LA-ICPMS Analyses Research Articles

Arsenocolusite in Pyrite Ores of the Saum Copper–Zinc Massive Sulfide Deposit, North Urals

Pyrite ores on the flanks of the Saum copper–zinc massive sulfide deposit are clastic sediments intensely transformed under conditions of acid diagenesis. Colusite in ores is confined to fine-grained pyrite clasts, which are rimmed by later small-crystalline pyrite aggregates. Colusite forms fine dissemination (1–3 µm) and large isometric grains (up to 50–100 µm), contains inclusions of sulvanite, and belongs to arsenocolusite in chemical compositions (wt %): 12.62–14.87 As, 0.19–0.64 Sb, 0.29–1.46 Sn, 3.05–3.23 V, and 1.51–3.20 Fe. The LA ICP MS analysis of fine-grained pyrite revealed minor Ga, Ge, In, and Se contents in composition of arsenocolusite, which are correlated with chemical elements of colusite according to isomorphous substitutions in its formula. Galena, tellurobismuthite, native gold, molybdenite, rutile, monazite, uraninite, and Ba-bearing muscovite are found in fine-grained pyrite in assemblage with colusite. Interaction of sulfide sediments with seawater led to their enrichment in seawater elements (V, Mo, and U) and the deposition of colusite in assemblage with molybdenite and uraninite from trace element-rich diagenetic fluids under their dehydration.

In situ geochemistry and Fe–O isotopic composition of iron oxides from the Pha Lek Fe deposit, northwest Truong Son orogenic belt, Laos: implications for ore-forming processes

The Pha Lek Fe-polymetallic deposit in the southwest of the Truong Son orogenic belt records the evolution and metallogenesis of the southeastern Asia Tethys. Debates remain on the roles the Late Triassic volcanism played in the formation of the iron oxides of the deposit. Petrographic and SEM studies led to the recognition of two dominant iron oxides (magnetite and hematite) and three stages of mineralization (pre-ore, syn-ore, and post-ore stages). In situ LA–ICP–MS analyses for trace elements and Fe and O isotopic analyses were applied to understand the origin of the iron oxides. Generally, iron oxide of the syn-ore stage has higher total trace elements than post-ore stage, and magnetite has higher lithophile elements, whereas hematite has higher chalocophile elements. The trace-element abundance in magnetite is most comparable to porphyry-skarn-hydrothermal magnetite, and hematite is more comparable to supergene and secondary, non-magmatic hydrothermal chemistry. All δ56Fe values of the iron-oxide separates are above 0‰ and have an igneous signature, and syn-ore stage magnetite has relatively higher δ56Fe values than the post-ore stage hematite. All δ18O values of the iron-oxide separates are below 1‰ and plot within the non-igneous field, and show a similar decreasing trend from syn-ore stage magnetite to post-ore stage hematite. We propose that the Triassic volcanic activities played a limited role during the mineralization process; the deposit was formed because of the Late Carboniferous–Early Permian, porphyry-skarn-related, magmatic hydrothermal alteration; and the mixing of non-magmatic fluid and/or the supergene weathering caused the wide reprecipitation of Fe oxides. An evolutionary mineralization model related to the low-angle subduction for the deposit is also proposed.

Toward a comprehensive study for multielemental quantitative LA-ICP MS bioimaging in soft tissues

