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The Hera Au–Pb–Zn–Ag deposit in the southeastern Cobar Basin of central New South Wales preserves calc-silicate veins and remnant sandstone/carbonate-hosted skarn within a reduced anchizonal Siluro-Devonian turbidite sequence. The skarn orebody distribution is controlled by a long-lived, basin margin fault system, that has intersected a sedimentary horizon dominated by siliciclastic turbidite, with lesser gritstone and thick sandstone intervals, and rare carbonate-bearing stratigraphy. Foliation (S1) envelopes the orebody and is crosscut by a series of late-stage east–west and north–south trending faults. Skarn at Hera displays mineralogical zonation along strike, from southern spessartine–grossular–biotite–actinolite-rich associations, to central diopside-rich–zoisite–actinolite/tremolite–grossular-bearing associations, through to the northern most tremolite–anorthite-rich (garnet-absent) association in remnant carbonate-bearing lithologies and sandstone horizons; the northern lodes also display zonation down dip to garnet present associations. High-T, prograde skarn assemblages rich in pyroxene and garnet are pervasively replaced by actinolite/tremolite–biotite-rich retrograde skarn which coincides with the main pulse of sulfide mineralization. The dominant sulfides are high-Fe–Mn sphalerite–galena–non-magnetic high-Fe pyrrhotite–chalcopyrite; pyrite, arsenopyrite; scheelite (low Mo) is locally abundant. The distribution of metals in part mimics the changing gangue mineralogy, with Au concentrated in the southern and lower northern lode systems and broadly inverse concentrations for Ag–Pb–Zn. Stable isotope data (O–H–S) from skarn amphiboles and associated sulfides are consistent with magmatic (or metamorphic) water and sulfur input during the retrograde skarn phase, while hydrosilicates and sulfides from the wall rocks display comparatively elevated δD and mixed δ34S consistent with progressive mixing or dilution of original magmatic (or metamorphic) waters within the Hera deposit by unexchanged waters typical of low latitude (tropical) meteoritic waters. High precision titanite (U–Pb) and biotite (Ar–Ar) geochronology reveals a manifold orebody commencing with high-T skarn and retrograde Pb–Zn-rich skarn formation at ≥403 Ma, Au–low-Fe sphalerite mineralization at 403.4 ± 1.1 Ma, foliation development remobilization or new mineralization at 390 ± 0.2 Ma followed by thrusting, orebody dismemberment at 384.8 ± 1.1 Ma and remobilization or new mineralization at 381.0 ± 2.2 Ma. The polymetallic nature of the Hera orebody is a result of multiple mineralization events during extension and compression and involving both magmatic and likely formational metal sources.

The limited literature data on gold-bearing albite–pyroxene rodingites are summarized for the Agardag ultramafic massif in southern Tuva. These data are supplemented by new mineralogical, geochemical, thermobarogeochemical, and isotopic–geochemical results in order to reveal the physicochemical mineral formation conditions and sources of ore matter and fluids on gold deposition in rodingites. Rodingites and associated schistose nephritoids are near-fault metasomatites and are confined to a latitudinal tectonic zone in antigorite serpentinites. They formed in two stages. Stage I minerals (pyroxene, albite, etc.) are rodingites and stage II minerals (Na-bearing actinolite, albite, etc.) are nephritoids and veinlets that intersect rodingites. Disseminated sulfides of the Cu–S series (chalcocite, digenite, etc.) and Au minerals (tetra-auricupride and electrum) were deposited during both stages. The temperature regime (500–250°C) and low amount of CO2 in fluid ( $${{{\text{X}}}_{{{\text{C}}{{{\text{O}}}_{{\text{2}}}}}}}$$ = 0.017–0.025) correspond to the formation conditions of typical bimetasomatic rodingites. The degree of oxidation of gas components in fluids CO2/(CO2 + Σreduced gases) increases from rodingites (0.189) to nephritoids (0.299) and antigorite serpentinites (0.738). The O isotopic composition of silicates and calculated O isotopic composition of the fluid during antigorite serpentinization (5.8 to 7.6‰ δ18Оfl and –66 to –69‰ δDfl) correspond to juvenile and magmatic water in contrast to metamorphic water during nephritization and rodingitization (6 to 9.9‰ δ18Оfl and –39 to –46‰ δDfl) with involvement of heavy oxygen that was subjected to the sedimentary cycle. It is suggested that the magmatic ore-bearing fluid (7.3–7.6 wt % NaCl-equiv) separated from gabbroic melts. The oxidized fluid was modified to a reduced fluid during interaction with ultramafic rocks. The mafic and ultramafic rocks were the source of Na, REE, Au, Ag, Cu, and Ni. Deformations with the formation of veins and filling of veinlets are favorable for a high local gold concentration.

This study determines the properties of hot spring waters and associated rocks, calculates reservoir temperatures and depths in the Mongolian Altai region, and constructs a conceptual model for geothermal water based on these results. The hot springs consist of HCO3-Na, SO4-Na, and HCO3-SO4-Na mixed type waters. The waters exhibit alkaline pH levels and temperatures in the range of 21.3–35°C. X-ray diffraction analyses of outcrop rocks reveal silicate and carbonate-type minerals such as quartz, albite, orthoclase, dolomite, mica, and actinolite, while correlation analysis indicates that the chemical composition of the hot spring water is directly related to rock mineral composition. Dissolution of albite, orthoclase, and dolomite minerals has played an important role in the chemical composition of the waters. Reservoir water circulation depths were 2615–3410 m according to quartz and chalcedony geothermometry. The results indicate that the spring water in the Mongolian Altai region comprises a low mineral content with alkaline pH levels and the reservoir temperature can reach up to 106°C. We also propose a conceptual model for geothermal water in the Chikhertei hot spring. The geothermal water in the Mongolian Altai region exhibits a potential for use in heating systems. Thematic collection: This article is part of the Hydrochemistry related to exploration and environmental issues collection available at: https://www.lyellcollection.org/cc/hydrochemistry-related-to-exploration-and-environmental-issues

Nipalarsite, Ni8Pd3As4, is a new platinum-group mineral discovered in the sulfide-bearing orthopyroxenite of the Monchetundra layered intrusion, Kola Peninsula, Russia (67°52′22″N, 32°47′60″E). Nipalarsite forms anhedral grains (5–80 µm in size) in intergrowths with sperrylite, kotulskite, hollingworthite, isomertieite, menshikovite, palarstanide, nielsenite and monchetundtraite enclosed in pentlandite, anthophyllite, actinolite and chlorite. Nipalarsite is brittle, has a metallic lustre and a grey streak. In plane-polarised light, nipalarsite is light grey with a blue tinge. Reflectance values in air (in %) are: 46.06 at 470 nm, 48.74 at 546 nm, 50.64 at 589 nm and 54.12 at 650 nm. Values of VHN20 fall between 400.5 and 449.2 kg.mm–2, with a mean value of 429.9 kg.mm–2, corresponding to a Mohs hardness of ~4. The average result of 27 electron microprobe wavelength dispersive spectroscopy analyses of nipalarsite is (wt.%): Ni 44.011, Pd 28.74, Fe0.32, Cu 0.85, Pt 0.01, Au 0.05, As 25.42, Sb 0.05, Te 0.39, total 99.85. The empirical formula (normalised to 15 atoms per formula unit) is: (Ni8.10Fe0.06)Σ8.16(Pd2.94Cu0.18)Σ3.12(As3.68Te0.03)Σ3.71 or, ideally, Ni8Pd3As4. Nipalarsite is cubic, space group Fm$\bar{3}$m, with a = 11.4428(9) Å, V = 1498.3(4) Å3 and Z = 8. The strongest lines in the powder X-ray diffraction pattern of synthetic Ni8Pd3As4 [d, Å (I) (hkl)] are: 2.859(10)(004), 2.623(6)(313), 2.557(6)(024), 2.334(11)(224), 2.201(35)(115,333), 2.021(100)(044), 1.906(8)(006,244) and 1.429(7)(008). The crystal structure was solved and refined from the single-crystal X-ray diffraction data of synthetic Ni8Pd3As4. The relation between natural and synthetic nipalarsite is illustrated by an electron back-scattered diffraction study of natural nipalarsite. The density calculated on the basis of the empirical formula of nipalarsite is 9.60 g.cm–3. The mineral name corresponds to the three main elements: Ni, Pd and As.

Research subject . High-magnesium rocks associated with the granitoid massifs of the Urals are represented by gabbro-diorites and their melanocratic varieties (hornblendites), as well as by diorites and quartz diorites. These rocks are composed of amphibole porphyrocrists frequently combined with clinopyroxene and phlogopite immersed in a basis of acid plagioclase with interstitial quartz and potassium feldspar. In addition to a high magnesium content of 0.5–0.8 units, these rocks are characterized by extremely high chromium contents of up to 1200 ppm. Methods . The study of the composition of high-magnesium rocks was performed using an ELAN 9000 inductively coupled plasma mass spectrometer, an SX-100 Cameca electron probe microanalyzer and an energy dispersive device INCAEnergy 450 X-Max 80. The detection limit for Cr 2 O 3 was equal to 0.05 wt. % and 0.2 wt. % for the microanalyzer and the energy dispersive device, respectively. Results . The two main mineral associations related to magmatic and post-magmatic processes are found to be different in terms of chromium behaviour. The average concentrations of chromium oxide in the minerals from the magmatic association varied within the range (wt. %) of 0.10–0.50, 0.29–0.68, 0.08-0.36 and 0.0–1.6 for different samples of clinopyroxene, amphibole, phlogopite and their variations, respectively. The post-magnetic association included minerals representing the products of postmagmatic (hydrothermal) transformation of pyroxenes and alumina amphibole into low-alumina magnesia hornblende, actinolite, titanite, epidote and muscovite. The transformation of chromospinelide at this stage had been accompanied by exchange processes with silicates, as a result of which the silicates were enriched with chromium. The average concentrations of chromium oxide in the minerals of this association were (wt. %) 0.24–0.80, 1.38–3.08, 1.03 and 3.5 in the samples of amphibole, epidote, titanite and muscovite, respectively. Conclusion . It is assumed that the crystallization of the early association of iron-magnesium silicates proceeded from aqueous high-magnesium melts. The subsequent post-magmatic change of such silicates led to the development of phases with a similar and occasionally higher chromium content. This fact can be explained by the interaction of silicates with chromite under the conditions of low fluid oxidation, which was insufficient for the formation of magnetite.

An investigation of the economically important Mashava Igneous Complex (MIC) in Zimbabwe was conducted using petrographic and silicate mineral compositions to gain some insights into its origin. The MIC, an ultramafic-mafic complex located in the western extremity of the Masvingo greenstone belt (MGSB), is composed of amphibole, serpentine, epidote, chlorite, clinopyroxene, orthopyroxene, plagioclase, and olivine. Spinel, sulfide minerals, and minor quartz as well as other opaque minerals are also present. The dominant mineral is serpentine, which displays a wide range in both FeO and SiO2 compositions, and the majority of this mineral belongs to the lizardite, chrysotile, and antigorite varieties. Amphiboles display a wide range in composition from tremolite and actinolite which are both consistent with greenschist facies metamorphism, through magnesiohornblende to tschermakite which are both consistent with amphibolite facies metamorphism. Clinozoisite is the only epidote type occurring in the MIC, whereas chlorite varies widely in composition which reflects the varying concentrations in iron and silica in this mineral. Chlorite types range from talc chlorite through penninite, diabantite, pycnochlorite, brunsvigite, ripidolite, and pseudothuringite. Plagioclase shows a wide compositional range from high albite to bytownite, with only two samples plotting in the alkali feldspar anorthoclase field. Pyroxene ranges in composition from enstatite through pigeonite and augite to diopside whereas olivine is rich in MgO with forsterite contents ranging from 80 to 89. Application of the chlorite geothermometry equation of Kranidiotis and MacLean (1987) yields temperatures ranging from ∼200–320 °C whereas temperatures ranging from 130 to 445 °C are obtained using equations of Lanari et al. (2014) for the formation of this mineral, generally consistent with low- to medium-grade metamorphic conditions. Chlorites in the North West Arm were formed at relatively lower temperatures (97–234 °C) than those at which chlorites in the Central Sector were formed (204–445 °C). Pressure estimates for the metamorphism of the MIC range from 3.8 to 7.3 kbars, which corresponds to depths of ∼13–25 km, respectively. Based on the different silicate mineral compositions of the North West Arm and the Central Sector, it is inferred that these two blocks underwent different petrogenetic and evolutionary histories but they were later juxtaposed, possibly during thrusting of the former onto its present position.

