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The fault-bounded Nashoba–Putnam terrane, a metamorphosed early Paleozoic, Ganderian arc/back-arc complex in SE New England, lies between rocks of Avalonian affinity to the southeast and middle Paleozoic sedimentary rocks, interpreted as cover on Ganderian basement, in the Merrimack belt to the northwest. U–Pb detrital zircon laser ablation inductively coupled plasma mass spectrometry analysis were conduced on six samples from the Nashoba terrane in Massachusetts and seven samples associated with the Merrimack belt in Massachusetts and SE New Hampshire to investigate their depositional ages and provenance. Samples from the Nashoba terrane yielded major age populations between ~560 and ~540 Ma, consistent with input from local sources formed during the Ediacaran–Cambrian Penobscot orogenic cycle and its basement rocks. Youngest detrital zircons in the terrane, however, are as young as the Early to Middle Ordovician. Six formations from the Merrimack belt were deposited between ~435 and 420 Ma based on youngest zircon age populations and crosscutting plutons, and yielded large ~470–443 Ma age populations. Three of these formations show only Gondwanan provenance. Three others have a mixed Gondwanan-Laurentian signal, which is known to be typical for younger and/or more westerly sedimentary rocks and may indicate that they are the youngest deposits in the Merrimack belt (late Silurian to early Devonian) and/or have been deposited in the equivalent of the more westerly Central Maine basin. Detrital zircon age populations from the Tower Hill Formation, along the faulted contact between the Merrimack belt and Nashoba terrane, are different from either of these tectonic domains and may indicate that the boundary is complex., Le terrane limité par des failles de Nashoba-Putnam, un complexe d’arc/arrière-arc métamorphisé gandérien du Paléozoïque précoce dans le sud-est de la Nouvelle-Angleterre, se trouve entre des roches ayant une affinité avalonienne au sud-est et des roches sédimentaires du Paléozoïque moyen, interprétées comme une couverture du socle gandérien, dans la ceinture de Merrimack au nord-ouest. Six échantillons provenant du terrane de Nashoba au Massachusetts et sept échantillons associés à la ceinture de Merrimack au Massachusetts et dans le sud-est du New Hampshire ont fait l’objet d’une analyse par spectrométrie de masse avec plasma à couplage inductif et par ablation par laser de datation U–Pb sur zircon détritique aux fins de l’examen de leurs âges sédimentaires et de leur provenance. Les échantillons provenant du terrane de Nashoba ont révélé des populations principalement âgées entre environ 560 et 540 Ma, ce qui correspond à la contribution des sources locales apparues durant le cycle orogénique édiacarien-cambrien de Penobscot et aux roches de son socle. Les zircons détritiques les plus récents dans le terrane remontent cependant seulement à l’Ordovicien précoce à moyen. Six formations de la ceinture de Merrimack se sont déposées à peu près entre 435 et 420 Ma selon les populations des âges les plus récents sur zircon et les plutons transversaux, et elles ont présenté de vastes populations âgées d’environ 470 à 443 Ma. Trois de ces formations témoignent uniquement d’une provenance gondwanienne. Trois autres évoquent de façon mixte le Gondwanien et le Laurentien, ce qui est reconnu comme un trait typique des roches sédimentaires plus récentes ou plus à l’ouest et qui pourrait révéler qu’il s’agit de dépôts plus récents dans la ceinture de Merrimack (du Silurien tardif au Dévonien précoce) ou qui se seraient mis en place dans l’unité équivalente du bassin plus occidental du centre du Maine. Les populations d’un âge sur zircon détritique de la Formation de Tower Hill le long de la zone de contact faillé entre la ceinture de Merrimack et le terrane de Nashoba diffèrent de l’un et l’autre de ces domaines tectoniques et pourraient indiquer que leur limite est complexe.

