Mineralogy and Petrology

The 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. Die 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.

Rift-related, late Eocene (≈ 60 Ma) alkaline-carbonatitec intrusions cover ≈ 1200 km2 south of the town of Chhota Udaipur, and form a subprovince within the alkaline magmatism that accompanies the tholeiitic Deccan Traps. They were emplaced temporally between late Deccan Trap flows and late dykes of basalt and picritic basalt. The subprovince comprises five main geographic occurrences (sectors): (1)Amba Dongar: a ring-complex of Ca-Mg-Fe-carbonatites, nephelinites to tephriphonolites, and fluorite deposits; (2)Siriwasan-Dugdha: an intrusive complex of Ca—carbonatites, nephelinites and trachytic rocks; (3)Phenai Mata: a nepheline syenite plug and dykes, plus dykes of tephrites to phonolites and lamprophyres (intimately associated with a layered tholeiitic gabbro—granophyre intrusion); (4)Panwad-Kawant: dykes and plugs of lamprophyres and tephrites to phonolites; (5)Bakhatgarh-Phulmahal: late basic-ultrabasic dykes only. The alkaline rocks range from ultrasodic to ultrapotassic, but are mostly nonperalkaline. Silica-undersaturated examples show higher incompatible and LIL element contents (Rb, K, Nb, Zr, Sr, Ba, LREE, etc.) than the associated tholeiites. However, the late basic-ultrabasic dykes display an continuum of alkaline-tholeiitic compositions. Possible parent magmas are represented among the primitive undersaturated basic dykes (including lamprophyres). The trachytic rocks are subalkaline, and may be genetically related to a tholeiitic rather than alkaline parent magma. Alkalisch-karbonatitische Intrusionen aus dem Obereozän (≈60 Ma) erstrecken sich über 1200 km2 südlich der indischen Stadt Chhota Udaipur und bilden einen Teil des alkalischen Komplexes, der die tholeiitischen Deccan Traps begleitet. Die Gesteine wurden während eines Rifting Prozesses intrudiert und lagern stratigraphisch zwischen Deccan Trap Tholeiiten und basaltischen bzw. pikritischen Ganggesteinen. Das Gebiet läßt sich in fünf geographische Regionen unterteilen: (1) Amba Dongar: ein ringförmiger Komplex aus Ca-Mg-Fe-reichen Karbonatiten, Nepheliniten und Tephriphonoliten mit Fluorit-Lagerstätten; (2) Siriwasan-Dugdha: eine Ca-reiche Karbonatit-Intrusion mit Nepheliniten und Trachyten; (3) Phenai Mata: Eine Nephelin-syenitische Intrusion und begleitende Ganggesteine aus Tephriten, Phonoliten und Lamprophyren, die mit einer magmatisch geschichteten tholeiitischen Gabbro Intrusion vergesellschaftet sind; (4) Panwad-Kawant: Lamprophyrische Ganggesteine neben Tephriten und Phonoliten; (5) Bakhatgarh-Phulmahal: späte basisch bis ultrabasische Ganggesteine. Die alkalischen Gesteine besitzen eine ultrapotassische bis extrem Na-reiche Zusammensetzung, nur vereinzelte Proben weisen jedoch peralkalischen Charakter auf. Silizium-untersättigte (alkalische) Proben besitzen in der Regel höhere Konzentrationen an Mantel-inkompatiblen Elementen (z.B. LREE, Nb und Zr) und LILE (z.B. Rb, Sr und Ba) als die benachbarten Tholeiite. Die späten basisch bis ultrabasischen Ganggesteine stellen ein Kontinuum von alkalischer bis tholeiitischer Geochemie dar. Die “primitiven” Silizium-untersättigten Ganggesteine (und Lamprophyre) repräsentieren vermutlich die Ausgangssehmelzen; die “subalkalischen” Trachyte dürften in genetischem Zusammenhang mit den Tholeiiten stehen.

