Bo Johanson

Identification of magnetic particulates in road dust accumulated on roadside snow using magnetic, geochemical and micro-morphological analyses.

The aim of this study is to test the applicability of snow surveying in the collection and detailed characterization of vehicle-derived magnetic particles. Road dust extracted from snow, collected near a busy urban highway and a low traffic road in a rural environment (southern Finland), was studied using magnetic, geochemical and micro-morphological analyses. Significant differences in horizontal distribution of mass specific magnetic susceptibility (χ) were noticed for both roads. Multi-domain (MD) magnetite was identified as the primary magnetic mineral. Scanning electron microscope (SEM) analyses of road dust from both roads revealed: (1) angular-shaped particles (diameter∼-300 μm) mostly composed of Fe, Cr and Ni, derived from circulation of motor vehicles and (2) iron-rich spherules (d∼2-70 μm). Tungsten-rich particles (d<2 μm), derived from tyre stud abrasion were also identified. Additionally, a decreasing trend in χ and selected trace elements was observed with increasing distance from the road edge.

Determination of refractory gold distribution by microanalysis, diagnostic leaching and image analysis

SummarySamples of drill core, ore and concentrates from the Proterozoic Suurikuusikko Au deposit, Kittilä, Central Lapland were studied by optical microscopy, image analysis, Secondary Ion Mass Spectrometer (SIMS), trace gold analysis by electron microprobe, and diagnostic leaching techniques to characterize the mode of occurrence of the gold. The main ore minerals are pyrite, arsenopyrite and gersdorffite, and the minor ore minerals include chalcopyrite, sphalerite, tetrahedrite, galena, bournonite and rutile. Graphite is found in all samples as microcrystalline grains. Pyrite, arsenopyrite and occasionally gersdorffite occur as disseminated intimately intergrown grains and as large grain aggregates. Diagnostic leaching tests show that an average of only 4.1% of the gold is in cyanide leachable form i.e. free gold, whereas on average 57% of the gold is bound to pyrite and arsenopyrite as inclusions or as lattice gold. The weight percentage of arsenopyrite and pyrite in the concentrate determined with image analysis on backscattered electron images is 65.2 and 34.7, respectively. Trace Au analyses done with EPMA using the Australian CSIRO-TRACE program from the drill core samples and concentrates show that the average gold content in pyrite is 46 ppm (192 analyses) and in arsenopyrite 279 ppm (136 analyses). The CSIRO-TRACE microprobe analyses correspond favourably to SIMS analyses, e.g. 69 ppm for pyrite (16 analyses) and 217 ppm for arsenopyrite (22 analyses). The distribution of gold in concentrates was calculated as free gold 4.1%, gold in pyrite 22.7%, and