We present a U-Pb detrital zircon age and provenance study of a sequence of metasedimentary rocks in the northwestern Thor–Odin high-grade gneiss dome within the Omineca crystalline belt of the Canadian Cordillera. Despite strong overprint by deformation and metamorphism, we successfully analyzed the age and provenance of six samples collected at various structural levels, using U-Pb detrital zircon laser-ablation–inductively coupled plasma–mass spectrometry (LA-ICP-MS) analysis. The Thor–Odin dome consists of Paleoproterozoic basement and a metasedimentary cover sequence of previously unknown age and tectonic significance. Our results indicate that the oldest units of this sequence may be Paleoproterozoic, and some of the oldest known metasedimentary rocks in the Canadian Cordillera, originally deposited on top of Laurentian basement rocks. The youngest rocks are Devonian and deposited shortly before the onset of widespread Late Devonian to early Mississippian igneous activity in the Selkirk Domain or Kootenay arc. The cover sequence of the Thor–Odin dome thus preserves some of both the oldest and the youngest (meta)sedimentary rocks deposited between the formation of supercontinent Columbia and the onset of igneous activity and convergence that marked the beginning of Cordilleran deformation and metamorphism. Parts of as many as ∼1.4 b.y. of sedimentary history are preserved in the Thor–Odin dome, implying that much information on the sedimentary history of the Canadian Cordillera may be hidden in other Cordilleran gneiss domes.

The Late Neoproterozoic Greendale Complex, located within the Avalon terrane of Nova Scotia, is a suite of appinitic rocks ranging from ultramafic to felsic in composition that were intruded during regional ensialic arc magmatism and crystallized at shallow crustal levels under conditions of high pH 2 O. Amphibole is the dominant mafic mineral in ultramafic to mafic rocks and displays the extraordinary variability in texture and modal abundance that is characteristic of appinite suites. These features allow sensitivity of amphibole composition (major, trace and REE) to the evolution of water-rich magma to be investigated. All amphiboles in mafic and ultramafic rocks are calcic, with (Ca + Na) B ≥ 1.34 and Si IV between 6.1 and 7.3. They predominantly range in composition from tschermakite to magnesiohornblende and display a dominance of edenite (Na,K A + Al IV = Si IV ) substitution. Although each sample exhibits remarkably uniform Mg# over a wide range in Si of up to one formula unit, the mafic rock amphiboles are characterized by lower (0.5 to 0.7) Mg#, compared to the ultramafic rocks (0.7 and 0.9). REE profiles are bow-shaped, and are characterized by depletion in LREE (La/Sm ≈ 0.61), a slight depletion in HREE (Gd/Yb ≈ 1.55) as well as a negative Eu anomaly, which is attributed to co-precipitation of plagioclase. REE and trace element profiles of ultramafic amphiboles are divided into two groupings. Group A amphiboles occur in all specimens analyzed and their REE profiles are very similar to the whole-rock analyses of the mafic rocks and to those predicted from amphibole/melt partition coefficients. In contrast, Group B amphiboles display relative enrichment in light REEs (La/Sm ≈ 2.05), have lower ΣREE, and lack a negative Eu anomaly relative to Sm and Gd. Group B amphiboles are more enriched in Th and U and show a more pronounced depletion in Nb, Ti, Y and HREE. Group B amphiboles probably grew in a reaction relationship with olivine and pyroxene, and their contrasting profiles suggest that partition coefficients traditionally used for petrogenetic modeling may not be appropriate for such amphiboles. Groups A and B are virtually indistinguishable with respect to the major elements used for amphibole classification, suggesting that REE and selected trace element data, when combined with textural observations, may provide important additional insights into phase equilibria and conditions of crystallization.