The Arqiale deposit, located in the southern Yili Block of Western Tianshan, Xinjiang, China, is a newly discovered large Zn-Pb deposit with a resource of approximately 10 million tons ore grading 9.65% Zn+Pb, and a certain amount of Cu and Ag. The Zn-Pb orebodies are tabular and lentoid in shape, developed along SW-striking and NW-dipping interlayer structures between the Lower Carboniferous Akeshake (mainly carbonate rocks) and Dahalajunshan (mainly volcanic rocks) formations. Garnet and pyroxene-rich skarn, formed in the early (prograde) stage of skarnization, occurs only locally as lenses within skarn bodies enriched in actinolite, tremolite, ilvaite, biotite, epidote, chlorite, calcite, quartz and fluorite, which were formed in the retrograde stage. Metallic minerals comprise sphalerite, galena, chalcopyrite, pyrite, and hematite. They mainly occur as disseminations, patches and massive ores, replacing retrograde skarn minerals and crosscut by later stage quartz and calcite veinlets. There is a general trend of increasing Cu contents and decreasing Zn/Pb ratios from the upper and south portion to the lower and north portion of the orebody. Rb-Sr dating of seven sphalerite samples yielded an isochron age of 339.5 ± 2.7 Ma, which is almost identical to the 341.8 ± 2.5 Ma age obtained from Sm-Nd dating of eight actinolite samples. Furthermore, zircon U-Pb dating yielded an age of 343 ± 6 Ma for a gabbro-diorite stock that is located about 600 m south of the Zn-Pb orebody. The age data indicate that the mineralization and retrograde skarnization were contemporaneous, and they are likely related to a magmatic intrusion of similar age which may be linked to the gabbro-diorite stock. Thus, although the direct causative intrusion has not been identified, the Arqiale deposit can be classified as a distal skarn deposit. The δ34SV-CDT values of 26 ore sulfide samples range from −7.1‰ to +1.3‰ with an average of −1.5‰. The 206Pb/204Pb, 207Pb/204Pb and 208Pb/204Pb ratios of 25 ore sulfide samples range from 18.266 to 18.880, 15.577 to 15.668 and 38.068 to 38.720, respectively, which are similar to the Early Carboniferous intrusions of the Wusun Range and partly overlap with the volcanic rocks of the Dahalajunshan Formation, and are different from the carbonate rocks of the Akeshake Formation. Based on these data, we propose that the Arqiale deposit formed from magmatic-hydrothermal fluids emanated from a concealed magmatic intrusion which may be located beneath the northern and deep part of the deposit. Much of the metals and sulfur may have been derived from the magmatic intrusions, although some of them may have also been extracted from the volcanic rocks underlying the deposit. The results of this study indicate that there is a great potential of finding more skarn Zn-Pb mineralization in Western Tianshan, where numerous Early Carboniferous arc-related intrusions with similar ages as the Arqiale deposit, in relation to the subduction of the Southern Tianshan Oceanic plate underneath the Yili-Central Tianshan Block, were emplaced into or beneath carbonate rocks.

Hydrous phases have been identified to be a significant component of martian mineralogy. Particularly prehnite, zeolites, and serpentine are evidence for low‐grade metamorphic reactions at elevated temperatures in mafic and ultramafic protoliths. Their presence suggests that at least part of the martian crust is sufficiently hydrated for low‐grade metamorphic reactions to occur. A detailed analysis of changes in mineralogy with variations in fluid content and composition along possible martian geotherms can contribute to determine the conditions required for subsurface hydrous alteration, fluid availability and rock properties in the martian crust. In this study, we use phase equilibria models to explore low‐grade metamorphic reactions covering a pressure‐temperature range of 0‐0.5 GPa and 150‐450 °C for several martian protolith compositions and varying fluid content. Our models replicate the detected low‐grade metamorphic/hydrothermal mineral phases like prehnite, chlorite, analcime, unspecified zeolites, and serpentine. Our results also suggest that actinolite should be a part of lower‐grade metamorphic assemblages, but actinolite may not be detected in reflectance spectra for several reasons. By gradually increasing the water content in the modeled whole rock composition, we can estimate the amount of water required to precipitate low‐grade metamorphic phases. Mineralogical constraints do not necessarily require an elevated geothermal gradient for the formation of prehnite. However, restricted crater excavation depths even for large impact craters are not likely sampling prehnite along colder gradients, either suggesting a geotherm of ~ 20 °C/km in the Noachian or an additional heat source such as hydrothermal or magmatic activity.

The Jalal-Abad iron oxide ± Cu ± Au ± Bi ± Co deposit is hosted in Early Cambrian volcanosedimentary units (CVSU) of the Kashmar–Kerman zone, Central Iran. Magnetite is the main ore mineral at depth and is associated with Na-Ca rich alteration, dominated by actinolite. Magnetite compositions (EPMA) are very low in TiO2 (0.03–0.07 wt%), V2O3 (0.02–0.06 wt%) and CoO (0.01> to 0.42 wt%). At intermediate to shallow levels potassic alteration is associated with chalcopyrite, pyrite, arsenopyrite, cobaltite, bismuthinite and gold. The mineralization occurs in massive, breccia matrix, open space filling, disseminated and vein-like styles. Gold occurs as small inclusions (

The potentially large Primorskoe epithermal Au-Ag deposit is represented by three areas: the Kholodnyi, Spiridonych, and Teplyi. It is located in the Omsukchan district of Magadan oblast, where mining is carried out at the largely similar Dukat, Lunnoe, Gol’tsovoe, Arylakh, Tidit, Pereval’noe, and other deposits. The deposit under review is located in the Kalalaga volcano-tectonic depression, where ore has been emplaced in a gently dipping sequence of Late Cretaceous ignimbrites and rhyolites more than 700 m in thickness crosscut by numerous intermediate and mafic dykes. According to drilling data, there is a leucocratic granite massif 400–500 m beneath the deposit, which is exposed on the surface in the northeastern part of the ore field. The presence of Bi-bearing galena and matildite, as well as medium- to high-temperature metasomatic facies (epidote and actinolite) and the specific physicochemical conditions of epithermal Ag-Au ore emplacement, attests to the above-intrusion position and the role of granitoids as high-temperature magmatic fluid generators responsible for supplying Bi and heating the host rock. The ore chemistry is quite consistent with its mineral composition. High Mn and Ag; elevated Au; low Cu, Pb, Zn, Sb, As, Bi, and Te; and low total REE concentrations were established, along with negative Eu and positive Ce anomalies. The high Te/Se, Sr/Ba, Y/Ho, and U/Th ratios in the ores are due to their location in the area influenced by the granitoid pluton. The physicochemical parameters of ore emplacement in the Teplyi area are unusual: high temperatures, low salt concentrations, and fluid densities typical of a “dry vapor” environment. The obtained data allow the Primorskoe to be classified as an intermediate sulfidation epithermal deposit. The data discussed below are of practical use for regional metallogenic forecasting, exploration, and economic assessment of epithermal Ag-Au deposits.

Hydrothermal veins and dykelets that cross-cut layered olivine gabbros deep in the plutonic section of the Samail Ophiolite, Sultanate of Oman, point towards the occurrence of hydrothermal circulation in the deep oceanic crust, and these features record interactions between rock and high temperature seawater-derived fluids or brines. Deep penetration of seawater-derived fluids down to 100 m above the Moho transition zone and the consequent interactions with the host rock lead to hydrothermal alteration from granulite facies grading down to greenschist facies conditions. Here we present a study of veins and dykelets formed by hydrothermal interaction cutting layered gabbro in the Wadi Wariyah, using petrographic, microanalytical, isotopic, and structural methods. We focus on amphiboles, which show a conspicuous compositional variation from high-Ti magnesiohastingsite and pargasite via magnesiohornblende and edenite, to Cl-rich ferropargasite and hastingsite (up to 1.5 a.p.f.u. Cl) and actinolite. These minerals record a wide range of formation conditions from magmatic to hydrothermal, and reveal a complex history of interactions between rock and hydrothermal fluid or brine in a lower oceanic crustal setting. Large variations in Cl content and cation configurations in amphibole suggest formation in equilibrium with fluids of different salinities at variable fluid/rock ratios. The presence of subsolidus amphibole extremely enriched in chlorine implies phase separation and brine/rock interactions. 87Sr/86Sr values of 0.7031 to 0.7039 and stable δ18O isotopic compositions of 4.1 to 5.6‰ of the different amphibole types suggest a rock-dominated environment, i.e. with low fluid/rock ratios. However, the slight departure from mean Oman isotope values may indicate there was some influence of seawater in the aforementioned fluid-rock interactions. Our study provides new petrological data for the subsolidus evolution of gabbro-hosted amphibole-rich veins in the presence of a seawater-derived fluid.

Renard 65, a diamondiferous pipe in the Neoproterozoic Renard kimberlite cluster (Quebec, Canada), is a steeply-dipping and downward-tapering diatreme comprised of three pipe-filling units: kimb65a, kimb65b, and kimb65d. The pipe is surrounded by a marginal and variably-brecciated country rock aureole and is crosscut by numerous hypabyssal dykes: kimb65c. Extensive petrographic and mineralogical characterization of over 700 m of drill core from four separate drill holes, suggests that Renard 65 is a Group I kimberlite, mineralogically classified as phlogopite kimberlite and serpentine-phlogopite kimberlite. Kimb65a is a massive volcaniclastic kimberlite dominated by lithic clasts, magmaclasts, and discrete olivine macrocrysts, hosted within a fine-grained diopside and serpentine-rich matrix. Kimb65b is massive, macrocrystic, coherent kimberlite with a groundmass assemblage of phlogopite, spinel, perovskite, apatite, calcite, serpentine and rare monticellite. Kimb65c is a massive, macrocrystic, hypabyssal kimberlite with a groundmass assemblage of phlogopite, serpentine, calcite, perovskite, spinel, and apatite. Kimb65d is massive volcaniclastic kimberlite with localized textures that are intermediate between volcaniclastic and coherent, with tightly packed magmaclasts separated by a diopside- and serpentine-rich matrix. Lithic clasts of granite-gneiss in kimb65a are weakly reacted, with partial melting of feldspars and crystallization of richterite and actinolite. Lithic clasts in kimb65b and kimb65d are entirely recrystallized to calcite + serpentine/chlorite + pectolite and display inner coronas of diopside-aegirine and an outer corona of phlogopite. Compositions are reported for all minerals in the groundmass of coherent kimberlites, magmaclasts, interclast matrices, and reacted lithic clasts. The Renard 65 rocks are texturally classified as Kimberley-type pyroclastic kimberlites and display transitional textures. The kimberlite units are interpreted to have formed in three melt batches based on their distinct spinel chemistry: kimb65a, kimb65b and kimb65d. We note a strong correlation between the modal abundances of lithic clasts and the textures of the kimberlites, where increasing modal abundances of granite/gneiss are observed in kimberlites with increasingly fragmental textures.

Unusual series of hybrid metasomatic mineral zones are well developed when the granitic pegmatite veins cross-cut through ultramafic rocks at the Hafafit complex, South Eastern Desert of Egypt. Two groups of mineralogical zones are developed; the first group related to the serpentinized ultramafic rocks (peridotite-related zones) comprises anthophyllite-, actinolite- and vermiculite-bearing zones, whereas the second group related to the pegmatite veins (pegmatite-related zones) comprises hercynite- and corundum-bearing zones. Tourmaline-rich zone only occurs when the pegmatite veins come in contact between ultramafic rocks and biotite-rich granitic gneiss. The mineral assemblages, bulk rock geochemistry and in situ mineral chemistry suggest a metasomatic origin for the hybrid zones. The mineral assemblages: corundum + margarite ± Ca-plagioclase, hercynite + corundum + garnet ± chlorite, and anthophyllite + actinolite + enstatite, in addition to the constrained garnet-biotite/phlogopite geothermometer, and the higher tourmaline XMg, strongly indicate amphibolite facies metamorphism for the ultramafic-pegmatite hybrid zones. The constrained temperature ranges between 500 and 700 °C and a pressure around 7 kbars, with pronounced increases of metamorphism from the outermost zone in the serpentinized ultramafic ongoing to the pegmatite mineral zones. Juxtaposition of two contrasting rock types (highly reactive hot SiO2-, alkali-rich melt and cool silica-deficient ultramafic rocks) side by side would results in an intense contact bimetasomatic elemental exchange. The SiO2, H2O and alkalies would be offered by pegmatite melt, while MgO, FeO and CaO were supplied by serpentinized ultramafic rocks. The small volume of pegmatite melt relative to the ultramafic rocks would be easily desilicated by SiO2 diffusion into the ultramafic rocks to form the monomineralic SiO2-rich minerals in the peridotite-related zones. Consequently, Al2O3 would be concentrated in the residual melt to form corundum and other Al-rich mineral phases in the pegmatite-related zones. The small size of pegmatite veins and refractory nature of the ultramafic rocks could be the reasons precluding the formation of colored gem corundum in the Hafafit complex. Restricted occurrence of tourmaline-rich zone at the ultramafic-granitic gneiss contact is attributed to the diffusion of B-rich fluids generated from the leaching of biotite-rich granitic gneiss.

