The origin and composition of carbonatite-derived carbonate-bearing fluorapatite deposits

Carbonate-bearing fluorapatite rocks occur at over 30 globally distributed carbonatite complexes and represent a substantial potential supply of phosphorus for the fertiliser industry. However, the process(es) involved in forming carbonate-bearing fluorapatite at some carbonatites remain equivocal, with both hydrothermal and weathering mechanisms inferred. In this contribution, we compare the paragenesis and trace element contents of carbonate-bearing fluorapatite rocks from the Kovdor, Sokli, Bukusu, Catalão I and Glenover carbonatites in order to further understand their origin, as well as to comment upon the concentration of elements that may be deleterious to fertiliser production. The paragenesis of apatite from each deposit is broadly equivalent, comprising residual magmatic grains overgrown by several different stages of carbonate-bearing fluorapatite. The first forms epitactic overgrowths on residual magmatic grains, followed by the formation of massive apatite which, in turn, is cross-cut by late euhedral and colloform apatite generations. Compositionally, the paragenetic sequence corresponds to a substantial decrease in the concentration of rare earth elements (REE), Sr, Na and Th, with an increase in U and Cd. The carbonate-bearing fluorapatite exhibits a negative Ce anomaly, attributed to oxic conditions in a surficial environment and, in combination with the textural and compositional commonality, supports a weathering origin for these rocks. Carbonate-bearing fluorapatite has Th contents which are several orders of magnitude lower than magmatic apatite grains, potentially making such apatite a more environmentally attractive feedstock for the fertiliser industry. Uranium and cadmium contents are higher in carbonate-bearing fluorapatite than magmatic carbonatite apatite, but are much lower than most marine phosphorites

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Sphalerite and pyrrhotite geothermometry of the new calumet sulphide deposit.

Pyrrhotite and sphalerite deposition temperatures were determined in the ores of New Calumet Mine, Quebec. Forty-five pyrrhotite and fifty-two sphalerite determinations were made taken from various samples. Out of these, both geothermometers were used in 18 specimens. In most cases both values were reasonably close. Only four specimens showed greater difference for the two geothermometers than 56°C, the mean difference being 17°C. The temperature values for pyrrhotite range from 350° to 484°C, of that of sphalerite from 370° to 538°C. Using these values, isotherms were drawn throughout the orebodies based on the sphalerite data. The pyrrhotite values did not show any apparent systematic variation. The sphalerite isotherms coincide with the down-dip trend of the principal ore zones. No significant change in deposition temperatures is shown with depth. The thermal gradients are steepest laterally. "Hot spots" in the major ore zones may indicate channel-ways through which mineralizing solutions travelled

The cadherin-binding specificities of B-cadherin and LCAM.

The cadherin family of calcium-dependent cell adhesion molecules plays an important part in the organization of cell adhesion and tissue segregation during development. The expression pattern and the binding specificity of each cadherin are of principal importance for its role in morphogenesis. B-Cadherin and LCAM, two chicken cadherins, have similar, but not identical, spatial and temporal patterns of expression. To examine the possibility that they might bind to one another in a heterophilic manner, we generated, by cDNA transfection, L-cell lines that express LCAM or B-cadherin. We then examined the abilities of these cells to coaggregate with each other and with other cadherin-expressing cells in short-term aggregation assays. The B-cadherin- and the LCAM-expressing cell lines segregate from P-, N-, or R-cadherin-expressing cells. B-cadherin- and LCAM-expressing cell lines, however, appear to be completely miscible, forming large mixed aggregates. Chick B-cadherin and murine E-cadherin also form mixed aggregates, indistinguishable from homophilic aggregates. Murine E-cadherin and chick LCAM coaggregate less completely, suggesting that the heterophilic interactions of these two cell lines are weak relative to homophilic interactions. These data suggest that heterophilic interactions between B-cadherin and LCAM are important during avian morphogenesis and help identify the amino acids in the binding domain that determine cadherin specificity