Estimating relative bed-load contributions by lithology counts

In gravel-bedded streams where bed material of a tributary differs distinctly in lithology from that of the main stream, rock-type percentages can be used to estimate bed-load contributions of the two streams. The rock type that shows the greatest difference in abundance between the two streams is selected as the indicator lithology. Percentages of this lithology are estimated in both the main stream and tributary stream above their junction, and also in the main stream at a distance sufficiently downstream from the junction to allow complete mixing. The fraction of bed load contributed by the main stream, p,is estimated by ,where is an estimate of the proportion of indicator rock fragments in the bed of the main stream above the junction, is an estimate of the proportion in the bed of the tributary above the junction, and is an estimate of the proportion in the bed of the main stream below the junction. The variance of is obtained as var ( )= [p₁q₁(p_r – p₂)²/n(p₁ – p₂)⁴] + [p₂q₂(p_r – p₁)²/n(p₁ – p₂)⁴] + [p_rq_r/n(p₁ – p₂)²].Although no estimate of actual quantity of bed load is provided, the indicator rock technique supplies data that can serve as a check on data obtained by means of empirical formulas or actual transport measurements.     

Estimation of covariance matrix from geochemical data with observations below detection limits

Multivariate statistical analyses have been extensively applied to geochemical measurements to analyze and aid interpretation of the data. Estimation of the covariance matrix of multivariate observations is the first task in multivariate analysis. However, geochemical data for the rare elements, especially Ag, Au, and platinum-group elements, usually contain observations the below detection limits. In particular, Instrumental Neutron Activation Analysis (INAA) for the rare elements produces multilevel and possibly extremely high detection limits depending on the sample weight. Traditionally, in applying multivariate analysis to such incomplete data, the observations below detection limits are first substituted, for example, each observation below the detection limit is replaced by a certain percentage of that limit, and then the standard statistical computer packages or techniques are used to obtain the analysis of the data. If a number of samples with observations below detection limits is small, or the detection limits are relatively near zero, the results may be reasonable and most geological interpretations or conclusions are probably valid. In this paper, a new method is proposed to estimate the covariance matrix from a dataset containing observations below multilevel detection limits by using the marginal maximum likelihood estimation (MMLE) method. For each pair of variables, sayY andZ whose observations containing below detection limits, the proposed method consists of three steps: (i) for each variable separately obtaining the marginal MLE for the means and the variances, , , , and forY andZ: (ii) defining new variables by and and lettingA=C+D andB=C–D, and obtaining MLE for variances, and forA andB; (iii) estimating the correlation coefficient _YZ by and the covariance _YZ by . The procedure is illustrated by using a precious metal geochemical data set from the Fox River Sill, Manitoba, Canada.     

Morphologische Betrachtungen an den Heidelberger synthetischen Quarzen

Zusammenfassung Die von Dr.Baumann, Heidelberg, synthetisierten Quarze zeichnen sich nicht nur durch eine außerordentliche Klarheit, sondern auch durch eine auffallende Morphologie aus. Es werden drei grundsätzlich verschiedene Typen beschrieben. Typ I ist pseudorhombisch; eine der a-Achsen verleiht ihm stark polare Gestalt. Als größte Fläche ist das re. trig. Prisma II. St. , entwickelt. Das Trapezoeder erscheint an zwei Stellen vizinal. Typ II ist nach einer der Winkelhalbierenden der a-Achsen gestreckt. In dieser Richtung betrachtet erscheint der Kristall tetragonal, da auf diese Weise die unter rechtem Winkel stehenden Flächen , (0001), und das Quadrat begrenzen. Dies sind zugleich die größtentwickelten Flächen. Typ III ist isometrisch; sämtliche Flächen (Prismen, beide Rhomboeder sowie das Basisendflächenpaar) sind etwa gleich stark entwickelt. In Richtung auf das pos. Rhomboeder betrachtet, erweckt dieser Typ den Eindruck eines kubischen Kristalles. Hier fehlen trig. Prisma und das Trapezoeder.