The Biely Vrch deposit in the Western Carpathians is assigned to the shallow, sulfide-poor porphyry gold deposit type and has an exceptionally low Cu/Au ratio. According to 3-D geochemical models, there is a limited spatial correlation between Au and Cu due to the primary introduction of gold by a salt melt and Cu by low-density vapor. Despite a rough spatial correlation of gold grades with quartz stockwork intensity, gold is hosted mostly by altered rock, exclusively in native form. Three main gold mineral assemblages were recognized here. In the deepest parts of the system, the K- and Ca-Na silicate gold assemblage is associated with minerals of high-temperature alteration (plagioclase, K-feldspar, actinolite), with gold grades and fineness depending on depth and potassium content of the host rock: K-silicate alteration hosts the lowest fineness gold (~ 914), whereas Ca–Na silicate alteration has the highest (~ 983). The intermediate argillic gold assemblage is the most widespread, with gold hosted mainly by chlorite, illite, smectite, and interstratified illite–chlorite–smectite minerals. The gold fineness is mostly variable (875–990) and inherited from the former gold mineral assemblages. The latest advanced argillic gold assemblage has its gold mostly in kaolinite. The extremely high fineness (~ 994) results from gold remobilization by late-stage aqueous magmatic-hydrothermal fluids. Uncommon bonanza-grade appears where the earlier gold mineral assemblages were further enriched by this remobilized gold. Primary precipitation of gold occurred during ascent and cooling of salt melts at 450 to 309 °C, mostly during retrograde quartz solubility.

The Saghand Anomaly 5 is located in the Bafq-Saghand metallogenic province in the Central Iranian geostructural zone and contains Ti, REEs, Y, U, and Th mineralization. The mineralization is related to alkali-metasomatism and occurs in peripheral alteration zones around the iron ore deposits. Alkali-metasomatism and mineralization were controlled by tectonic activity along fault zones from ductile to brittle regimes of deformation. A metasomatic zoning is developed from outermost unaltered lithologies (subvolcanic diorite and quartz diorite host rocks) inwards to albite-actinolite metasomatite, phlogopite-actinolite metasomatite, and ultimately to magnetite orebodies. The last widespread hydrothermal event corresponds to an epidote2 ± chlorite ± calcite2 ± quartz paragenesis superimposed on all previous mineral associations. Microscopy studies reveal that ilmenite, davidite, allanite-(La), Ti–Y–U–Th-Oxide, REE-Oxide, rutile, and titanite and lesser amounts of thorite are ore minerals of Saghand Anomaly 5. The Ti–REE–Y–U–Th mineralization is related to Na–Ca-metasomatism and Ca-alteration and occurs as disseminated in albite-actinolite metasomatites and locally as veinlet-type in aplites and granites. The geochemical investigations indicate a calc-alkaline and continental-margin arc setting for granite and associated diorite-quartz diorite host rocks in the Saghand Anomaly 5. The REE patterns of the mineralized metasomatites show LREE enrichment and strong Eu negative anomalies. The presence of REE-rich hydrothermal phases suggests a significant mobilization and deposition of REEs, especially La, Ce and Y, by high temperature hydrothermal solutions within the Saghand Anomaly 5. The measured temperatures range from ∼748° to ∼766° C and ∼703° to ∼737° C for Na–Ca-metasomatic and K–Ca-metasomatic stages, respectively, using the magnetite1-actinolite and magnetite2-phlogopite oxygen isotope pairs, respectively. Both δD and δ18O values of actinolite and phlogopite indicate a magmatic source of actinolite and phlogopite forming fluids. In addition, C and O isotopic data of calcite2, from the late veinlets, indicate a magmatic origin of fluids in equilibrium with calcite2 and the formation temperature of 350 to 400° C.

The Se-Chahun Fe-P ore deposit is located in the Bafq mining district in the Central Iranian tectono-magmatic zone and contains REE and Th mineralization. The ore deposit consists of a magnetite-apatite massive ore that is significantly modified by late-stage metasomatic fluids that finally formed brecciated rocks within and at the margin of the ore deposit. Geochemical data from the rhyolitic rocks, Fe-P ore body and breccia as well as isotopic data from the breccia within the Se-Chahun Fe-P ore bodies, have been used to deduce the magmatic origin of the Fe-P ore zone and to assess the significance of post-magmatic processes with late-stage metasomatic fluids and the effects of these processes on remobilization of magmatic originated REE and concentration and deposition of Th. The chondrite-normalized REE patterns of the mineralized rocks in both the Fe-P ore and the Th mineralization zone demonstrate LREE enrichment and strongly negative Eu anomalies (Eu/Eu* = 0.25–0.91 for Th mineralization). δD and δ18O for actinolite paragenetic to Th-bearing silicates are estimated to be between −73.29 to −42.04 and 6.65 to 7.71, respectively, which lie within the both fields of magmatic and metamorphic fluids. Na-Ca metasomatism (which is evidenced by brecciation) has been a continuous process affecting the host rock, and the Fe-P ore body. Apatite, monazite, and Ti-La-Ce-Y-Nd-oxides are the main REE-bearing phases in the Fe-P ore body (REE≫Th) that are precipitated during magnetite crystallization whereas Th silicates (huttonite and thorite) occur within the breccia (Th ≫ REE) and were deposited from a late Th- and carbonate-rich fluid. Th mineralization occurred with late sodic-calcic fluids and Th-bearing minerals are paragenetic to actinolite, red albite, magnetite, titanite, calcite, and pyrite. Paragenetic association of Th minerals and actinolite, titanite, and calcite in carbonate veins and veinlets point to transportation of Th by carbonate complexes. The pH, fluid/rock ratio, Ca/Na ratio, and higher capability of Th (with respect to REE) in formation of carbonate complexes and lower concentration of Th (with respect to REE) in the source region are the most important geochemical parameters that triggered Th (Th ≫ REE) mineralization at the end of alkali metasomatism.

Traditional metallogenic models posit that porphyry–skarn Cu systems form in subduction and collision zones. However, in eastern China, many important Late Mesozoic porphyry–skarn deposits have formed in intracontinental settings related to lithospheric break-up during the celebrated tectonothermal, Yanshanian event. The Xiaohekou Cu skarn deposit in the southern Qinling Orogen presents an ideal case study to describe such ore deposit geology, using mineral and fluid inclusion analysis, in addition to sulfide and granitoid S Pb isotope studies. A detailed metallogenic process model for the intracontinental skarn Cu deposit is proposed. The authors recognize four main paragenetic stages: (I) anhydrous skarn, (II) hydrous skarn–Fe oxide, (III) quartz–polymetallic sulfide, and (IV) carbonate–quartz. Stage I is characterized by high temperatures (346–547 °C), high to moderate salinities (6.74–49.2 wt% NaCleqv), together with acidic and oxidizing H2O-NaCl fluids. From early to late anhydrous skarn stage, un-zoned grossular (Adr24–31Gr68–74), a grossular–andradite alternation series with wide zones (Adr26–68Gr31–72) and diopside (Di73–91Hd8–24)–pure andradite with dense oscillation zones (Adr68–100Gr0–30) crystallized sequentially, representing a gradual shift toward higher fO2 conditions. Diopside-hosted fluid inclusions (FIs) contain halite-bearing three phase (H-type), liquid-rich two-phase (L-type), and vapor-rich two-phase (V-type) inclusions, suggesting such fluids were sourced from a silicate melt and stage I & II boiling of magmatic-hydrothermal fluids at lithostatic depths of 1.1–3.3 km.. The FIs in actinolite (stage II) are characterized by homogenization temperatures (Th) of 273–502 °C and salinities of 4.34–42.8 wt% NaCleqv. Cooling and dilution of the ore-forming hydrothermal fluid, as well as the high fO2 conditions were responsible for the hydrous skarn alteration in addition to magnetite and specularite deposition. Stage III constitutes the principal Cu mineralizing event. Quartz from this stage contains distinctive liquid-rich inclusions, with Th of 143–423 °C and salinity of 2.07–17.8 wt% NaCleqv. Their Th values include two populations (210–270 °C and 303–359 °C) suggesting a commingling of hot magmatic-hydrothermal fluid and meteoric water accompanied by a significant fO2 decrease and pH increase was a principal factor behind chalcopyrite-pyrite-pyrrhotite deposition. The fluids in stage IV (81–218 °C and 0.18–14.1 wt% NaCleqv) are likely be the chilled equivalent of fluid from the Cu mineralization stage which equilibrated with marble. S Pb isotopes reveal that the metals were derived from the granitic rocks and produced by hybrid (mantle+crust)-derived magmas. We propose hydrothermal fluids exsolved from the cooling granitic magma contributed the majority ore-forming materials. Whereas ore-forming fluids clearly interacted with country rocks affecting ore precipitation, skarn development and deposit geometry and emplacement. Devonian host rocks donated little if any of either sulfur or base metals to the mineralization process.

Los Guindos scheelite (±Zn, Bi, Sn, Ag) skarn presents mineral assemblages and a mineral chemistry similar to other worldwide strongly reduced W skarn deposits. Its reduced nature is defined based on the predominance of subcalcic garnets, Mo-free scheelite and absence of magnetite. Both the prograde and retrograde stages are evident at Los Guindos scheelite skarn. The prograde skarn is characterized by three zones: A zone I of garnet + helvine (Gr57Sps24Ad19Alm8 - Sps50Alm24Gr22Ad3; Grt + Hlv); a zone II of clinopyroxene + garnet (Di67Hd24Jo9 + Gr66Sps19Ad12Alm3; Cpx + Grt) and a zone III of garnet + vesuvianite (Gr73Ad22Sps3Alm2 - Gr58Sps22Ad10Alm9; Grt + Ves). Retrograde skarn is mainly represented by epidote - actinolite and minor F-rich actinolite (0.663 apfu of F) – potassium feldspar - chlorite (chamosite/clinochlore: ∼ 50/50) – muscovite – calcite - quartz. A hydrothermal stage developed in temporal continuity with retrograde skarn formed variable infilling associations of the following species: epidote – actinolite – scheelite – fluorite – calcite – quartz – sphalerite and chlorite. Scheelite mineralization process was triggered by an increase of Ca released during retrograde skarn replacements and was deposited during the following hydrothermal infilling stage. Other than sphalerite, minor bismuthinite and tetradymite, andorite, lillianite, gustavite, matildite and kësterite occur as hydrothermal associations after scheelite deposition. Scheelite-free reaction skarn preceding scheelite skarns was observed. Geobarometric calculations in this reaction skarn suggests an initial confining pressure of 2.5 kbar for the Los Guindos scheelite skarns. This pressure matches the estimated emplacement pressure of the Devonian-Carboniferous Achala batholith reported by previous authors. Geochemical correlation analyses suggest that this magmatism may have contributed mineralizing fluids channeled through regional structures and lithological contacts, causing infiltration metasomatism that originated scheelite (±Zn, Bi, Sn, Ag) mineralization in Cambrian and Ordovician country rocks. U-Pb analyses (LA-ICP-MS) of garnet in the Los Guindos scheelite skarn gave an age of 361 ± 11 Ma representing the age of the prograde stage of scheelite skarns and it should be framed within the Devonian-Carboniferous Metallogenic Epoch. Fil: Espeche, María José. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas Físicas y Naturales. Museo de Mineralogía y Geología "Dr. A. Stelzner"; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba; Argentina Fil: Wan, Bo. Chinese Academy of Sciences; República de China Fil: Lira, Raul. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas Físicas y Naturales. Museo de Mineralogía y Geología "Dr. A. Stelzner"; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba; Argentina Fil: Seltmann, Reimar. Natural History Museum; Reino Unido