Quantitative localization of metals in biological tissue sections is critical to obtain insight into metal toxicity mechanisms or their beneficial characteristics. This study presents the development of a quantitative LA-ICP MS bioimaging methodology based on the polymer film strategy and internal standardization. To maximize the number of elements mapped, an aqueous soluble polymer (dextran) was selected. Among the elements studied, the great majority (eight out eleven), i.e., Co, Ni, Cu, Zn, Se, Mo, Cd and Pt, exhibited linear regression after LA-ICP MS analysis of metal-spiked polymer standards. Methodology performances were carefully assessed as a function of the three internal standards (In, Rh and Ir) considered, the analytical operational conditions (ICP power, addition of O2 to ICP, and laser fluency) and the thickness of the biological tissue section. The results indicated that three groups (Co, Mo; Ni, Cu, Pt; and Zn, Se, Cd) of elements could be distinguished from their analytical response as a function of analytical conditions and the internal standard. These different element behaviors appeared to be mainly First Ionization Potential dependent (FIP). For elements with lower FIP (Co, Ni, Cu, Mo and Pt), differential responses due to carbon load in the ICP MS plasma could be efficiently corrected as a function of analytical conditions. Matrix effects were more pronounced for higher FIP elements (i.e., Zn, Cd and Se), and analysis of <10-μm thin sections without the addition of O2 to ICP MS plasma is recommended. LODs are in the range of 0.1–0.5 μg g−1 for Co, Mo, Cu, Ni, Pt and Cd as well as 0.9 and 1 μg g−1 for Zn and Se, respectively. The methodology was validated by means of a homemade metal-spiked kidney homogenate analyzed by LA-ICP MS imaging, and Co, Ni, Cu, Mo, and Pt provided the closest concentrations (5–29% bias) to the target values determined by ICP MS after mineralization. The methodology was applied to two types of clinical human samples undergoing different sample preparation protocols that did not affect internal standard homogeneity in the polymer film. This methodology is the first reported for the quantitative bioimaging of eight elements simultaneously.

Thermal regime reconstruction and fluid inclusion LA–ICP–MS analysis on intermediate-sulfidation epithermal Pb–Zn veins: Implications for porphyry Cu deposits exploration in the Xianhualing District, Anhui, China

The Xianhualing District at Jinzhai in the northern Dabie Orogen, China, is a significant area for Pb–Zn–Cu–Au polymetallic exploration. The main rocks in the area are mica–quartz schist of the Neoproterozoic Foziling Group, and magmatic rocks which are controlled by two sets of faults striking NNE and NW. Recent drilling has revealed that the orebody occurs mainly in mica–quartz schist in the form of breccia and veinlets. Major ore minerals include pyrite, sphalerite, galena, chalcopyrite, magnetite, gold, silver, and silver sulfosalts, with alteration assemblages of predominantly quartz, sericite, calcite, and chlorite. Three types of fluid inclusions occur in quartz–sulfide vein samples collected from eight drill-holes: two-phase liquid-rich inclusions (type I), two-phase vapor-rich inclusions (type Ⅱ), and halite-bearing inclusions (type III). Microthermometric studies of type I and Ⅱ fluid inclusions indicate homogenization temperatures of 161–378 °C and salinities of 0.5–7.8 wt% NaCl equivalent. Fluid inclusion microthermometric data and mineralization and alteration characteristics indicate an intermediate-sulfidation epithermal environment. Current exploration is focused on the location of potential deep porphyry mineralization associated with epithermal mineralization. In this study, 28 drill-core samples from different levels were selected for fluid inclusion microthermometry to elucidate fluid-evolution pathways and hence to determine the likelihood of porphyry bodies. The consistent fluid inclusion petrography, distribution patterns, and fluid-evolution trends indicate that the deeper part of the Dongchong area may have been the regional thermal center of fluid flow. The estimated mineralization depths of type III fluid inclusions are in the range 0.4–1.5 km, indicating a relatively shallow formation. Fluid chemical compositions obtained from single-inclusion laser-ablation–inductively coupled plasma–mass spectrometry (LA–ICP–MS) analyses support the occurrence of a single magmatic–hydrothermal fluid source, which has a degree of mixing with meteoric water and a small amount of basinal brines during the migration path, and the fluid evolution pattern agrees well with the fluid inclusion mapping result. Quartz-vein hosted fluid inclusions contain significant amounts of Pb, Zn, and Cu, indicating good exploration prospects for porphyry Cu mineralization at depth.

Occurrence of Liddicoatite-Bearing LCT Pegmatites in Sirohi Region, Northwest India and their Rare Metal Potentiality