In the present paper current results of experimental investigation of the phase system Pd-Fe-Ni-S at 900°C, 725°C, 550°C and 400°C as well as of the phase system Pt-Fe-As-S at 850°C and 470°C are summarized. A preliminary note on the system Pt-Pd-As-S is added. Individual phase assemblages are presented, data on solubility of PGE in base metal sulphides/arsenides or alloys are given and solid solution ranges of important minerals are described as a function of temperature and phase assemblage. The extent and role of sulphide/arsenide melts in these systems are presented together with hints for, and examples of the application of the current experimental results for the explanation of ore-geological processes. In der vorliegenden Arbeit werden bisherige Ergebnisse experimenteller Untersuchungen in den Phasensystemen Pd-Fe-Ni-S bei 900°C, 725°C, 550°C sowie 400°C, bzw. Pt-Fe-As-S bei 850°C und 470°C zusammengefasst. Vorläufige Anmerkungen zum System Pt-Pd-As-S werden gegeben. Die Phasenbeziehungen und die Löslichkeitsdaten von PGE's in Buntmetall-Sulfiden/Arseniden sowie deren Verbindungen werden präsentiert. Die Mischungsbereiche der wichtigsten Minerale werden als Funktion von Temperatur und Phasenvergesellschaftung diskutiert. Die Rolle von Sulfid/Arsenid Schmelzen in diesen Systemen und Beispiele für die Anwendung dieser experimentellen Ergebnisse zur Erklärung lagerstättenkundlicher Prozesse werden beschrieben.

Electrum, hessite, petzite and sylvanite have been recorded from veins at Tyndrum, Scotland. Electron probe micro-analyses have also revealed two un-named Ag-Te-S phases. Fluid inclusion studies suggest that the mineralising fluids responsible for the precious metal mineralization contained ∼ 7.0 mol % CO2 and 7 wt % NaCl. TH (temperature of homogenisation) determinations were in the range 295°C to 325°C and a depth of vein formation ∼ 4 km is indicated. Mineral precipitation was probably caused by cooling and adsorption of gold onto pyrite. Δ34S values of + 1.8%o for galena from the Au + Ag + Te veins suggest a different (possibly igneous) sulphur source to that producing the Pb +Zn vein mineralization in the Tyndrum area. Although an age of ∼ 380 Ma was obtained using K-feldspar in the veins the data are not conclusive. It is argued that the Au + Ag mineralization at Tyndrum is due to hydrothermal activity related to Cu +Mo mineralization associated with the Late Caledonian granites. In der Gang-Vererzung von Tyndrum, Schottland, kommen eine Gold-Silber-Legierung, Hessit, Petzit und Sylvanit vor. Außerdem ergaben Mikrosondenanalysen das Vorhandensein von zwei unbekannten Ag-Te-S Phasen. Die Untersuchungen von Flüssigkeitseinschlüssen zeigen, daß die für die frühe Mineralisation verantwortlichen Lösungen ∼ 7.0% Mol.% CO2 und 7 Gew.% NaCl enthalten haben. Die Homogenisie-rungstemperaturen liegen im Bereich von 295-325°C und weisen auf eine Tiefe der Gangentstehung von ∼ 4 km hin. Die Au-Ag-Te Mineralbildung kam vermutlich durch Abkühlung und Adsorption von Gold auf Pyrit zustande. Δ34S-Werte von + 1.8%0, gemessen an Bleiglanz aus Au-Ag-Te-Gängen deuten eine magmatische Schwefelherkunft an, während die Pb-Zn-Gangmineralisation eine andere Schwefelquelle vermuten läßt. Die Altersdatierung der Gänge von ∼ 380 Mio. Jahren läßt sich derzeit noch nicht sinnvoll interpretieren. Es wird angenommen, daß die Au-Ag-Vererzung von Tyndrum durch hydrothermale Aktivität im Zusammenhang mit einer an spätkaledonische Granite gebundenen Cu-Mo-Vererzung entstanden ist.

