Hematite Quartz Research Articles

Parameter Optimization of the Separation Process for Hematite and Quartz Mixture Minerals Based on a Cyclone Centrifugal Separator

The current centrifugal concentrators do not continuously concentrate heavy minerals of large mass weight—for example, in the processing of iron oxides. A cyclone centrifugal separator is a new type of beneficiation equipment that has been developed on the basis of the principles of centrifugal separation and hydrocyclones. In this study, a cyclone centrifugal separator was used for the beneficiation of a hematite–quartz mixture, and the separation effect under different operating conditions was analyzed. The results showed that various factors, such as the feeding concentration, the feeding pressure, and the number of fluidization holes in the separation cone, had a significant influence on the separation performance of the cyclone centrifugal separator. The single-factor separation test results showed that the appropriate operating conditions were a feeding concentration of 10%, a feeding pressure of 120 kPa, a 40-hole separation cone, a settling port pressure of 70 kPa, and an overflow port pressure of 50 kPa. The results of the open circuit separation test that was designed on the basis of the single-factor experiment showed that the concentrate grade of Fe in the hematite–quartz mixture, with 44.12% Fe, was 54.42% after beneficiation, indicating better beneficiation separation effects. This study provides a new approach for the beneficiation of a large number of difficult-to-select hematite ores in China, and can provide a reference for the further expansion and application of the cyclone centrifugal separator in the field of mineral processing.

Differentiation of Multi-lithotypes Olistostromal Occurrences Associated with Iron Enrichment and Mineralization Within the Ophiolites of Choman Area, NE Iraq

The discovery of multi-lithotypes olistostromes deposits associated with potentially economically viable iron ore mineralizations in the Rayat region of NE Iraq are described in this study. The depositional and differentiation-classification characteristics of multi-lithotypes of olistostromes with distinct depositional and characteristics are reported here through detailed petrographic, mineralogical, and geochemical data, that allowed for mineralization mechanisms assessment and associated hydrothermal and alteration processes. Ferruginous conglomerate lithotypes occur below the sandstone olistostromes lithotypes section of the investigated series. Through the ferruginous conglomerate olistostromes (FCO) lithotypes there is a layer of potentially iron ore containing iron oxide (up to %42.55), quartz with some minor spinel content. Below the FCO, there are the horizons of (FOpO and FSO), they are also rich in hematite quartz and calcite with some minor spinel content. A 2m thick transition zone (TZ), separate poorly mineralized ophiocarbonatic olistostrome (OpCO) from the FCO. The multi-lithotypes of olistostrome from bottom to top are (serpentinite olistostrome (SO), Ophiocarbonatic olistostrome (OpCO), ferruginous serpentinite olistostrome (FSO), ferruginous ophiocarbonatic olistostrome (FOpCO), ferruginous conglomerate olistostrome (FCO), and sandstone olistostrome (SstO). In addition to Fe, the other potential economic importance element includes nickel (507 to 5816 mg/kg) and cobalt (47.2 to 328.3 mg/kg). The findings indicate that the Rayat olistostromes such as (SO, FSO, OpCO, FOpCO, FCO, and SstO) and the transition- zone (TZ) originated from a mixture of early hydrothermal alteration of serpentinites. The finding of olistostromes in the Rayat, exposes NE Iraq as a potential mineral-rich secto

Selective Flocculation Study of Hematite in HematiteQuartz-Kaolinite System in Presence of Ca2+, Mg2+ and Fe3+ Ions. Part1: Optimization of Ligand

Separation of ultrafine hematite from quartz and kaolinite gangue minerals using selective flocculation technique is markedly affected by the state of inter mineral interaction which is governed by type and content of polyvalent metal ions. Because of the presence of polyvalent metal ions hetracoagulation of gangue minerals is widely acknowledged, thus selective flocculation of ultrafine hematite from associated gangue minerals is challenging task when their concentration is above 10 ppm. This study has shown that state of strong interaction of gangue minerals with hematite due to presence of 15 ppm Ca2+, 3 ppm Mg2+ and 3 ppm Fe3+ ions can be weakened by addition of optimal dose of Sodium Hexametaphosphate (SHMP) ligand. The optimization of ligand dose is achieved through analysis of Zeta Potential (ZP) as a function of slurry pH. It is noted that 50 ppm of SHMP is sufficient to restore the ZP of hematite, where selective dispersion of the slurry constituents are possible. Our results further showed that conventional strategy of obtaining minimum difference of ±30 mV in the ZP of hematite and gangue minerals quartz and kaolinite would not work especially in the presence of 15 ppm Ca2+, 3 ppm Mg2+ and 3 ppm Fe3+ ions. Attempts to achieve the minimum threshold difference in the ZP of the minerals will cause over dispersion.