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Summary Quarz crystals, grown by Dr.Baumann, Heidelberg, are remarkable not only for their extraordinary transparency but also for a conspicuous morphology. Three completely different types are described. Type I is pseudo-orthorhombic; one of the a-axes causes a strongly polar appearance. Largest face is the right trig. prism II. position . The trapezohedron appears in two positions as vicinals. Type II is alongated parallel to one of the bisectrices of the a-axes. Viewed in this direction the crystal seems to be tetragonal, as the faces , (0001), and , which are at right angles to each other, form a square; these faces are at the same time the largest ones. Typ III is isometric; all the faces (prisms, both rhombohedrons, and the pinacoid) are of approximately the same size. Viewed in the direction upon the pos. rhombohedron this type appears to be cubic. The trig. prism and the trapezohedron are here missing.

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Mit 4 Figuren und 3 Textabbildungen

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Herrn Professor Dr.F. Machatschki zum 70. Geburtstag gewidmet.     

A regional gradient in the composition of metamorphic fluids in pelitic schist,Pecos Baldy,New Mexico

Two metamorphic isograds cut across graphitic schist near Pecos Baldy, New Mexico. The southern isograd marks the first coexistence of staurolite with biotite, whereas the northern isograd marks the first coexistence of andalusite with biotite. The isograds do not record changes in temperature or pressure. Instead, they record a regional gradient in the composition of the metamorphic fluid phase. Ortega Quartzite, which contains primary hematite, lies immediately north of the graphitic schist. Mineral compositions within the schist change gradually toward the quartzite, reflecting gradients in and . The chemical potential gradients, locally as high as 72 cal/m in and 9 cal/m in , controlled the positions of the two mapped isograds. The staurolite-biotite isograd records where fell below 0.80, at near 10^–23 bars; the andalusite-biotite isograd records where fell below 0.25, at near 10^–22 bars. Dehydration and oxidation were coupled by graphite-fluid equilibrium.The chemical potential gradients apparently formed during metamorphism, as graphite in schist reacted with hematite in quartzite. Local oxidation of graphite formed CO₂ which triggered dehydration reactions along the schistquartzite contact. This process created a C-O-H fluid which infiltrated into overlying rocks. Upward infiltration, local fluid-rock equilibration and additional infiltration proceeded until the composition of the infiltrating fluid evolved to that in equilibrium with the infiltrated rock. This point occurs very close to the staurolite-biotite isograd. Pelitic rocks structurally above this isograd show no petrographic evidence of infiltration, even though calculations indicate that volumetric fluid/rock ratios may have exceeded 15 and thin, rare calc-silicate beds show extensive K-metasomatism and quartz veining.     

The pleochroism of a gem-quality enstatite in the region of the OH stretching frequency,with a stereochemical interpretation

Summary The pleochroic behaviour of a gem-quality enstatite from Tanzania was investigated in the region =2500 to 4000 cm^–1. Two sharp absorption bands at =3410 cm^–1 and =3510 cm^–1 are interpreted to be caused by OH stretching vibrations. As their absorption coefficients are considerably larger parallel to [001] (=direction of the silicate chains) than perpendicular to this direction, the OH dipoles have to be oriented approximately parallel to [001]. On this basis, a stereochemical interpretation of the incorporation of the OH groups into the structure is given.

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Der Pleochroismus eines Enstatits von Edelsteinqualität im Gebiet der OH-Streckfrequenz und seine kristallchemische Interpretation

Zusammenfassung Das pleochroitische Verhalten eines Enstatits von Edelsteinqualität aus Tansania wurde im Bereich =2500 bis 4000 cm^–1 untersucht. Von zwei scharfen Banden bei =3410 cm^–1 und 3510 cm^–1 wird angenommen, daß sie durch OH-Streckschwingungen herrühren. Da ihre Absorptionskoeffizienten parallel zu [001] (=Richtung der Silikatketten) beträchtlich größer sind als senkrecht dazu, müssen die OH-Dipole ungefähr parallel zu [001] liegen. Auf dieser Basis wird der Einbau der OH-Gruppen in die Struktur diskutiert.