siehe Details auch in
https://uni-koeln.academia.edu/ManfredBundschuh
in meinen Kapiteln über Ur-und Frühgeschichte und Geowissenschaften

please see details also in
https://uni-koeln.academia.edu/ManfredBundschuh
in my chapters about Prehistory and Geosciences

In previous work,Gunter et al. (1993), suggested water-rock reactions in deep aquifers in sedimentary basins could sequester injected-CO2-waste from industry, thereby reducing greenhouse gas emissions. Experiments, carried out at 105°C and 90 bars CO2 pressure, to test the validity of this mineral-trapping of CO2 were unsuccessful due to sluggish kinetics of reaction. The most significant change recorded by the reaction products from these experiments was a large increase in alkalinity, which was attributed to very small amounts of water-mineral reaction. A computer model, PATHARC.94, was used to interpret this change in alkalinity and to predict the path and time necessary to reach equilibrium. Substantial trapping of CO2 by formation of siderite, calcite and aqueous bicarbonate ions was predicted to occur in 6 to 40 years. Potential errors as high as two orders of magnitude were estimated based on a thorough examination of the kinetic data used in the modelling. In order to achieve reasonable time estimates, “reactive” surface areas were approximated by 100 micron spherical grains in the computer model. This represents a smaller cumulative surface area than actually present in the experiment. When these results are extrapolated to the field, where the aquifers are at lower temperatures,Perkins andGunter (1995a), concluded that CO2-trapping reactions are expected to take 100s of years to complete. This is sufficient time for the trapping to occur as the residence time of a packet of fluid in a deep low-permeability aquifer in a sedimentary basin is measured in 10,000s to 100,000s of years. In früheren Arbeiten habenGunter et al. (1993) Wasser-Gesteinsreaktionen in tiefen Aquiferen in Sedimentbecken vorgeschlagen, die injiziertes CO2 aus industriellen Abgasen aufnehmen, und damit die Treibhausgasemissionen reduzieren könnten. Experimente wurden bei 105°C und 90 bar CO2-Druck durchgeführt, um die Anwendbarkeit dieser mineralischen Fallen für CO2 zu testen; wegen der langsamen Reaktions-Kinetik waren diese nicht erfolgreich. Die markanteste Änderung, die diese Experimente in den Reaktionsprodukten hervorriefen, war eine beträchtliche Zunahme der Alkalinität, die auf geringfügige Wasser-Mineralreaktionen zurückgehen dürfte. Ein Computermodell, PATHARC 94, wurde benützt, um diese Änderungen der Alkalinität zu interpretieren und die erforderlichen Zeiten und Pfade vorherzusagen, die notwendig sind, um Gleichgewicht zu erreichen. Signifikanter Einbau von CO2 durch Bildung von Siderit, Calcit und Bikarbonat-tonen sollte dementsprechend in 6 bis 40 Jahren stattfinden. Mögliche Fehler, die bis in zwei Größenordnungen gehen können, wurden aufgrund einer sorgfältigen Überprüfung der kinetischen Daten, die hier benützt wurden, ermittelt. Um sinnvolle Zeitmaßstäbe zu erreichen, wurden im Computermodell “reaktive” Ober flächen durch 100 Mikron große kugelförmige Körner repräsentiert. Dies stellt eine kleinere Gesamtoberfläche dar, als die, die tatsächlich im Experiment vorhanden ist. Wenn diese Ergebnisse ins Gelände extrapoliert werden, wo die Aquifere niedrigere Temperaturen aufweisen, kommenPerkins undGunter (1995a) zu dem Schluß, daß ein vollständiger Einbau von CO2 hunderte von Jahre benötigen würde. Diese Zeiträume sind ausreichend, da die Verweildauer einer Fluid-Menge in einem tief gelegenen Aquifer mit niedriger Permeabilität in einem sedimentären Becken in Größenordnungen von 10.000 bis 100.000 von Jahren gemessen wird.