Rare and trace element study of pegmatites around Sibagaon area of Sirohi region, Rajasthan, India revealed that the pegmatites are of rare element class and LCT (Li–Cs–Ta) type. Rare metal concentration in these pegmatites is notably high against crustal abundance, with Li ranging from 1007 to 10785 ppm, Rb from 1285 to 9147 ppm, Cs from 36 to 1142 ppm, Ta from 12 to 386 ppm, Sn from 54.22 to 2283.61 ppm and F from 2724 to 48,275 ppm. Integration of EPMA and LA-ICPMS analyses indicated that the main Li-bearing mineral in pegmatites is lepidolite with Li ranging from 21,599 to 28,178 ppm, which is economically worthwhile to process for Li, followed by elbaite and rare mineral liddicoatite, which has not been reported so far in India. Rare earth element (REE) distribution pattern shows enrichment of LREEs than HREEs, indicating that pegmatites are fractionated and thus causing enrichment of rare metals. This reporting of liddicoatite-bearing LCT pegmatites from Sirohi region with high anomalous values of rare metals can therefore be a good prospect for rare metal exploration in India in the present economic scenario. These pegmatites have indicated a syn-collisional signature and may be related to the accretion of Marwar craton with greater Indian land mass along the Phulad Shear zone.

Geology and geochronology of the super-large Bailongshan Li–Rb–(Be) rare-metal pegmatite deposit, West Kunlun orogenic belt, NW China

The Bailongshan pegmatite deposit is a newly discovered super-large Li–Rb–(Be–Ta–Nb) rare-metal deposit in the West Kunlun orogenic belt, northwest China. Fifty-two rare-metal orebodies (50–1230 m long by 1.5–157 m wide) have been discovered by detailed field surveying, making up a metallogenic field that is larger than 8250 × 400 m. The deposit is estimated to have ore reserves of more than 5.06 million tonnes (t) Li2O, 160,020 t BeO, 316,200 t Rb2O, 40,060 t Nb2O5, and 10,750 t Ta2O5. Pegmatite dikes are zoned around a granodiorite batholith, ranging from barren through orebodies rich in Be, Nb, Ta, Rb, and Li with increasing distance from the batholith, similar to the classical model of a zoned Li–Ce–Ta (LCT)-type pegmatite. LA–ICP–MS analyses of coltan and zircon yield 206Pb/238U ages of 208.1 Ma and 212.3 Ma, respectively, representing the emplacement ages of the pegmatites and granodiorite. These data indicate a temporal link between the emplacement of the granodiorite batholith and rare-metal mineralization in the pegmatites, and that the Bailongshan rare-metal pegmatites are temporospatially related to the granodiorite batholith. The Bailongshan pegmatites and other rare-metal pegmatite deposits in the West Kunlun orogenic belt likely make up a >600-km-long Li metallogenic belt, and further exploration for rare-metal pegmatites should be focused on the area adjacent to Late Triassic granitoid plutons in the belt. This belt likely extends to the East Kunlun and West Sichuan rare-metal belts, forming the >2000-km-long, Late Triassic West Kunlun–Songpan–Garzê rare-metal metallogenic belt.

Host minerals of Li–Ga–V–rare earth elements in Carboniferous karstic bauxites in southwest China

The Carboniferous karstic bauxite-bearing rock series in central Guizhou Province in southwest (SW) China is rich in trace elements, particularly Li, Ga, V, and rare earth elements (REEs), which have potential for comprehensive utilization as independent deposits or associated resources. However, the host minerals of Li, Ga, V, and REEs are not well-constrained because the sedimentary rocks are characteristics by complex mineral composition and fine mineral particles. This situation considerably hinders the compressive utilization of these trace elements in bauxite. Herein, laser ablation–inductively coupled plasma–mass spectrometry (LA–ICP–MS) was successfully applied to element geochemistry analysis of hydrous minerals (diaspore/boehmite, kaolinite, and illite) in karstic bauxite samples, based on the principle that laser ablation data of all oxides were normalized to the sum of 100% minus the total volatile components of the mineral chemical formula. The analysis showed signal stabilization. Results indicated that the bivariate plots of selected elements had characteristics similar to statistical results of whole-rock samples from global bauxites, thereby indicating that the LA–ICP–MS analysis data were reliably but artificially herein. Combined with whole-rock geochemistry studies, the analysis results revealed that smectite may be the main host minerals of Li. Furthermore, Ga was enriched in diaspore/boehmite; V was mainly enriched in iron-bearing minerals, particularly chlorite; and REE-independent minerals, such as monazite, were the main host minerals of REEs in the Carboniferous karstic bauxite in SW China. This study contributed to the knowledge on the use of in-situ method for the element geochemistry investigation of hydrous minerals and sedimentary rocks.