El Romeral is one of the largest iron oxide-apatite (IOA) deposits in the Coastal Cordillera of northern Chile. The Cerro Principal magnetite ore body at El Romeral comprises massive magnetite intergrown with actinolite, with minor apatite, scapolite, and sulfides (pyrite ± chalcopyrite). Several generations of magnetite were identified by using a combination of optical and electron microscopy techniques. The main mineralization event is represented by zoned magnetite grains with inclusion-rich cores and inclusion-poor rims, which form the massive magnetite ore body. This main magnetite stage was followed by two late hydrothermal events that are represented by magnetite veinlets that crosscut the massive ore body and by disseminated magnetite in the andesite host rock and in the Romeral diorite. The sulfur stable isotope signature of the late hydrothermal sulfides indicates a magmatic origin for sulfur (δ34S between − 0.8 and 2.9‰), in agreement with previous δ34S data reported for other Chilean IOA and iron oxide-copper-gold deposits. New 40Ar/39Ar dating of actinolite associated with the main magnetite ore stage yielded ages of ca. 128 Ma, concordant within error with a U-Pb zircon age for the Romeral diorite (129.0 ± 0.9 Ma; mean square weighted deviation = 1.9, n = 28). The late hydrothermal magnetite-biotite mineralization is constrained at ca. 118 Ma by 40Ar/39Ar dating of secondary biotite. This potassic alteration is about 10 Ma younger than the main mineralization episode, and it may be related to post-mineralization dikes that crosscut and remobilize Fe from the main magnetite ore body. These data reveal a clear genetic association between magnetite ore formation, sulfide mineralization, and the diorite intrusion at El Romeral (at ~ 129 Ma), followed by a late and more restricted stage of hydrothermal alteration associated with the emplacement of post-ore dikes at ca. 118 Ma. Therefore, this new evidence supports a magmatic-hydrothermal model for the formation of IOA deposits in the Chilean Iron Belt, where the magnetite mineralization was sourced from intermediate magmas during the first Andean stage. In contrast, the beginning of the second Andean stage is characterized by shallow subduction and a compressive regime, which is represented in the district by the emplacement of the Punta de Piedra granite-granodiorite batholith (100 Ma) and marks the end of iron oxide-apatite deposit formation in the area.

Iron Oxide-Apatite deposits (IOA) have been found and investigated in the Tarom district, NW Iran. This area is a part of the Cenozoic Alborz-Azarbaijan magmatic belt in the foreland of the Arabia–Eurasia collision zone of the Alpine-Himalayan Orogen. In this region, volcanic and volcanoclastic rocks (Karaj Formation) are the main units which were later followed by the intrusion of late Eocene plutonic rocks. These intrusions are metaluminous I-type granitoids and have high-K calc-alkaline to shoshonitic affinity. The IOA deposits are mainly hosted by quartz monzonitic rock. These deposits occur as veins and veinlets with brecciated, banded and massive textures. Mineralogicaly, the IOA deposits are composed of magnetite, apatite, monazite, actinolite, clinopyroxene, pyrite, chalcopyrite, quartz and calcite. Rare earth element mineralization in the Tarom area is related to the IOA deposits. These elements are mainly concentrated in apatite crystals. Exploration studies indicate REE grades up to 1% in apatite crystals and up to 0.7% in the magnetite-apatite ore. These studies demonstrate that LREEs are more enriched compared to HREEs in magnetite-apatite ores, while actinolitic zones have less enrichment of LREE/HREE. Chondrite normalized REE patterns of IOA ores in the Tarom area are similar and show strong LREE/HREE fractionation and negative Eu anomaly. These similar REE patterns indicate that these units have a common origin. Magnetite-actinolite ores and actinolitic zones indicate flat patterns with low fractionation of LREE/HREE along with negative Eu anomaly. REE patterns of IOA deposits in Tarom area are similar to that of Kiruna-type Fe deposits. Furthermore, comparison of chondrite-normalized REE patterns of IOA ores with those of quartz monzonite host rock indicating very similar patterns. These similar patterns demonstrate that the mentioned quartz monzonitic intrusions and IOA deposits originated from a common magmatic source.

The geochemical and isotopic investigations were provided on the Upper Eocene Senj mafic intrusion and Mo-Cu mineralization to better understand the tectono-magmatic evolution and metallogeny of the central part of the Alborz magmatic belt. The Senj mafic intrusion is composed of gabbro to monzodiorite and monzonite in lithology, and intruded as a sill into volcano-sedimentary rocks of the Eocene Karaj Formation. The Karaj Formation consists of volcano-sedimentary rocks, such as altered crystalline to shaly tuffs. The Senj intrusion (39.7 ± 0.4 Ma) shows LILE and LREE enrichment and negative anomaly of Nb, Ta and Ti, the geochemical signatures similar to those from subduction-related mafic magmas. The Hf-O zircon analyses yield eHf(t) values of + 4.1 to + 11.1 and δ18O values of + 4.8 to + 6.2‰. The zircon isotopic signatures together with shoshonitic affinity in the Senj mafic samples suggest partial melting of an enriched lithospheric mantle that had already been metasomatized by slab-derived melts and fluids. The Mo-Cu mineralization mainly occurs as veins and veinlets in the volcano-sedimentary rocks of the Karaj Formation and is dominated by molybdenite with minor amounts of chalcopyrite, bornite, pyrite and tetrahedrite-tennantite. The associated gangue minerals are tremolite, actinolite, quartz, calcite, chlorite and epidote. The Senj Mo-Cu deposit formed in volcano-sedimentary rocks following the emplacement of the Late Eocene Senj sill. The source of molybdenite in the Senj deposit is dominantly from crustal materials as it is revealed by Re contents in the molybdenite minerals (0.5 to 0.7 ppm). In fact, the molybdenite occurrence may be a remobilization process related to the emplacement of the Senj mafic magma.

The Ediacaran BISF at Hormuz Island is a newly identified glaciogenic iron-salt deposit in the Tethyan margin of Gondwana. The BISF was formed by synchronous riftogenic A-type submarine felsic volcanism and evaporate deposition. The mineralization occurs in a proximal felsic tuff cone and jaspilitic distal zones and contains 1 million tonne of hematite-rich ore with an average grade of 58% Fe. The ore structure shows cyclicity of macrobandings, mesobandings and microbandings of anhydrite, halite, hematite and chert, which marks a new record in BIFs geohistory. The alteration minerals in the proximal and distal zones are actinolite, ripidolite, epidote, sericite, tourmaline, clinochlore, anhydrite and clay minerals. The occurrence of metamorphosed polygenetic bullet-shape dropstones in BISF attests that there was probably a continuous process of ice melting, episodic submarine volcanism and exhalative hydrothermal banded iron salt formation during the Late Ediacaran time. The non-metamorphosed Neoproterozoic stratigraphy, the presence of genus Collenia, U-Pb dating (558 ± 7 Ma) and the marked negative δ13C excursion in cap carbonates are representative of Late Ediacaran glaciation, which has been identified worldwide. The REE+Y display light REE enrichment, unusually strong Tb-Tm anomaly, a weak positive Y anomaly, but no distinguished Eu and Ce anomalies, reflecting the glaciogenic nature of the BISF. The contents of Zr, Hf, Nb, Ta, Th, La, Ce and Y in BISF, dropstones, halite and cap carbonates are similar to those of the Neoproterozoic glaciogenic BIFs. Also, the Ni/Fe, P/Fe ratios and Fe/Ti – Al/Al + Fe + Mn + Ca + Na + K diagram suggest an exhalative hydrothermal Ediacaran-type BISF. The absence of brecciated magnetite in the ore association and the low contents of copper (9–493 ppm) and gold (

Uranium–lead isotopes and trace elements of titanite from the Chengchao iron skarn deposit (Daye district, Eastern China), located along the contact zones between Triassic marine carbonates and an early Cretaceous intrusive complex consisting of granite and quartz diorite, were analyzed using laser ablation inductively coupled plasma mass spectrometry to provide temporal constraints on iron mineralization and to evaluate its potential as a reference material for titanite U–Pb geochronology. Titanite grains from mineralized endoskarn have simple growth zoning patterns, exhibit intergrowth with magnetite, diopside, K-feldspar, albite and actinolite, and typically contain abundant primary two-phase fluid inclusions. These paragenetic and textural features suggest that these titanite grains are of hydrothermal origin. Hydrothermal titanite is distinct from the magmatic variety from the ore-related granitic intrusion in that it contains unusually high concentrations of U (up to 2995 ppm), low levels of Th (12.5–453 ppm), and virtually no common Pb. The REE concentrations are much lower, as are the Th/U and Lu/Hf ratios. The hydrothermal titanite grains yield reproducible uncorrected U–Pb ages ranging from 129.7 ± 0.7 to 132.1 ± 2.7 Ma (2σ), with a weighted mean of 131.2 ± 0.2 Ma [mean standard weighted deviation (MSWD) = 1.7] that is interpreted as the timing of iron skarn mineralization. This age closely corresponds to the zircon U–Pb age of 130.9 ± 0.7 Ma (MSWD = 0.7) determined for the quartz diorite, and the U–Pb ages for zircon and titanite (130.1 ± 1.0 Ma and 131.3 ± 0.3 Ma) in the granite, confirming a close temporal and likely genetic relationship between granitic magmatism and iron mineralization. Different hydrothermal titanite grains have virtually identical uncorrected U–Pb ratios suggestive of negligible common Pb in the mineral. The homogeneous textures and U–Pb characteristics of Chengchao hydrothermal titanite suggest that the mineral might be a suitable internal reference material for U–Pb dating.

Primary ore-forming minerals retain geochemical signatures of magmatic crystallization information and can reveal the petrochemical conditions prevalent at the time of their formation. The Baogutu deposit is a typical reduced porphyry Cu deposit. Amphibole and biotite Fe 3+ /ΣFe ratios, minerals (feldspar, biotite, amphibole, zircon and apatite), in situ elemental and apatite Nd isotopic compositions were determined by Mossbauer spectroscopy, electron probe microanalysis, and laser ablation multiple-collection inductively coupled plasma mass spectrometry, respectively, to investigate the magma oxidation state, petrogenesis, source features, and to constrain the carbon species at magmatic stages for the intrusive phases. The results show that the primary plagioclase and amphibole in the mineralized diorite to granodiorite porphyry and post ore hornblende diorite porphyry are distinct (An 26-55 versus An 60-69 ; Mg-hornblende versus tschermakite). In particular, the amphibole shows distinct major and trace element compositions with light rare earth element enrichments and negative Eu anomalies in Mg-hornblende and light rare earth element depletions and no Eu anomalies in tschermakite. All the analyzed biotites are primary igneous phases with a biotite phenocryst profile showing significant variations of Zn, Cr, Sc and Sr from core to rim. These results may indicate the occurrence of mixing between two distinct magmas during mineral formation. Titanium in zircon and Si ∗ in amphibole thermometries indicate that magma crystallized at >900 °C and continued to ∼650 °C. In situ apatite Nd isotope (eNd(t) = 5.6–7.6, T DM2 = 620–460 Ma), indicate absence of significant reduced sedimentary contamination and the source of juvenile lower crust. Slightly decreasing Fe 3+ /ΣFe ratios from biotite and amphibole to whole rock indicate decreasing oxygen fugacity during magma crystallization. Recalculated biotite compositions according to Fe 3+ /ΣFe ratios indicate f O 2 values of less than Ni-NiO buffer (NNO) which show slightly lower values than that estimated according to zircon/melt distribution coefficients Ce anomalies (∼ΔNNO + 0.6). These values are consistent with the features of reduced porphyry Cu deposits. Crystallization of other mineral phases significantly affects the reliability of oxybarometer of zircon/melt distribution coefficients Eu anomalies and Mn contents in apatite. This oxidation state suggests that only CO 2 was present at the magmatic stage, and implies that CH 4 formed during CO 2 reduction occurring later hydrothermal alteration. The alteration of primary amphibole to actinolite released Ti, Al, Fe, Mn, Na and K to the fluid with later precipitation of titanite, albite and minor ilmenite and magnetite during actinolite alteration.

Dissolution kinetic experiments of actinolite in water were performed using a flow-through reactor at temperatures from 20 to 400 °C and 23.5±0.5 MPa. The results indicate that the steady-state release rates of the different elements of actinolite vary with temperature. Generally, Ca, Mg, Fe, and Al dissolve more quickly than Si at temperatures from 20 °C to near 300 °C, but slower from 300 to 400 °C. The Si release rate increases with temperatures from 20 to 300 °C and then decreases from 300 to 400 °C. Si release rate reaches the maximum at 300 °C. Amorphous Si-rich surface layers occur at temperature 300 °C. Water property variations within the critical region strongly affect the dissolution rates and the modification of surface.

