Phlogopitization of pyroxenite; its bearing on the composition of carbonatite magmas

SummaryPhlogopitization of pyroxenite is common in contact zones between clinopyroxenites and carbonatite dikes of the Cargill ultramafic rock—carbonatite complex near Kapuskasing, Ontario. The most typical development is a mica zone 1–10 cm wide but phlogopite is also developed in a more pervasive manner throughout the groundmass of several types of ultramafic rock. Fenitization is most commonly thought of as a process whereby aegirine and riebeckitic amphiboles are formed in the host rock while feldspar is recrystallized and silica progressively removed. Phlogopitization of pyroxenite can properly be referred to, however, as a type of fenitization. It is clearly related to the intrusion of carbonatite into pyroxenite and is further testimony to the fact that many carbonatite magmas are initially alkalic but lose alkalies to the surrounding rocks and crystallize as calcitic and dolomitic carbonatite with alkali contents restricted to the amounts that could be fixed as micas, pyroxenes or amphiboles. This in turn is controlled by the silica and alumina activity of the carbonatite magma. Abundant evidence for considerable amounts of fluorine in carbonatite magmas suggests that alkalies may be transported into the country rocks as fluorides. It is further suggested that late-stage feldspathization in carbonatite complexes is explained by the abstraction of potassic halide solutions from the crystallizing carbonatite magma. The conclusion seems inescapable that alkali carbonatite magmas, far from being the curiosity thought by many petrologists, are in fact very common during the evolutionary history of carbonatites. The common calcitic and dolomitic carbonatites have not generally crystallized from a magma of the same composition but are the residue remaining after the abstraction of an alkali-rich aqueous fluid. Consequently, there is a need to redesign the experimental phase equilibrium approach to problems of carbonatite genesis in order to take account of the presence of alkalies in most carbonatite magmas.

Estimation of Chlorinated Pesticide Residues in Animal and Vegetable Oils

A procedure for the determination of chlorinated pesticide residues in cottonseed oil, hydrogenated marine oil, seal oil, butter oil, and processed beef tallow is described. The oil is spread in the form of a thin film over a large surface area provided by Celite 545. The pesticides are extracted from the oil-coated Celite with 80% aqueous acetonitrile, partitioned into Skellysolve F, and cleaned up on a basic alumina (activity III) column. Gas chromatography with an electron capture detector is used for qualitative and quantitative estimations. The average recovery of six commonly used chlorinated pesticides (aldrin, dieldrin, heptachlor, heptachlor epoxide, lindane, and p,p'-DDT) at levels of 0.1 and 0.25 ppm ranged from 82 to 106%.

Amphiboles in alkaline rocks of Koraput, Orissa

SummaryThe chemistry and optics of the amphiboles in alkaline rocks of Koraput, Orissa, India, are described. The variation in chemical characters of the amphiboles is consistent with the variation in rock composition. With progressive fractionation the mineral shows increasing replacement of magnesium by iron while Ca is not affected by such replacement. The trend in variation is comparable to that in pyroxenes of alkaline basaltic magmas. The entry of Ti into the structure of amphibole appears to be favoured by alumina activity and concentration of Ti in the magma. Optical characters vary with the iron : magnesium ratio and titanium content of the mineral. The water content of the magma had an important influence on the composition of the mafic minerals in the rocks.