Halogen-element (F, Cl, and Br) behaviour in apatites, scapolite, and sodalite : an experimental investigation with field applications
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This is the first systematic experimental investigation of partitioning of Br between apatites and coexisting melts and the uptake of Br by scapolite and sodalite. Twenty-nine partitioning experiments between fluorapatite (FAP) /chlorapatite (ClAP) and coexisting melts were conducted in the system of CaO-P2O5-CaF2-CaCl2–NaBr at 1120 degree C to 1400 degree C and atmospheric pressure. The partition coefficients (D) with errors of 1 sigma in parentheses are as follow: DF (ClAP/melt) 3.59(64) at 1120 degree C to 4.13(22) at 1330 degree C DF (FAP/melt) 1.05(4) at 1220 degree C to 1.07 at 1400 degree C DCl (ClAP/melt) 1.07(1) at 1120 degree C to 0.83 at 1330 degree C DCl (FAP/melt) 0.127(2) at 1250 degree C to 0.115 at 1400 degree C DBr (ClAP/melt) 0.32(9) at 1120 degree C to 0.42(5) at 1330 degree C DBr (FAP/melt) 0.020(3) at 1220 degree C to 0.016 at 1400 degree C Seven exchange experiments at one atmospheric pressure and 800 to 1000 degree C yield the following distribution coefficients for Br-Cl exchanges between marialitic scapolite or sodalite and coexisting hydrous NaCl-NaBr melts: KD (marialite-melt) = 0.92 +/- 0.10 and KD (sodalite-melt) = 1.18 +/- 0.10. Therefore, the Cl/Br values in marialitic scapolite and sodalite closely reflect the halogen proportions of their coexisting melts or fluids. The second part of this thesis project analyzes the halogen (F, Cl, Br) contents in natural fluorapatite and scapolite by X-ray fluorescence microprobe (XRF) for Br and electron microprobe (EMPA) for other elements. All selected localities and environments are interesting, because the origins of the parental fluids/melts are controversial. The halogen compositions of 29 natural apatite grains from the Aoshan fluorapatite-magnetite deposit (China), the Oka carbonatite complex (Quebec), and Chinese mantle xenoliths and 36 scapolite samples from the Tieshan Fe-Cu skarn deposit (China), the Nickel Plate gold deposit (British Columbia), and the Grenville pegmatite/skarn/vein deposits (Ontario and Quebec) have been analyzed by electron microprobe (EMPA) and X-ray fluorescence microprobe (XRF). Twenty six whole-rock samples from the Aoshan deposit have also been analyzed by XRF for major and trace elements. Fluorapatite from the Aoshan fluorapatite-magnetite deposit is Cl-bearing with 0.38-0.98 wt% Cl, 1.83-3.45 wt% F, and 0-52 ppm Br. Fluorapatite from Chinese mantle xenoliths has similar halogen compositions to the Aoshan fluorapatite. Fluorapatite from the Oka carbonatite has trace amounts of chlorine (up to 0.052 wt%) and bromine (from 9 to 57 ppm). Applications for the experimental results suggest that the Aoshan Fe-Cu deposit has Cl/Br values comparable to those of mantle sources and that the anomalously low Cl/Br values in Oka fluorapatite require Br-enriched sources. The Cl/Br values (weight) of marialitic scapolite from the Tieshan Fe-Cu deposit cluster around 626 +/- 92, supporting an origin involving hydrothermal brines from associated evaporites. Scapolite-group minerals in the exoskarns of the Nickel Plate Au skarn deposit have Cl/Br from 560 to 570, higher than those (110 to 180) of their counterparts in the endoskarns and vuggy cavities. This variation is attributable to an increased involvement of magmatic water from distal to proximal zones. Similarly, scapolite-group minerals in the Grenvillian U-Th-Mo-REE pegmatite-skarn-vein deposits vary widely in Cl/Br from 80 to 380, indicative of mixed sources of hydrothermal fluids from magmatic sources and from associated sedimentary rocks. The experimentally determined partition coefficients of halogens between minerals (apatites, scapolite, and sodalite) and fluids/melts of this study have wide applications in the interpretation of source and evolution of hydrothermal fluids in mineralization processes and other geological systems. Applications of those partition coefficients to selected mineral deposits and mantle xenoliths confirm their significance.
DegreeDoctor of Philosophy (Ph.D.)
CommitteeStauffer, Melvyn R.; Reid, R. Stephen; Milne, Douglas; Lentz, David; Kerrich, Robert; Ansdell, Kevin M.
Copyright DateAugust 2005
synthetic experiment of apatite
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