Petrography, microthermometry, and isotopy of the gold veins from Vetas, Santander (Colombia)

The gold mineralization located in Vetas, Santander, consists of auriferous quartz veins hosted in Bucaramanga gneiss rocks, intrusive Jurassic rocks, and intrusive to porphyritic Miocene rocks. This study identified four mineralizing events: (1). Sericite, carbonate (ankerite and calcite?), massive and microcrystalline quartz, sphalerite, adularia, albite, galena, thin pyrite, pyrrhotite, chalcopyrite. The age for this stage is 10.78 ±0.23Ma (Ar/Ar on sericite). (2). Molybdenite, magnetite with exsolution of ilmenite, As-pyrite, sphalerite, fine-grained pyrite and little chalcopyrite quartz with huge, feathery, fine mosaic, flamboyant and microcrystalline textures and, tourmaline and sericite. (3). Gold and tennantite associated with sphalerite, fine- and coarse-grained pyrite, As-pyrite, chalcopyrite like inclusions, and quartz with flamboyant, mosaic, massive and “comb” textures, and tourmaline. Stage 2 and 3 happened from 7.58 ±0.15 Ma to 6,89±0,41Ma (Ar/Ar on sericite). (4). Thick, thin, and pyrite with arsenic, hematite and microcrystalline quartz (forming breccia texture), and sericite. The age for this stage is 5.24 ±0.10 (Ar/Ar on sericite). Post-mineral: quartz comb, alunite, halloysite, kaolinite, and ferrum hydroxides. The stable isotopes, ∂18O, ∂D, and ∂34S and fluid inclusions analysis infer that fluids were producing a mixture of meteoric and magmatic fluids with low salinity and minimum trapping temperatures between 200°C to 390°C. The mineralogy association, and fluid inclusions, in the first event show characteristic of low sulfidation epithermal. The second stage was hottest and with more magmatic signature over printed an intermediate sulfidation system; show a little more salinity on the fluids and more mineralogical diversity, the third and four events, could show an evolution of this fluid, where it was cooling and impoverishing on metals. Two initials stages are contemporaneous with two magmatic Miocene pulses on the area: the first one of granodiorite composition 10, 9± 0.2 Ma (U/Pb zircon), and the other one rhyodacite with 8.4 ±0.2 y 9.0 ± 0.2 Ma.

Mineralogy of Chub Lake-Type Hematite Deposits in St. Lawrence County, NY

Numerous localities of specular hematite have been found in the Grenville Province in St. Lawrence County, New York. Here, we focus on six of them: the Dodge mine, the Chub Lake prospect, the Toothaker Creek prospect, the Bowman prospect, the Whitton prospect, and the Toothaker Pond prospect. We used literature research, interviews, and personal observations to establish the history of each site as a source of mineral specimens. We examined extensive holdings of specimens from each site in the New York State Museum. We used sight identification, chemical tests, x-ray diffraction, and scanning electron microscopy with energy dispersive spectroscopy as necessary to identify all the mineral species present. We had determinations made of the stable oxygen isotope content of quartz, hematite, and calcite from the Chub Lake prospect, reported as 18O relative to Vienna Standard Mean Ocean Water (VSMOW). We conclude that these occurrences formed from groundwaters at a temperature of about 170 °C in areas of low topography on the surface of the Precambrian basement rocks. Two hypotheses for this process are presented and evaluated. Well-crystallized specimens of bladed specular hematite and Cumberland-habit quartz are the most common minerals found. Noteworthy accessory crystallized minerals include barite, calcite, and goethite. All six deposits are relatively free of sulfides, so that secondary goethite formed from weathering of iron-rich carbonates at some sites. It is likely that more such deposits will be discovered in this region in the future.

Flotation recovery of rare earth oxides from hematite–quartz mixture using sodium oleate as a collector

