Showing papers in "Mineralium Deposita in 1968"

The theory of metasomatic zoning

Abstract: The main features of the theory of metasomatic zoning, developed by the author, are here exposed. The basic differential equations of metasomatic zoning, of the infiltration as well as of the diffusion type, are deduced for the conditions of local equilibrium, the kinetic phenomena being neglected. The sharpness of the fronts of replacement and other regularities of metasomatic columns are established and the differences between infiltration and diffusion columns are shown. The mathematical model of the “outstripping wave of acidic components” in the flow of postmagmatic solutions is discussed, in relation with the “acidic filtration effect”, i.e., with the higher filtration rate of acidic components as compared with basic ones. The passage of this acidity wave causes the acid leaching of metals out of rocks and their subsequent concentrated redeposition in veins. One may therefore speak of a lateral and vertical hydrothermal acid-base differentiation.

Les structures gigognes: morphologie mathématique et interprétation métallogénique

Abstract: Ce texte a pour but d'analyser la notion d'echelle, ou de niveau d'heterogeneite, d'un phenomene geologique, a l'aide d'outils de morphologie mathematique tels que la «fonction intrinseque» de la theorie des variables regionalisees de G. Matheron. Une premiere etude experimentale montre comment les structures s'emboitent les unes dans les autres dans un depot sedimentaire comme le gisement de fer de Lorraine. Puis, en formulant theoriquement ces imbrications de structures, on montre comment les deux types de fonctions intrinseques observes couramment, le type transitif et le type de wijsien se relient l'un a l'autre. Mais la morphologie mathematique ne peut pas dire pourquoi des structures gigognes en progression geometrique existent.

The Cu-Se system

Abstract: Phase-relations in the Cu-Se system were determined by evacuated silica-tube experiments. The phase diagram up to 1100° C was obtained from the results of differential thermal analyses of pure compounds and of their mixtures. The phases in the system are: Cu2Se — undergoes a polymorphic transformation at 150° C. The symmetry of the low temperature form is not yet known. The high form is cubic with a fluorite-type structure. Cu2−xSe — cubic, with x variable in a very narrow range, at room temperature. Cu3Se2 — tetragonal, breaks down to Cu2−xSe and CuSe at 150° C. CuSe — hexagonal below 60° C and, presumably, orthorhombic at higher temperature, melts incongruently at 387° C to Cu2−xSe and a Se-rich liquid. CuSe2 — orthorhombic, melts incongruently at 347° C to CuSe and a Se-rich liquid. The presence of an eutectic at 523° C was inferred from differential thermal heating and cooling curves.

The Broken Hill ore body, Australia

Abstract: The paper reviews recent works on the Broken Hill ore body to see what data is available on the origin and history of the ore. A high grade metamorphism is recognizable (the Willyama Metamorphism) and this was followed by a number of retrograde metamorphic events. The characteristics of these events is described and this is followed by an analysis of the hypothesis that there is a stratigraphic control of Broken Hill type mineralization. It is concluded that any control that does exist is of a regional nature and that the evidence is equally as good for a restriction of mineralization to areas of high grade metamorphism. Many of the isotopic and geochronological results for Broken Hill are not diagnostic as far as ore genesis is concerned. They do present an internally consistent set of data that records three major events, the Willyama Metamorphism and introduction of the Broken Hill type mineralization at 1700 m. y., the intrusion of the Mundi Mundi Granite and cross cutting pegmatites at 1560 m. y., and retrograde metamorphism and introduction of the Thackaringa Mineralization at or prior to 500 m.y. The sulphides have been deformed in the retrograde schist zones and the ore therefore predates this event. But there is no evidence at the moment that unambiguously establishes that the sulphides were present prior to the Willyama Metamorphism. If it was present prior to or during the Willyama Metamorphism and there is no period of deformation prior to the first recognizable folds at Broken Hill, then the sulphide mass was initially grossly discordant with bedding.

