cretaceous Red Beds

AbstractIn order to study the rotations of crustal material along the boundary faults in the southeastern Tibetan Plateau, and to better understand the tectonic evolution of this region, in this study we conducted a paleomagnetic study of Cretaceous red beds in the Binchuan and Xiangyun sections near the Chenghai‐Binchuan fault, a branch fault at the northern end of the Red River fault in China. Analyses of rock magnetic properties and magnetization components, combined with scanning electron microscopy, show that two types of hematite are present in the Lower Cretaceous rocks: pigmentary hematite and specularite. High‐temperature components (HTCs) were isolated by stepwise thermal demagnetization between 300 and 660°C carried by pigmentary hematite and all of the HTCs are of normal polarity. An additional magnetization component carried by specular hematite cannot be isolated efficiently. Progressive unfolding of both the Binchuan and Xiangyun sections shows that the best grouping of the precision parameter was obtained at 75%–80% untilting, indicating that the remanence of syn‐folding origin is carried by pigmentary hematite. These syn‐folding remanent magnetizations indicate the Binchuan and Xiangyun sections accumulated 20.5 ± 5.3° of clockwise rotation and 9.9 ± 4.6° of counterclockwise rotation, respectively, with respect to East Asia since the early Cretaceous, despite the two sections being only ∼45 km apart. The counterclockwise rotation of the Xiangyun section was likely caused by the left‐lateral shear motion of the Red River Fault; and since the Miocene, the Binchuan section experienced integral clockwise rotations, together with most parts of the Chuan‐Dian Block.

Geology of the Copper Mineralization in Proterozoic Ajabgarh Meta-Sediments of, Dokan-Dariba Belt, Sikar District Rajasthan Northwestern India

The Khetri copper belt is a well-known metallotect in northern part of Delhi fold belt in Rajasthan. On the eastern margin of the Khetri sub basin of North Delhi basin separated by a basement high, another sub basin Alwar-Ajabgarh sub basin exposes that a thick sequence of Ajabgarh group of rocks overlies a thick arenaceous sequence of Alwar group of Delhi Super Group of rocks. The Ajabgarh meta sediments here in the Neem Ka thana area are characterized by presence of Bornite dominated copper mineralization with silver association and minor presence of Pb. The mineralization has been described by various workers as strata-bound, hypogene and IOCG. But these inferences are based on part information and the inference drawn is sectorial in nature. The current study includes a holistic study based on exploration over a period of more than two decades and the data generated suggest thereof, that this syngenetic sulphide mineralization associated with the sedimentation of marl and carbonate rocks. Subsequently it has been relocated during 2nd deformation accompanied by epigenetic component of mineralization depicted in terms of vein filled coarse grained aggregates of bornite and chalcopyrite disposed across the general disposition of litho-package. The EPMA and fluid inclusion data generated from the area indicate association of typical hydrothermal environment minerals like, Perkrite, Wittchenite, Aguilarite, Molybdnite etc. The mineralizing fluids have been trapped between the temperature ranges of 130°C to 375°C with average being 250°C to 300°C. The fluid salinity also varies from near pure hot water to moderately saline fluid indicative of multi-episodic mineralization of syngenetic nature coupled with epigenetic component. The ore textures indicate 500°C temperature range; certain intergrowths of minerals like specular hematite and bornite suggest the occurrence of hypogene environment induced due to emplacement of granite/pegmatite on the eastern and southern margins of the belt. The strata bound nature suggests the euxogenic environment facilitated by carbonate facies of rocks. The parallelism of sulphide with the rock fabric was attained during first deformation and the epigenetic component coupled with the hypogene assemblage was deposited during the D2 deformation in the brittle ductile shear zones and limb shears, between the temperature ranges of 130°C to 570°C as deduced from petrochemical data. Hence a comprehensive model is suggested here on evolution of process of mineralization in the Neem Ka Thana belt.