A large number of podiform chromitite bodies of massive, disseminated and nodular type have been located in ultramafic units, composed of depleted mantle harzburgite and dunite of the Marmaris Peridotite from Ortaca (Muğla, SW Turkey). The chromite ore bodies are surrounded by dunite envelopes of variable thickness, exhibiting transitional boundaries to harzburgite host rocks. Chromitites, containing a large number of inclusions, i.e. silicates, base metal sulphides and alloys, and platinum-group minerals (PGM) have a wide range of chemical composition. The Cr# [Cr/(Cr + Al)] values of most chromitites are high (0.61–0.81) and Mg# [Mg/(Mg + Fe2 + )] values range between 0.65 and 0.71 with TiO2 content lower than 0.24 wt.%, which may reflect the crystallization of chromites from boninitic magmas in supra-subduction setting environment. Platinum-group minerals (PGM) such as laurite, erlichmanite and Os–Ir alloys, silicates such as olivine, clinopyroxene and amphibole, and base metal sulphides (BM-S), alloys (BM-A) and arsenides (BM-As) are found as inclusions in chromite or in the serpentine matrix. Platinum-group element (PGE) concentrations of the Ortaca chromitites (OC) are low in all samples. Total PGE (Ir + Ru + Rh + Pt + Pd) ranges from 63 ng/g to 266 ng/g and Pd/Ir ratios range between 0.23 and 4.75. PGE content is higher and the Pd/Ir ratio lower in Cr-rich chromitites compared to Al-rich ones. There is a strong negative correlation between the Cr# and Pd/Ir ratios (r=−0.930). The PGE patterns show a negative slope from Ru to Pt and a positive slope from Pt to Pd. The low PGE content in the majority of the OC may reflect a lack of sulphur saturation during an early stage of their crystallization. The laurite compositions show a wide range of Ru–Os substitution caused by relatively low temperature and increasing f(S2) during the chromite crystallization. The high Cr# of and hydrous silicate mineral inclusions in chromite imply that chromite crystallized in a supra-subduction setting.

Water solubility and speciation have been studied in melts from the system albite-nepheline. Water solubility was determined at PH2O = 200 MPa and T = 1200ºC using Karl Fischer titration (KFT) and weight loss methods. It increases from 5.8 ± 0.1 wt. % in the albite melt to 7.25 ± 0.25 % in the nepheline melt. The solubility dependence has a sigmoidal shape with a steep increase in the Ab40-Ab60 compositional range. The densities of the hydrous glasses have been measured using the thermal-gradient method. Infrared (IR) combination bands of molecular H2O and hydroxyl groups in these glasses demonstrate a systematic shift to lower frequencies with increasing alkalinity. The data are consistent with the appearance of aluminate species (Al-O-Al fragments) appearing at 40-60 wt.% nepheline (Ab60-Ab40).

Palaeoproterozoic (∼1.6 Ga) lamprophyres occur as dykes, plugs and lava flows within the Mahakoshal supracrustal belt of the Jungel Valley, Central India. Although metamorphosed under greenschist facies conditions, the lamprophyres still retain remnants of the diagnostic igneous textures viz., porphyritic-panidiomorphic habit of mafic phenocrysts, leucocratic (carbonate-rich) ocelli and volatile-rich mineralogy. The studied lamprophyres are mineralogically uniform but texturally variable (porphyritic to aphanitic). Chemically they are silica undersaturated, ultrabasic, dominantly alkaline (some of them have normative nepheline) through mildly alkaline to sub-alkaline, sodic to mildly potassic and their magmas are primitive as well as evolved. The lamprophyres are characterized by Ni and Cr abundances and MgO sufficiently high to indicate a mantle source. The chondrite-normalized REE patterns confirm crystallization from a LREE enriched magma. Combined petrological and geochemical studies classify them as belonging to alkaline lamprophyre category in general and camptonites in particular. Geochemistry also suggests that their magmas are not affected by any crustal contamination. This study establishes the occurrence of lamprophyres in the Jungel area and brings to end the speculations about their mistaken identity. The presence of a wide spectrum of undersaturated alkaline magmatism comprising lamprophyres, syenites, tinguites, and possibly kimberlties, highly carbonated rocks and ultrabasic rocks as intrusives in the Mahakoshal supracrustal belt undoubtedly highlights the presence of a carbonate-rich palaeo- to early Proterozoic alkaline province. The occurrence of greenschist facies metamorphosed lamprophyres of Palaeoproteorozoic age in the eastern central Indian shield is also significant in the context of re-construction of ancient continental fits as similar rocks of comparable age have been reported from the Yilgarn and Pilbara cratons of Western Australia.