Die Bedeutung geochemisch-stratigraphischer Bezugshorizonte für die Altersstellung der Antimonitlagerstätte von Schlaining im Burgenland, Österreich

Abstract: Es wird die Frage gestellt, ob es bei der Entwicklung unseres Planeten typische, an weltweite Lineamente gebundene Metallzufuhren in die Erdkruste gab, die ihren Erzinhalt so schicht- und zeitgebunden absetzten, das er als Zeitmarke gewertet und zu stratigraphischen Einstufungen und Parallelisierungen auch fossilleerer Gesteine verwendet werden kann. Die Existenz derartiger „geochemischer Leitschichten“ mit typischen „Leitparagenesen“ und diejenige „geochemisch-stratigraphischer Bezugshorizonte“ wird bejaht. Sie wird an Hand von Antimonitlagerstatten mit Scheelitfuhrung bzw. an reinen schichtgebundenen Scheelitvorkommen (mit zum Teil Molybdan-, Beryllium- oder Goldfuhrung) diskutiert. Hierbei wird naher auf die Altersstellung und Genese der Antimonitvorkommen von Schlaining im osterreichischen Burgenland (in der Rechnitzer Schieferserie) eingegangen. Diese liegen raumlich isoliert zwischen den schichtgebundenen, altpalaozoischen Antimonit/Zinnober-Scheelit-Lagerstatten der Ostalpen und denen der Westkarpaten, die gemeinsam als ein „geochemisch-stratigraphischer Bezugshorizont“ gewertet werden. Daraus wird fur die Schlaininger Antimonitvorkommen das bereits in neueren, ungarischen Arbeiten fur die Rechnitzer Schieferserie angegebene, altpalaozoische Alter bestatigt.

On the geographical association of strata-bound ore deposits with evaporites

Abstract: Upwelling leads on the one hand to an enrichment of trace metals in marine sediments, on the other hand to a lack of precipitations in the coastal area. This explains the geographical association between strata-bound ore deposits and evaporites.

The system Pb-As-S

Abstract: Silica-tube quenching experiments and gold-tube pressure experiments were used to study phase relations in the PbS-rich portion of the system Pb-As-S. Emphasis was placed on determining the P-T-X stability relations of jordanite, the most Pb-rich of the synthetic Pb-As-S compounds. Jordanite, Pb9As4S15, is stable below 549 ± 3° C, at which temperature it melts to galena, liquid, and a sulfur-rich vapor phase. Confining pressures of up to 2 Kb do not measurably change this reaction temperature. Density measurements on synthetic material show that the jordanite cell contains 3 (Pb9As4S15); space group P21/m requires that the cell content be expressed as either Pb28−xAs12S46−x or Pb26+xAs12S44+x, with the former much more probable from a structural point of view. In both cases 0.8 < x < 1.4 and the situation is thus quite different from the usual case of defect structures, such as pyrrhotite, Fe1−xS, which shows considerable range of solid solution. Heating experiments on natural gratonite (Pb9As4S15) show that this mineral is most probably a low-temperature dimorph of jordanite, the inversion occurring below 250° C. Experiments have also confirmed the extensive substitution of Sb for As in jordanite, as suspected from chemical analyses of the isostructural mineral geocronite (Pb28−x(As,Sb)12S46−x).

Some genetic aspects of the Mt. Lyell mineralisation

Abstract: A description is given of the mineralogy and textures of the Mt. Lyell copper ores. A number of different ore types have been recognised. It is argued, on the basis of textural evidence, that the host rocks and sulphide ores have been affected by Middle Devonian tectonic activity and that the mineralisation is, therefore, pre-Middle Devonian in age. A genetic relationship between mineralisation and Cambrian volcanism is indicated by the presence of exhalative sedimentary-type ores at the Tasman shaft and Blow mines. The mineralisation as a whole ranges in type from volcanic hydrothermal to exhalative sedimentary. Mineralisation in the Ordovician clay sediments is thought to have arisen by leaching of iron and copper from the nearby Cambrian volcanics. This may have occurred in Ordovician or in more recent times.