The Chadormalu is one of the largest known iron deposits in the Bafq metallogenic province in the Kashmar-Kerman belt, Central Iran. The deposit is hosted in Precambrian-Cambrian igneous rocks, represented by rhyolite, rhyodacite, granite, diorite, and diabasic dikes, as well as metamorphic rocks consisting of various schists. The host rocks experienced Na (albite), calcic (actinolite), and potassic (K-feldspar and biotite) hydrothermal alteration associated with the formation of magnetite–(apatite) bodies, which are characteristic of iron oxide copper-gold (IOCG) and iron oxide-apatite (IOA) systems. Iron ores, occurring as massive-type and vein-type bodies, consist of three main generations of magnetite, including primary, secondary, and recrystallized, which are chemically different. Apatite occurs as scattered irregular veinlets in various parts of the main massive ore-body, as well as apatite-magnetite veins and disseminated apatite grains in marginal parts of the deposit and in the immediate wall rocks. Minor pyrite occurs as a late phase in the iron ores. Chemical composition of magnetite is representative of an IOA or Kiruna-type deposit, which is consistent with other evidence. Whole rock geochemical data from various host rocks confirm the occurrence of Na, Ca, and K alteration consistent with the formation of albite, actinolite, and K-feldspar, respectively. The geochemical investigation also includes the nature of calc-alkaline igneous rocks, and helps elaborating on the spatial and temporal association, and possible contribution of mafic to felsic magmas to the evolution of ore-bearing hydrothermal fluids. Fluid inclusion studies on apatites from massive- and vein-type ores show a range of homogenization temperatures from 266 to 580 °C and 208–406 °C, and salinities from 0.5 to 10.7 wt.% and 0.3–24.4 wt.% NaCl equiv., respectively. The fluid inclusion data suggest the involvement of evolving fluids, from low salinity-high temperature, to high salinity-low temperature, in the formation of the massive- and vein-type ores, respectively. The δ34S values obtained for pyrite from various parts of the deposit range between +8.9 and +14.4‰ for massive ore and +18.7 to +21.5‰ for vein-type ore. A possible source of sulfur for the 34S-enriched pyrite would be originated from late Precambrian-early Cambrian marine sulfate, or fluids equilibrated with evaporitic sulfates. Field observations, ore mineral and alteration assemblages, coupled with lithogeochemical, fluid inclusion, and sulfur isotopic data suggest that an evolving fluid from magmatic dominated to surficial brine-rich fluid has contributed to the formation of the Chadormalu deposit. In the first stages of mineralization, magmatic derived fluids had a dominant role in the formation of the massive-type ores, whereas a later brine with higher δ34S contributed to the formation of the vein-type ores.

The Kaladawan Fe–Mo ore field in Altyn (Xinjiang Province, NW China) contains six Fe (–Mo) deposits, with total proven reserves of 60 Mt Fe and 10,000 t Mo. Tabular, lensoidal and stratiform orebodies occur in the Cambrian foliated marble, phyllite, carbonaceous slate, chlorite–sericite schist and quartz–sericite schist along the exocontact zone of the Kaladawan granite. Skarns are extensively developed and dominated by garnet, pyroxene, epidote, tremolite and actinolite, with minor chlorite, zoisite, quartz and calcite. Ore minerals are mainly magnetite and molybdenite. Five alteration and mineralization stages (I–V) were identified: the prograde (I) and retrograde (II) skarns are characterized by assemblages of garnet–pyroxene and epidote–tremolite–actinolite, respectively, intruded and replaced by mineral assemblages of magnetite–epidote–zoisite (III), quartz–sulfides (IV) and calcite–chlorite (V) in younging order. The Kaladawan garnet contains more andradite (61.2–94.4 mol%) than grossularite (37.5–5.0 mol%). Pyroxene is Mg-rich and Fe-poor, with an endmember range of 55.4–94.7 mol% diopside and 42.5–4.7 mol% hedenbergite. Amphibole comprises mainly tremolite and actinolite. The Kaladawan skarn mineral contents resemble typical skarn Fe and Mo deposits. In-situ LA-ICP-MS magnetite trace element analysis had identified unusually high Mg, Mo and Cr concentrations. The high Mo and the absence of molybdenite inclusions in magnetite suggest that the hydrothermal fluids may have been Mo-rich. The magnetite also contains similar (Ti + V) and (Al + Mn) values with typical skarn Fe deposits. Therefore, the Kaladawan Fe–Mo mineralization is best attributed to be skarn-type, and related to the Kaladawan granite intrusion.

The Half Dome Granodiorite, Yosemite National Park, California, is recognized in the field by euhedral, fresh-looking, black hornblende phenocrysts up to 2 cm in length. This variety of granodiorite typifies intermediate-age hornblende-phyric units of Cretaceous nested plutonic suites in the Sierra Nevada batholith. Although only inclusions of feldspar are evident in hand samples, the phenocrysts are riddled with up to 50% inclusions of every major mineral found in the host granodiorite plus metamorphic minerals formed during cooling. Amphibole compositions within single phenocrysts vary from actinolite with less than 1 wt% Al 2 O 3 to magnesiohornblende with over 8 wt%. Elemental zoning within the amphibole is highly irregular on the micrometer scale, showing patches and polygonal zones with dramatically different compositions separated by sharp to gradual transitions. The chemical compositions of entire phenocrysts are equivalent to hornblende plus a small proportion of biotite, suggesting that the non-biotite inclusions are the result of metamorphism of the phenocrysts. Backscattered electron imaging shows evidence of brecciation that may have been the result of volume changes as hornblende was converted to actinolite. Pressure calculations using the Al-in-hornblende barometer show unreasonably wide variations on the micrometer scale that cannot have been produced by temperature or pressure variations during crystallization. These hornblende phenocrysts would thus be unsuitable for geobarometry, and caution must be used to avoid similarly zoned phenocrysts in the application of the Al-in-hornblende geobarometer.

Potentially toxic elements (PTEs) hosted in asbestos elongate mineral particles is one of the factors that determines their toxic/pathogenic effects. This study quantifies and compares these elements in terms of major, minor and trace element concentrations (Si, Mg, Ca, Al, Fe, Mn, Cr, Co, Ni, Cu, Zn, Be, V, As, Rb, Sb, Ba, Pb, Sr) in various types of asbestos using micro X-ray fluorescence (μ-XRF) and inductively coupled plasma mass spectrometry (ICP-MS), in order to understand how they contribute to asbestos-related diseases. Chrysotile, tremolite asbestos and actinolite asbestos extracted from the Gimigliano-Mount Reventino Unit (Calabria Region, Southern Italy) were used for this study. In the minerals analysed, high concentrations of Cr (171 ppm) and Be (2.9 ppm) were found in tremolite asbestos and chrysotile respectively. When calculating the pseudo-total concentrations of trace elements in the samples, the largest amounts were detected in tremolite asbestos, followed by actinolite asbestos and chrysotile. However, since other metals such as Mn and Fe (minor elements) are known to induce toxicity, and considering their input to the overall balance, actinolite contained the largest amount of PTEs and in this case chrysotile proved to be more toxic than tremolite asbestos. Furthermore, the potential leaching of PTEs, released by chrysotile, tremolite and actinolite asbestos-containing rocks, into the soil and water supply is also discussed. Since asbestos elongate mineral particles can be widespread in the environment (i.e. air, rocks, soil, water), it is essential to quantify the toxic elements present in asbestos elongate mineral particles in order to prevent asbestos-related diseases. The knowledge obtained from this study will provide us with a better understanding of asbestos-related lung cancer.

Aurora is a platinum-group element (PGE) prospect hosted in the Northern Limb of the Bushveld Complex, South Africa. It is one of only three deposits discovered in the Northern Limb so far to be hosted in the melanocratic-leucocratic gabbroic cumulates of the Main Zone of the Rustenberg Layered Suite (Aurora, Moorddrift and Waterberg T Zone deposits), rather than in predominantly ultramafic rocks (e.g. Platreef). The host cumulates at Aurora have been divided into three principal units and they intrude the dolomites of the lower Transvaal Supergroup. Base metal sulphide (BMS) mineralisation with PGE is present in the leucogabbronorites and gabbronorites of Unit 2, and in coarse grained gabbronorite veins which intrude the peridotites of Unit 1. These veins contain up to 50% interstitial pyrrhotite-pentlandite-chalcopyrite ± pyrite. Unit 2 contains 1–3% pentlandite-pyrrhotite-chalcopyrite assemblages, and 1–5% chalcopyrite ± pyrite/pyrrhotite associated with hydrothermal alteration. The PGE content of Aurora however is predominantly controlled by the presence of platinum-group minerals (PGM), not BMS. LA-ICP-MS analysis of sulphides shows the BMS in Aurora have lower PGE concentrations than other Bushveld magmatic sulphides, with pentlandite carrying much lower concentrations of Pd (average 23 ppm) than the Platreef or the Merensky Reef. SEM-EDS analysis of 26 sections characterised 995 platinum-group minerals (PGM) and precious metal-bearing minerals (PMM), with a total area of 27850 μm2 and an average size of 28.2 μm2. Of the PGM and PMM identified in Aurora 85% (by area) are Pd-Te-Bi minerals, with 6% Pd-Te minerals, 4% electrum and 3% Ag-Te minerals, along with minor Pd-Bi, Pd-As, Pt-Te-Bi, Pt-As and Pt-S minerals that collectively comprise 2% of total area. Only 25% of the PGM and PMM in Aurora are BMS hosted, with the rest hosted in silicates. Of the total PGM and PMM area 22% are hosted in alteration-silicates (quartz, chlorite or actinolite) in an alteration halo around sulphides. Unusually, 52% of the PGM and PMM are spatially removed from BMS, instead hosted in alteration silicates and within cracks in primary silicates away from any BMS. This indicates a multi-stage ore genesis model, with hydrothermal remobilisation of PGE important for ore formation. The style and host rocks for mineralisation in the Aurora deposit are fundamentally different from other deposits in the Northern Limb of the Bushveld hosted in ultramafic rocks, such as the Platreef, GNPA member deposits and the F zone of the Waterberg deposit, all of which contain a greater diversity of PGM and BMS with higher precious metal contents. The mineralisation most similar to Aurora is the T Zone of the Waterberg deposit, located to the north of Aurora, which been suggested to be an along-strike equivalent of the Aurora Main Zone mineralisation. However, despite strong similarities in PGM mineralogy and S isotope signatures there are significant differences in BMS mineralisation and host lithology meaning it is unlikely they are directly linked stratigraphically. At present it seems more likely that Aurora and the Waterberg T Zone reflect similar fluid-influenced processes operating in different parts of the Main Zone, perhaps at different times and in different structural basins, rather than a continuous mineralised zone along strike.

Documentation of textures, modes and compositions of minerals in metamorphosed basalts across two greenschist-to-lower amphibolite facies sequences (Flin Flon, Manitoba and Rossland, British Columbia) was combined with a compilation of the literature data to assess equilibrium and disequilibrium processes across this important transition zone. At Flin Flon and Rossland, the greenschist–amphibolite facies transition occurs over a narrow spatial interval marked by hornblende-in, oligoclase-in and actinolite-out isograds. The data suggest the existence of stable miscibility gaps separating coexisting actinolite and hornblende, and coexisting albite and oligoclase, in the lowermost amphibolite facies. However, actinolite and hornblende show a divergence in compositions going upgrade across the oligoclase-in isograd, suggestive of disequilibrium between the new, progressively more aluminous hornblende and metastably persisting actinolite. Likewise, coexisting albite and oligoclase compositions show no evidence for converging compositions at higher temperatures, suggesting they do not remain in equilibrium across a miscibility gap. Compositional gaps within epidote phases are attributed to disequilibrium preservation of lower grade epidote compositions to higher grade conditions, rather than the existence of a miscibility gap at greenschist and amphibolite facies conditions. Recognition of equilibrium and disequilibrium relations highlights the difficulty of using natural compositional datasets to extract information on miscibility gaps and more generally to extract a–X relationships. The greenschist-to-amphibolite facies transition is controlled principally by the consumption of chlorite, which primarily occurs upon crossing the oligoclase-in isograd, concomitant with conversion of actinolite to hornblende and albite to oligoclase. The result is a focused pulse of devolatilization over a small spatial and thermal interval.