Froth flotation plays a significant role in the beneficiation of rare earth elements (REE) minerals from differing ores. Monazite has been identified as one of the principal REE minerals in most iron oxide silicate rich tailings generated in Australia from the extraction of primary commodities such as copper and gold. These tailings generally contain hematite and quartz as the major gangue minerals. A previous investigation has identified almost identical flotation response between monazite and hematite in the presence of anionic collectors. Therefore, it is necessary to investigate the feasibility of selective flotation of rare earth oxides (REO) in monazite from hematite–quartz mixtures, to identify cost-effective processing methods. The flotation conditions for selective REO separation from model minerals mixtures were tested in a 1.2 L Denver flotation cell using sodium oleate as a collector. Sodium silicate and starch were tested as depressants for hematite and quartz. Results from the flotation tests revealed that the increased dosage of sodium oleate led to an increase in REO recovery with a corresponding decrease in upgrade, and increased hematite (Fe2O3) and quartz (SiO2) recoveries. In the absence of depressants, the separation of REO from a low grade mixture (0.83% REO feed grade) was unselective, where 3000 g/t sodium oleate recovered 98% REO at a grade of 1.31% (enrichment ratio, E = 1.58) along with 77% Fe2O3 and 37% SiO2 recoveries. However, the depressants reduced the flotation recovery of Fe2O3 and SiO2, which was shown by an improvement in REO grade. The flotation recovery of REO decreased to 84% with a corresponding increase in grade to 4.13% when 1000 g/t sodium silicate was used in the presence of 3000 g/t sodium oleate. Furthermore, 1000 g/t starch in the presence of 3000 g/t sodium oleate increased REO concentrate grade to 5.56% although the recovery decreased to 65%. Subsequently, a rougher–scavenger flotation test conducted with the mixed depressants (sodium silicate: starch, 1:1) produced a final concentrate recovering 61% REO at a grade of 6.25%. This study has shown that REO can be separated selectively from hematite–quartz rich mixtures by flotation when using sodium oleate as the collector and sodium silicate and starch as depressants.

Interaction of sinking behaviour of Saharan dust and lithogenic and biogenic fluxes in the Canary Basin

Saharan dust events are currently the predominant source of lithogenic particles in the Canary Basin. In order to quantify this input and its relationship with the biogenic fluxes, a sediment trap was deployed in a free-drifting system at 150 m depth, 50 km off the north coast of Gran Canaria (Canary Islands). The mineralogy of the lithogenic particles included illite, calcite, hematite quartz, barite and kaolinite. The biogenic matter was composed of chitin, transparent exopolymer particles, and carbonates from foraminifera and gastropod shells. The average Saharan dust flux over the ocean surface was approximately 5±4 mg m–2 day-1. The lithogenic, carbonate and chitin fluxes were 0.8±0.6, 6.0±7.4 and 154±386 mg m–2 day-1, respectively. A fairly strong Saharan dust event during sampling was observed in the trap, with a delay of three days in the peaks of lithogenic and biogenic fluxes. The theoretical settling velocity of the lithogenic particles associated with Saharan dust events at 150 m depth was vStokes=275 m day-1, and the experimental settling was about 50 m day-1. The associated sinking behaviour of particulate organic carbon and biogenic and lithogenic fluxes observed in this study may contribute to a more realistic prediction of these fluxes in carbon biological pump models.

Camanchacaite, chinchorroite, espadaite, magnesiofluckite, picaite and ríosecoite: six new hydrogen-arsenate minerals from the Torrecillas mine, Iquique Province, Chile

AbstractThe new minerals camanchacaite, NaCaMg2[AsO4]2[AsO3(OH)2], chinchorroite, Na2Mg5(As2O7)2(AsO3OH)2(H2O)10, espadaite, Na4Ca3Mg2[AsO3(OH)]2[AsO2(OH)2]10(H2O)6·H2O, magnesiofluckite, CaMg(AsO3OH)2(H2O)2, picaite, NaCa[AsO3OH][AsO2(OH)2] and ríosecoite, Ca2Mg(AsO3OH)3(H2O)2, were discovered on two closely related specimens collected from the Torrecillas mine, Iquique Province, Chile. These minerals occur as secondary phases on massive quartz–hematite also in association with anhydrite, gypsum, halite and talmessite. Camanchacaite is monoclinic,C2/c,a= 12.470(9),b= 12.554(9),c= 6.848(9) Å, β = 113.75(2)°,V= 981.3(16) Å3andZ= 4. It has a protonated alluaudite-type structure. Chinchorroite is triclinic,P$\bar{1}$,a= 8.7777(2),b= 8.8570(3),c= 9.7981(7) Å, α = 91.097(6), β = 110.544(8), γ = 103.167(7)°,V= 690.43(7) Å3andZ= 1. The structure contains abbreviated chains of five edge-sharing Mg octahedra that are linked by pyroarsenate and hydrogen-arsenate groups. Espadaite is orthorhombic,Ccca,a= 12.3649(10),b= 22.181(2),c= 18.3292(13) Å,V= 5027.1(7) Å3andZ= 4. The structure is based on heteropolyhedral sheets of formula {Ca3Mg2[AsO3(OH)]2[AsO2(OH)2]10}4−that contain large voids; NaO6polyhedra occupy the interlayer region. Magnesiofluckite is triclinic,P$\bar{1}$,a= 8.4143(6),b= 7.5321(5),c= 6.8917(4) Å, α = 82.477(6), β = 97.682(6), γ = 95.379(6)°,V= 427.84(5) Å3andZ= 2. It is isostructural with fluckite. Picaite is monoclinic,P21/c,a= 7.2474(4),b= 14.6547(7),c= 7.2624(5) Å, β = 99.520(7)°,V= 760.70(8) Å3andZ= 4. The structure contains chains of edge-sharing Na− and Ca octahedra with bridging AsO3(OH) and AsO2(OH)2tetrahedra. Ríosecoite is triclinic,P$\bar{1}$,a= 6.8110(9),b= 7.3156(12),c= 11.7773(17) Å, α = 83.466(6), β = 84.394(6), γ = 79.779(6)°,V= 571.95(15) Å3andZ= 2. The structure contains tetramers of edge-sharing CaO7and CaO8polyhedra linked by MgO6octahedra and bridging AsO3(OH) groups to form chains.