Découverte de minéralisations uranifères au Niger

Abstract: Les auteurs presentent l'histoire de la decouverte des minerais d'uranium au Niger. Les premiers indices connus sont lies a ceux du cuivre, dans la region d'Azelik (Departement d'Agades). Les travaux de prospection aerienne et au sol ainsi que les travaux d'investigation par sondages ont dure plus de huit ans et ont permis de prouver l'importance du cadre geologique dans lequel les concentrations uraniferes ont pris naissance et, pour finir, d'apprecier les facteurs favorables au remaniement de ces premieres concentrations et a leur evolution vers des mineralisations d'uranium stratiformes, economiquement exploitables. L'accent est porte plus particulierement sur la tectonique du socle cristallin, le volcanisme hyper-alcalin et les variations climatiques.

The pre-evaluation of the possible profitability of exploration prospects

Abstract: The need for exploration and discovery is apparent from the doubling of tonnage mined about each 12 years. The dependency of exploration expenditure on profits and cash flow is indicated. The capital outlays for selected U.S. and Canadian mines are listed, Tables 1 and 2. The increasing exploration risk, i.e., money spent per discovery, necessitates that criteria be evolved to evaluate exploration projects on the basis of their profitability potential. This involves the chance of occurrence, the chance of actual discovery and the chance of sufficient economic value. These factors are discussed and their evaluation is outlined. An operational equation is set up, and the return on an exploration venture, and a series of exploration ventures, versus the odds against involved, are presented as a possible means of pre-evaluating exploration projects.

The gold fraction of the Witwatersrand conglomerates from the Orange Free State goldfield (South Africa)

Abstract: An investigation of the gold fraction of the Witwatersrand conglomerates from the Orange Free State goldfield (South Africa) has confirmed that the bulk of this metal is concentrated within the bottom parts of the “reefs”, mostly near the footwall contacts. This, together with other criteria, suggests that the distribution of the metal was governed by sedimentary processes. On the other hand, the shape of the gold grains, as well as the general fabric of the gold-enriched layers, often lack conspicuous sedimentary characteristics. Subsequent metamorphism has obviously produced marked structural modifications and a limited textural rearrangement of the gold and its host-rock, thus obliterating to a certain degree the primary alluvial character of the metallization. The large-scale reconstitution of the gold fraction was effected either by a mechanical reshaping of the malleable and ductile gold particles, or by an intermediate solution process followed by reprecipitation. These processes took place more or less in situ. Accordingly, the original sedimentary distribution pattern was not profoundly affected, whereas the individual allogenic gold grains were transformed into authigenic ones or sometimes even into major gold aggregates. Electron-probe microanalysis established that the gold contains on the average between 9.9 and 12.4% silver, which is also suggestive of an alluvial origin. In spite of some uncertainties arising from the camouflaging effect of “pseudohydrothermal” reconstitution processes and from the absence of hydraulic equilibrium between gold and several demonstrably detrital heavy minerals, an integration of all available data strongly supports a modified placer theory for the origin of the Witwatersrand gold.

Nouvelles données sur la genèse des bauxites à mur karstique du sud-est de la France

Abstract: En de nombreux secteurs du Sud-Est de la France, des breches separant la bauxite de son mur, des fossiles et des figures de sedimentation ont ete decouverts, au sein meme de la bauxite: ces elements prouvent que le minerai ne s'est pas forme au lieu meme ou on le trouve aujourd'hui. C'est un sediment qui s'est depose en milieu aqueux, sous forme de bauxite deja constituee, apres avoir subi un transport, en milieu aqueux egalement. Une etude petrographique detaillee montre que ce transport s'est effectue par etapes au cours desquelles la bauxite a continue a subir le phenomene de lateritisation. Les bauxites sont le vestige d'anciens profils de laterite-bauxitique, ferrugineux et alumineux, cuirasses, qui ont ete demanteles. La repartition verticale des differents niveaux de bauxite montre qu'ils peuvent, souvent, constituer des profils inverses de laterites primaires dont on peut interpreter le depot a la faveur de la theorie de la bio-rhexistasie de H. Erhart. Les bauxites ont ete piegees par des sediments de nature lithologique et d'âges divers, qui constituent leurs toits et auxquels elles passent progressivement, ce qui confirme leur caractere sedimentaire.

