| Abstract | Two suites of felsic intrusions were emplaced during the later parts of the Appalachian orogenic cycle in New Brunswick. However, just those associated with crustal thickening processes of Acadian
orogeny, post Acadian uplift, and Neo-Acadian orogeny are mineralized with granophile elements to form Sn, W, Mo, Cu, Bi, Sb, and Au deposits, as well as Ta, Li, base-metals, and U mineralization. Biotite major element classification indicated that
these intrusions are mostly A- and S-type granitoids and their hybrid varieties; some I-type granitoids are also present in the area. Magmatic biotite from forty-two of these Devonian intrusions was studied by electron microprobe (EPMA) and LA-ICP-MS
at the University of New Brunswick. Whereas major elements are typically constant from core to rim, biotite grains can show remarkable trace element zoning. LA-ICP-MS trace element maps were also produced when permitted by the size of the biotite,
frequency of the mineral inclusions, degree of alteration, and the laser spot size required to achieve sub-ppm detection limits. In this study, unaltered biotite grains with minor mineral inclusions, and diameters larger than 300 ?m, display
trace-element zoning patterns. Furthermore, smaller biotite tends to be more susceptible to intracrystalline diffusion. As a result, their elemental zoning should be further studied and cross-checked with other characteristics. Results of this study
showed LILE zoning, including Cs, Ba, and Rb, for most of the biotite grains. As these elements are highly incompatible, any zoning can be a result of the magma evolution history recorded within the biotite crystalline structure. Any other trace
element pattern following them will also be of an igneous source. For example, biotite grains from the Pleasant Ridge granite show an increase from core to rim for Cs and Sn and a decrease for W and Sc. Copper is also high along the cleavages where
biotite is weakly altered to chlorite. These observations coupled with an increase in F/Cl content from 770 to 1300 indicate that fractional crystallisation of this granite led to Sn mineralization. Tin is positively correlated with Fe/(Fe+Mg), but
negatively correlated with FeT/Ti; this relationship may indicate that the Sn content of biotite increases with low fo2 and low temperatures as indicated by the iron/magnesium ratio. According to the results, the use of biotite as an indicator of
trace element changes within granitic systems was achieved; with the help of other types of data, the composition of biotite may be a useful tool to indicate a difference between barren and mineralized granophile-element rich systems. |