In-situ major and trace element chemistry of melanite from Tieshan Fe–Cu skarn deposit, Hubei Province, Eastern China: Implications for hydrothermal fluid evolution

The Tieshan Fe–Cu skarn deposit is located in the Edong ore district, the largest ore district of the Middle–Lower Yangtze River Metallogenic Belt (MLYRMB) in Eastern China. The Fe–Cu mineralization is spatially associated with the Tieshan pluton, which intruded the carbonates of the Lower Triassic Daye Formation. The orebodies are predominantly hosted along the intrusive contact zone between the (quartz)-diorite and (dolomitic)-marble. EMPA analysis shows that the Tieshan garnets belong to high-Ti andradite, with TiO2 contents ranging from 0.03 to 2.59 wt%, and is designated as melanite. The melanite contains low Na content, suggesting the absence of Na+-REE3+ coupled substitution. LA–ICP–MS analysis shows high total LREE (∑LREE), low ∑HREE and positive Eu anomalies, suggesting high fO2 and rapid growth of the melanite. Compared with other Ti-rich garnets worldwide, the Tieshan melanite grains are more Al-rich and Si-rich, and shows negative SiO2 vs. TiO2 correlation, which suggests predominant Ti-substitution in the tetrahedral site. The more positive Eu anomalies and higher percentage of andradite are present in the rim (than in the core), indicating lower salinities and higher fO2 of the late-stage ore-forming fluid. The magmatic-hydrothermal fluid source of these garnets supports the metasomatic ore genesis at Tieshan.

The origin and evolution of V-rich, magnetite dominated Fe-Ti oxide mineralization; Northwest River Anorthosite, south-central Labrador, Canada

Zones of massive to semi-massive Fe-Ti oxide mineralization are present in the Northwest River Anorthosite, a ca. 1625-Ma Paleoproterozoic massif-type anorthosite located in the Grenville Province of south-central Labrador. The oxide mineralization is predominantly composed of coarse to very-coarse grained V-rich magnetite with less abundant coarse granular ilmenite and pleonaste that formed by exsolution from the primary, chemically impure magnetite; all observed oxide minerals have complex and abundant subsolidus reequilibration and exsolution textures. Using petrography, oxide mineral chemistry, whole-rock geochemistry, and oxide-anorthosite field relationships, a three-process model is proposed for the formation of the oxide mineralization: (1) late-stage magmatic crystallization of impure magnetite; (2) concentration of Fe-Ti oxides via solid-state remobilization; and (3) reequilibration during subsequent post-emplacement cooling and Grenvillian metamorphism. These subsolidus processes significantly modified the primary magmatic composition of the magnetite through exsolution and reequilibration. Results from in-situ magnetite EPMA and LA-ICPMS analyses were plotted on magnetite mineral chemical discrimination diagrams. The data display a wide spread and typically do not plot exclusively in the expected anorthosite-hosted Fe-Ti-V magnetite fields. This is most likely due to modification of magnetite chemistry during subsolidus cooling and reequilibration. As such, care must be taken when using magnetite discrimination diagrams for Fe-Ti-V deposits given the complex petrogenetic histories that magnetite within these types of deposits experience.

Ore-formation mechanism of the Weilasituo tin–polymetallic deposit, NE China: Constraints from bulk-rock and mica chemistry, He–Ar isotopes, and Re–Os dating