Contrôle et modèle génétique de minéralisations en galène de type »Red-Beds«

Abstract: Les mineralisations Pb-Zn peneconcordantes du gisement de Largentiere sont liees a 5 niveaux d'une formation detritique continentale (Buntsandstein) qui repose sur le socle hercynien (Massif-Central). Si a l'echelle regionale, les metaux lourds se disposent le long d'une frange qui marque la bordure d'un bassin penesalin, les corps exploites a Largentiere sont sous l'etroite dependance de la paleotopographie locale reconstituee a partir des formes sedimentologiques des interlits argileux. Les observations de detail indiquent une mise en place des metaux immediatement posterieure au depot des sediments qui les supportent. L'ensemble des observations et interpretations immediates s'explique logiquement par une fixation des sulfures le long de l'interface entre une nappe phreatique continentale et une nappe sulfatee, reductrice et liee au bassin. Ce modele paleohydrogeologique permet de selectionner les criteres fondamentaux de ce type de gisement.

Primary ‘cut-and-fill’ channels and gravitational diagenetic features

Abstract: Ore beds with fluorite and sphalerite occur in the Cave-In-Rock fluorite district, Illinois in the upper part of the Mississippian System; in the upper parts of the Fredonia and Joppa Members of the Ste. Genevieve Formation and in the upper part of the Downeys Bluff Formation. Sedimentary structures within the upper two horizons are described and discussed. Primary ‘cut-and-fill’ channels usually contain broken pieces of dolomite, limestone, shale, sandstone, fluorite and sphalerite. Some of the channels show geopetal features. Horizontal stylolitic seams bend downward and their thicknesses increase while their amplitudes decrease near and along the channel slopes. Another geopetal feature consists of clastic shale fragments which have mechanically filled from above into an open crack formed in the hydroplastic carbonate mud below. A number of features known as “collapsed structures” prove to be ‘cut-and-fill’ structures of primary origin. During the compaction, carbonate beds were reduced in thickness by at least 37% through styloitization. The relationships between primary sedimentary channels and fluorite-sphalerite ore rocks suggest that the latter may have been deposited during or after the formation of such sedimentary structures, i. e., during various stages of diagenesis.

Kontinentalverschiebung und Erzprovinzen

Abstract: Die Moglichkeiten der Kontinentalverschiebung werden durch einen Versuch der Parallelisierung von Erzprovinzen und -epochen uberpruft und nach orogenetischen Perioden unterschieden. Wahrend einzelne Gebiete, z. B. Brasilien und Westafrika verbluffende Ahnlichkeit zeigen, ist die Ubereinstimmung anderswo schlecht oder fehlt ganz, u.a. naturlich auch wegen fehlender Information. Ruckschlusse, die Herkunft der Metalle betreffend, konnten gezogen werden.

Neue Untersuchungsergebnisse zur Genese der im östlichen Teil der Erzprovinz von Cartagena (Spanien) gelegenen Blei-Zinkerz-Vorkommen

Abstract: Im ostlichen Teil der Sierra von Cartagena (Spanien) wurden Blei-Zinkerzvorkommen untersucht. Es wurden zwei Vererzungsphasen nachgewiesen. Die altere, primare Vererzung tritt in einem 5 m machtigen Konglomerat auf und ist streng schichtgebunden. Eine Vererzung der liegenden Gesteine fand nicht statt. Erze und Nebengestein erlebten eine intensive tektonische Uberpragung. Hierdurch wurde der primare Mineralbestand teilweise mobilisiert und als jungere Erzbildung wieder abgesetzt. Eine hydrothermal-metasomatische Entstehung der Vererzung im Konglomerat ist abzulehnen.