Physicochemical Conditions of the Existence of Early Cambrian Chemotrophic Microbiota in the Zone of Influence of Sulfide Ore-Forming Hydrothermal Solutions

Complex studies of the Early Cambrian Kyzyl-Tashtyg pyrite deposit (East Tuva) allowed us to reconstruct the paleohydrothermal systems, to understand the physicochemical conditions of hydrothermal processes, and to study the patterns of existence of ancient hydrothermal biota in the zone of activity of solutions participating at all stages of the formation of ore-bearing structures starting from the influence of postmagmatic fluids and up to low-temperature hydrotherms. The data on the biota reported were obtained during study of the objects occurring in the zone of influence of relatively low-temperature hydrothermal systems. In some cases, microorganisms were found in basaltic complexes hosting ore bodies; in other cases, fauna was related to the ferrous–siliceous deposits. It was found that microorganisms in basaltic amygdules were formed at temperatures of ~110–140°C under the influence of hydrothermal solutions of the Kyzyl-Tashtyg deposit. Much lower temperatures (up to 100°C) existed during the evolution of microfossils in the quartz–hematite hydrothermal structures of the Kyzyl-Tashtyg deposit.

Investigation of reddening patterns of dune sands — The megabarchans of Al-ghord Lahmar (Khnifiss National Park, South-West of Morocco)

The present paper aims to investigate the geological and environmental parameters controlling the redness of sand at the megabarchans located nearby Khnifiss lagoon (SW of Morocco). Mineralogical investigation either by laboratory or remotely sensed data showed the abundance of a mixed composition of Quartz, Carbonates and mafic minerals with a dominance of Hematite Quartz coated grains. Also, grain size analysis revealed the heterogeneity of the megabarchans sand and the dominance of fine and well to very well sorted sand with a mean grains size of (0.2mm). Mineralogical species were adequately distributed according to their size and density. We noted the dominance of iron bearing minerals including: Magnetite, Hematite, Ilmenite, Ulvospinel, and Pyroxenes, in the very fine fraction (<63μm). Yet, the coarser fractions (>63) μm knew a dominance of Hematite coated Quartz, Carbonates and Feldspars. These both fractions are carried by wind with almost the same threshold motion, which meant that the size could compensate the density. That explains their deposition in the same environment. The megabarchans migrated over the past 325years with a rate of 2m/year. Thus, grains may undergo many turnover cycles until they can be reactivated by wind. Climatic parameters such as precipitations with 164mm/year, the frequent stormy events that bring a flash flooding, in addition to the high humidity and important fog and dew provide a source of moisture that make the megabarchans a moistened environment encouraging the iron oxidation. Thus, the abundance of a source of iron and a source of moisture, in addition to the stability of the megabarchans, and their water holding capacity remained the effective factors that led to the megabarchans redness.

Two Types of Archaean Supracrustal Belts in the Bundelkhand Craton, India: Geology, Geochemistry, Age and Implication for Craton Crustal Evolution