China’s W–Sn resources are dominant on a global scale. A series of Sn–polymetallic deposits has been found in recent years at depth on the flanks of known volcanic–subvolcanic Cu–Pb–Zn–Ag deposits in the Southern Great Xing’an Range, NE China. The large-scale Weilasituo tin–polymetallic deposit, formed at the depth of the Weilasituo Cu–Zn deposit, is most typical of these types of deposit. Tin–polymetallic orebodies are hosted in the early Paleozoic Xilingol Complex, and their mineralization is closely related to Early Cretaceous quartz porphyry. In this contribution, bulk-rock and mica chemical compositions, Re–Os geochronology, and He–Ar isotopic analyses are described in addressing the ore-formation mechanism of the deposit. Geochemical characteristics indicate that the ore-bearing quartz porphyry corresponds to the I-type granite serie. Five types of mica have been identified in the study area based on detailed petrography and EPMA and LA–ICP–MS analyses: (i) early magmatic Fe–Li mica in albitized quartz porphyry; (ii) late magmatic Fe–Li mica in mineralized quartz porphyry; (iii) hydrothermal Fe–Li mica in a cryptoexplosive breccia pipe (distributed around breccia fragments); (iv) Fe–Li mica in quartz veins; and (v) Fe–Li mica in plagioclase gneiss (wall rock). Magmatic zinnwaldite from the upper mineralized part of the quartz porphyry is enriched in Nb (100–160 ppm) and Ta (100–150 ppm). Hydrothermal zinnwaldite from the explosive breccia, quartz veins, and surrounding gneiss is unusually rich in Mg (up to 3.4 wt% MgO) and Sn (up to 200 ppm). 3He/4He ratios of the Weilasituo tin–polymetallic and Cu–Zn deposits are in the ranges 3.38–4.91 Ra and 4.8–4.9 Ra, respectively, indicating ore-forming fluids sourced from mixed crustal and mantle materials. Molybdenite Re–Os dating of W mineralization yielded an isochron age of 129.0 ± 4.6 Ma, similar to the porphyry crystallization and mineralization ages of the Weilasituo tin–polymetallic deposit, and also consistent with the mineralization age of the Cu–Zn deposit. We propose a new metallogenic model, with all subtypes of W–Sn–Cu–Pb–Zn–Ag mineralization in the Weilasituo area belonging to a single complex metallogenic system. Compared with other ore districts, ore-related granitoids in the Southern Great Xing’an Range display relatively uniform emplacement ages and were derived from partial melting of juvenile lower crust rather than old basement. Their ore-forming fluid source was greater influenced by mantle fluids than which found in South China.

The Fate of Platinum-Group Minerals in the Exogenic Environment—From Sulfide Ores via Oxidized Ores into Placers: Case Studies Bushveld Complex, South Africa, and Great Dyke, Zimbabwe

Diverse studies were performed in order to investigate the behavior of the platinum-group minerals (PGM) in the weathering cycle in the Bushveld Complex of South Africa and the Great Dyke of Zimbabwe. Samples were obtained underground, from core, in surface outcrops, and from alluvial sediments in rivers draining the intrusions. The investigations applied conventional mineralogical methods (reflected light microscopy) complemented by modern techniques (scanning electron microscopy (SEM), mineral liberation analysis (MLA), electron-probe microanalysis (EPMA), and LA-ICPMS analysis). This review aims at combining the findings to a coherent model also with respect to the debate regarding allogenic versus authigenic origin of placer PGM. In the pristine sulfide ores, the PGE are present as discrete PGM, dominantly PGE-bismuthotellurides, -sulfides, -arsenides, -sulfarsenides, and -alloys, and substantial though variable proportions of Pd and Rh are hosted in pentlandite. Pt–Fe alloys, sperrylite, and most PGE-sulfides survive the weathering of the ores, whereas the base metal sulfides and the (Pt,Pd)-bismuthotellurides are destroyed, and ill-defined (Pt,Pd)-oxides or -hydroxides develop. In addition, elevated contents of Pt and Pd are located in Fe/Mn/Co-oxides/hydroxides and smectites. In the placers, the PGE-sulfides experience further modification, whereas sperrylite largely remains a stable phase, and grains of Pt–Fe alloys and native Pt increase in relative proportion. In the Bushveld/Great Dyke case, the main impact of weathering on the PGM assemblages is destruction of the unstable PGM and PGE-carriers of the pristine ores and of the intermediate products of the oxidized ores. Dissolution and redistribution of PGE is taking place, however, the newly-formed products are thin films, nano-sized particles, small crystallites, or rarely µm-sized grains primarily on substrates of precursor detrital/allogenic PGM grains, and they are of subordinate significance. In the Bushveld/Great Dyke scenario, and in all probability universally, authigenic growth and formation of discrete, larger PGM crystals or nuggets in the supergene environment plays no substantial role, and any proof of PGM “neoformation” in a grand style is missing. The final PGM suite which survived the weathering process en route from sulfide ores via oxidized ores into placers results from the continuous elimination of unstable PGM and the dispersion of soluble PGE. Therefore, the alluvial PGM assemblage represents a PGM rest spectrum of residual, detrital grains.