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With 3 Figures     

Johillerit,Na(Mg,Zn)3 Cu(AsO4)3, ein neues Mineral aus Tsumeb,Namibia

Zusammenfassung Die chemische Analyse des neuen Minerals Johillerit mit der Elektronenmikrosonde ergab: Na₂O 5,4, MgO 18,3, ZnO 5,4, CuO 15,8 und As₂O₅ 55,8, Summe 100.7%. Aus diesem Ergebnis wurde die idealisierte Formel Na(Mg, Zn)₃ Cu(AsO₄)₃ abgeleitet. Johillerit ist monoklin mit der RaumgruppeC2/c. Die Gitterkonstanten sind:a=11,870 (3),b=12,755 (3),c=6,770 (2) , =113,42 (2)°,Z=4. Die stärksten Linien des Pulverdiagramms sind: 4,06 (5) (22 ), 3,50 (4) (310), 3,25 (8) (11 ), 2,75 (10) (330, 240), 2,64 (5) (311, 13 , 40 ), 1,952 (4) (13 , 35 ), 1,682 (4) (20 , 460), 1,660 (5) (40 , 71 , 550, 64 ), 1,522 (4) (442, 153, 13 ). Es bestehen enge strukturelle Beziehungen zwischen Johillerit und O'Danielit, Na(Zn, Mg)₃H₂(AsO₄)₃, sowie einigen synthetischen. Verbindungen.Johillerit ist violett durchscheinend. Die Spaltbarkeit nach {010} ist ausgezeichnet und nach {100} und {001} gut.H (Mohs)3.D=4,15 undD _X =4,21 g·cm^–3. Das Mineral ist optisch zweiachsig positiv, 2V80 (5)°. Die Werte der Lichtbrechung sindn =1,715 (4),n =1,743 (4) undn =1,783 (4). Die Auslöschung istn b und auf (010)n c16°. Johillerit ist stark pleochroitisch mit den AchsenfarbenX=violett-rot,Y = blauviolett undZ = grünblau. Das neue Mineral kommt in radialstrahligen Massen gemeinsam mit kupferhaltigem Adamin und Konichalcit in zersetzem Kupfererz von Tsumeb, Namibia, vor. Die Benennung erfolgte nach Prof. Dr.J.-E. Hiller (1911–1972).

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Johillerite, Na(Mg, Zn) ₃ Cu(AsO ₄ ) ₃ , a new mineral from Tsumeb, Namibia

Summary Electron microprobe analysis of the new mineral johillerite gave Na₂O 5.4, MgO 18.3, ZnO 5.4, CuO 15.8, and As₂O₅ 55.8, total 100.7%. From this result, the ideal formula is given as Na(Mg, Zn)₃ Cu(AsO₄)₃. Johillerite crystallizes monoclinic,C2/c. The unit cell dimensions are:a=11.870(3),b=12.755 (3),c=6.770 (2) , =113.42 (2)°,Z=4. The strongest lines on the X-ray powder diffraction pattern are: 4,06 (5) (22 ), 3,50 (4) (310), 3,25 (8) (11 ), 2,75 (10) (330, 240), 2,64 (5) (311, 13 , 40 ), 1,952 (4) (13 , 35 ), 1,682 (4) (20 , 460), 1,660 (5) (40 , 71 , 550, 64 ), 1,522 (4) (442, 153, 13 ). There is a close relationship between johillerite, o'danielite, Na(Zn, Mg)₃H₂(AsO₄)₃, and some synthetic compounds. Johillerite is violet in colour, transparent. Cleavage is {010} perfect, {100} and {001} good.H (Mohs)3.D=4.15 andD _X =4.21 g·cm^–3. The mineral is optically biaxial positive, 2V80 (5)°. The refractive indices are:n =1.715 (4),n =1.743 (4),n =1.783 (4). The extinction isn b and on (010)n c16°. Strongly pleochroic with axial coloursX=violet-red,Y=bluish violet andZ=greenish blue. The new mineral was found in radiated masses together with cuprian adamite and conichalcite in an oxidized copper ore from Tsumeb, Namibia. It is named in honour of Prof. Dr.J.-E. Hiller (1911–1972).

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Mit 1 Abbildung     

Zur Bestimmung einer definierten mittleren Lichtbrechung optisch einachsiger Minerale im Dünnschliff

Zusammenfassung Durch Gangunterschiedsbestimmungen in der auf dem Drehtisch eingemessenen Kreisschnittebene optisch einachsiger Kristalle läßt rich eine mittlere Lichtbrechung theoretisch ableiten and experimentell direkt bestimmen. Ein graphisches and ein rechnerisches Verfahren zur Gewinnung der aus den Ganguntersehieden wird entwickelt and an Quarz, Korund, Zirkon, Turmalin und Eisenorthoklas ausprobiert. Man erhält für die mittlere Lichtbrechung Werte, die günstigenfalls mit der Immersionsmethode an Genauigkeit vergleichbar sind.     