Abstract: Two Archaean supracrustal complexes are documented in the Bundelkhand craton viz. 1) the Central Bundelkhand greenstone complex (formed the Babina and Mauranipur belts), and 2) the Southern Bundelkhand metasedimentary (paragneisses, schists) complex (formed the Girar belt). The Central Bundelkhand greenstone complex consists of (i) an early assemblage composed of basic-ultrabasic, felsic volcanics, banded iron formation (BIF), and (ii) a late assemblage which contains felsic volcanics. The U-Pb zircon ages of felsic volcanics from the early assemblage, formed in an arc-type subduction setting, are 2813 Ma (Mesoarchaean). The U-Pb zircon ages of felsic volcanics from the late assemblage, which also occur in subduction settings as an active continental marginal type, are 2542 Ma (Neoarchaean). The Girar belt, located in the southern part of the craton, consists generally of metasedimentary rocks namely quartzites and BIFs. Quartzites are represented by fuchsite- and hematite-bearing quartz arenite and lesser quartz pebble conglomerates that have been subjected to low-grade metamorphism. BIF is represented by thinly-bedded quartz–hematite (±magnetite) rocks. Some lenses of marble and chlorite schist are present at the contact between the two formations. BIF is fairly rich in Cr and Ni, poor in Zr, Hf, Ba, Th, Sr, Yb and Lu, and displays a distinct positive Euanomaly (Eu/Eu* = 1.14-2.46). Zircons from quartzites give two U-Pb ages: 3432±9.7 Ma and 3252±6.4 Ma. The Sm-Nd isotope study of quartzite from the Girar belt shows that the TDM is 3.29 Ga. This TDM correlates well with the U-Pb ages of zircon and indicates that the continental crust in the Girar area began to form in the Paleoarchaean (3.4-3.2 Ga). The Central Bundelkhand greenstone complex was thus formed in a subduction-accretion setting in Mesoarchaean (ca 2.8 Ga) and Neoarchaean (2.54 Ga) time, and the Southern Bundelkhand metasedimentary complex originated in a sedimentary basin on the old continental crust apparently at ca ~ 2.7 Ga.

Tube fossils from gossanites of the Urals VHMS deposits, Russia: Authigenic mineral assemblages and trace element distributions

The occurrence, types, morphology, and mineralogical characteristics of tube microfossils were studied in gossanites from twelve VHMS deposits of the Urals. Several types of tube microfossils were recognized, including siboglinids, polychaetes and calcerous serpulids, replaced by a variety of minerals (e.g. hematite–quartz, hematite–chlorite, carbonate–hematite) depending on the nature of the substrate prior to the formation of the gossanites. Colonial hematite tube microfossils (~150μm across,1–2mm long) are composed of hematitic outer and inner walls, and may exhibit a cellular structure within their cavities. Spherical forms are saturated with Fe-oxidizing bacteria inside the tubes – probably analogues of trophosomes. Colloform stromatolitic outer wall surfaces are characterized by the presence of numerous interlaced filaments of hematite (2–3μm diameter, up to 1–2mm long). Between tube microfossils, the hematitized cement contains bundles of hematitized filaments with structures similar to the hyphae of fungi. Hematite–chlorite tube microfossils are scattered in gossanites, mostly as biological debris. They are typically 30 to 300μm in diameter and 1 to 5mm long. The layered structure of their tube walls is characterized by hematite–quartz and chlorite layers. Abundant filamentous bacteria coated by glycocalix and chlorite stromatolite are associated with hematite–chlorite tubes. The carbonate–hematite tube microfossils (up to 300μm across, 2–3mm long) occur in carbonate-rich gossanites. The tubes are characterized by fine (~10μm thick) walls of hematite and cavities dominated by relatively dark carbonate or hematite. Carbonates may be present both in walls and cavities. Stromatolite-like leucoxene or hematite–carbonate aggregates were also found in association with tubes. Randomly oriented filaments are composed of ankerite. Single filaments are composed of individual cells, typically smaller than 100nm across, similar to that of magnetotactic bacteria.Three dimensional tomographic images of all types of tube microfossils demonstrate a clear wavy microlayering from outer and inner walls, which may reflect segmentation of the tube worms. The traces of burrowing or fragments of glycocalix with relict spheres are typical of tube microfossils from gossanites.The carbon isotopic composition of carbonates associated with tube microfossils from hematite–quartz, hematite–carbonate, and hematite–chlorite gossanites average−7.2, − 6.8, –22.8‰, PDB, respectively. These values are indicative of a biogenic origin for the carbonates. The oxygen isotopic composition of these carbonates is similar in all three gossanite types averaging +13.5, +14.2, +13.0‰ (relative to SMOW), and indicative of active sulfate reduction during the diagenetic (and anadiagenetic) stages of the sediments evolution. The trace element characteristics of hematite from tube microfossils are characterized by high contents of following trace elements (average, ppm): Mn (1529), As (714), V (540), W (537), Mo (35), and U (5). Such high contents are most likely the result of metal and metalloid sorption by fine particles of precursor iron hydroxides during the oxidation of sulfides and decomposition of hyaloclasts via microbially-mediated reactions.

Application of Image Analysis to Identify Quartz Grains in Heavy Aggregates Susceptible to ASR in Radiation Shielding Concrete.