In situ analyses of hafnium isotopes in zircon combined with U–Pb zircon ages, and trace element data, provide new information on the characterization and evolution of magnetite–apatite (“Kiruna-type”) deposits and the tectonic environments in which they occur. The Lyon Mountain granite in the Adirondack Mountains of New York is the host to numerous zircon-bearing magnetite–apatite deposits. Hafnium isotopic compositions and rare earth element contents in individual zircon crystals were measured in situ in both the host granites and the ore bodies by laser ablation inductively coupled plasma-mass spectrometry. Hafnium isotopic compositions in the ore zircon can be divided into two groups: those that have initial eHf ( t ) values that are indistinguishable from those of the host granites (e.g., eHf ( t ) less than + 7) and are typical of relatively juvenile Proterozoic crust, and those that have extremely radiogenic eHf ( t ) values (as high + 40). Two models are proposed to explain the observed eHf ( t ) values in the zircon crystals: 1) early-formed ore bodies containing magnetite, apatite, and clinopyroxene were remobilized by secondary fluid alteration, releasing Zr and Hf for the crystallization of new zircon; or alternatively, 2) fluids responsible for ore formation have interacted with garnet-bearing rocks during retrograde metamorphism, scavenging rare earth elements and radiogenic Hf. Previous work done to determine the U–Pb ages from the same zircon crystals, which were analyzed for the Hf isotopic composition in this study, revealed that ore bodies record a mineralizing event that is 20 to 60 m.y. younger than the age of granite emplacement. This age discrepancy, plus the highly radiogenic eHf ( t ) values in the ore zircon crystals, suggests that the fluids responsible for this younger event could not have been derived from the granite hosts. These data argue that magnetite–apatite deposits in the LMG have multiple mineralizing events superimposed upon one another and that early-formed deposits may be reworked, modified and redeposited by fluids subsequent to magma crystallization.

The Central Maine Basin and Merrimack Trough are Silurian basins that formed adjacent to or were accreted to the Laurentian margin during the Acadian orogeny. The Early Devonian Carrabassett Formation of the Central Maine Basin and the Kittery Formation of the Merrimack Trough have major and trace element compositions indicative of a passive continental margin provenance, not unlike the older formations of the Central Maine Basin that are thought to have been derived from Laurentian sources. However, both the Carrabassett and Kittery formations have paleocurrent indicators of outboard sources. The Carrabassett Formation is one of the youngest formations of the Central Maine Basin and was deposited just prior to the Acadian orogeny. The Carrabassett and Kittery formations have major and trace element concentrations suggestive of passive margin turbidites derived from intermediate to felsic sources, inconsistent with a juvenile Avalonian provenance. The Carrabassett Formation contains detrital zircon grains that match the ages of peri-Gondwanan Ganderia. Unlike the dominance of positive bulk-rock εNd values that are characteristic of Avalonia, Ganderia has negative εNd values that are a better match for the negative εNd values of the Carrabassett and Kittery formations. However, Ganderia accreted to Laurentia during the Salinic orogeny, prior to the deposition of the Carrabassett Formation, and was basement to the sediments of the Central Maine Basin upon which the Carrabassett and other formations were deposited. Wedging of Ganderia by Avalonia during the initial stages of the Acadian orogeny may have uplifted Ganderia, forming highlands outboard of the Central Maine Basin that served as the source of the Carrabassett Formation sediments. RÉSUMÉ Le bassin central du Maine et la cuvette de Merrimack constituent des bassins siluriens s’étant formés le long de la marge laurentienne ou s’y étant accrétés au cours de l’orogenèse acadienne. La Formation du Dévonien précoce de Carrabassett, dans le bassin central du Maine, et la Formation de Kittery, de la cuvette de Merrimack, présentent des compositions en éléments majeurs et traces signalant une provenance d’une marge continentale passive, à l’instar des formations plus âgées du bassin central du Maine qu’on pense originaires de sources laurentiennes. Les formations de Carrabassett et de Kittery comportent toutefois des indicateurs de paléocourants de sources extérieures. La Formation de Carrabassett constitue l’une des formations les plus récentes du bassin central du Maine; elle s’est mise en place juste avant l’orogenèse acadienne. Les caractéristiques géochimiques et géochronologique des formations de Carrabassett et de Kittery pourraient par conséquent permettre l’identification du terrane de collision. Les formations de Carrabassett et de Kittery possèdent des concentrations d’éléments majeurs et traces évoquant les turbidites de marge passive en provenance de sources intermédiaires à felsiques, ce qui est contradictoire avec une origine avalonienne juvénile. La Formation de Carrabassett comporte des grains détritiques de zircon correspondant aux âges du Ganderia périgondwanien. Contrairement à la prédominance de concentrations εNd positives de roche en vrac caractéristiques d’Avalonia, Ganderia présentent des concentrations εNd négatives qui cadrent mieux avec les concentrations εNd négatives des formations de Carrabassett et de Kittery. Ganderia s’est toutefois accrété à Laurentia au cours de l’orogenèse salinique, avant le dépôt de la Formation de Carrabassett, et il a constitué le socle des sédiments du bassin central du Maine sur lesquels Carrabassett et d’autres formations se sont déposées. L’enfoncement d’Avalonia sous Ganderia au cours des stades initiaux de l’orogenèse acadienne pourrait avoir soulevé Ganderia, formant un massif à l’extérieur du bassin central du Maine qui a servi de source aux sédiments de la Formation de Carrabassett. [Traduit par la redaction]