gold in arsenopyrite 73.2%. Both arsenopyrite and pyrite show strong zoning when treated for 1–2 min with KMnO4 dissolved in sulphuric acid, and trace Au microprobe analyses show that the zonal bands reflect different concentrations of gold in the minerals. Free gold was not found by optical microscopy, but a rare mineral search technique using TURBO-SCAN runs on the drill core samples and concentrates located 111 gold grains. The grains have a large compositional variation from silver-bearing gold to electrum and Au-Ag-amalgam.ZusammenfassungProben von Bohrkernen, Erzen und Konzentraten aus der proterozoischen Goldlagerstätte Suurikuusikko, Kittilä, Zentrallappland, wurden mittels optischer Mikroskopie, Bildanalyse, Sakundär ionen messenspektrographie (SIMS), Gold-Spurenanalyse mit der Elektronen-Mikrosonde (EMS) und mit diagnostischen Lösungsverfahren untersucht, um die Art des Auftretens des Goldes zu charakterisieren. Die Haupterzminerale sind Pyrit, Arsenopyrit und Gersdorffit. Nebengemengteile sind Chalcopyrit, Zinkblende, Tetrahedrit, Bleiglanz, Bournonit sowie Rutil. Graphit kommt in allen Proben in Form mikrokristalliner Körner vor. Pyrit, Arsenkies und gelegentlich auch Gersdorffit treten als Imprägnation in engster Verwachsung und in Form größerer Kornaggregate auf. Diagnostische Lösungsversuche haben gezeigt, daß durchschnittlich nur 4.1% des Goldes von Cyanid gelöst wird, i.e. als Freigold vorliegt, während 57% des Goldes an Einschlüsse und in dem Gitter von Pyrit und Arsenkies gebunden ist. Mittels Bildanalyse an BSE- Bildern konnte der Anteil von Arsenkies in den Konzentraten mit 65.2, der Anteil von Pyrit mit 34.7 Gew.% ermittelt werden. Spurenanalyse auf Gold an Bohrkernproben und Konzentraten mit der EMS, unter Benützung des australischen CSIRO-TRACE Programmes, zeigen, daß der durchschnittliche Goldgehalt von Pyrit bei 46 ppm (192 Analysen), jener von Arsenkies bei 279 (136 Analysen) liegt. Die CSIRO-TRAGE Mikrosondenanalysen stimmen bevorzugt mit SIMS Analysen überein; z.B. Pyrit: 69 ppm (16 Analysen), Arsenkies: 217 ppm (22 Analysen). Die Berechnung der Goldverteilung in den Konzentraten ergibt 4.1% freies Gold, 22.7% Gold in Pyrit, und 73.2% Gold in Arsenkies. Sowohl Arsenkies als auch Pyrit zeigen starken Zonarbau, nachdem sie für 1–2 min mit in Schwefelsäure gelöstem KMnO4 behandelt wurden. Die Mikrosondenanalysen auf Gold belegen, daß die einzelnen Wachstumszonen mit unterschiedlichen Goldkonzentrationen korrelieren. Freies Gold konnte nicht mittels normaler optischer Mikroskopie gefunden werden, aber mit dem Programm TURBO-SCAN für das automatische Suchen nach seltenen Mineralen an Bohrkernproben und Konzentraten konnte man 111 Goldkörner lokalisieren. Die Körner zeigen eine große Variation in ihrer Zusammensetzung, die von silberführendem Gold über Elektrum bis hin zu Au-Ag-Amalgamreicht.

