Biotite chemistry as a monitor of magma fertility and mineralisation potential: results from the Devonian granitoids of New Brunswick
Bibliographic record
Abstract
There are over 150 granitoid intrusions in the New Brunswick; however, all the mineralised intrusions formed in relation to Acadian and Neoacadian orogenic phases of Appalachian accretion. These granitoids range in age from 423 to 360 Ma, and include examples of pre-, syn-, late-, and post-tectonic emplacement with affinities ranging from primitive to highly evolved A-, S-, and I-types granitoids along with their hybrid varieties. Many of these are spatially and temporally related to specific styles of mineralization, producing deposits of Sn, Ta, Li, Sb, W, Mo, Cu, and Au, as well as other base-metals and U. Igneous biotite crystallises over a wide range of conditions and reacts very sensitively to physio-chemical conditions like halogen and oxygen fugacities, pressure, temperature and chemical composition of the magmas. This sensitivity makes biotite a suitable mineral for identifying the petrogenetic processes, mineralization and alteration of the host granitic rocks. The following features make biotite a valuable probe of magma composition: i) 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; ii) it is the most readily available indicator of oxidation state; and iii) it can provide information about the F and Cl composition of the magma. Previous studies have shown that biotite, and to lesser extent hornblende and magnetite, continuously equilibrates with host liquids. Consequently, a core-to-rim study of these minerals and their compositional zoning can provide a record of magma evolution so that the origin and evolution of granitoids can be documented. The aim of this study is to calculate fluoride and chloride activity of aqueous fluids based on measuring F and Cl contents in the minerals containing hydroxyl and halogens, using a combination of electron microprobe and Laser Ablation ICP-MS. These data will be combined and compared with whole-rock trace element geochemistry. The results are expected to help constrain crystallisation conditions, volatile exsolution, and fluorine-chlorine activity of fluids associated with these intrusions, and also to examine the degree of subsolidus re-equilibration using various geothermobarometry techniques. By linking these results to the various styles/types of granitoids and their associated mineralisation it is hoped to establish biotite composition as a robust indicator of an intrusions ore potential.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.001 | 0.002 |
| Science and technology studies | 0.001 | 0.001 |
| Scholarly communication | 0.001 | 0.000 |
| Open science | 0.000 | 0.001 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.001 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".