The sources and temporal evolution of fluids related to distal skarn mineralization strongly influence the minerals that form, but remain poorly understood. In this study, we use the lithium and chlorine isotopic compositions of fluid-inclusion leachates (FIL) to elucidate the nature and evolution of fluids that formed the Luziyuan distal skarn Zn–Pb–Fe–(Cu) deposit, China. The δ7Li values of prograde skarn stage rhodonite FIL (+5.37‰–+7.31‰) are similar to those of typical magmatic fluid. The δ7Li values (+11.69‰–+12.54‰) of actinolite FIL are higher than those of rhodonite FIL; this is attributed to Rayleigh fractionation within a closed magmatic–hydrothermal system. It is inferred that up to 70% of fluid-borne Li is sequestered by hydrous minerals during retrograde skarn alteration, consistent with conclusions drawn from previous studies of fluid-inclusions. The δ7Li values of galena FIL (+9.78‰–+13.19‰), black sphalerite FIL (+11.62‰), and reddish-brown sphalerite (+10.44‰–+11.66‰) overlap with those of actinolite FIL, indicating that phase separation occurred during Zn–Pb mineralization at the Luziyuan deposit. The low δ7Li values of light-yellow sphalerite FIL (+6.75‰) and calcite FIL (+3.95‰–+6.49‰) record external fluid input, probably meteoric water. The positive δ37Cl values of rhodonite FIL (+1.82‰–+1.83‰) are consistent with those of magmatic fluids. However, the δ37Cl values of actinolite FIL (+0.49‰) are lower than those of rhodonite FIL, indicating that FIL within hydrous minerals might not record fluid sources reliably.

Magnetite deposits comprise a very small volume of a serpentinized peridotite body that constitutes the Eretria chrome mine of the East Othris ophiolite in central Greece. Magnetite deposits have been examined to aid determination of their mode of occurrence, mineralogy and origin. Research attention has been focused on an ore body that consists of a ~30 cm-thick pod of semi-massive to massive magnetite (~75%–85% modal) hosted in a serpentinite shear zone. The silicate matrix of magnetitite (~10%–15% modal) is composed of unstrained serpentine, chlorite and subordinate amounts of andradite and actinolite. Base metal sulfides (BMS; ~5%–10% modal) and phosphates are dispersed between the magnetite grains. Variably altered Cr-spinel crystals are poikilitically enclosed within magnetite. The investigated ore samples show great variations in the Cu (890–9530 ppm), Ni (190–3260 ppm), Co (120–2180 ppm) and Zn (20–1240 ppm) contents. The δ18ΟSMOW value for magnetite from a magnetitite sample is −2.2‰. The undeformed nature of the silicate minerals in magnetitite points toward crystal growth from a post-magmatic fluid. The low Ni, Mn, Mg and high Si contents in magnetite suggest that it was not derived from fluids produced concurrent to serpentinization. The presence of phosphates, BMS and hydrosilicates suggest that the ore forming fluids were acidic and halogen-bearing. Our preferred hypothesis for the formation of magnetitite is that mixing of upwelling, metal-rich brines along the dilational segments of the host shear zone caused saturation of the ensuing fluids with Fe, which eventually prompted magnetite precipitation. The T estimates deduced from mineralogy, with an uppermost limit of ~460 °C required, and cessation of mineralization at ~150–100 °C, are consistent with the ambient T present within a cooling oceanic lithospheric slab. In analogy with some modern serpentinite-hosted BMS deposits at rifted settings, the BMS-bearing magnetitite of Eretria may represent part of an ancient seafloor hydrothermal system. Our study provides important insights into the initiation and episodicity of hydrothermal activity in oceanic settings.

In Halifax, Nova Scotia, 149 victims of the 1912 sinking of the Titanic lie beneath petrologically identical "black granite" headstones. Those headstones, supplied by the White Star Line, arrived in Halifax in late 1912, but no known historical document reveals their source. They consist of medium- to coarse-grained olivine-bearing gabbro, with cumulus phases consisting of randomly oriented euhedral plagioclase laths, corroded olivine, and titaniferous magnetite, and intercumulus material consisting of augite with reaction rims of hornblende, both of which are variably altered to actinolite and biotite. Three types of forensic evidence [quantitative – radiometric age of 422.1 ± 1.3 Ma (n = 17), mean olivine FeO/(FeO + MgO) values ranging from 0.43 to 0.46, augite rim trace- element compositions (35 elements), and whole-rock chemical compositions (48 elements), including statistical analysis of all these data showing no significant differences between the headstones and their putative source quarry; qualitative – mineral assemblages, modal proportions, textural parameters, style and degree of alteration; and circumstantial – regional reputation, quarrying history, local logistics, regional transportation, McGrattan marker] connect the Titanic headstones to the Saint George Batholith in southwestern New Brunswick. Precise matching of any dimension stone to its source quarry is problematic, because that material connects only to a void in the quarry. Ideally, all physical-chemical-temporal properties of the dimension stone and source quarry should match, both quantitatively and qualitatively, but in reality only the ages must almost certainly match. Thus it is remotely possible for the right quarry to mismatch most of the properties of the dimension stone, and for a wrong quarry to match most of the properties of the dimension stone. However, in the case of the Titanic headstones, the cumulative weight of all the quantitative, qualitative, and circumstantial evidence, combined with a process of elimination and application of Ockham’s razor, indicate that the Charles Hanson quarry near Bocabec, southwestern New Brunswick, is the likely source for the gabbroic Titanic headstones in Halifax, Nova Scotia.

The Xiaobaishitou W (–Mo) deposit is located in the eastern segment of the Central Tianshan, northwestern China. The deposit represents a skarn system distributed in the contact zones of biotite granite and crystalline limestone of the Mesoproterozoic Kawabulag Group. The Xiaobaishitou deposit is characterized by a typical calc-silicate mineralogy dominated by garnet, diopside and wollastonite, with minor epidote, tremolite, actinolite, chlorite, quartz, fluorite and calcite. The prograde and retrograde skarns are characterized by garnet–clinopyroxene–wollastonite and epidote–tremolite–actinolite–chlorite, respectively, intruded and replaced by mineral assemblages of scheelite–cassiterite–magnetite, quartz–sulfides and calcite–quartz–fluorite in younger order. Six molybdenite samples from the deposit yielded Re − Os isotope model ages ranging from 239.7 ± 3.6 Ma to 251.4 ± 3.6 Ma. The zircon crystals from biotite granite and Mo-mineralized granite yield weighted 206Pb/238U age of 242 ± 1.7 and 240.5 ± 2.1 Ma, respectively. Both the zircon U − Pb and the molybdenite Re − Os ages obtained in this study fall in a narrow span of 242–240 Ma, which suggest that the Xiaobaishitou W (–Mo) system was formed in the Triassic. The Re contents of the molybdenites range from 40.33 to 64.67 ppm, suggesting that the ore-forming materials were derived mainly from continental crust together with the involvement of minor mantle components. Combined with the 87Sr/86Sr ratios of tungsten-bearing quartz veins from other studies, which scatter between 0.707153 and 0.709877, demonstrating mixing between two end-member isotopic compositions of crust and mantle. It can be concluded that the Indosinian Xiaobaishitou deposit was formed in a tectonic transition from collisional crust shortening and thickening to post-collisional extension and thinning.

The newly discovered Handagai skarn Fe–Cu deposit is located in the northern Great Xing'an Range of NE China and is hosted by the Ordovician Luohe Formation. The orebodies that form the deposit are generally concordant with the bedding within these sediments, and are spatially related to areas of skarn development. The Fe–Cu mineralization in this area records four stages of paragenesis, namely prograde skarn, retrograde skarn, quartz–sulfide, and quartz–carbonate stages. The Handagai deposit is a calcic skarn that is dominated by an andradite–diopside–epidote–actinolite assemblage. The mineralogy and geochemistry of the skarn indicate that it formed from a hydrothermal fluid that altered the carbonate units in this area to a garnet (And42–95Grs4–53) and pyroxene (Di71–78Hd22–29Jo0–2) bearing skarn. The epidote within the skarn has an epidote end-member composition, with the chlorite in the skarn dominantly Fe-rich, indicating that these minerals formed in an Fe-rich environment. The petrographic, microthermometric, and Raman spectroscopic analysis of fluid inclusions within garnet, epidote, actinolite, quartz, and calcite precipitated at different stages of formation of the Handagai deposit indicate that mineralization-related fluid inclusions are either liquid-rich two-phase H2O–NaCl (type I), gas-rich two-phase H2O–NaCl (type II), three-phase (liquid + vapor + solid) H2O–NaCl (type III), or CO2–H2O–NaCl inclusions (type IV). The early stages of mineralization are associated with all four types of inclusion, whereas the later stages of mineralization are only associated with type I and II inclusions. Inclusion homogenization temperatures vary between the four stages of mineralization (370 °C–530 °C and > 600 °C, 210 °C–290 °C, 190 °C–270 °C, and 150 °C–230 °C, from early to late, respectively), with salinities also varying between the earlier and later stages of mineralization (11–18 and > 45, 7–15, 6–9, and 3–7 wt.% NaCl equivalent (equiv.), respectively). The majority of the inclusions within the Handagai deposit have homogenization temperatures and salinities of 200 °C–350 °C and 4–14 wt.% NaCl equiv., respectively, indicating that this is a medium–high temperature and medium–low salinity type deposit. The fluid inclusions were trapped at pressures of 11 to 72 MPa, corresponding to depths of 0.4 to 2.9 km. The geology, mineralogy, geochemistry, and fluid inclusions microthermometry indicate that the Handagai deposit formed as a result of contact infiltration metasomatism, with the deposition of ore minerals resulting from a combination of factors that include boiling as a result of reduced pressure, cooling, and fluid mixing.

Chlorite, ordered mixed-layer chlorite-smectites, laumontite, quartz and albite are the most widespread alteration assemblage in cone-building and near-vent successions of lavas, autoclastic, pyroclastic and resedimented volcaniclastic deposits of the Oligocene Smrekovec Volcanic Complex, Slovenia. Randomly interstratified corrensite-chlorite with ~ 70–80% of corrensite layers (R0 Cr-Ch) is less common in occurrence and associated either with clinoptilolite and heulandite in fine-grained vitric tuffs, or with prehnite, laumontite, actinolite, analcime and albite in extensively altered and/or fractured host-rocks. The assemblage with clinoptilolite and heulandite indicates the temperatures of formation of

Ferro-ferri-hornblende is a new member of the amphibole supergroup (IMA-CNMNC 2015-054). It has been found in a rock specimen from the historical collection of Leandro De Magistris, which was collected at the Traversella mine (Val Chiusella, Ivrea, Piemonte, Italy). The specimen was catalogued as ‘speziaite', and contains a wide range of amphibole compositions from tremolite/actinolite to magnesio-hastingsite. The end-member formula of ferro-ferri-hornblende is A□BCa2c(Fe+Fe3+)T(Si7Al) O22W(OH)2 , which requires SiO2 43.41, Al2O3 5.26, FeO 29.66, Fe2O3 8.24 CaO 11.57, H2O 1.86, total 100.00 wt.%. The empirical formula derived from electron microprobe analysis and single-crystal structure refinement for the holotype crystal is A(Na0.10K0.13) Σ=0.23B(Ca 1.93Na0.07)Σ=2.00C(Mg1.16Fe2+3.21Mn0.O6Fe3+0.45 Al0.12Ti 0.01)Σ=5.01T(Si7.26Al0. 74)Σ=8.00 O22W(OH1.89F0.01C10.10)Σ=2.00- Ferro-ferri-hornblende is biaxial (-), with α = 1.697(2), P = 1 .722(5), γ = 1.726(5) and 2V (meas.) = 35.7(1.4)°, 2V (calc.) = 43.1°. The unit-cell parameters are a = 9.9307(5), b = 18.2232(10), c = 5.3190(3) Å, β = 104.857(1)°, V= 930.40 (9) Å3, Z= 2, space group C2/m. The a:b:c ratio is 0.545:1:0.292. The strongest eight reflections in the powder X-ray pattern [d values (in Å), I, (hkl)] are: 8.493, 100, (110); 2.728, 69, (151); 3.151, 47, (310); 2.555, 37, (); 2.615, 32, (061); 2.359, 28, (); 3.406, 26, (131); 2.180, 25, (261). Type material is deposited in the collections of the Museo di Mineralogia, Dipartimento di Scienze della Terra e dell'Ambiente, Università di Pavia, under the catalogue number 2015-01. Sample M/U15285 from the historical collection of Luigi Colomba, presently at the Museo Regionale di Scienze Naturali di Torino, was also checked, and the presence of ferro-ferri-hornblende was confirmed.