Alkali-silica reaction (ASR) is considered as a potential aging-related degradation phenomenon that might impair the durability of concrete in nuclear containments. The objective of this paper is the application of digital analysis of microscopic images to identify the content and size of quartz grains in heavy mineral aggregates. The range of investigation covered magnetite and hematite aggregates, known as good absorbers of gamma radiation. Image acquisition was performed using thin sections observed in transmitted cross-polarized light with λ plate. Image processing, consisting of identification of ferrum oxide and epoxy resin, and the subsequent application of a set of filtering operations resulted in an adequate image reduction allowing the grain size analysis. Quartz grains were classified according to their mean diameter so as to identify the reactive range. Accelerated mortar bar tests were performed to evaluate the ASR potential of the aggregates. The SiO2 content in the heavyweight aggregates determined using the image analysis of thin sections was similar to XRF test result. The content of reactive quartz hematite was 2.7%, suggesting that it would be prone to ASR. The expansion test, according to ASTM C1260, confirmed the prediction obtained using the digital image analysis.

Role of silica and alumina content in the flotation of iron ores

Indian low grade iron ores mostly contain quartz, gibbsite, and clay as the major impurities. Depending upon the ore characteristics, in many instances froth flotation has to be used to recover the hematite and other iron oxides from the ground ores. In this context, the difference in silica and alumina content in low grade iron ores is brought to bear on the prospects of iron ore flotation. For this purpose, pure minerals like hematite, quartz, gibbsite, and clay have been used to prepare synthetic mixtures and analyzed to determine the difference in floatability. The results are compared against natural iron ores with variations in silica and alumina content. The flotation results with oleic acid and dodecylamine show better recovery of iron values in the hematite–quartz mixture as well as in the naturally occurring high silica ore compared to the hematite–clay mixture and the high alumina ore respectively. Similarly results on a variety of iron ores show that high silica content as quartz in the ore causes less hindrance in the flotation of iron ore, whereas the presence of silica as clay inhibits the flotation response of iron ore. The scanning electron microscopic (SEM) studies indicate that clay particles cover the surface of hematite, making it less selective for interaction with the collector. The surface potential studies of clay and quartz suggest that charge reversal takes place for quartz treated with dodecylamine (DDA), but for the DDA adsorption on clay, negative potential values are noted beyond a pH of 4.6.

Geophysical models of the Montresor metasedimentary belt and its environs, central Nunavut, Canada

Recent identification of hydrothermally altered rocks and breccia in the underexplored Montresor belt of Paleoproterozoic metasedimentary rocks suggests the possible presence of undiscovered mineralization. This study examines potential field data from the region with the goal of identifying subsurface features that could be associated with or serve as vectors to mineralization (subsurface alteration zones, faulting and (or) igneous intrusions). Gravity data were used to model regional and local geological features using known geology and physical properties from the study area and environs as constraints, and documents dense intrusive bodies underlying the Paleoproterozoic sequences. Maps of transformed apparent magnetic susceptibility values outline corridors of weak magnetization that correspond to observed zones of non-magnetic breccia and epidote–hematite–quartz alteration. Imputing the apparent susceptibility and rock property information into a magnetic forward model defines the geometry of this alteration zone, which is best explained as a northerly dipping non-magnetic or demagnetized, metasomatized intrusive sheet. The presence of previously undocumented igneous intrusions, their association with demagnetized hydrothermal breccia, and the continuity of the demagnetized zone suggests additional prospective areas within the region. This geological–geophysical framework for the nature and geometry of the Montresor belt and its surrounds highlights the importance of integrated modelling for areas with limited data.

Distribution, mineralogy and geochemistry of silica-iron exhalites and related rocks from the Tyrone Igneous Complex: Implications for VMS mineralization in Northern Ireland