A mineralogical mass balance has been calculated for the fraction of platinum group elements (PGE) incorporated as solid solution in sulfides and sulfarsenides and the fraction that occurs as major constituents in platinum group minerals (PGM) in the Kelly Lake Ni-Cu-PGE sulfide deposit in the Copper Cliff offset, Sudbury. Low levels of PGE in sulfides were determined quantitatively for the first time in Sudbury ores by laser ablation microprobe-inductively coupled plasma-mass spectrometry (LAM-ICP-MS), providing significantly more accurate data on the inventory and mineralogical distribution of the PGE than in previous studies. The majority of the Pt (98%), Rh (97%), and Ir (86–91%), and lesser but still large fractions of Pd (77–87%) and Ru (67–71%), occur as discrete PGM with the remainder occurring (in decreasing abundance) in solid solution in gersdorffite (1,700 ppm ∑PGE), pentlandite (1.35 ppm), chalcopyrite (0.5 ppm), and pyrrhotite (0.3 ppm). Although the PGE are present in low concentrations in sulfides, the abundances of these phases can be high enough to constitute a significant fraction of the total PGE. In particular, significant proportions of the Pd (14–23%) and Ru (~30%) in the Kelly Lake samples are hosted by sulfides and sulfarsenides. This has important implications for the genesis of the PGE, for the redistribution of the PGE during cooling and hydrothermal alteration, and for metal recovery during ore beneficiation.

We have performed six experiments in which we equilibrated monosulfide solid solution (mss) with sulfide melt in evacuated silica capsules containing solid buffers to fix oxygen and sulfur fugacity, at temperatures of 950°C, 1000°C and 1050°C at bulk concentrations of ∼50 ppm for each of the PGE and Au, 5% Ni, and 7% Cu. Concentrations of O, S, Fe, Ni and Cu were determined by electron microprobe, whereas precious metal concentrations were determined by laser-ablation inductively-coupled mass spectrometry. Partition coefficients of all elements studied show minimal dependences on oxygen fugacity from the IW to the QFM buffers when sulfur fugacity is fixed at the Pt-PtS buffer. Cu, Pt, Pd and Au are strongly incompatible and Ru remains moderately to strongly compatible under all conditions studied. At all oxygen fugacities, at the Pt-PtS sulfur buffer, Ir and Rh remain highly compatible in mss. In the single run at both low oxygen and low sulfur fugacity Ir and Rh were found to be strongly incompatible in mss. At QFM and Pt-PtS the partition coefficient for Ni shows weak temperature dependence, ranging from 0.66 at 1050°C to 0.94 at 950°C. At lower oxygen and sulfur fugacity Ni showed much more incompatible behavior. Comparison with the compositions of sulfide ores from the Lindsley deposit of Sudbury suggests that the sulfide magma evolved under conditions close to the QFM and Pt-PtS buffers. The compatible behavior observed for Ni, Ir and Rh at Lindsley and most other magmatic sulfide deposits hosted by mafic rocks requires equilibration of mss and sulfide liquid at moderately high sulfur fugacity and low temperatures near to the solidus of the sulfide magma. We argue that this constraint requires that the sulfide magma must have evolved by equilibrium crystallization, rather than fractional segregation of mss as is commonly supposed.