Characterization of uraninite using a FIB–SEM approach and its implications for LA–ICP–MS analyses

Focused ion beam (FIB) coupled with scanning electron microscopy (SEM) investigations were performed on pristine and altered areas of two uraninite samples in order to better understand their 3-dimensional mineralogical and chemical nature, and their impact on trace element abundances obtained by laser ablation inductively coupled plasma mass spectrometry (LA–ICP–MS) analyses. Trace element contents determined by both LA- and solution mode (SM)–ICP–MS analyses together with FIB results identify Pb as the optimal internal standard for LA–ICP–MS analyses of uraninite since it is a major chemical constituent, part of the structure, and similar in abundance to the trace elements of interest.

Ore genesis of the Bake gold deposit, southeastern Guizhou province, China: Constraints from mineralogy, in-situ trace element and sulfur isotope analysis of pyrite

The Bake gold deposit is exceptional for its high native gold abundance relative to the other orogenic gold deposits in the southeastern Guizhou district. The grades of gold can be up to 2 to 3 wt% in bonanza ore, and native gold preferentially occurs within voids and fractures in pyrite, arsenopyrite and quartz. Gold content can be up to 6.9 ppm in hydrothermal pyrite, however, the majority of the pyrite analyses have Au contents less than 1 ppm (mean = 0.32 ppm) based on LA-ICPMS analyses. Meanwhile, EMPA reveals that arsenopyrite has a maximal Au content of up to 0.14 wt%, but most analyses are below detection limit (0.01 wt%). Moreover, native gold grains in cataclastic pyrite and arsenopyrite are commonly high-purity with fineness ranging from 949 to 977. Given that paragenetically early hydrothermal pyrite and arsenopyrite contain variable but relatively high gold concentrations than later generations of sulfide, it is suggested that early invisible gold may have been remobilized to form at least part of the microscopic visible gold. Post-mineralization shear zones, which cut the vein-bearing anticline, may have led to the deformation of the lode quartz vein system on the macro level, and microscopically, sulfide fragmentation and elemental remobilization. Although diagenetic pyrite from unaltered host rocks is enriched in invisible gold with mean values at 0.83 ppm, evidence supporting the release of Au from them is weak. Corresponding evidence comes from the distinct sulfur isotope signatures in different pyrite generations. Diagenetic pyrite has δ34S values in the narrow range of +9.27‰ to +10.75‰, whereas hydrothermal pyrite shows a broad range (+6.81‰ to +17.42‰), based on LA-MC-ICPMS analyses. The Mesoproterozoic Lengjiaxi Group underlying the Xiajiang Group is most likely the source region, on the basis of geological background and assuming the metamorphic devolatilization model.

Ancient Biographies: Trace Element Analysis to Investigate Provenance and Transportation Mechanisms of Late Bronze Age Glass

LA-ICPMS analysis was carried out on a scaraboid blue glass bead (Hunterian Museum Glasgow, D.1921.39) excavated from Tomb 27 in Gurob, in the Southern Fayum region of Egypt. Gurob is known to have been the site of a palace established in the reign of Tuthmosis III (1479-1425 BC). The tomb was located at the northernmost point of the New Kingdom cemetery and was undisturbed, containing the remains of seven females and two children, and was dated by the excavators to between the reigns of Amenophis I (1525-1504 BC) and Tuthmosis III. The glass scarab was coloured by copper and trace element values of La, Cr, Ti and Zr exhibited compositional consistency with glasses from Mesopotamia, rather than from Egypt. Therefore, the glass scarab represents a rare example of Mesopotamian glass to be discovered in Egypt, in addition to being some of the earliest glass found. The finds support iconographic references in the Hall of the Annals at Karnak to the import of early glass into Egypt. The implication is that these beads represent luxury items transported into Egypt by high-ranking foreign women perhaps in connection with the Gurob harem palace.