Iron formations, hematitic cherts (jaspers), ‘tuffites’, silica-iron exhalites and other metalliferous chemical sedimentary rocks are important stratigraphic marker horizons in a number of volcanogenic massive sulfide (VMS) districts worldwide, forming during episodes of regional hydrothermal activity. The VMS prospective ca. 484–464Ma Tyrone Igneous Complex of Northern Ireland represents a structurally dissected arc-ophiolite complex that was accreted to the composite margin of Laurentia during the Grampian orogeny (ca. 475–465Ma), and a potential broad correlative to the VMS-rich Buchans–Robert's Arm arc system of the Newfoundland Appalachians. Silica-iron-rich rocks occur at several stratigraphic levels in the Tyrone Igneous Complex spatially and temporally associated with rift-related basalts (e.g., Fe–Ti-rich eMORB, IAT, OIB) and zones of locally intense hydrothermal alteration. In the ca. 475–474Ma lower Tyrone Volcanic Group, these rocks are characterized by massive, 1–5m thick blood-red jaspers, hematitic siltstones and mudstones, and intensely silica-hematite altered tuffs and flows. Their mineralogy is dominated by quartz–hematite±magnetite–(chlorite-sericite±tremolite/actinolite), with Fe concentrations rarely exceeding 10wt.%. Relict textures (including the presence of coalesced spherules of silica-iron oxides) in rocks exposed at Tanderagee NW, Creggan Lough and Tory's Hole are indicative of seafloor exhalation, whereas replacement of the original volcanic stratigraphy is evident to varying degrees at Tanderagee, Beaghbeg and Bonnety Bush. In the structurally overlying ca. 473–469Ma upper Tyrone Volcanic Group, chemical sedimentary rocks include recrystallized: (i) thin and laterally-restricted jaspers in thick sequences of graphitic pelite at Boheragh; and (ii) laterally-persistent sulfidic cherts and ironstones dominated by quartz–hematite–magnetite–(chlorite) or quartz–pyrite–(chlorite) in sequences of tuff at Broughderg. Compared to chemical sedimentary rocks associated with VMS deposits worldwide, their geochemical characteristics are most similar to silica-iron exhalites of the Mount Windsor Subprovince (SE Australia) and jaspers of Central Arizona, Bald Mountain (Northern Maine), the Urals, Iberian Pyrite Belt and Løkken ophiolite (Norway). Positive Eu anomalies (at Slieve Gallion and Tanderagee NW), elevated Cu+Pb+Zn, Au, Fe/Ti, Fe/Mn, Sb, Ba/Zr and Fe+Mn/Al, together with low REE, Sc, Zr and Th, are indicative of a greater hydrothermal component and potentially more VMS-proximal signatures. Based on bulk ironstone geochemistry, Bonnety Bush, Tanderagee NW-Creggan Lough, Broughderg and Drummuck (Slieve Gallion) are considered the most VMS prospective areas in the Tyrone Igneous Complex and warrant further exploration.

Unusual morphological forms of hodrušite from the Rozália vein, Hodruša-Hámre near Banská Štiavnica (Slovak Republic)

Rare Cu–Bi sulphosalt, hodrusite, occurs in the Rozalia vein (levels X–XIV of the Rozalia mine, Hodrusa-Hamre ore deposit near Banska Stiavnica, central Slovakia) in two unusual morphological forms. The first type are brownish bronze thin acicular striated crystals, up to 3 mm long, in drusy cavities of quartz–hematite gangue, which are usually grouped into chaotic or irregular aggregates. The second hodrusite type comprises flattened columnar aggregates, up to 1.5 cm long, overgrown by hematite in quartz gangue. These aggregates are distinctly striated with brownish bronze colour and metallic lustre. Abundant W- and Al-rich hematite, chalcopyrite, kaolinite/dickite, siderite, baryte, rare bismuthinite and kupcikite were found in the association. The earliest columnar aggregates of hodrusite are locally substantially replaced by bismuthinite; these hodrusite–bismuthinite aggregates are further intensively pushed back by hematite displaying W- and Al-rich zones. Acicular crystals of hodrusite in gangue cavities were later than bismuthinite and hematite and their formation was related to remobilisation of Cu and Bi from earlier altered gangue. Powder X-ray diffraction data and chemical composition of both hodrusite types are similar; their unit-cell parameters were refined (monoclinic space group C2/m) as: a 17.552(5), b 3.905(1), c 27.167(9) A, β 92.44(3) o

Fluid evolution and mineralization stages of the quartz–hematite ± sulfide veins from the Kuh-e Dom gold prospect, Central Iran

Fluid evolution and mineralization stages of the quartz–hematite ± sulfide veins from the Kuh-e Dom gold prospect, Central Iran

Detrital zircon without detritus: a result of 496-Ma-old fluid–rock interaction during the gold-lode formation of Passagem, Minas Gerais, Brazil

