Magmatic biotite and its use to distinguish barren and mineralized granitic systems in New Brunswick, Canada
Bibliographic record
Abstract
Forty-two different Devonian granitoid intrusions in New Brunswick were studied for this project. They formed by crustal growth processes during the Acadian orogeny, post-Acadian uplift, and Neoacadian orogeny and most are associated with granophile element deposits, such as Sn, W, Mo, Cu, Bi, In, Sb, Au, and possibly Ta and Li, as well as base-metals and U mineralization. These intrusions were emplaced pre-, syn-, late-, and posttectonically between 423 and 360 Ma with affinities ranging from primitive to highly evolved A-, S-, and I-types granitoids. The aim of this study is to find a way to differentiate barren and mineralized granitic systems using biotite compositional systematics since it is highly sensitive to physico-chemical changes of its host, and continuously reequilibrates with host and derivative fluids. Therefore, core to rim studies of this mineral and analysis of its compositional zoning may reveal the origin and evolution history of the hosting granitoid and the different types of associated mineralization. Mineralized and barren granitoids are characterized by different chemical variations in biotite. For instance, biotite from a mineralized granitoid is characterized by lower Mg and Ti, and higher Al content relative to biotite from a barren granitoid. A combination of electron microprobe (EPMA) and laser ablation ICP-MS (LA-ICP-MS) was used to identify major, minor, trace elements, and halogen contents of biotite; these results were used to calculate fluoride and chloride activity of aqueous fluids associated with these intrusions, based on F and Cl contents in the mineral.*** Microprobe studies indicated homogeneous intragranular major element composition; crystallization temperature was calculated using Ti-In-biotite geothermometer, which gave a range of 670 to 750 ± 25°C . However, hydroxyl exchange biotite-apatite thermometer confirmed sub-solidus processes disturbed these systems resulting in a lower temperature around 300. Biotite grains from the highly fractionated bodies of the Pleasant Ridge, