Physico-chemical processes of silicates in the estuarial region. III. Preliminary in-situ studies of the mechanism of reactive silicate removal: distribution of suspended Si, Fe, and Al

1980 ◽  
Vol 27 (12) ◽  
pp. 858
Keyword(s):  
Chemical Processes ◽  
In Situ Studies ◽  
Physico Chemical

Supergene gold mineralogy at Ashanti, Ghana: Implications for the supergene behaviour of gold

1992 ◽  
Vol 56 (385) ◽  
pp. 545-560 ◽  
Author(s):  
R. J. Bowell
Keyword(s):  
Shear Zones ◽  
Chemical Processes ◽  
Chemical Dissolution ◽  
Fine Grained ◽  
Quartz Veins ◽  
Physico Chemical ◽  
Supergene Enrichment ◽  
Host Rocks ◽  
Gold Bearing

AbstractAt the Ashanti concession, Ghana, gold-bearing quartz veins and disseminated sulphide lodes occur in narrow (1-3 m) shear zones with altered argillites and metatholeiite host rocks. The mineralisation is concealed by up to 10 m of kaolinite-mica forest ochrosol soils, beneath which is a saprolitic zone of leached rock extending down 60-70 m to the hypogene ore zone. In the unweathered hypogene orebody, gold occurs as free grains in quartz, as sub-microscopic inclusions in the disseminated arsenopyrite, as gold tellurides and as aurostibite. The gold is released from the hypogene orebody by physical dissaggregation and chemical dissolution, the latter involving hydroxyl, thiosulphate, cyanide, and fulvate complexing. Dissolution and reprecipitation of the gold appears to have taken place largely in situ with little evidence of supergene enrichment. Consequently, the gold mineralogy of the soils is complex with residual and secondary gold grains exhibiting widely different textural and compositional characteristics. Residually enriched grains display pitted, rounded surfaces and have silver-depleted rims, while supergene gold grains are compositionally homogenous and have unpitted surfaces. The supergene grains display platelet, dendritic, irregular and octahedral habit. A fine grained spongy form of gold has also been observed from weathered telluride-bearing quartz veins. Much of the secondary gold is intergrown with iron oxides and hydroxides. The gold mineralogy of the Ashanti soils appears to be controlled by physico-chemical processes active during the lateritic pedogenesis producing residual and supergene enrichment of gold.

Physico-chemical changes in metal-spiked sediments deployed in the field: Implications for the interpretation of in situ studies

Chemosphere ◽  
2011 ◽  
Vol 83 (4) ◽  
pp. 400-408 ◽  
Author(s):  
Nicole A. Hill ◽  
Emma L. Johnston ◽  
Catherine K. King ◽  
Stuart L. Simpson
Keyword(s):  
Chemical Changes ◽  
In Situ Studies ◽  
Physico Chemical

On the development of internal chemical zonation in small mafic dykes

2009 ◽  
Vol 147 (1) ◽  
pp. 1-12 ◽  
Author(s):  
SOFYA CHISTYAKOVA ◽  
RAIS LATYPOV
Keyword(s):  
Chemical Processes ◽  
Complete Understanding ◽  
Abrupt Increase ◽  
Mafic Dykes ◽  
Physico Chemical ◽  
Geochemical Study ◽  
Flow Differentiation ◽  
Compositional Pattern

AbstractThree dolerite dykes (Small, 3.2 cm; Middle, 13.5 cm; Thick, 50 cm) from Torsholma Island, SW Finland, reveal distinctly different internal zonation that becomes more complicated with increasing thickness of the dykes. The Small Dyke shows a systematic inward increase in normative Pl (An+Ab+Or) and a decrease in normative An (100*An/(An+Ab)), whole-rock MgO, Mg number (100*Mg/(Mg+Fetotal)), TiO2, K2O and Zr. The Middle Dyke exhibits the same compositional pattern at the margins, while the centre is distinguished by an abrupt increase in normative Pl and An, whole-rock Sr and Mg number. From the margins inwards, the Thick Dyke displays first a compositional pattern identical to that observed in the Small Dyke and the margins of the Middle Dyke. This is followed by a region where whole-rock MgO, Mg number and normative An start increasing inwards, while the transition to the centre of the dyke is characterized by a compositional pattern similar to that in the centre of Middle Dyke. The origin of chemical zonation in these dykes is attributed to the operation of three independent physico-chemical processes, namely: the Small Dyke formed exclusively by progressive changes in the composition of inflowing magma; the Middle Dyke by changes in composition of inflowing magma (margins) and concentration of plagioclase and olivine phenocrysts by flow differentiation (centre); the Thick Dyke by changes in composition of inflowing magma (margins),in situcumulate growth against dyke sidewalls (middle) and flow differentiation (centre). Systematic changes in these processes and, as a result, in internal chemical zonation, likely take place in response to crystallization of magma under less supercooled conditions with increasing dyke thickness. A comprehensive geochemical study of the internal zonation of small mafic dykes worldwide is required to develop a complete understanding of the processes operating in mafic dykes.

Preparation of integrated circuits for TEM electromigration in situ studies

1986 ◽  
Vol 44 ◽  
pp. 882-883
Author(s):  
J. V. Maskowitz ◽  
W. E. Rhoden ◽  
D. R. Kitchen ◽  
R. E. Omlor ◽  
P. F. Lloyd
Keyword(s):  
Integrated Circuits ◽  
Crystallographic Orientation ◽  
Silicon Wafers ◽  
Minimum Size ◽  
Test Vehicle ◽  
In Situ Studies ◽  
Boron Doped ◽  
Doped Silicon ◽  
Drill Holes

The fabrication of the aluminum bridge test vehicle for use in the crystallographic studies of electromigration involves several photolithographic processes, some common, while others quite unique. It is most important to start with a clean wafer of known orientation. The wafers used are 7 mil thick boron doped silicon. The diameter of the wafer is 1.5 inches with a resistivity of 10-20 ohm-cm. The crystallographic orientation is (111).Initial attempts were made to both drill and laser holes in the silicon wafers then back fill with photoresist or mounting wax. A diamond tipped dentist burr was used to successfully drill holes in the wafer. This proved unacceptable in that the perimeter of the hole was cracked and chipped. Additionally, the minimum size hole realizable was > 300 μm. The drilled holes could not be arrayed on the wafer to any extent because the wafer would not stand up to the stress of multiple drilling.

Nucleophilicity and its parametrization

1989 ◽  
Vol 54 (1) ◽  
pp. 117-135
Author(s):  
Oldřich Pytela ◽  
Vítězslav Zima
Keyword(s):  
Regression Analysis ◽  
Linear Correlation ◽  
Correlation Equation ◽  
Chemical Processes ◽  
General Tendency ◽  
Orbital Interaction ◽  
Physico Chemical ◽  
Physical And Chemical ◽  
Two Parameter ◽  
Better Than

The method of conjugate deviations based on the regression analysis has been suggested for construction of a new nucleophilicity scale. This method has been applied to a set of 28 nucleophiles participating in 47 physical and chemical processes described in literature. The two-parameter nucleophilicity scale obtained represents-in the parameter denoted as ND-the general tendency to form a bond to an electrophile predominantly on the basis of the orbital interaction and-in the parameter denoted as PD-the ability to interact with a centre similar to the proton (basicity). The linear correlation equation involving the ND, PD parameters and the charge appears to be distinctly better than the most significant relations used. The correlation dependences have the physico-chemical meaning. From the position of individual nucleophiles in the space of the ND and PD parameters, some general conclusions have been derived about the factors governing the reactivity of nucleophiles.

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