Zircon and xenotime occur in tourmaline-rich hydrothermal pockets in the auriferous lode of Passagem de Mariana, a world-class gold deposit. Zircon grains show pristine oscillatory zoning, but many of them are altered, exhibiting porous domains filled with graphite. Uranium–Pb dating of zircon, using in-situ laser ablation–inductively coupled plasma–mass spectrometry, yields ages between 3.2 and 2.65 Ga, which match those for detrital zircon of the footwall quartzite of the > 2.65-Ga-old Moeda Formation. Discordant analyses point to zircon-age resetting during the Brasiliano orogeny at ca. 500 Ma. This interpretation is supported by U–Pb dating of euhedral xenotime immediately adjacent to altered zircon within the same tourmaline pocket. The xenotime grains give a Concordia age of 496.3 ± 2.0 Ma, which is identical to that determined for monazite of a quartz–hematite vein-type deposit (i.e., jacutinga lode) in the region (Itabira), another important mineralisation style of gold. The occurrence of relatively abundant inherited detrital zircon, but absence of rock fragments in the tourmaline pocket investigated here, implies that detrital material was completely replaced by tourmaline. The graphite overprint on the altered detrital zircon attests to a reducing fluid, which was likely formed by fluid–rock interaction with carbonaceous phyllite of the Batatal Formation, the host rock of the Passagem lode.

First data on the chemical composition and morphology of gold in the Tuba Kain deposit (South Urals)

926 The Tuba Kain deposit discovered in the early 20th century is located in the southwestern part of the Eastern Baymak ore-bearing zone confined to the western slope of the Magnitogorsk megastructure of the Southern Urals (Fig. 1). The ore field is composed of volcanogenic and volcano-sedimentary rocks of the Devonian Irendyk, Yarlykap, and Ulutau formations intruded by subvolcanic bodies of dacite porphyrites [1–3]. The rocks of the Eifelian Irendyk Formation distributed in the northwestern and central parts of the ore field are represented by lapilli and agglomerate tuffs of mixed composition with subordinate intercalations of gravel to psammitic tuffs. The lithological– petrographic composition of rock fragments is highly variable imparting variegated coloration to rocks: quartzites, hematite–quartz varieties, quartz porphyries, amygdaloid basalt porphyrites, and diorites. The overlying cherts of the Upper Eifelian Yarlykap Formation are approximately coeval with the Karamyltash Formation and Bugulygyr Horizon of the eastern areas. The rocks of the Givetian–lower Frasnian Ulutau Formation are developed in the western and southern parts of the ore field. The rock composition is relatively uniform with the dominant share of tuffstones and, less commonly, tuffaceous siltstones. The subvolcanic bodies occurring in the central, northern, and eastern parts of the ore field are represented by massive compact plagioclase and hornblende–plagioclase andesite–dacite and dacite porphyrites. At the beginning of the Tuba Kain deposit exploitation, it represented a submeridional gold–barite vein up to 5 m thick occurring among foliated rocks. The vein became exhausted and the residual ore-bearing complex is now represented by secondary quartzites with tourmaline and chlorite–sericite–quartz metasomatites. Their composition is as follows (wt %): SiO 2, 26.74–58.38; TiO 2, 0.35–0.76; Al 2O3, 8.41– 12.18; F 2O3, 7.28–10.06; MnO, 0.0; MgO, 3.93–4.15; CaO, 0.12–0.16; Na 2O, 2.38–2.55; K 2O, 1.24–2.92; P2O5, 0.02–0.11; S tot , 0.32–5.02; Ba, 1.59–28.05; Zn, 0.0051–0.0218; Cr, 0.0–0.0092; V, 0.0142–0.170; Sr, 0.0023–0.0634; Zr, 0.0076–0.0270. The rocks confined usually to contacts of subvolcanic dacite porphyrites are characterized by the following composition (wt %): SiO 2, 69.91; TiO 2, 0.36; Al 2O3, 14.02; F2O3, 3.84; MnO, 0.05; MgO, 1.87; CaO, 1.54; Na 2O, 4.87; K 2O, 0.09; P 2O5, 0.08; S tot , 0.01; Ba, 00233; Zn, 0.0011; Cr, 0.0011; Ni, 0.0085; V, 0.0003; Sr, 0.0306; Zr, 0.0148, Nb, 0.0011; Rb, 0.0010. These rocks are accompanied by tuffs of the Irendyk and Ulutau formations with mixed compositions (wt %): SiO 2, 59.09–67.86; TiO 2, 0.32–0.45; Al 2O3, 11.91–19.23; F2O3, 2.05–5.24; MnO, 0.02–0.13; MgO, 2.19–5.39; CaO, 0.11–2.71; Na 2O, 1.10–4.26; K 2O, 1.80–3.63; P2O5, 0.05–0.10; S tot , 0.06–1.15; Ba, 0.57–9.51; Zn, 0.0069–0.0596; Cr, 0.0015–0.0110; Ni, 0.0005– 0.0032; V, 0.0024–0.0081; Sr, 0.0027–0.0620; Zr, 0.0112–0.0245; Nb, 0.0006–0.0010; Rb, 0.0012–