Comparisons of PGE measurements by laser-ablation microprobe (LAM–ICP–MS) with micro-PIXE analyses on the same sulfide grains were made in order to assess data quality. Pyrrhotite, pentlandite and chalcopyrite from a few samples of disseminated ores of the Noril’sk I intrusion and massive ore from the Talnakh deposit, Russia, were analyzed for Pd and Rh by microPIXE and for all PGE by LAM–ICP–MS. Micro-PIXE analyses employed focused proton beams of 8 � 15 � m for grains in heavy-mineral separates and 15 � 20 � m for grains in hand samples. These represent analyzed volumes of about 2,350 � m 3 in pyrrhotite and 5,900 � m 3 for Pd in pentlandite. LAM analyses were performed with a focused, 266-nm laser beam fired at 0.3 mJ/ pulse and 10 Hz, resulting in 35–40 � m spots and analyzed volumes of about 85,000 � m 3 . Fused pyrrhotite standards separately doped with Pd, Ru, and Rh were synthesized for LAM–ICP–MS, and calibrated against sintered pyrrhotite PGE standards of Ballhaus & Sylvester (2000). The level of Pd, Ru and Rh varies by ~4 to 9% (1� ) in the fused pyrrhotite standards at a 50-� m sampling scale. The LAM and micro-PIXE results for the natural sulfides are quite comparable, with the large majority of determinations falling within 33% of each other for both Pd and Rh on the same spot. This agreement is considered encouraging for use of the LAM–ICP–MS for trace PGE analysis, considering the large differences in volumes analyzed, and in probable trace-element heterogeneity in the grains and standards. The reasonable concordance of most Pd and Rh results by LAM–ICP– MS and micro-PIXE indicates the potential of the LAM–ICP–MS technique. LAM analyses of the natural sulfides for Pt, Ir and Os were made using the standards of Ballhaus & Sylvester (2000). Platinum is more enriched in pentlandite (n = 10) than in pyrrhotite (3.2 ± 1.2 versus 0.73 ± 0.60 ppm) from Noril’sk (MP6–97), but Ir (0.94 ± 0.32 versus 1.38 ± 0.13 ppm) is only slightly higher in pyrrhotite (n = 10), whereas Os (~0.5 ppm) is comparably enriched in both minerals. Noril’sk chalcopyrite contains trivial amounts of all PGE except Pd (6.6–15 ppm).

Laser-ablation quadrupole ICP-MS analyses of molybdenite samples from Preissac, Quebec, and Mokrsko, Belcice and Kasperske Hory gold deposits in the Bohemian Massif, Czech Republic, for Re and radiogenic 187 Os suggest the presence of strong zoning in Re and in 187 Os/ 187 Re values within grains. The zoning patterns indicate decoupling of daughter 187 Os from parent 187 Re after molybdenite crystallization. Whereas Re is not homogeneously distributed in the molybdenite grains studied, the lack of correlation between the calculated 187 Os/ 187 Re value and the Re content also reflects the mobility of 187 Os within individual grains of molybdenite. Such decoupling of Re and Os could affect the accuracy of Re-Os ages if disturbed portions of molybdenite are sampled for dating by conventional isotope-dilution N-TIMS or ICP-MS techniques. The results re-emphasize the critical need for homogenization of quantities of molybdenite sufficiently large to capture the bulk Os/Re of the sample to be dated by these methods. Laser-ablation sampling, when used with a multicollector magnetic-sector ICP-MS instrument, is able to produce Re-Os ages with a precision better than 2% (1 � m) from single spots in certain old and Re-rich molybdenite grains, but would be difficult to use as a dating tool given the extreme 187 Os/ 187 Re heterogeneity seen in individual grains.