Ore-Forming Processes at the Xiajinbao Gold Deposit in Eastern Hebei Province: Constraints from EPMA and LA-ICPMS Analysis

The Xiajinbao gold deposit is located at the northern margin of the North China Craton. Hydrothermal pyrites belonging to three stages were identified: Py1; Py2; and Py3. Geochemical study of these pyrites was conducted using electron probe microanalysis and laser ablation inductively coupled plasma mass spectrometry to investigate the distributions of minor and trace elements, constrain pyrite genesis, and to obtain an improved understanding of the ore-forming processes. Py1 and Py2 contain high concentrations of Au and are interpreted to have been deposited from fluids from a dominantly magmatic source. Py3 grains have the lowest Co/Ni ratios. All generations of pyrite were deposited by mixing of meteoric waters with magmatic-hydrothermal fluids. Boiling of early ore-forming fluids led to the precipitation of Py1 and gold. Decreasing fO2 in the ore-forming system resulted in the formation of Py2 and gold. Fluid mixing was the dominant controlling factor for the precipitation of Py3 together with small amounts of gold.

Age and Sources of Metasandstone of the Chiney Subgroup (Udokan Group, Aldan Shield): Results of U–Th–Pb Geochronological (LA–ICP–MS) and Nd Isotope Study

Results of U–Th–Pb LA–ICP–MS analysis of detrital zircons from metasandstones of the Chiney Subgroup (Udokan Group, Aldan Shield) have been obtained. It has been revealed that rocks of the Paleoproterozoic (about 1.90, 1.98, and 2.50 Ga) and Neoarchean (2.55 and 2.72 Ga) were their provenance sources. Deposition of the Chiney Subgroup occurred in the interval 1.87–1.90 Ga and was separated in time from the accumulation of the Kodar Subgroup siliciclastics (2.1–2.3 Ga).

The 920–900 Ma Bahia-Gangila LIP of the São Francisco and Congo cratons and link with Dashigou-Chulan LIP of North China craton: New insights from U-Pb geochronology and geochemistry

A widespread mafic sill and dyke unit (the Pedro Lessa suite) adjacent to the southeastern São Francisco (SF) craton (eastern South America) is dated as 940 ± 42 Ma, 912 ± 17 Ma, and 986 ± 64 Ma (based on combined ID-TIMS and LA-ICPMS analyses on baddeleyite grains) on the Santa Maria de Itabira gabbroic intrusion. These ages suggest membership in the previously defined ca. 920–900 Ma Large Igneous Province (LIP) (herein referred to as the Bahia-Gangila LIP) of the reconstructed São Francisco and formerly adjacent Congo craton (Africa). Additional mafic and felsic units throughout the SF craton are also linked (based on a literature review), thus expanding the size of the reconstructed LIP to ca. 1,500,000 km2. Geochemistry reveals high Ti OIB signature for most units and low Ti E-MORB composition for the Gangila flood basalts, marking the initiation of attempted ocean opening. Geochemistry of the Bahia-Gangila LIP is also compared with the ca. 920–900 Ma Dashigou-Chulan LIP of the North China craton, and implications for three possible reconstructions of SF/Congo craton with the North China craton are considered.

Geochemical, zircon U–Pb–Hf, and whole‐rock Sr–Nd isotopic study of Late Jurassic Sanming A‐type granite in the Wuyi area, Fujian province, Southeast China

The Sanming pluton is the only Late Jurassic A‐type granitic intrusion in the Wuyi area, west Fujian Province, Southeast China, and its formation has important implications for our understanding of the tectonic evolution of the region. The U–Pb ages of 157 ± 1 Ma and 159 ± 1.1 Ma were obtained for the pluton by zircon LA–ICP–MS analysis, which is interpreted to be the crystallization age of the Sanming pluton (i.e., Late Jurassic). The pluton has the geochemical characteristics of A‐type granite, such as high K2O+Na2O contents (average 7.703 wt%), FeOT/(FeOT + MgO) ratios (average 0.85), and high 10,000 Ga/Al values and Zr + Nb + Ce + Y (380–446.1 ppm, average 419.2 ppm) contents, but relatively low CaO, Sr, and Eu contents. Zircon saturation temperatures range from 875 °C to 890 °C, also similar to other A‐type granites. The (87Sr/86Sr)i ratios (0.707368–0.71102) and εNd(t) and εHf(t) values (−5.54 to −6.09, and −6.93 to −1.07, respectively), the 2‐stage Nd model ages of 1.50–1.55 Ga, and 2‐stage Hf model ages of 1.25–1.62 Ga, suggest the pluton was derived by extensive fractionation of melts containing both mantle materials and Mesoproterozoic crustal components. The Sanming A‐type granitic pluton is younger than adakitic rocks in the region (162 Ma), suggesting a localized transition from compressional to intraplate extensional tectonics at 162–159 Ma, with mantle‐derived material playing a crucial role in the formation of A‐type granites in the Wuyi Mountain area. This tectonic transition is explained by localized rollback of the subducting Pacific plate.