Davulalan A-type granitoid-associated Cu, Mo, Pb, Zn, and REEs mineralization, Central Anatolia, Turkey

In recent years, due to the high-reserve metallic and/or non-metallic mines detected in A-type granitoids, this interest is growing in these granitoids. Davulalan syenitoid is one of the A-type granitoids which are intruded in the Central Anatolian Crystalline Complex (CACC) in Turkey. This research discusses the ore productivity and fertility of the Davulalan syenitoid based on field studies, petrographic examinations, and geochemical data. The syenitoid consist of alkaline composition syenite and quartz-syenite, and calcic composition nepheline-syenite rocks. Two type mineral occurrences as vein and veinlets (stockwork) bearing Cu (up to 60 ppm), Mo (up to 308 ppm), Pb (up to 3600 ppm), Zn (up to 745 ppm), and REEs (up to 880 ppm), which are located in the center of the syenitoid and the contact zones of the marbles. As microscopically, argillization, sericitization, chloritization, carbonization, and silicification in the samples where are between the veins. The veins and veinlets include mainly galena, chalcopyrite, pyrite, native gold, magnetite, maghemite, specular hematite and hematite as ore minerals, and calcite, fluorite and quartz as gangue minerals. The geochemical data of unaltered/altered samples show tending to the K-feldspar and argillic/sericite alterations. Due to its similar to the Ocean Island Basalt (OIB) composition, strongly evolved and fractionated, likely high oxygen fugacity, the syenitoid a productive and fertility in terms of Cu, Mo, Pb, Zn, and REEs.

Mineralogy of a rare Ediacaran epidote‐bearing trondhjemitic complex from the Nubian Shield: Insights into P‐T conditions of magma emplacement

Igneous epidote occurring in tonalite–trondhjemite–granodiorite (TTG) rocks provides valuable insight into the physiochemical parameters of their magmatic system. Epidote has been identified within a newly discovered, rare, Ediacaran, high‐Al TTG‐suite at the Fannani Igneous Complex (FIC), Nubian Shield. The objective is to assess P–T conditions of magma emplacement using petrographic‐, mineral chemical data, and thermobarometry methods. The TTG‐suite is made up of ubiquitous oligoclase, variable contents of quartz, K‐feldspar, amphibole, biotite, epidote, accessory titanite, zircon, apatite and magnetite. Feldspars vary from An14 to An26 in plagioclase, with K‐feldspar having near‐end‐member compositions (Or91–Or95). Amphiboles are Al‐rich (AlT = 1.65–2.04 atoms per formula unit [apfu]), calcic (Ca = 1.83–1.93, apfu), with average Mg/(Fe + Mg) of 0.44, and are ferroedenite–edenite–ferropargasite. Biotites are moderately Fe‐rich (Fe/(Fe + Mg) = 0.50–0.58) characteristic of type ‘C’–biotite of calc–alkaline orogenic rocks. Epidote exhibits pistacite components [Ps = Fe3+/(Fe3++Al)] of Ps24–Ps33, typical of magmatic epidote. The average crystallization pressure of 5.41 kbar (calculated using the Al‐in‐Hb barometer) is consistent with the presence of magmatic epidote and reflects the mesozonal crustal levels of emplacement. The Hb–Plag–geothermometer produced an average crystallization temperature of 721°C. These values fall within experimentally‐determined P–T ranges of stability of magmatic epidote with fO2 buffered from nickel‐nickel‐oxide (NNO) to hematite (HM). The FIC rocks were developed from a wet, subsolvus, orogenic, Al‐rich magmatic system. Findings reported here could have implications for conditions of magma emplacement and mineralogical characterization of TTGs occurring within various continental masses.