Oxygen, hydrogen, sulfur, and carbon isotopes have been analyzed in the Pea Ridge magnetite-apatite deposit, the largest historic producer among the known iron deposits in the southeast Missouri portion of the 1.5 to 1.3 Ga eastern granite-rhyolite province. The data were collected to investigate the sources of ore fluids, conditions of ore formation, and provenance of sulfur, and to improve the general understanding of the copper, gold, and rare earth element potential of iron deposits regionally. The δ 18 O values of Pea Ridge magnetite are 1.9 to 4.0‰, consistent with a model in which some magnetite crystallized from a melt and other magnetite—perhaps the majority—precipitated from an aqueous fluid of magmatic origin. The δ 18 O values of quartz, apatite, actinolite, K-feldspar, sulfates, and calcite are significantly higher, enough so as to indicate growth or equilibration under cooler conditions than magnetite and/or in the presence of a fluid that was not entirely magmatic. A variety of observations, including stable isotope observations, implicate a second fluid that may ultimately have been meteoric in origin and may have been modified by isotopic exchange with rocks or by evaporation during storage in lakes. Sulfur isotope analyses of sulfides from Pea Ridge and seven other mineral deposits in the region reveal two distinct populations that average 3 and 13‰. Two sulfur sources are implied. One was probably igneous melts or rocks belonging to the mafic- to intermediate-composition volcanic suite that is present at or near most of the iron deposits; the other was either melts or volcanic rocks that had degassed very extensively, or else volcanic lakes that had trapped rising magmatic gases. The higher δ 34 S values correspond to deposits or prospects where copper is noteworthy—the Central Dome portion of the Boss deposit, the Bourbon deposit, and the Vilander prospective area. The correspondence suggests that (1) sulfur either limited the deposition of copper or was cotransported with copper, and (2) sulfur isotope analysis may be useful in evaluating southeast Missouri iron deposits for copper and possibly for gold.

New pseudosection modeling was applied to better constrain the P-T conditions and evolution of glaucophane-bearing rocks in the Tamayen block of the Yuli belt, recognized as the world's youngest known blueschist complex. Based on the predominant clinoamphibole, textural relationships, and mineral compositions, these glaucophane-bearing high-pressure rocks can be divided into four types. We focused on the three containing garnet. The chief phase assemblages are (in decreasing mode): amphibole + quartz + epidote + garnet + chlorite + rutile/titanite (Type-I), phengite + amphibole + quartz + garnet + chlorite + epidote + titanite + biotite + magnetite (Type-II), and amphibole + quartz + albite + epidote + garnet + rutile + hematite + titanite (Type-III). Amphibole exhibits compositional zoning from core to rim as follows: glaucophane → pargasitic amphibole → actinolite (Type-I), barroisite → Mg-katophorite/taramite → Fe-glaucophane (Type-II), glaucophane → winchite (Type-III). Using petrographic data, mineral compositions, and Perple_X modeling (pseudosections and superimposed isopleths), peak P-T conditions were determined as 13 ± 1 kbar and 550 ± 40 °C for Type-I, 10.5 ± 0.5 kbar and 560 ± 30 °C for Type-II (thermal peak), and 11 ± 1 kbar and 530 ± 30 °C for Type-III. The calculations yield higher pressures and temperatures than previously thought; the difference is about 1-6 kbar and 50-200 °C. The three rock types record similar P-T retrograde paths with clockwise trajectories; all rocks followed trajectories with substantial pressure decrease under near-isothermal conditions (Type-I and Type-III), with the probable exception of Type-II where decompression followed colder geotherms. The P-T paths suggest a tectonic environment in which the rocks were exhumed from maximum depths of ~45 km within a subduction channel along a relative cold geothermal gradient of ~11-14 ˚C km-1. This article is protected by copyright. All rights reserved.

Microanalysis of Fe 3+ /∑Fe in geological samples using synchrotron-based X-ray absorption spectroscopy has become routine since the introduction of standards and model compounds. Existing calibrations commonly use least-squares linear combinations of pre-edge data from standard reference spectra with known coordination number and valence state acquired on powdered samples to avoid preferred orientation. However, application of these methods to single mineral grains is appropriate only for isometric minerals and limits their application to analysis of in situ grains in thin sections. In this work, a calibration suite developed by acquiring X-ray absorption near-edge spectroscopy (XANES) data from amphibole single crystals with the beam polarized along the major optical directions (X, Y, and Z) is employed. Seven different methods for predicting %Fe 3+ were employed based on (1) area-normalized pre-edge peak centroid, (2) the energy of the main absorption edge at the location where the normalized edge intensity has the highest R 2 correlation with Fe 3+ /∑Fe, (3) the ratio of spectral intensities at two energies determined by highest R 2 correlation with Fe 3+ /∑Fe, (4) use of the slope (first derivative) at every channel to select the best predictor channel, (5 and 6) partial least-squares models with variable and constant numbers of components, and (7) least absolute shrinkage and selection operator models. The latter three sophisticated multivariate analysis techniques for predicting Fe 3+ /∑Fe show significant improvements in accuracy over the former four types of univariate models. Fe 3+ /∑Fe can be measured in randomly oriented amphibole single crystals with an accuracy of ±5.5–6.2% absolute. Multivariate approaches demonstrate that for amphiboles main edge and EXAFS regions contain important features for predicting valence state. This suggests that in this mineral group, local structural changes accommodating site occupancy by Fe 3+ vs. Fe 2+ have a pronounced (and diagnostic) effect on the XAS spectra that can be reliably used to precisely constrain Fe 3+ /∑Fe.

International audience; Electron back-scattered diffraction (EBSD) maps and crystal-preferred orientation (CPO) of eclogite-facies (omphacite and garnet) and amphibolite-facies (hornblende and actinolite) phases are reported for understanding the rheological behaviour of crust during subduction. Two types of eclogites from the subduction-related high-pressure/low-temperature type Sanbagawa metamorphic belt, Japan, have been investigated. Type-I eclogite (sample Sb-1) is composed of garnet, omphacite, secondary actinolite and hornblende. Type-II eclogite (samples Sb-2 and Sb-2a) are mainly composed of omphacite, garnet, and retrograde hornblende with no actinolite. Omphacite, the peak eclogite-facies phase, exhibits L-type CPO (maximum density of [001] axes parallel to and high density of {110} poles normal to the lineation) in Type-I eclogite, suggesting intra-crystalline plasticity with [001] {110} and {110} active slip systems, indicating a constrictive strain regime at mantle depths. Omphacite in Type-II eclogite exhibits a similar fabric but with much weaker CPO. Using the LS-index symmetry analysis (one for the end-member L-type, zero for the end-member S-type, and intermediate values for LS-types), a progressive change in LS index of 0.80 for Type-I and 0.61 to 0.44 for Type-II eclogites is observed. These values suggest a transition from axial extension parallel to the lineation for Sb-1 and weaker CPO associated with pure or simple shear for Sb-2 and Sb-2a. Garnet, the second dominant phase in the eclogite-facies stage, exhibits weak and complex fabric patterns in all eclogite types, behaved like rigid bodies and does not show plastic deformation. Amphibolite-facies phases (e.g., hornblende and actinolite) exhibit more than two types of CPO. Hornblende and actinolite in Type-I eclogite have a strong CPO along [001] axes aligned parallel to the lineation, indicating homotactic crystal growth probably by the replacement of omphacite during the early stages of retrogression. Type-II eclogites have weak CPO in hornblende but with characteristic alignment of [001] parallel to the lineation and other poles to planes (100), (010), and {110} normal to the lineation. This fabric might have resulted from a cataclastic deformation and could be related to the late-"D1" deformation stage in the Sanbagawa metamorphic belt.

A suite of samples collected mainly from river cobbles in the Mt. Hibernia Complex in SE Jamaica includes metamorphosed basaltic and clastic sedimentary rocks, which are interpreted here as part of a Cretaceous accretionary prism. The metabasic rocks occur as blueschists and greenschists, whereas the metasedimentary rocks are former greywackes s.l ., or psammopelites, and can now be characterized as phyllites. Eight characteristic mineral assemblages can be defined within the metabasic sample suite, involving amphibole (Na amphibole and/or actinolite), pumpellyite, lawsonite, epidote, chlorite, titanite, phengite, albite and quartz. Augite is an important relict phase of the magmatic source rocks. White mica, chlorite and quartz predominate in the phyllites in variable proportions, but Na amphibole, epidote, albite and titanite may also be important. Calculated P–T pseudosections show that the assemblage glaucophane–pumpellyite–chlorite occurs only in a restricted field along the lower P–T limit of the blueschist facies. Pseudosections also indicate that peak P–T conditions for the blueschist samples studied here lie in the range 6.5–7.2 kbar and 310–340°C, that is at the upper stability limit of pumpellyite and lawsonite, and in the range 6.4–7.8 kbar and 340–380°C for greenschist samples. The P–T range for phyllites overlaps with both. Thus, blueschists and greenschists represent comparable pressure but different temperature conditions of formation. Literature data on the mapped distribution of metabasic rock types suggests an isobaric metamorphic field gradient in the Mt. Hibernia Complex, with temperatures increasing slightly but significantly from blueschist to greenschist zones. We interpret this gradient as reflecting either increasing temperatures in the accretionary complex away from the subducting slab or thermal re-equilibration in a cooling subduction zone. Sodium-Ca amphiboles, predominantly winchite, are commonly observed as rims around Na amphibole and formed together with albite porphyroblasts during decompression. Comparison with published information on the miscibility gap between Na and Ca amphiboles shows that many of these compositions fall within this gap for temperatures around 350°C. Thus, these amphiboles either grew metastably below the critical temperature of the gap, or some as yet undefined parameter must be responsible for drastically altering the shape of the gap. Published descriptions of deformation in the Mt. Hibernia Complex show that coaxial pure shear initially predominates, as is common in accretionary complexes; however, a late shearing event, postulated here to be caused by the collision between the Great Arc of the Caribbean and the continental margin of North America at 75–70 Ma, is held responsible for the rapid exhumation of the combined blueschist–greenschist sequence.

Iron oxide–apatite (IOA) ore deposits occur globally and can host millions to billions of tons of Fe in addition to economic reserves of other metals such as rare earth elements, which are critical for the expected growth of technology and renewable energy resources. In this study, we pair the stable Fe and O isotope compositions of magnetite samples from several IOA deposits to constrain the source reservoir of these elements in IOAs. Since magnetite constitutes up to 90 modal% of many IOAs, identifying the source of Fe and O within the magnetite may elucidate high-temperature and/or lower-temperature processes responsible for their formation. Here, we focus on the world-class Los Colorados IOA in the Chilean iron belt (CIB), and present data for magnetite from other Fe oxide deposits in the CIB (El Laco, Mariela). We also report Fe and O isotopic values for other IOA deposits, including Mineville, New York (USA) and the type locale, Kiruna (Sweden). The ranges of Fe isotopic composition (δ56Fe, 56Fe/54Fe relative to IRMM-14) of magnetite from the Chilean deposits are: Los Colorados, δ56Fe (±2σ) = 0.08 ± 0.03‰ to 0.24 ± 0.08‰; El Laco, δ56Fe = 0.20 ± 0.03‰ to 0.53 ± 0.03‰; Mariela, δ56Fe = 0.13 ± 0.03‰. The O isotopic composition (δ18O, 18O/16O relative to VSMOW) of the same Chilean magnetite samples are: Los Colorados, δ18O (±2σ) = 1.92 ± 0.08‰ to 3.17 ± 0.03‰; El Laco, δ18O = 4.00 ± 0.10‰ to 4.34 ± 0.10‰; Mariela, δ18O = (1.48 ± 0.04‰). The δ18O and δ56Fe values for Kiruna magnetite yield an average of 1.76 ± 0.25‰ and 0.16 ± 0.07‰, respectively. The Fe and O isotope data from the Chilean IOAs fit unequivocally within the range of magnetite formed by high-temperature magmatic or magmatic–hydrothermal processes (i.e., δ56Fe 0.06–0.49‰ and δ18O = 1.0–4.5‰), consistent with a high-temperature origin for Chilean IOA deposits. Additionally, minimum formation temperatures calculated by using the measured Δ18O values of coexisting Los Colorados magnetite and actinolite separates (630 °C) as well as Fe numbers of actinolite grains (610–820 °C) are consistent with this interpretation. We also present Fe isotope data from magmatic magnetite of the Bushveld Complex, South Africa, where δ56Fe ranges from 0.28 ± 0.04‰ to 0.86 ± 0.07‰. Based on these data and comparison to published Fe and O stable isotope values of igneous magnetite, we propose extending the magmatic/high-temperature δ56Fe range to 0.86‰. Considering that the Chilean IOAs and Kiruna deposit are representative of IOA deposits worldwide, the Fe and O stable isotope data indicate that IOAs are formed by high-temperature (magmatic) processes.