L'indice de Lodestar, dans la partie orientale de Terre-Neuve, contient des concentrations importantes d'or dans des breches magmatiques-hydrothermales polymictes mineralisees en sulfures. La teneur maximale, 58.5 g/t d'or, caracterise un echantillon quelconque d'arsenopyrite massive. Les echantillons d'autres mineraux du minerai sulfure, la pyrite, par exemple, ne montrent pas de teneurs comparables. Nous en deduisons que l'or serait directement lie a l'arsenopyrite. Les echantillons contenant des sulfures ont ete etudies avec une batterie de techniques analytiques. Les developpements recents d'analyse in situ par ablation au laser avec plasma a couplage inductif et spectrometrie de masse (LAM-ICP-MS) ont mene a de nouvelles observations a propos de la distribution des elements traces dans les mineraux. Les analyses LAM-ICP-MS ont ete faites pour determiner si l'or est distribue de facon homogene dans les sulfures, en particulier l'arsenopyrite, ou s'il se presente sous forme de micropepites. Les resultats LAM-ICP-MS demontrent que l'indice Lodestar contient des concentrations d'or atteignant 201 g/t. L'or est reparti de facon homogene dans la structure de l'arsenopyrite, sans effet de micropepites. Les autres sulfures, la pyrite et la chalcopyrite, par exemple, contiennent des teneurs en or tres faibles. Les teneurs en or de l'arsenopyrite dans des echantillons individuels varient, probablement en fonction des teneurs en arsenic. Parce que nous n'avons pas pu deceler l'or par les autres techniques micro-analytiques, cet element doit etre incorpore chimiquement dans la structure; on pourrait donc le qualifier d'or "invisible".

Determining the primary compositions of continental flood basalts has proven allusive because of the masking effects of crustal contamination. The Higganum dike (Connecticut, USA) that fed the Talcott basalt of the Central Atlantic Magmatic Province hosts strongly zoned clinopyroxenes. The cores are Mg- and Cr-rich, containing up to 1 wt % Cr2O3. The grains show optical and major, minor, and trace element continua between cores and their mantles and rims, indicating that the cores are early crystallizing phenocrysts, not xenocrysts. Laser ablation inductively coupled plasma mass spectrometry analyses of the cores were used to calculate liquid compositions of the most primitive component in the Higganum system and to make inferences about composition of continental flood basalt parental magmas. The Cr-rich cores yield calculated liquids with Mg numbers of 63. The high-Cr contents of these calculated liquids indicate the absence of significant clinoproxene or chromite fractionation. Olivine or orthopyroxene fractionation may have lowered the liquid Mg number but would not have significantly influenced the calculated incompatible trace element patterns. Extended rare earth element diagrams for the most Cr-rich liquids show enrichment in incompatible elements, similar to arc basalts. Prominent negative Nb anomalies are present as are distinct positive Pb anomalies indicative of the influence of subduction zone fluids in the mantle source. Calculated liquid Ba/La values range from 3 to 30, also suggestive of fluid input. These data indicate that the mantle source experienced subduction zone fluid metasomatism. Subsequent crustal contamination is evident in bulk-rock Nd and Sr isotopic compositions.