Platinum-, palladium- and gold-rich arsenide ores from the Kylmäkoski Ni-Cu deposit

SummaryThe Kylmäkoski deposit consists of a disseminated primary Ni-Cu mineralization hosted by a differentiated ultramafic body. It also shows sulfide veins (tens of meters long and up to 20 cm thick) that evolve laterally to massive Ni-arsenide ores. In these sulfide/arsenide veins, three different ore assemblages can be distinguished: 1) sulfide ores (S ores) composed of pyrrhotite, pentlandite and chalcopyrite with minor amounts of cubanite, sphalerite and argentopentlandite which locally occurs intergrown with Ag-free pentlandite; 2) sulfide/arsenide ores (S/As ores) made up of the former S ores corroded and replaced by nickeline (locally with graphite), with gersdorffite filling discordant veins, abundant minute grains of sudburyite and accessory molybdenite, ullmanite, stibnite, galena and breithauptite; 3) arsenide ores (As ores) composed of nickeline, maucherite and disseminated, zoned cobaltite, with minor chalcopyrite, cubanite, sperrylite, sudburyite, electrum, galena, altaite and pilsenite. These veined ore assemblages were generated by the remobilization of primary, late magmatic arsenide-rich ores (well represented in the Vammala mine) by the intrusion of pegmatitic fluids derived from the partial melting of the metasedimentary country rocks.The early fractional crystallization of the monosulfide solid solution produced a residual As-rich melt that collected most noble metals (specially Pt, Pd and Au) leaving the primary Ni-Cu sulfide ores impoverished in these elements. In fact, late magmatic arsenide ores from Vammala contain up to 42.5 ppm Pd (in the form of extremely fine inclusions of sudburyite in nickeline and maucherite, and dissolved in trace amounts in the lattice of the latter Ni arsenides) and 9.6 ppm Au (concentrated in abundant minute inclusions of electrum in Ni arsenides). Later, during the remobilization of the primary arsenide ores of Kylmäkoski, Pd concentrated both in S/As and As ores in the form of sudburyite and in a rare PdBi compound. It also occurs in trace amounts in nickeline from S/As ores and in maucherite from As ores. Pt mainly concentrated in As ores as sperrylite and, in minor amounts in pilsenite and in cobaltite coronas around sperrylite. It occurs in trace amounts in the cores of zoned cobaltite. Gold is always present in the form of irregular grains of electrum in As ores.ZusammenfassungDie Lagerstätte Kilmäkoski ist eine disseminierte primäre Ni-Cu-Vererzung, die in einem differenzierten ultramafischen Körper aufsitzt. Hier treten auch Sulfid-Gänge, die bis zu Zehnern von Metern lang und bis zu 20 cm mächtig sein können, auf; aus diesen entwickeln sich lateral massive Nickel-Arsenid Erze. Drei Erzparagenesen können in diesen Sulfid-Arsenid-Gängen unterschieden werden: 1. Sulfidische Erze mit Pyrrhotin, Pentlandit, Kupferkies und geringen Mengen von Cubanit, Zinkblende und Argentopentlandit der örtlich mit Ag-freiem Pentlandit verwachsen ist 2. Sulfid-Arsenid Erze, die aus korrodierten und durch Rotnickelkies verdrängten Sulfid-Erzen bestehen. Diese führen örtlich Graphit, Gersdorffit kommt als Füllung diskordanter Gänge vor. Außerdem gibt es verbreitet kleine Körner von Sudburyit und akzessorischem Molybdänit, Ullmanit, Antimonglanz, Bleiglanz und Breithaup tit. 3. Arsenid-Erze, die aus Rotnickelkies, Maucherit und disseminiertem, zonarem Kobaltit, mit Kupferkies, Cubanit, Sperrylit, Sudburyit, Elektrum, Bleiglanz, Altait und Pilsenit als Nebengemengteile bestehen. Diese gangförmigen Erzparagenesen entstanden durch die Remobilisation von primären, spätmagmatischen Arsenidreichen Erzen, die in der Vammala-Mine sehr gut aufgeschlossen sind, und auf die Intrusion pegmatitischer Fluide zurückgehen, die durch teilweises Aufschmelzen der metasedimentären Nebengesteine entstanden sind.Die frühe fraktionierte Kristallisation der Monosulfid Solid Solution führte zu einer residualen As-reichen Schmelze, die den Großteil der Edelmetalle (besonders Pt, Pd und Au) aufgenommen und die primären Ni-Cu Sulfiderze an diesen Elementen verarmt zurückgelassen hat. Spätmagmatische Arseniderze aus Vammala enthalten bis zu 42,5 ppm Pd (in Form von extrem feinkörnigen Einschlüssen von Sudburyit in Rotnickelkies und Maucherit, und als Spurengehalte im Gitter der späten Nickel-Arsenide), sowie 9,6 ppm Au, das hauptsächlich in den verbreiteten winzigen Einschlüssen von Electrum in Nickelarseniden vorkommt. Während der späteren Remobilisierung der primären Arseniderze von Kylmäkoski wurde Pd sowohl in S/As und As-Erzen in der Form von Sudburyit und in einer seltenen Pd-Bi Verbindung konzentriert. Es kommt auch als Spurenelement im Rotnickelkies aus S/As-Erzen und im Maucherit aus As-Erzen vor. Pt is vorwiegend in As-Erzen konzentriert, und zwar als Sperrylit, sowie in geringen Mengen in Pilsenit und in Colbaltit-Rändern um Sperrylit. Es kommt in Spurenelementen in den Kernen von zonaren Kobaltiten vor. Gold liegt stets in Form unregelmäßiger Elektrum-Körner in As-Erzen vor.