Koritnigit,Zn[H2O|HOAsO3], ein neues Mineral aus Tsumeb,Südwestafrika

Zusammenfassung Das neue Mineral Koritnigit ist ein wasserhaltiges Zinkhydrogenarsenat der Formel Zn[H₂O|HOAsO₃]. Die chemische Analyse (Elektronenmikrosonde und T.G.A.) ergab: As₂O₅ 51,75%, ZnO 35,97% und H₂O 12,3%, Summe 100,0%. Die HOAsO₃-Ionen wurden IR-spektroskopisch nachgewiesen. Koritnigit ist löslich in kalter, verdünnter HCl und HNO₃.Die Gitterkonstanten sind:a ₀=7,948(2),b ₀=15,829(5),c ₀=6,668(2) Å, =90,86(2), =96,56(2), =90,05(2)^o,V=833,2(4)ų,V=8. Die Raumgruppe ist . Die stärksten Linien des Pulverdiagramms sind: 7,90(10) (020,100), 3,83(7) ( ), 3,16(9) ( ) 2,926(4) (150), 2,679(4) ( ), 2,461(6) ( ), 2,186(5) ( ), 1,969(4) (400), 1,649(3) (004).Koritnigit ist wasserklar bis durchscheinend weiß. Idiomorphe Kristalle sind nicht bekannt. Die Spaltbarkeit nach {010} ist ausgezeichnet und auf {010} sind Spaltspuren nach [001] und nach [100] erkennbar. Härte 2.G=3,54 g·cm^–3,D _x =3,56 g·cm^–3. Koritnigit ist optisch zweiachsig positiv, 2V70(5)^o. Die Werte der Lichtbrechung sind:n =1,632(5),n =1,652(3) undn =1,693(3).Koritnigit wurde auf der 31. Sohle der Tsumeb-Mine, Südwestafrika gefunden. Er kommt als Sekundärmineral in Paragenese mit Cu-Adamin, Stranskiit und drei weiteren, vorerst nicht identifizierten mineralen in Zersetzungshohlräumen von Tennantit vor.

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Koritnigite, Zn[H₂O|HOAsO₃], a new mineral from Tsumeb, South West Africa

Summary The new mineral koritnigite is a hydrated zinc hydrogen arsenate with the formula Zn[H₂O|HOAsO₃]. Chemical analysis (electron microprobe and t.g.a.) gave: As₂O₅ 51.75%, ZnO 35.97%, and H₂O 12.3%, total 100.0%. The HOAsO₃ ions were determined by IR spectroscopy. Koritnigite is soluble in cold diluted HCl and HNO₃. The unit cell dimensions are:a ₀=7.948(2),b ₀=15.829(5),c ₀=6.668(2)Å, =90.86(2), =96.56(2), =90.05(2)^o,V=833.2(4) ų,Z=8. The space group is . The strongest lines of the powder pattern are: 7.90(10) (020, 100), 3.83(7) ( ), 3.16(9) ( ), 2.926(4) (150), 2.679(4) ( ), 2.461(6) ( ), 2.186(5) ( ), 1.969(4)(400), 1.649(3) (004).

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Mit 2 Abbildungen

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Herrn Univ. Prof. Dr.H. Meixner zum 70. Geburtstag gewidmet.     

The crystal structure of a triclinic roscherite

Summary The crystallography of roscherite is more complicated than previously thought. Single crystal X-ray work on material from Foote Mine (California) gave triclinic symmetry. The unit cell corresponding to the one adopted for monoclinic roscherite hasa=15.921,b=11.965,c=6.741 Å, =91°04, =94°21, =89°59 1/2, space group . The least-squares refinement of the structure using 2380 non zero reflections with anisotropic temperature factors resulted in a conventional reliability factorR=0.060.The X-ray study indicates the formula while that proposed for monoclinic roscherite is The atomic arrangements of both varieties of roscherite are very similar. The lowering of symmetry is caused by the segregation of the trivalent cations into only half of the sites of a monoclinic point position. Crystallochemical considerations suggest that the symmetry of roscherite does not depend on the kind of trivalent cations occupying the 6-coordinated position, but rather by the ratio between trivalent and divalent metal ions.

