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

Abstract

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 SiO2 (<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.

Oxygen Fugacity and Volatile Content of Syntectonic Magmatism in the Neoarchean Abitibi Greenstone Belt, Superior Province, Canada

“…The ƒO 2 values obtained from REE dependent method [51,67,69] provide significantly different results when applied to pristine and non-pristine apatite and zircon grains, as was also noted for the Muscocho Pluton [101]. For example, the apatites from the Opémisca intrusion provide a wide range of log(ƒO 2 ) estimates from −17.2 • C to −18.3 at 700 • C. The lowest ƒO 2 values are likely due to LREE-rich inclusions.…”

“…Cerium and Eu anomalies in apatite are dependent on ƒO 2 , bulk rock composition, temperature, pressure, as well as co-existing mineral assemblage (e.g., plagioclase fractionation modifies Eu/Eu*) [64][65][66]. For apatite, Ce and Eu anomalies were displayed and interpreted using the binary diagram of Azadbakht [67].…”

“…. Limits between these three types are defined according to previous studies [64,67]. The S1 and S4 samples from the Saussure intrusion are from granite and syenite phases, respectively.…”

“…Apatite from the Lac Line and Opémisca intrusions is strongly altered according to textural observations, i.e., porous texture, abundance of cracks, lack of oscillatory zoning and resorption texture. This alteration is accompanied by variation of the Na, Si, Fe, K, Al, and S content of apatite and by REE remobilization that is likely a consequence of hydrothermal alteration [67,89,90] and/or of the co-crystallization of accessory minerals, such as monazite and feldspar [91,92].…”

“…Diagram displaying the Eu anomalies (Eu/Eu*) vs. Ce anomalies (Ce/Ce*) of apatite; with Eu* = 0.5*(Sm N + Gd N ), Ce* = 0.5*(La N + Pr N ). Limits between these three types are defined according to previous studies[64,67]. The S1 and S4 samples from the Saussure intrusion are from granite and syenite phases, respectively.…”