|Title||Magmatic mica and its potential as an indicator of magma fertility in the granitoids of New Brunswick|
Lentz, D; McFarlane, C|
|Source||Geological Association of Canada-Mineralogical Association of Canada, Joint Annual Meeting, Abstracts Volume vol. 37, 2014 p. 16 Open Access|
|Links||Online - En ligne (PDF 8.75 MB)|
|Publisher||Geological Association of Canada|
|Publisher||Mineralogical Association of Canada|
|Meeting||GAC-MAC Joint annual meeting; Fredericton, NB; CA; May 21-23, 2014|
|Related||This publication is related to Magmatic mica and its
potential as an indicator of magma fertility in the granitoids of New Brunswick|
|Area||Lake George; Fredericton|
|Lat/Long WENS|| -67.5000 -66.5000 46.0000 45.7500|
|Subjects||igneous and metamorphic petrology; geochemistry; granodiorites; intrusive rocks; igneous rocks; gold; molybdenum; tungsten; antimony; mineralization; vein deposits; magmatism; analytical methods;
biotite; amphibole; magma differentiation; magmatic deposits; copper; uranium; mica; tantalum; lithium; Acadian Orogeny; Devonian|
|Program||Targeted Geoscience Initiative (TGI-4) Intrusion/Porphyry Ore Systems|
|Released||2014 01 01|
|Abstract||The mineralized intrusions of New Brunswick are related to crustal growth processes that occurred during Acadian Orogeny, post Acadian uplift, and Neo-Acadian Orogeny. They were emplaced pre-, syn-,
late-, and post-tectonically between 423 and 360 Ma. These intrusions have affinities ranging from primitive to highly evolved A-, S-, and I-types granitoids, and are associated with Sn, Ta, Li, Sb, W, Mo, Cu, and Au, as well as base-metals and U
Biotite crystallizes over a wide range of conditions and reacts very sensitively to physiochemical conditions of the magma; this sensitivity makes mica a great mineral for identifying the petrogenetic, mineralization, and
alteration processes of the host granitic rocks. The following features make biotite a valuable probe of magma composition: 1) It is the most important reservoir of any excess aluminium in granites that do not contain modal garnet, cordierite, or the
Al2SiO5 polymorphs; therefore, it directly reflects the peraluminosity of the host magma in such rocks, 2) it is the most readily available indicator of oxidation state, and 3) it can provide information about the F and Cl content of the magma.
Mineralized and barren rocks are characterized by different chemical variations in biotite. For instance, mineralized biotite is characterized by lower Mg and Ti contents relative to biotite from barren rocks; they also have higher amount of Al
comparing to biotite from barren phases.
Several studies have shown that biotite, continuously equilibrates with the host liquids. Therefore, core-to-rim study of this mineral and its compositional zoning may provide a record of magma evolution so
that the origin and evolution of granitoids can be discerned. Furthermore, the chemical composition and the colour of this mineral strongly reflects the tectonic origin of its host. For instance, the bright red colour of biotite indicates
peraluminous collisional granitic pluton and reflects a high total Fe content with low Fe3+/(Fe2+ + Fe3+) and probably the presence of Ti4+.
In part this study aims to calculate fluoride and chloride activity of aqueous fluids based on F and Cl
contents in the minerals containing hydroxyl and halogens determined by combined electron microprobe and LA ICP-MS analysis. The final data will be compared to the whole rock geochemistry. These results are expected to help constrain crystallization
conditions, volatile exsolution and fluorine-chlorine activity of fluids associated with these intrusions. They should also indicate the degree of subsolidus re-equilibration via various geothermobarometry techniques.