Une méthode permettant de mettre en évidence le caractère ordonné de la distribution de certains gîtes minéraux

Abstract: On decrit une methode de calcul par analogie optique qui permet de mettre en evidence des groupements lineaires de gisements sur la carte metallogenique. L'appartenance des gisements aux differents systemes de groupements permet de leur attribuer des caracteres de position qui semblent correles a certains de leurs caracteres propres. Dans la mesure ou les faits observes sont significatifs, ils sont utilisables dans le domaine de la metallogenie previsionnelle.

The source of metals and gangue elements in epigenetic deposits

Abstract: The metals, gangue elements, and volatiles in epigenetic deposits probably came from the country rocks that enclose, lie below, or lie lateral to the deposits. From their sites in the country rocks the elements were mobilized during metamorphism or were collected by deep seated circulating ground waters or brines. Most elements probably migrate by diffusion and are concentrated by the action of dilatant structures or as a result of chemical reaction with favourable rocks such as limestones.

Géologie des minerais de fer oolithiques

Abstract: Dans cet article, l'auteur presente la geologie des minerais de fer oolithiques. Apres avoir rappele le mode de formation et les conditions de depot des oolithes dans le gisement Lorrain, l'auteur decrit les differentes etapes de l'evolution du minerai de fer: etat initial, puis transformations par diagenese, epigenese et metamorphisme. Il decrit ensuite les differents types de depots, l'environnement geographique et les bassins d'alimentation possibles, qui se modifient legerement, au cours de la formation des couches successives, pendant l'epoque «Toarcien terminal-Aalenien». Une extension de ce mode de formation aux autres types de minerais de fer stratiforme est envisagee.

The formation of pyrite from hydrated iron oxide in aqueous solution at 20°C

Abstract: Experiments are described in which pyrite is synthesized at room temperature and atmospheric pressure from hydrated iron oxides and hydrogen sulphide under conditions similar to those expected in the natural environment. This synthesis differs from earlier work in that oxygen was rigorously excluded from the system and the pH was 5.6. During a later ageing period a reaction appears to take place in which iron monosulphide is converted to pyrite at pH 5.85.

Artificial diagenesis in quartz sand and carbonate rocks

Abstract: Diagenetic changes in carbonates and sand can be produced in the laboratory through injection of sea water These changes are comparable to those found in the natural environment and are shown on photomicrographs Artificial sea water of known composition under a partial pressure of carbon dioxide was injected through a composite lithology representing a shallow marine shelf After passage of water for several days, the diagenetic alterations in the sediments were studied under a petrographic microscope The study includes (1) the interrelation of the chemistry of the water in sediments and the mineralogy of the sediments, (2) the factors which control the processes of calcite and silica precipitation, (3) the processes responsible for transforming sediments into hard rock and, (4) the sequence of these processes

Applicability of palaeomagnetism of pyrrhotite to ore-genetic studies

Abstract: Pyrrhotite has never before been used in palaeomagnetic investigations, being highly anisotropic magnetically. The aim of this paper is to show that fine-grained pyrrhotite aggregates of hydrothermal origin can be used for palaeomagnetic purposes. This has been proved with polymetallic Turkaňk veins from Kutna Hora in Central Bohemia as an example. It can be assumed that other localities with occurrence of hydrothermal pyrrhotite aggregates which contain directionless, uniformly scattered pyrrhotite grains and therefore forming a magnetically isotropic medium may be suitable for palaeomagnetic studies.

Betekhtinite from Mt. Lyell, tasmania

Abstract: Betekhtinite occurs in specimens of recrystallised galena from the North Lyell orebody. Its chemical composition is Cu 59.0, Pb 17.3, Fe 2.7, S 20.6, total 99.6. The thermal stability of betekhtinite is briefly discussed.

