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 (0.1 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.

The Acadian-related granitoids of New Brunswick are herein divided into geochemically defined groups to ascertain whether magmatic process related trends differentiate barren from mineralized granitoids. The Juniper Barren and Lost Lake granites have some similar characteristics (i.e. lowest SiO2, highest transition element contents, high-K calc-alkaline, metaluminous), but do not constitute a defined geochemical group. They have the characteristics of unfractionated (oxidized) I-type granites, and neither are associated with significant mineralization. Group NB-1 granites are metaluminous to peraluminous, high-K calc-alkaline, light rare-earth element (LREE) enriched with small negative Eu anomalies, and high Nb/Ta and Zr/Hf ratios. Group NB-1 intrusions are interpreted to be unfractionated reduced I-type granite formed via partial melting in an arc system and subsequently contaminated by reducing crustal rocks. The reduced component is critical for the formation of tungsten mineralization. Group NB-2 granites are high-K calc-alkaline, metaluminous to peraluminous I-type granite characterized by K2O contents greater than Na2O, and are LREE enriched with pronounced negative Eu anomalies. Group NB-2 granites are unfractionated to weakly fractionated I-type granite generated from different degrees of partial melting of mixed mantle - older crustal protolith with an igneous quartzo-feldspathic composition. Group NB-3 granites include the most evolved intrusions examined during this study. They are characterized by the highest SiO2 content, Gottini index and K/Rb ratio, and have the lowest Zr/Hf, Nb/Ta, La/Sm and Eu/Eu* ratios. They are considered highly evolved I-type granite formed via crustal thinning related to crustal delamination following the juxtaposition of crustal terranes during the Acadian Orogeny.

Biotite grains from 22 felsic intrusions in New Brunswick were mapped in situ using a laser ablation-inductively coupled plasma-mass spectrometer (LA-ICP-MS). We investigated the extent to which biotite can retain its magmatic zoning patterns and, where zoning does exist, how it can be used to elucidate early to late stage, syn-magmatic to post-crystallization processes. Although the major element and halogen contents of the examined biotite phenocrysts are homogeneous, two-thirds of the grains display trace-element zoning for Ba, Rb, and Cs. The results also indicated that zoning is better retained in larger grains (i.e., > 500 × 500 μm) with minimal alteration and mineral inclusions. An exceptionally well-zoned Li-rich siderophyllite from the Pleasant Ridge topaz granite in southwestern New Brunswick shows Ti, Ta, Sn, W, Cs, Rb, and V (without Li or Ba) zoning. Cesium values increase from 200 to 1400 ppm from core to rim. Conversely, Sn and W values decrease toward the rim (50 to 10 and 100 to 10 ppm, respectively). Tantalum and Ti values show fewer variations but drop abruptly close to the rim of the grain (100 to 20 and 2000 to 500 ppm, respectively). These observations may indicate crystallization of mineral phases with high partition coefficients for these highly incompatible elements (except Ti) (e.g., cassiterite and rutile) followed by fractionation of a fluid phase at a later stage of magma crystallization. The preservation of zoning may indicate rapid cooling post-crystallization of the parent magma.

The South Nepisiguit River Plutonic Suite consists of various phases of felsic to mafic plutonic rocks of early Devonian age in northern New Brunswick. The felsic portion of this intrusive suite includes a large pluton of homogeneous, peraluminous biotite granite (the Mount Elizabeth Granite), which is flanked on its western side by the alkaline Mount LaTour Granite. New in situ and mineral separate U-Pb Laser Ablation-Inductively Coupled Plasma Mass Spectro-metry analyses of monazite and zircon grains from both sides of the suite define a crystallization age of 417.3 ± 0.96 Ma for the Mount Elizabeth Granite and 417.7 ± 4.4 Ma for the Mount LaTour Granite. The new data confirm previous geochronological work and indicate a close temporal relationship between these felsic phases of this plutonic suite.