The eastern part of the agpaitic Khibina complex is characterized by the occurrence of dykes of various alkali silicate rocks and carbonatites. Of these, picrite, monchiquite, nephelinite and phonolite have been studied here. Whole rock and mineral geochemical data indicate that monchiquites evolved from a picritic primary magma by olivine+ magnetite fractionation and subsequent steps involving magma mixing at crustal levels. None of these processes or assimilation/magma mixing of wall rocks or other plutonic rocks within the complex can entirely explain the geochemical and Nd–Sr-isotopic characteristics of the monchiquites (i.e. a covariant alignment between (87Sr/86Sr)370=0.70367, (143Nd/144Nd)370=0.51237 and (87Sr/86Sr)370=0.70400, (143Nd/144Nd)370=0.51225 representing the end points of the array). This signature points to isotopic heterogeneities of the mantle source of the dyke-producing magma. The four mantle components (i.e. depleted mantle, lower mantle plume component, EMI-like component and EMII-like component) must occur in different proportions on a small scale in order to explain the isotopic variations of the dyke rocks. The EMII-like component might be incorporated into the source area of the primary magma by carbonatitic fluids involving subducted crustal material. The most likely model to explain the small-scale isotopic heterogeneity is plume activity. The results of this study do not provide any support to a cogenetic origin (e.g. fractionation or liquid immiscibility) for carbonatite and monchiquite or other alkali-silicate dyke rocks occurring in spatial proximity. Instead, we propose that both, carbonatite and picrite/monchiquite, originated by low-degree partial melting of peridotite. Textural observations, mineralogical data, and C and O isotopic compositions suggest incorporation of calcite from carbonatite in monchiquite and the occurrence of late-stage carbothermal fluids.

Rhyolite from the Deh Salm area, Lut block, Iran, is a 10-km-long flow unit that crops out as a 6-m thick sub-horizontal sheet (<5° dip) underlain by agglomerate and overlain by crystal lithic tuff. The ryholite contains phenocrysts of garnet, plagioclase and amphibole phases residing in a cryptocrystalline groundmass consisting of plagioclase, K-feldspar and quartz. Euhedral garnet phases range in size from 0.2 to 3.0 mm, have inclusions of ilmenite, rutile, apatite and zircon, and show no reaction/resorption microtextures. Electron microprobe analysis reveals that the garnet is homogeneous, lacks substantial chemical zoning and is dominantly almandine with subordinate pyrope, grossular, spessartine and andradite. The absence of inclusions of metamorphic minerals within garnet as well as the lack of included metamorphic rock fragments in the host rhyolite rule out a xenocrystic origin for the garnet. The garnet phases have low CaO content and variable MnO concentration, resembling those formed from S-type magma. The host rhyolite contains quartz, K-feldspar, and amphibole, has normative corundum, and is peraluminous. Inclusions within garnet as well as the chemistry of the garnet and the host rhyolite suggest that the garnet is a phenocryst phase crystallized from a deep-rooted (>25 km) crustal-derived peraluminous magma. It is likely that the peraluminous feature of the magma, inherited from partial melting of metapelitic source rocks, has favoured crystallization of garnet. Upon rising to higher levels, the garnet phases were in equilibrium with the host magma and thus were preserved as relatively large euhedral crystals in the Deh-Salm rhyolite.