Origin of placer laurite from Borneo: Se and As contents, and S isotopic compositions

Abstract We examined grains of the platinum-group mineral, laurite (RuS2), from the type locality, Pontyn River, Tanah Laut, Borneo, and from the Tambanio River, southeast Borneo. The grains show a variety of morphologies, including euhedral grains with conchoidal fractures and pits, and spherical grains with no crystal faces, probably because of abrasion. Inclusions are rare, but one grain contains Ca-Al amphibole inclusions, and another contains an inclusion of chalcopyrite+bornite+pentlandite+heazlewoodite (Ni3S2) that is considered to have formed by a two-stage process of exsolution and crystallization from a once homogeneous Fe-Cu-Ni sulphide melt. All grains examined are solid solutions of Ru and Os with Ir (2.71−11.76 wt.%) and Pd (0.31−0.66 wt.%). Their compositions are similar to laurite from ophiolitic rocks. The compositions show broad negative correlations between Os and Ir, between As and Ir, and between As (0.4−0.74 wt.%) and Se (140 to 240 ppm). Laurite with higher Os contains more Se and less Ir and As. The negative correlations between Se and As may be attributed to their occupancy of the S site, but the compositional variations of Os, Ir and As probably reflect the compositional variation of rocks where the crystals grew. Ratios of S/Se in laurite show a narrow spread from 1380 to 2300, which are similar to ratios for sulphides from the refractory sub-arc mantle. Sulphur isotopic compositions of laurite are independent of chemical compositions and morphologies and are similar to the chondritic value of 0‰. The data suggest that S in laurite has not undergone redox changes and originated from the refractory mantle. The data support the formation of laurite in the residual mantle or in a magma generated from such a refractory mantle, followed by erosion after the obduction of the host ultramafic rocks.

The ash formation during co-combustion of wood and sludge in industrial fluidized bed boilers

Abstract Ashes from an industrial bubbling fluidized bed (BFB) and a circulating fluidized bed (CFB) boilers burning biomass and paper mill sludges are characterized. Bulk sampling was carried out with a simultaneous low pressure impactor sampling (BLPI) and with on-line monitoring of submicron ash gas phase size distribution. The principal ash forming mechanism was sintering of 1–10 μ m inorganic paper filler particles, into 5–200 μ m ash agglomerates. Despite few spherical particles no ash melting was detected. The fraction of vaporized and condensed ash was below 0.1 mass% in both units as determined with BLPI and with on-line monitoring. According to elemental mass size distributions no significant vaporization of any main element occurred including sodium and potassium. Wall deposit observed on refractory lining in BFB furnace was composed of sintered ash binding large ash and sand particles in the structure. No molten phases were detected to participate in the layer growth. Most quartz sand grains in the bed were covered by a thin layer of small ash particles, below 5 μ m in size.

Metamorphism and Chromite in Serpentinized and Carbonate-Silica-Altered Peridotites of the Paleoproterozoic Outokumpu-Jormua Ophiolite Belt, eastern Finland