Platinum-group elements and gold in sulfide melts from modern arc basalt (Tolbachik volcano, Kamchatka)

Sulfide melt inclusions entrapped in primitive olivine phenocrysts can be used to understand the compositions of early sulfide melts that may ultimately contribute to magmatic sulfide ore deposits. Sulfide globules hosted in olivine (86–92mol% Fo) from the Tolbachik basalt (the 1941 eruption) are characterized in terms of their major and trace element abundances using electron microscopy and LA–ICP–MS analysis. Distribution of major elements within individual sulfide globules varies from homogeneous to heterogeneous. Phases include monosulfide solid solution (MSS) and intermediate solid solution (ISS) intergrowths and exsolved low-temperature minerals such as pyrrhotite, pentlandite, chalcopyrite and cubanite. Trace elements (platinum-group elements — PGE, Ag, Te, Au, Pb and Bi) are also present in solid solution in sulfide phases and as micron-sized particles (“nuggets”). Such nuggets of dominantly Au, Pt, Au–Pd and Pd–Te are contained randomly within sulfide matrices or, more commonly, at phase boundaries. Nuggets are also attached to outer surfaces of sulfide globules. Concentrations of PGE in sulfides follow a log normal distribution over four orders of magnitude. The highest measured noble metal concentrations in the analyzed globules (436ppm Au+PGE) are 13.3ppm Au, 115ppm Pt and 299ppm Pd, whereas 40% of globules have <15ppm of noble metals. Gold and PGE concentrations correlate, suggesting these elements were concentrated by the same process(es). We propose that a number of anomalous concentrations of one or several noble metals in the analyzed globules can be best explained by entrapment of Au–PGE-rich particles (solid or liquid) from the silicate melt. Although the individual Tolbachik sulfide globules have variable PGE abundances, their mean composition resembles those of major PGE-sulfide ore deposits (e.g., Norilsk, Sudbury, Platreef and Merensky Reef).

U–Pb detrital zircon ages from the Paleozoic Marbella Conglomerate of the Malaguide Complex (Betic Cordilleras, Spain). Implications on Paleotethyan evolution

The Marbella Conglomerate (Betic Cordilleras, SW Spain) is a poorly sorted and polymictic rock of vaguely constrained Late Carboniferous age interlayered within a sandy sequence. It contains variable amounts of pebbles of quartzite, gneiss, deformed granitoid, schist, aplite, dacite and other volcanic rocks among others, which makes it a potential target for detrital zircon provenance studies. In order to decipher provenance we combined U–Pb SHRIMP and LA–ICP-MS analyses on zircons obtained from single pebbles of deformed rocks (schist, granitoids) and detrital zircons from the sandy sequence, respectively. The age spectra of the detrital zircons indicates that at least the sedimentation took place soon after the start of the Permian according to the youngest detrital zircon age (≈286Ma), and it involved the denudation of terranes with rocks bearing Paleoproterozoic, Neoproterozoic, Cambro-Ordovician, Devonian and Carboniferous zircon age clusters. In contrast with the Permian age of the detrital zircons from the sandstones, igneous (ca. 532 and 516Ma) and metamorphic (ca. 356Ma) U–Pb SHRIMP Concordia ages were obtained from the pebbles. The different age clusters observed could be correlated to igneous, metamorphic and detrital rocks from an already eroded terrane similar to the Ossa-Morena Zone of the Iberian Variscan Belt. Therefore, we propose that most of the sedimentation of the Marbella Conglomerate took place along the western border of the Paleotethys at the north margin of Gondwana during the dismantling of the Variscan orogenic edifice and/or the Neotethys ocean opening and the birth of the Cimmerian ribbon continent.