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Die Kristallstruktur eines triklinen Roscherites

Zusammenfassung Die Kristallographie des Roscherites ist komplizierter als man bisher annahm. Einkristall-Röntgenuntersuchungen an Material von Foote Mine (Kalifornien) ergaben trikline Symmetrie. Die Elementarzelle, welche der für monoklinen Roscherit angenommenen entspricht, hata=15,921,b=11,965,c=6,741 Å, =91°04, =94°21, =89°59 1/2, Raumgruppe . Die Verfeinerung der Struktur mit der Methode der kleinsten Quadrate ergab unter Verwendung anisotroper Temperaturfaktoren für 2380 beobachtete Reflexe einen konventionellen ZuverlässigkeitsindexR=0,060.Die Röntgenuntersuchung weist auf die Formel , während für monoklinen Roscherit vorgeschlagen wurde. Die Atomanordnungen beider Abarten des Roscherites sind sehr ähnlich. die Symmetrieerniedrigung wird dadurch hervorgerufen, daß die dreiwertigen Kationen nur die Hälfte der Positionen einer monoklinen Punktlage besetzen. Kristallchemische Überlegungen weisen darauf hin, daß die Symmetrie nicht von der Art der dreiwertigen Kationen, welche eine 6-koordinierte Punktlage besetzen, abhängt, sondern vielmehr von dem Mengenverhältnis zwischen 3-wertigen und 2-wertigen Metallionen.

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With 1 Figure     

Colquiriit,ein neues Fluoridmineral aus der Zinnlagerstätte von Colquiri in Bolivien

Zusammenfassung Colquiriit tritt in Vergesellschaftung mit Ralstonit, Gearksutit, Zinkblende, Madocit und Pyrit im Bereich der Zinnlagerstätte von Colquiri in Bolivien auf. Das als selten zu betrachtende Mineral bildet maximal cm-große xenomorphe durchscheinende bis durch-sichtige Körner von weißlicher Farbe. Es zeigt keine Spaltbarkeit. Härte ca. 4; Dichte (gem.) 2,94, (ber.) 2,95 g/cm³;n 1,385±0.002,n 1,388±0,002, einachsig oder schwach zweiachsig, negativ. Colquiriit kristallisiert trigonal, Raumgruppe oderP31c,a ₀ 5,02,c ₀ 9,67 Å,Z=2. Stärkste Linien des Pulverdiagramms: 3,98(7) ; 3,23(10) ; 2,22(9) ; 1,736(8) . Eine chemische Analyse ergab: Li 3,1, Na 0,34, Mg 0,55, Ca 22,8, Al 13,4, F 58,0, Gewichtsverlust (105 °C) 0,5, Summe 98,69%, woraus sich die idealisierte Formel LiCaAlF₆ ableiten läßt. Beim Erhitzen wird das Gitter zwischen 800 und 900°C zerstört.

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Colquiriite, a new fluoride mineral from the Colquiri tin deposit in Bolivia

Summary Colquiriite occurs at the Colquiri tin deposit in Bolivia and is associated with ralstonite, gearksutite, sphalerite, madocite and pyrite. The mineral, which probably is a rare species, forms anhedral translucent to transparent white grains reaching up to 1 cm in size. No cleavage; hardness about 4; density (meas.) 2.94, density (calc.) 2.95 g/cm³;n 1.385±0.002,n 1.388±0.002, uniaxial or weakly biaxial, negative. Colquiriite is trigonal,a ₀ 5.02,c ₀ 9.67 Å, space group orP31c,Z=2. The strongest lines of the powder pattern are: 3.98(7) ; 3.23(10) ; 2.22(9) ; 1.736(8) . The chemical analysis gave: Li 3.1, Na 0.34, Mg 0.55, Ca 22.8, Al 13.4, F 58.0, weight loss (105 °C) 0.5, sum 98.69%, leading to the idealized formula LiCaAlF₆. Heating experiments show that the lattice breaks down between 800 and 900 °C. The new mineral and its name have been approved by the I.M.A. Commission on New Minerals and Mineral Names.