Zur Bedeutung der methodischen Probennahme für genetische Untersuchungen von Bauxit-Lagerstätten am Beispiel der Oberkreide-Bauxite der Parnass-Kiona-Zone Griechenlands

Abstract: Die Diskussionen uber die Diaspor-Boehmit-Genese in Bauxit-Lagerstatten stutzten sich im wesentlichen auf die Untersuchung einzelner Profile. Bei der Bearbeitung griechischer Bauxitvorkommen der Parnass-Kiona-Zone ergab sich jedoch, das die Frage der Diaspor-Boehmit-Verteilung nur durch eine flachenhafte, netzartige Probenentnahme mit Dezimeter-Abstanden geklart werden kann. Diese Untersuchungsmethodik ist von entscheidender Bedeutung fur das Studium der Diaspor-Boehmit-Genese. Es gelang, im Gelande makroskopisch Diaspor- von Boehmit-Bauxiten zu unterscheiden. Es zeigte sich, das die Lage von Diaspor und Boehmit im Profil nicht konstant ist. Somit erscheint es unumganglich, die bisherigen Vorstellungen uber die Diaspor-Boehmit-Genese zu uberprufen.

Ore mineral relations in the Cuyuna sulfide deposit, Minnesota

Abstract: The Cuyuna sulfide deposit is located in south central Aitkin County in an outlying area of the Cuyuna Iron Range, Minnesota. The principal ore minerals are pyrrhotite and pyrite, whereas magnetite and marcasite are subordinate. In addition, sphalerite, chalcopyrite, arsenopyrite, ilmenite, covellite, hematite, and goethite are present in minor quantities. Four generations of pyrite two generations of marcasite and three generations of Magnetite have been recorded. The genetic and textural relations displayed by the ore minerals indicate that an iron formation, originally containing sedimentary sulfide and carbonate facies, was profundly modified through subsequent metamorphic and supergene events.

Zur Petrographie der Bauxitlagerstätten auf der „Charnockite-suite“ im Salemdistrikt und in den Nilgiri-Hills, Südindien

Abstract: Von fossilen — wahrscheinlich alttertiaren — Bauxiten auf Charnockiten in den Shevaroy-Hills und in den Nilgiri-Hills/Sudindien, die sich unter Reliktgefugeerhaltung isovolumetrisch umwandelten, wurden drei Profile quantitativ chemisch und mineralogisch untersucht. Chemismus und Mineralzusammensetzung variieren stark in Abhangigkeit von der Petrographie des Ausgangsgesteins. Na, K, Ca, Mg und die Hauptmenge der Kieselsaure wurden abtransportiert. Al und Fe erfuhren eine relative und in bestimmten Bereichen eine absolute Anreicherung. Die Mineralumwandlung im Fruhstadium der Verwitterung lief in zwei Phasen ab: 1. Losung und Ausfallung auf Spaltrissen der Minerale, 2. Losung und Ausfallung an Stelle der reliktischen Mineralkerne.

Variations in carbon and oxygen isotope ratios as a possible guide to ore

Abstract: Contour maps showing variations in carbon and oxygen isotope ratios may be useful as a guide to ore. Previous literature suggests that the isotopic composition of carbon is related to the environment in which it is deposited. Sedimentary syngenetic ore deposits are also related to the depositional environment in which they occur and should therefore be related to the isotopic composition of the carbon deposited along with the ore. Although metamorphism may obscure palaeontological and stratigraphic indicators of environment, the isotopic composition of organic carbon appears to be unaffected by it. Previous literature suggests that variations in oxygen isotopes can be used also as a guide to certain epigenetic ore deposits.

On the textures and paragenesis of the gold-quartz-tourmaline veins of Ondonoc, W.-Ethiopia

Abstract: The gold-quartz-tourmaline veins of Ondonoc occur in diorites and schists and follow the non-distortion planes of the theoretical strain ellipsoid. Textural studies reveal a sequence of crystallization phases. In addition to an early prismatic tourmaline, a late phase “metasomatic” tourmalinization is recognized. The gold occurs mainly with pyrite which, in turn, is considered to belong to a late phase with ankerite and prochlorite. Micromylonitization and other tectonic influences are recognizable and bodies of the country rock, e.g. schists and tourmalinefels, are engulfed and tectonically mobilized within these veins, thus rendering the interpretation of the paragenesis more difficult.