Fluid inclusion and stable isotope constraints on the genesis of epithermal base-metal veins in the Armaqan Khaneh mining district, Tarom-Hashtjin metallogenic belt, NW Iran

Rashtabad, Aqkand and Jalilabad are neighbouring epithermal base-metal deposits in the Armaqan Khaneh mining district of the Tarom-Hashtjin metallogenic belt, northwestern Iran. Mineralised veins in these deposits consist of pyrite, chalcopyrite, galena, sphalerite with lesser bornite and minor amounts of specular hematite. The gangue mineralogy includes quartz, chlorite, and calcite in ore veins and sericite/illite, and sericite–epidote–chlorite–calcite in vein haloes. At Rashtabad and Jalilabad, primary LV fluid inclusion assemblages homogenise into liquid at 150–285 °C and 120–342 °C, respectively. The corresponding salinities, respectively, vary between 7.4–12.9 and 7.8–13.5 wt% NaCl equiv. At Aqkand, LV inclusions show a T h(total) of 229–353 °C and salinities of 7.4–9.8 wt% NaCl equiv. Calculated δ18Owater values of quartz samples at Rashtabad, Aqkand, and Jalilabad are +1.0‰ to +9.6‰ Vienna-Standard Mean Ocean Water, signifying that the ore-forming fluid progressed from magmatic to meteoric water. Sulfur isotopic values of sulfides range from −6.0 to −2.2‰ Vienna Cañon Diablo Troilite (averaging −3.7‰), indicate sulfur was derived from a rather homogeneous magmatic source that was oxidised by meteoric water through fluid mixing. Our data suggest that Rashtabad, Aqkand and Jalilabad are an intermediate-sulfidation type of epithermal mineralisation formed from a well-mixed source that experienced extensive fluid mixing and boiling. KEY POINTS The Rashtabad, Aqkand and Jalilabad deposits of the Armaqan Khaneh mining district are intermediate-sulfidation style of epithermal mineralisation. Fluid boiling and mixing facilitated hydrothermal alteration and mineralisation. Oxygen isotope values suggest that the ore–fluid system evolved from magmatic to meteoric. Sulfur derived from a magmatic source was oxidised by meteoric water through fluid mixing.

Mapping specular hematite ore beneficiation routes to industrial application standards

The purpose of this study is to determine the appropriate method for micaceous iron ore processing and production per-industrial application standards. After identifying the characteristics of the samples (with XRF, XRD, mineralogical analyzes), gravity and magnetic separation tests were carried out. Quartz and hematite are the main minerals of micaceous hematite ores. Silica grade as the major impurity varies from 10% to 68%. The total iron content of the samples also varies from 15% to 62%. A jig and shaking table did not provide a good result in micaceous hematite beneficiation to achieve the standard of its specific applications. Gravity concentration by the spiral in the size range of -200 and -300 μm has led to the production of iron concentrates with a grade of 62.34% and 64.84%, respectively. The recovery values for the two experiments are 13.50% and 12.60%, respectively. Therefore, the spiral did not provide a good result in the micaceous iron ore beneficiation. High-intensity magnetic separation (1.2 T) has resulted in a product with a grade and recovery of 65.98% and 88.35%, respectively. The experimental design utilizing the Taguchi method considering the increasing of grade or recovery priority indicated that for micaceous iron beneficiation with a priority of recovery increasing, the feeder frequency, roll speed, and adjustable gate angle should be at 6.5 Hz, 95 rpm, and 20°, respectively. However, for micaceous iron beneficiation with a priority of grade increasing, the feeder frequency, roll speed, and adjustable gate angle should be at 2.5 Hz, 135 rpm, and 60°, respectively.

Improving the sinter productivity with increased specular iron ore in sinter blend

Specular iron ores are medium grade iron ores suitable for the use in agglomeration process. However, due to their hard texture, undesirable particle size and shape, poor assimilation performance and low reactivity at high temperature, its uses in agglomeration is very limited and restricted to almost 3-10% at most of the plants. In the present study, the effect of specular iron ore on sintering performance and sinter qualities are examined. It was observed that an increased proportion of specular iron ore in sinter blend showed poor sintering performance in both laboratory scale studies and plant scale trials. In the present work, the effect of blending of specular iron ore with goethite iron ore in sinter mix on sintering performance was examined and an optimum iron ore blend ratio for sustainable performance and quality was proposed. To increase the specular iron ore usage in sintering, goethitic iron ore up to 30% was introduced in sinter blend to overcome the deteriorating nature of specular iron ore. The goethite iron ore contains chemically bonded water which gets removed at higher temperatures (300-500?C) during sintering. The evaporated water gets cooled at lower bed and condenses which retards the air flow during sintering process and thus the combustion zone stays for longer time allowing better melt assimilation and sinter qualities. The poor melt assimilation of specularite is thus countered in presence of goethite iron ore. Having better reactive and hydrophilic nature of goethite iron ore, nullifying or reducing the ill effect of poor reactive and hydrophobic characteristics of specular iron ore during granulation and sintering process. Therefore, the blended specular and goethite iron ore resulted in improved sintering rate and consequently improved sinter productivity. The present work proposed usage of up to 30% of specular iron ore when blended with goethite iron ore in sinter making.