     

Verdreifachte Achsenbilder an den Magnesitkristallen von Asturreta in Spanien

Zusammenfassung Die nach einer Scheinbasis tafeligen Magnesitkristalle von Asturreta (und ebenso ähnliche Dolomitkristalle aus den Magnesitlagerstätten Sunk, Oberdorf und Lanersbach) liefern bei Einbettung in den meisten üblichen Immersionsmitteln bei konoskopischer Beobachtung nicht ein, sondern drei einachsige Achsenbilder. Die Erscheinung wird nicht etwa durch Verzwillingung verursacht, sondern, da die Scheinbasis aus zahlreichen winzigen, streng parallelen r aufgebaut ist, durch einen Summeneffekt der symmetriebedingten -Flächenlagen in Abhängigkeit vom Einbettungsmittel. Das konnte durch Rechnung und Messung bewiesen werden.Mit 4 Textabbildungen.     

Redox states of lithospheric and asthenospheric upper mantle

The oxidation state of lithospheric upper mantle is heterogeneous on a scale of at least four log units. Oxygen fugacities ( ) relative to the FMQ buffer using the olivine-orthopyroxene-spinel equilibrium range from about FMQ-3 to FMQ+1. Isolated samples from cratonic Archaean lithosphere may plot as low as FMQ-5. In shallow Proterozoic and Phanerozoic lithosphere, the relative is predominantly controlled by sliding Fe³⁺-Fe²⁺ equilibria. Spinel peridotite xenoliths in continental basalts follow a trend of increasing with increasing refractoriness, to a relative well above graphite stability. This suggests that any relative reduction in lithospheric upper mantle that may occur as a result of stripping lithosphere of its basaltic component is overprinted by later metasomatism and relative oxidation. With increasing pressure and depth in lithosphere, elemental carbon becomes progressively refractory and carbon-bearing equilibria more important for control. The solubility of carbon in H₂O-rich fluid (and presumably in H₂O-rich small-degree melts) under the P,T conditions of Archaean lithosphere is about an order of magnitude lower than in shallow modern lithosphere, indicating that high-pressure metasomatism may take place under carbon-saturated conditions. The maximum in deep Archaen lithosphere must be constrained by equilibria such as EMOG/D. If the marked chemical depletion and the orthopyroxene-rich nature of Archaean lithospheric xenoliths is caused by carbonatite (as opposed to komatiite) melt segregation, as suggested here, then a realistic lower limit may be given by the H₂O +C=CH₄+O₂ (C-H₂O) equilibrium. Below C –H₂O a fluid becomes CH₄ rather than CO₂-bearing and carbonatitic melt presumably unstable. The actual in deep Archaean lithosphere is then a function of the activities of CO₂ and MgCO₃. Basaltic melts are more oxidized than samples from lithospheric upper mantle. Mid-ocean ridge (MORB) and ocean-island basalts (OIB) range between FMQ-1 (N-MORB) and about FMQ +2 (OIB). The most oxidized basaltic melts are primitive island-arc basalts (IAB) that may fall above FMQ+3. If basalts are accurate probes of their mantle sources, then asthenospheric upper mantle is more oxidized than lithosphere. However, there is a wide range of processes that may alter melt relative to that of the mantle source. These include partial melting, melt segregation, shifts in Fe³⁺/Fe²⁺ melt ratios upon decompression, oxygen exchange with ambient mantle during ascent, and low-pressure volatile degassing. Degassing is not very effective in causing large-scale and uniform shifts, while the elimination of buffering equilibria during partial melting is. Upwelling graphite-bearing asthenosphere will decompress along -pressure paths approximately parallel to the graphite saturation surface, involving reduction relative to FMQ. The relative will be constrained to below the CCO equilibrium and will be a function of . Upwelling asthenosphere whose graphite content has been exhausted by partial melting, or melts that have segregated and chemically decoupled from a graphite-bearing residuum will decompress along -decompression paths controlled by continuous Fe³⁺-Fe²⁺ solid-melt equilibria. These equilibria will involve increases in relative to the graphite saturation surface and relative to FMQ. Melts that finally segregate from that source and erupt on the earth's surface may then be significantly more oxidized than their mantle sources at depth prior to partial melting. The extent of melt oxidation relative to the mantle source may be directly proportional to the depth of graphite exhaustion in the mantle source.     

