Apatite Chemical Compositions from Acadian-Related Granitoids of New Brunswick, Canada: Implications for Petrogenesis and Metallogenesis

摘要

The geochemistry of apatite crystals from fifteen fertile and infertile Acadian-related granitoids of New Brunswick (Canada) was studied in situ , using electron microprobe and laser ablation-inductively coupled plasma-mass spectrometry to further investigate petrogenesis and fertility index among these intrusions. The results indicate a clear geochemical contrast between barren and mineralized samples where apatite grains from barren intrusions are the most hydrous (OH 0.3 wt. %), with lowest Mn (1700 ppm), Fe (800 ppm), and Sn (0.01 ppm). In contrast, apatite grains from Cu-Mo related intrusions are distinguished by higher Cl (0.1 wt. %), (La/Yb) N ratios of 21.17, (Eu/Eu*) N ratios of 0.30, and LREE/HREE ratios of 6.03. Apatites from Sn-W related magmatic suites have the highest F (3 wt. %), Mn (5350 ppm), Fe (2200 ppm), Y (4900 ppm), Sn (2 ppm), and the lowest Cl (0.01 wt. %), Sr (60 ppm), U (18 ppm), Th (29 ppm), (Eu/Eu*) N ratios (0.01), and (La/Yb) N ratios (0.88). Lastly, apatite grains from Mo-bearing systems have the lowest SiO 2 (0.4 wt. %), Sr (33 ppm), Th (28 ppm), a moderate Mn (~3800 ppm), Y (~3500 ppm), and highest FeOt (0.9 wt. %). However, the results indicated apatite Mn, Sr, LREE/HREE, and (Eu/Eu*) N ratios as the best fertility indices used for discriminating barren from fertile granite intrusions.