Matrix-matched calibration by natural zircon standards and analysis of natural materials as a reference are the principle methods for achieving accurate results in inicrobeam U-Pb dating and Hf isotopic analysis. We describe a new potential zircon reference material for laser ablation ICP-MS that was extracted from a potassic granulite facies rock collected in the southern part of the Bohemian Massif (Plesovice, Czech Republic). Data from different techniques (ID-TIMS, SIMS and LA ICP-MS) and several laboratories suggest that this zircon has a concordant U-Pb age with a weighted mean (206)Pb/(238)U date of 337.13 +/- 0.37 Ma (ID-TIMS, 95% confidence limits, including tracer calibration uncertainty) and U-Pb age homogeneity on the scale used in LA ICP-MS dating. Inhomogeneities in trace element composition due to primary growth zoning prevent its use as a calibration standard for trace element analysis. The content of U varies from 465 ppm in pristine parts of the grains to similar to 3000 ppm in actinide-rich sectors that correspond to pyramidal faces with a high degree of metamictization (present in ca. 30% of the grains). These domains are easily recognized from high intensities on BSE images and should be avoided during the analysis. Hf isotopic composition of the Plesovice zircon (>0.9 wt.% Hf) is homogenous within and between the grains with a mean (176)Hf/(177)Hf value of 0.282492 +/- 0.000013 (2SD). The age and Hf isotopic homogeneity of the Plesovice zircon together with its relatively high U and Pb contents make it an ideal calibration and reference material for laser ablation ICP-MS measurements, especially when using low laser energies and/or small diameters of laser beam required for improved spatial resolution.

X-ray diffraction (XRD), Mossbauer spectrometry (MS), secondary ions mass spectroscopy (SIMS) and laser-ablation microprobe–inductively coupled plasma–mass spectrometry (LAM–ICP–MS) were used to study mineral samples of Colombian auriferous ores collected from the “El Diamante” mine, located in the municipality of Guachavez-Narino, in Colombia. The samples were prepared as polished thin sections and polished sections. From XRD data, quartz, sphalerite and pyrite were detected and their respective cell parameters were estimated. From MS analyses, pyrite, arsenopyrite and chalcopyrite were identified; their respective hyperfine parameters and respective texture were deduced. Multiple regions of approximately 200 × 200 μm in each sample were analyzed with SIMS; the occurrence of “invisible gold” associated mainly with pyrite and secondarily with arsenopyrite could thus be assigned. It was also found that pyrite is of the arsenious type. Spots from 30 to 40 μm in diameter were analyzed with LAM–ICP–MS for pyrite, arsenopyrite and sphalerite; Au is “homogeneously” distributed inside the structure of the arsenious pyrite and the arsenopyrite (not as inclusions); the chemical composition indicates similarities of this “invisible gold”, forming a solid solution with arsenious pyrite and arsenopyrite. One hundred nineteen and 62 ppm of ‘invisible gold’ was quantified in 21 spots analyzed on pyrite and in 14 spots on arsenopyrite, respectively.

Os albititos uraníferos de Lagoa Real são rochas que passaram por várias modificações após a formação. A datação química U-Th-Pb por microssonda eletrônica e datação U-Pb por LAICP-MS dos minerais dos albititos revelaram cristalização e metamorfismo isoquímico do protólito (sienitos sódicos portadores de U) em cerca de 2,0-1,9 Ga durante as fases finais do evento orogênico Orosiriano, quando a primeira geração de uraninitas foi formada. Mobilizações múltiplas de urânio e chumbo promovidas por pelo menos cinco eventos hidrotermais (1,7 Ga, 1,5 Ga, 1,3 Ga, 1,1 Ga e 1,0 Ga) foram detectadas nos albititos. A provável formação de um segundo grupo de uraninitas e/ou o reajuste do relógio U-Pb das uraninitas mais antigas durante o evento orogênico Brasiliano (0,5 Ga) também ocorreram., Lagoa Real uraniferous albitites are rocks which went through multiple modifications after formation. Electron microprobe chemical U-Th-Pb and LA-ICP-MS U-Pb dating of minerals of albitites reveal protolith (U-bearing sodic syenites) crystallization and isochemical metamorphism at ca. 2.0-1.9 Ga during the final stages of the Orosirian orogenic event, when the first generation of uraninites was formed. Multiple uranium and lead mobilization promoted by at least five hydrothermal events (ca. 1.7 Ga, ca. 1.5 Ga, ca. 1.3 Ga, ca. 1.1 Ga, and ca. 1.0 Ga) was detected in the albitites. A probable formation of a second uraninite group and/or resetting of UPb clock of older uraninites during the Brasiliano orogenic event at ca. 0.5 Ga also took place.