Systematic study of liquidas phase relations in olivine melilitite +H2O +CO2 at high pressures and petrogenesis of an olivine melilitite magma

Near-liquidus phase relationships of a spinel lherzolite-bearing olivine melilitite from Tasmania were investigated over a P, T range with varying , , and . At 30 kb under MH-buffered conditions, systematic changes of liquidus phases occur with increasing ( = CO₂/CO₂ +H₂O+olivine melilitite). Olivine is the liquidus phase in the presence of H₂O alone and is joined by clinopyroxene at low . Increasing eliminates olivine and clinopyroxene becomes the only liquidus phase. Further addition of CO₂ brings garnet+orthopyroxene onto the liquidus together with clinopyroxene, which disappears with even higher CO₂. The same systematic changes appear to hold at higher and lower pressures also, only that the phase boundaries are shifted to different . The field with olivine- +clinopyroxene becomes stable to higher with lower pressure and approaches most closely the field with garnet+orthopyroxene+clinopyroxene at about 27 kb, 1160 °C, 0.08 and 0.2 (i.e., 6–7% CO₂+ 7–8% H₂O). Olivine does not coexist with garnet+orthopyroxene+clinopyroxene under these MH-buffered conditions. Lower oxygen fugacities do not increase the stability of olivine to higher and do not change the phase relationships and liquidus temperatures drastically. Thus, it is inferred that olivine melilitite 2927 originates as a 5% melt (inferred from K_{2 O} and P₂O₅ content) from a pyrolite source at about 27kb, 1160 dg with about 6–7% CO₂ and 7–8% H₂O dissolved in the melt. The highly undersaturated character of the melt and the inability to find olivine together with garnet and orthopyroxene on the liquidus (in spite of the close approach of the respective liquidus fields) can be explained by reaction relationships of olivine and clinopyroxene with orthopyroxene, garnet and melt in the presence of CO₂.     

The volatile component of quaternary ignimbrite magmas from the North Island,New Zealand

Ignimbrites from the central North Island consist mainly of glass or its devitrified product (70–95%); their phenocryst mineralogy is varied and includes plag., hyp., ti-mag., ilm., aug., hblende, biot., san., qtz, ol., with accessory apatite, zircon and pyrrhotite. The Fe-Mg minerals can be used to divide the ignimbrites into four groups with hyp.+aug. reflecting high quench temperatures and biot.+hblende +hyp.+aug., low quench temperatures. Oxygen fugacities lie above the QMF buffer curve and even in ignimbrites with low crystal contents the solid phases apparently buffered fO₂. Some ignimbrites contain the assemblage actinolite, gedrite, magnetite and hematite, reflecting post-eruption oxidation. The mineralogy also allows estimation of using pyrrhotite and thence , . The assemblage biotite-sanidine can be used to estimate and thence . Water fugacity is calculated in a variety of ways using both biotite and hornblende as well as the combining reaction . It is high and approaches P _total in most ignimbrites (~4kb) but is lower in unwelded pumice breccias. Comparison of temperature estimates using mineral geothermometers for the various phenocryst phases suggests that the ignimbrite magmas showed temperature differences of 60–100 °C and pressure differences of several kilobars. Individual magma chambers therefore, would have extended over several kilometres vertically. The chemical potential of water may have been constant through the magma.     

Zur Interpretation von Pyrrhotin-Gefügen

Zusammenfassung Die Gefüge von Pyrrhotinerzen von vier Lagerstätten wurden mit einem Röntgentexturgoniometer untersucht. Alle Proben zeigen eine Einregelung von (0001) ± parallel zur Ebene der Lagigkeit (s) der Erze. Die Gefügediagramme der (10 2)-, (11 0)- und (10 0)-Reflexe von drei Fundpunkten haben orthorhombische Symmetrie. Die gleichen Diagramme der vierten Lagerstätte sind hexagonal.Die orthorhombischen Gefüge werden durch eine Deformation mit einfacher Scherung erklärt. Mit Hilfe eines Rechenprogrammes wurden entsprechende synthetische Gefügediagramme erzeugt. Ihre Ähnlichkeit mit der Mehrzahl der natürlichen Texturen macht das angenommene Modell wahrscheinlich. Auch kann geschlossen werden, daß die Proben — ausgenommen diejenigen mit nicht hinreichend deutbarer hexagonaler Symmetrie — durch eine Scherverformung entstanden sind.Gelegentlich scheint es möglich, durch Gefügeuntersuchungen an Erzen Rückschlüsse auf die tektonische Geschichte der Lagerstätte bzw. auf deren Beanspruchung zu ziehen.