The Qiaxia Fe–Cu deposit is located on the southern Altay margin, Xinjiang, China, and is hosted in the submarine volcanic–sedimentary rocks of the Lower Devonian Kangbutiebao Formation. Ore genesis of the Qiaxia deposit plays an important role on understanding the metallogenesis of submarine volcanic-hosted Fe deposits. In the Qiaxia deposit, stratiform and podiform Fe orebodies are conformable with host sequence strike, whereas lenticular Cu mineralization is closely related to skarn. Wall-rock alteration is dominated by silicification with minor skarn (actinolite, chlorite, diopside, and tremolite). Based on field evidence and petrographic observations, the paragenesis of the Qiaxia deposit includes the following three periods: (1) a volcanic–sedimentary period characterized by the formation of barite and Fe orebodies; (2) a magmatic–hydrothermal period with the formation of skarn-type Cu mineralization; and (3) a regional metamorphism period. The volcanic–sedimentary period shows moderate temperature and moderate- to low-salinity fluids with compositions of predominantly K+, Cl−, and SO42− in the liquid phase and H2O, CO2, and N2 in the gaseous phase. By contrast, the regional metamorphism period reveals high- to moderate-temperature and high- to low-salinity fluids and compositions of predominantly Na+, K+, Cl−, and SO42− in the liquid phase and H2O, CO2, N2, CH4, and C2H6 in the gaseous phase. The H–O isotopic compositions suggest that the volcanic–sedimentary period involved both magmatic fluids and seawater, while the fluids of the regional metamorphism period were derived from a mixture of metamorphic water and deeply circulated meteoric water. Sulfur isotope analysis shows that sulfur of volcanic–sedimentary period is mainly formed from thermochemical sulfate reduction of seawater sulfate, while sulfur of the magmatic–hydrothermal period reveals a mantle-derived source. The metamorphic quartz diorite yields a zircon U–Pb age of 398.9 ± 6.2 Ma (MSWD = 0.31). Combining with the available data, we conclude that the Fe orebodies formed from 413 to 399 Ma. The geological and geochemical evidence presented in this paper suggest that the Qiaxia deposit was initially a volcanic–sedimentary Fe deposit, which was overprinted by a later skarn Cu mineralization, and finally underwent greenschist-facies metamorphism.

The North Qilian Orogen in NW China hosts several commercial quality serpentine jade deposits, although nephrite jade has not so far been reported from this region. Here, we investigate a green nephrite (tremolite) jade from Yushigou ophiolite suite in the North Qilian orogen. We present results from petrographic, scanning electron microscopy (SEM), X-ray diffraction, Electron microprobe analyses (EMPA) and zircon U-Pb geochronological studies to characterize the nephrite jade and its genetic setting. Our results suggest that the high-quality green nephrite jade is predominately composed of tremolite and actinolite, with transformation to actinolite with increasing of Fe and Cr, together with minor chlorite, calcite, magnetite, and titanite. In contrast, the serpentine jade consists mainly of antigorite with minor magnesite, talc, calcite, magnetite, chromite, and apatite. Zircon U-Pb dating yields a lower intercept age of 500 ± 12 Ma, representing the formation age of the Yushigou ophiolite. A few young zircon grains yield a weighted mean age of 227.9 ± 5.3 Ma, which is interpreted to represent the crystallization age of the tremolite, in response to the tectonics associated with late Paleo-Tethys to early Neo-Tethys. Accordingly, we propose that the host serpentinites in this region formed within a Late Cambrian supra-subduction zone through water-rock interaction, involving Ca-rich and COH-bearing fluid systems. The Ca- or COH-bearing fluids released from mantle-derived magma, and then migrated to higher levels during late metamorphic-metasomatic processes in the Mesozoic, finally generating the nephrite jade. Moreover, our study also provides insights into the tectonic processes associated with the formation of jade within subduction zone settings.

The Palaeoproterozoic Kerry Road deposit is one of the oldest examples of volcanogenic massive sulfide (VMS) mineralization. This small VMS deposit (~500,000 tons grading at 1.2% Cu, 3.5% Zn) is hosted in amphibolite facies mafic-siliciclastic units of the c. 2.0 Ga Loch Maree Group, Scotland. Sulfide mineralization consists of pyrite and pyrrhotite with subordinate chalcopyrite and sphalerite, occurring in disseminated, vein and semi-massive to massive textures. The deposit was highly deformed and metamorphosed during the c. 1.8–1.7 Ga Laxfordian Orogeny. Textural relationships of deformed sulfide minerals, related to early Laxfordian deformation (D1/D2), indicate initial high pressure-low temperature (100 MPa, 150 °C) conditions before reaching peak amphibolite facies metamorphism, as evident from pyrrhotite crossing the brittle/ductile transition prior to chalcopyrite. Late Laxfordian deformation (D3/D4) is marked by local retrograde greenschist facies at low pressure and temperature ( Microprobe analyses of amphiboles record evidence of the original alteration halo associated with the Kerry Road deposit, with a systematic Mg- and Si- enrichment from ferrotschermakite (~150 m) to Mg-hornblende (~90 m) to actinolite (0 m) on approach to the VMS deposit. Furthermore, whole rock geochemistry records a progressive enrichment in Si, Cu, Co, and S, and depletion in Al, Ti, V, Cr, Y and Zr with proximity to the VMS system. These elemental trends, together with amphibole geochemistry, are potentially useful exploration vectors to VMS mineralization in the Loch Maree Group, and in similar highly deformed and metamorphosed terranes elsewhere.

The Zaghar and Sarabadan copper-(gold) deposits are located in the northern part of the Urumieh-Dokhtar magmatic belt. Mineralization occurred in contact of the post-Eocene diorite-tonalite stocks with the upper Triassic-Jurassic shale and sandstone series in the Zaghar, and lower Eocene volcanic and pyroclastic rocks in the Sarabadan. Based on field observation and mineralogical studies, three stages of mineralization can be distinguished: (1) prograde skarn; (2) retrograde skarn; and (3) supergene stages. The prograde skarn is characterized by association of andradite, diopside, cordierite, and minor actinolite. The retrograde skarn stage is divided into two sub-stages: (1) retrograde skarn I; and retrograde skarn II. The retrograde skarn I, is marked by deposition of the main alteration minerals (e.g., tremolite, actinolite, chlorite, epidote), magnetite, ilmenite, pyrrhotite, pyrite, barite, and small amount of other sulfide minerals. The retrograde skarn II or quartz-sulfide-carbonate stage, is characterized by quartz and calcite vein-veinlets associated with Cu-Au mineralization. The supergene stage is marked by Fe oxy-hydroxides, covellite, malachite, azurite, and minor clay minerals and calcite. Ore-forming fluids associated with the quartz, calcite, and sphalerite from the retrograde II stage of mineralization is represented by LVS fluid inclusions with the temperature of 218–512 °C and salinity of 6.73–59.09 wt% NaCl, and LV type fluids with the temperature of 130–215 °C and salinity of 1.70–30.00 wt% NaCl equivalent. Stable isotope analysis of quartz yielded values of −85.30 to −60.70 δD‰, and +7.82–9.60‰ δ18Ofluid, indicating that the ore-forming fluids were mainly magmatic fluids with some contributions from meteoric waters. The δ34S values of pyrite vary from +4.90–8.10‰, demonstrate that the sulfur in deposit was probably originated from the magma. The geological and geochemical features introduce the Zaghar and Sarabadan as Cu-(Au) skarn deposits are related to the magmatic-hydrothermal activity of diorite stocks within continental magmatic arc.

The Aqishan deposit, located in the Eastern Tianshan, Xinjiang, China, is a newly discovered large-scale Zn-Pb deposit with a proven reserve of 1.94 Mt Pb and Zn metal at an average grade of 1.05%. The Zn-Pb orebodies are tabular and lentoid in shape, developed within skarnized carbonates and calcareous volcanoclastic rocks of the Yamansu Formation. The skarn mineral assemblages are characterized by abundant garnet, epidote, chlorite, actinolite, calcite and quartz, with minor amounts of pyroxene. Metallic minerals, comprising sphalerite, galena, chalcopyrite, pyrite, pyrrhotite and arsenopyrite, mainly occur as disseminations and irregular patches within the skarn. Re-Os dating of five syn-ore stage pyrite samples yielded an isochron age of 301 ± 13 Ma, which is in agreement with the 306 ± 2.8 Ma age obtained from the granodiorite porphyry occurring at southeast part of the Aqishan Zn-Pb deposit. The eHf(t) values of zircon from the granodiorite porphyry vary from + 9.62 to + 14.69, suggesting a juvenile crust source. The δ34 SV-CDT values of 22 sulfide samples range from −11.6‰ to −2.76‰, with an average of −5.08‰. The 206Pb/204Pb, 207Pb/204Pb and 208Pb/204Pb ratios of 9 sulfide samples range from 18.102 to 18.336, 15.539 to 15.655, and 37.929 to 38.479, respectively, which are similar to the Carboniferous grantoids of the Aqishan area and partly overlap with the volcanoclastic rocks of the Yamansu Formation. Based on these data, we propose that the Aqishan deposit formed from magmatic-hydrothermal fluids that emanated from the granodiorite porphyry. Much of the metals were derived from the magmatic intrusions with minor contributions from the volcanoclastic rocks, whereas the sulfur may have been mainly extracted from the country rocks with slight contributions from a magmatic source. The close genetic relationships between the Carboniferous magmatism and skarn type Zn-Pb mineralization in the Aqishan area as well as other deposits in the region suggests a great potential of finding more analogous deposits in the Eastern Tianshan, where carbonates or calcareous volcanoclastic rocks and plutons that related to the subduction of the Northern Tianshan Oceanic slab beneath the Yili-Central Tianshan Terrane during Late Paleozoic are well-developed.

The Chagangnuoer magnetite deposit in western Tianshan (NW China) is hosted by submarine volcanic rocks and marble lens, with a resource of >220 Mt Fe at 38 wt%. Two major orebodies FeI and FeII are current in production. Pervasive garnet skarn, magnetite, actinolite–epidote, and marble zones are developed at Chagangnuoer. Paragenetic sequences are divided into garnet–pyroxene (I), magnetite–pyrite ± chalcopyrite (II), actinolite–epidote–K-feldspar (III), garnet ± tremolite ± scapolite (IV), magnetite ± hematite (V), actinolite–epidote (VI), and sulfide–calcite–quartz (VII) stages. A diorite beneath the FeII and a granodiorite with skarn alteration have zircon U-Pb ages of 329 ± 2 and 317 ± 4 Ma, respectively. These intrusions have high potassic to shoshonitic, metaluminous affinities, and significant Nb, Ta, Ti and Sr anomalies. Stage II magnetite has δ18OV-SMOW compositions of 1.9–3.5‰, higher than Stage V magnetite (0.5–2.1‰), indicating a hydrothermal fluid source of magmatic origin. The δ18O values of garnet, actinolite, epidote and quartz range from 4.1 to 12.2‰. Stage VII calcite has δ13CV-PDB of −2.0 to −0.8‰ and δ18O of 8.9 to 9.9‰, lower than for the marble (average δ13C + 2.3‰, δ18O 12.8‰). δ34SV-CDT compositions for pyrite and chalcopyrite from Stages II and VII vary between 0.8 and 13.1‰. The isotopic compositions imply that minor non-magmatic sources (e.g., marine carbonate, seawater, and meteoric water) have been circulated into hydrothermal fluids producing the skarn alterations and associated iron mineralization. The early-stage skarn alteration and main Fe mineralization relate to the emplacement of diorite stock at depth, whereas the late-stage skarn-magnetite assemblages are intimately associated with the granodiorite. The Chagangnuoer deposit is concluded to be magnetite skarns formed by magmatic-hydrothermal fluids that emanated from the dioritic and granodioritic magmas intruding above a sub-arc mantle wedge and that metasomatized intensely with the Carboniferous andesitic-rhyolitic volcanic rocks and carbonate.