The 1.95 Ga Outokumpu-Jormua ophiolite belt of eastern Finland contains numerous mafic-ultramafic, predominantly peridotitic bodies which, despite amphibolite-facies metamorphism and pervasive deformation, retain compelling evidence of a residual mantle origin. These rocks therefore currently represent the oldest documented examples of exhumed mantle lithosphere, so information concerning their primary igneous mineral assemblages and textures and chemical and isotopic characteristics is of considerable scientific value. Although several earlier studies have argued for the preservation of primary mineral assemblages, field and petrographic evidence presented here show that the protolith peridotites had already experienced pervasive low-T serpentinization prior to Svecofennian orogenic deformation, during which they were progressively deserpentinized via antigorite metaserpentinites to olivine-talc-anthophyllite-enstatite-bearing metaperidotites. evidence is also presented to show that the premetamorphic serpentinization event was closely followed by extensive low-T (< 250°C) metasomatic alteration of the marginal parts of the ultramafic bodies to carbonate-silica rocks which, during the subsequent prograde metamorphism, were converted to the distinctive chromite-bearing carbonate-skarn-quartz rocks comprising the Outokumpu rock assemblage. Because these quartz rocks are intimately associated with the Outokumpu Cu-Co-Zn-Ni deposits and have generally been regarded as metamorphosed siliceous seafloor exhalative deposits, the revised interpretation presented here has important implications for ore formation as well. equilibrium mineral assemblages in the interior parts of the ultramafic bodies (low XCO2) define four regional metamorphic zones, expressed as an east to west increase in the peak dehydration temperatures from 500° to 775°C, at 3-5 kbar. Large ultramafic bodies commonly show core to margin zoning from talc via anthophyllite- to enstatite-bearing assemblages, reflecting synmetamorphic core-margin gradients in XCO2, attributed to infiltration of CO2 released by decarbonation reactions in previously formed talc-carbonate and carbonate-silica alteration zones. The only primary igneous phase identified in this study was chromite, which occurs as scattered relict cores within large altered grains. These are relatively common in metaserpentinites, but also occur in metaperidotites and even in carbonate-skarn-quartz rocks. even though Mg, Fe2+, and Zn abundances in these relict chromites may have been somewhat modified, absolute concentrations and ratios of Cr and Al appear to be essentially unmodified. The lobate to amoeboid morphology and observed Cr# range (0.41-0.67) of the best-preserved grains are more consistent with residual depleted lherzolite to harzburgite textures than a cumulate origin. However, during regional metamorphism, most mantle chromites were either pervasively altered to ferrian chromites and Cr-magnetites or (where CO2 and S fugacities were high, such as within smaller ultramafic bodies, or at the margins of larger bodies) to high-Cr (Cr2O3 = 50-70 wt%; Cr# = 0.7-1.0) chromites; with further increase in metamorphic grade, the latter typically recrystallized to mostly spongy/chessboard-textured grains. This interpretation contrasts with previously held views, where high-Cr chromites were considered as residual chromites in ultradepleted residual peridotites. Our study demonstrates that Cr-spinel textures and compositions in amphibolite-facies ultramafic rocks may, to a large degree, be influenced by the metamorphic and metasomatic history of the enclosing host rocks. Clearly, valid application of Cr-spinel as a petrotectonic indicator requires, at least for medium and higher-grade ultramafic rocks, a thorough understanding of the metamorphic and hydrothermal history of the host rocks. Interpretation of the quartz rocks of the Outokumpu assemblage as silicified peridotites demands a reappraisal of the widely accepted concept of the Outokumpu-type sulfide ores as a type example of Precambrian ophiolite—related seafloor hydrothermal sulfide deposits. As an alternative, we tentatively propose a syntectonic hydrothermal origin.

Multidisciplinary analysis of Finnish esker sediment in radon source identification.

In order to define the naturally-occurring radioactive materials that are the source of radon in natural environments, a comprehensive analytical (geochemical, physical and chemical) methodology was employed to study sand samples from the Hollola esker in the city of Hollola (Lahti area, Finland). Techniques such as gamma-spectrometry, emanation measurements, sequential chemical extraction, scanning electron microscopy (SEM), electron probe microanalyses (EPMA) and inductively-coupled plasma mass spectrometry (ICP-MS) were used to determine the potential source of radon. Monazite and xenotime, uranium- and thorium-bearing minerals and potential radon sources, occurred in significant amounts in the samples and were also the main reason for the distribution of uranium and thereby radium in separate grain-size fractions. Following deposition, the esker sand has been exposed to no significant weathering, and radium has not therefore been much separated from uranium. However, considering its non-compatibility with crystal lattices, it was recognized rather in easily leachable species (44% of the total (226)Ra) than uranium (21% of the total (238)U) in our analyses. The smallest grain-size fraction of the esker sand had a higher emanation power (0.24) than the other fractions (around 0.17). Due to the small relative proportion of this fraction, however, it contributed only slightly to the total emanation (4%). The emanation power of the leachable species was about three times higher (ca. 0.20) than that of the species tightly bound to the crystal lattice (ca. 0.07).

The Significance of Cumulus Chlorapatite and High-temperature Dashkesanite to the Genesis of PGE Mineralization in the Koitelainen and Keivitsa-Satovaara Complexes, Northern Finland