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The fabrics of pyrrhotite ores from four deposits are determined by means of an X-ray texture goniometer. All specimens show (0001) ± parallel to the plane of schistosity (s) of the ores. The pole figures of the (10 2)-, (11 0)-, and (10 0)-reflections from samples of three localities are of orthorhombic symmetry. The same pole figures from the fourth deposit show hexagonal symmetry.The fabrics of pyrrhotite with orthorhombic symmetry are explained assuming a model with a deformation by simple shear. Synthetic diagrams are plotted using a program which simulates the conditions of this model. The synthetic diagrams are in good agreement with most of the measured ones, and this argues for the validity of the suggested model on the one hand and on the other hand confirms that these pyrrhotite fabrics may have been formed by simple shear. The fabrics with hexagonal symmetry seem to be produced by a quite different mechanism.In some cases one may infer from the results of the fabric analysis of ores to the tectonical history and the mode of deformation of the ore deposit.

     

A Coupled Riverine-Marine Fractionation Model for Dissolved Rare Earths and Yttrium

Fractionation of yttrium (Y) and the rare earth elements (REEs) begins in riverine systems and continues in estuaries and the ocean. Models of yttrium and rare earth (YREE) distributions in seawater must therefore consider the fractionation of these elements in both marine and riverine systems. In this work we develop a coupled riverine/marine fractionation model for dissolved rare earths and yttrium, and apply this model to calculations of marine YREE fractionation for a simple two-box (riverine/marine) geochemical system. Shale-normalized YREE concentrations in seawater can be expressed in terms of fractionation factors ( _ij ) appropriate to riverine environments ( ) and seawater ( ):

Stochastic modeling of gold mineralization in the Champion lode system of Kolar gold fields (India)

Stochastic modeling of gold mineralization in the Champion lode of Kolar gold fields was carried out using assay data taken from developmental headings. After dividing the lode into 71 horizontal and 18 vertical strata, autoregressive (AR), moving average (MA), and autoregressive and moving average (ARMA) models were developed and applied. The model selection with the acf and pacf for the various strata showed that in most of the cases, ARMA modeling of first-order would forecast gold headings with a reasonable degree of confidence. This was substantiated by comparing the coefficients of variation. From a parsimony point of view, AR (1) model may also be considered valid. The best overall models are: ARMA (1, 1), ; AR (1), , where a_t is N (0, _a ² ), x is in logarithms of in-dwt, and t is in block units of 100 ft. The applications of these models to a specific stratum are given. These models would also be helpful to describe the characteristics of the gold mineralization process of this lode.     

Calculation of Uncertainty in the Variogram

There are often limited data available in early stages of geostatistical modeling. This leads to considerable uncertainty in statistical parameters including the variogram. This article presents an approach to calculate the uncertainty in the variogram. A methodology to transfer this uncertainty through geostatistical simulation and decision making is also presented.The experimental variogram value for a separation lag vector h is a mean of squared differences. The variance of a mean can be calculated with a model of the correlation between the pairs of data used in the calculation. The data here are squared differences; therefore, we need a measure of a 4-point correlation. A theoretical multi-Gaussian approach is presented for this uncertainty assessment together with a number of examples. The theoretical results are validated by numerical simulation. The simulation approach permits generalization to non-Gaussian situations.Multiple plausible variograms may be fit knowing the uncertainty at each variogram point, . Multiple geostatistical realizations may then be constructed and subjected to process assessment to measure the impact of this uncertainty.     

Maximum entropy and shear strain of shear zone

The principle of maximum entropy can be used to determine the shear strain in natural shear zones. When the margin of a shear zone is assumed, the principle leads to the truncated exponential distribution of the shear strain. Ifx is the distance remote from the shear zone center, which possesses the maximum shear strain, the shear strain (x) is given by

Topological properties of random crack networks

The junctions of cracks in mudcrack, patterned ground, and columnar joint patterns can be categorized into Y, T,and Xtypes. The mean number of sides, ,to the polygonal areas in such nets is = 2(2J_T + 3J_Y + 4J_X)/(J_T + J_Y + 2J_X)where J_T, J_Y,and J_X are the proportions of T, Y,and Xjunctions, respectively.