Seismicity recorded in hematite fault mirrors in the Rio Grande rift

AbstractExhumed fault rocks provide a textural and chemical record of how fault zone composition and architecture control coseismic temperature rise and earthquake mechanics. We integrated field, microstructural, and hematite (U-Th)/He (He) thermochronometry analyses of exhumed minor (square-centimeter-scale surface area) hematite fault mirrors that crosscut the ca. 1400 Ma Sandia granite in two localities along the eastern flank of the central Rio Grande rift, New Mexico. We used these data to characterize fault slip textures; evaluate relationships among fault zone composition, thickness, and inferred magnitude of friction-generated heat; and document the timing of fault slip. Hematite fault mirrors are collocated with and crosscut specular hematite veins and hematite-cemented cataclasite. Observed fault mirror microstructures reflect fault reactivation and strain localization within the comparatively weaker hematite relative to the granite. The fault mirror volume of some slip surfaces exhibits polygonal, sintered hematite nanoparticles likely created during coseismic temperature rise. Individual fault mirror hematite He dates range from ca. 97 to 5 Ma, and ~80% of dates from fault mirror volume aliquots with high-temperature crystal morphologies are ca. 25–10 Ma. These aliquots have grain-size–dependent closure temperatures of ~75–108 °C. A new mean apatite He date of 13.6 ± 2.6 Ma from the Sandia granite is consistent with prior low-temperature thermochronometry data and reflects rapid, Miocene rift flank exhumation. Comparisons of thermal history models and hematite He data patterns, together with field and microstructural observations, indicate that seismicity along the fault mirrors at ~2–4 km depth was coeval with rift flank exhumation. The prevalence and distribution of high-temperature hematite grain morphologies on different slip surfaces correspond with thinner deforming zones and higher proportions of quartz and feldspar derived from the granite that impacted the bulk strength of the deforming zone. Thus, these exhumed fault mirrors illustrate how evolving fault material properties reflect but also govern coseismic temperature rise and associated dynamic weakening mechanisms on minor faults at the upper end of the seismogenic zone.

Iron production in Ptolemaic Egypt: From the Abu Gerida specular hematite mines to the Hamama smelting workshop

AbstractAlthough ancient Egypt has a firmly established record of mining and metallurgy of gold and copper, iron production in ancient Egypt is less well documented. Evidence of ancient iron manufacture in Egypt is to be found in the burnt plant remains, slag fragments, and a furnace‐like structure discovered in the Hamama workshop in the Eastern Desert of Egypt. The iron ore required for iron production was delivered from the nearby specular hematite mines of the Abu Gerida area. This Egyptian specularite is geochemically distinguished from other Mediterranean varieties of specularite such as those in Elba, Tuscany, and Seriphos Island. The bloomery iron smelting process in the Hamama workshop produced two types of slags: furnace slags and tapping slags. These two types show different petrographic features and geochemical signatures. Some of the geochemical signatures of the slags, such as their high calcium contents, were derived from charcoal, while others were related to the ore used during the smelting process. Radiocarbon dating of the charred plant remains from the Hamama workshop suggests that the iron smelting activities took place in the early Ptolemaic era. Iron production was seasonal and was conducted by locals who most likely had dynamic socioeconomic ties with the urban centers of the Nile valley.