Several PGE mineralizations are known from the 2435 Ma-old Koitelainen layered intrusion and the adjacent Keivitsa-Satovaara (K-S) complex. In Koitelainen, transient sulphide separation gave rise to sulphidic PGE mineralizations (Pd-Pt- Au) in the lower zone and upper main zone. PGE, without visible sulphides, occur in Lower Chromitites (Pd-Pt) in the lower zone, in ultramafic pegmatoid pipes (Pt) in the main zone, and in the Upper Chromitite layer (Ru-Pt-Pd) of the lower upper zone. A peculiar peridotite-mixed rock in the main zone is underlain by a Pt-enriched layer, a setting reminiscent of the Stillwater PGE reef. PGE removed by these mineralizations had little effect on the overall buildup of PGE in the rest of the magma; by far the most of PGE precipitated with the last sulphide saturation at 95% level, in magnetite gabbro (Pt-Au-Pd). In the upper part of the K-S complex, assimilation of sedimentary sulphides triggered the deposition of massive sulphides. PGE occur only in overlying meagre disseminations (Pt-Pd-Au), and reach the highest concentrations in chromite-rich rocks (Os-Pt-Pd) at the roof. The distribution of PGE in these intrusions has an unusual pattern. Disseminated and massive sulphides in lower parts, with low PGEsulph (down to ≤10 ppb), are overlain by sulphide-poor mineralizations with high PGEsulph(from 20–13 000 to ∞ ppm). This feature persists, and even increases during crystallization, the principal PGE concentrations being located at or near the roof. Association of PGE with primary Cl-minerals suggests that the odd behaviour of PGE was due to an association between PGE and chlorine.

Low-temperature, platinum-group elements-bearing Ni arsenide assemblage from the Atrevida mine (Catalonian Coastal Ranges, NE Spain).

The Atrevida vein is located at the south-western edge of the Catalonian Coastal Ranges, Spain. This vein extends for more than 3 km and is hosted by Silurian and Carboniferous metasediments, late Hercynian granites and continental conglomerates of Lower Triassic age. The Silurian metasediments contain massive sulphide layers with disseminations of platinum-group element (PGE)-bearing, Fe-Ni arsenides. Vein fi lling largely consists of banded and brecciated baryte rimmed by a complex polymetallic assemblage of Co-Ni-As-Bi-Ag(-U) ores. The Ni arsenide and sulpharsenide assemblage occurs only where the vein cuts the sulphide-bearing Silurian metasediments, and consists of nickeline, maucherite, rammelsbergite, gersdorffi te and Ni-skutterudite. These Ni arsenides and sulpharsenides display rosettes, spherules, colloform and botryoidal textures, as well as subhedral crystals. The chemical compositions of these arsenide-sulpharsenide minerals exhibit limited cation substitution but substantial anion substitution of As by S and Sb, exceeding the expected theoretical values at low temperatures. This suggests that most of them formed under disequilibrium conditions. Ni arsenides and sulpharsenides also contain trace PGE. Palladium (up to 157 ppm) is the most abundant PGE, and occurs in solid-solution in all the phases studied, but shows the highest values in rammelsbergite and Niskutterudite. Pt only occurs in massive nickeline (54–1338 ppm Pt) and in zoned gersdorffi te (29–360 ppm Pt) formed at the end of the depositional sequence of arsenides. The Ni arsenide and sulpharsenide ores at the Atrevida mine formed by reduction of PGE-bearing, oxidizing fl uids at temperatures close to, or slightly above 100 °C. These oxidizing fl uids most probably collected their PGE budget from the nearby mineralized black shales. During the crystallization of the veined, Ni arsenide and sulpharsenide ores, Pd partly concentrated in the early nickeline and maucherite, but mainly fractionated to the late solutions from which rammelsbergite and Ni-skutterudite precipitated. Pt concentrated only in the latest nickeline and gersdorffi te.

Offset-type PGE mineralisation in the Sotkavaara Intrusion, northern Finland: an association with zones of low-cr clinopyroxenite

isation is correspondingly rich, or that placer gold is a consequence of authigenic processes. Straight twin boundaries (Figure 1) are a consequence of annealing above 250°C, and these are present in all hypogene grains studied (Hough et al. 2007). Placer grains exhibit the same feature, invalidating an authigenic origin. Furthermore deformation of the twin boundaries could find application in predicting distance travelled in the surficial environment. This study is the first to systematically characterise the internal crystallography of gold from a lode and placer source. Future research will integrate data from composition studies (electron microprobe, trace element mapping by LA-ICP-MS) with gold crystallography with a view to further illuminating ore forming processes at specific localities.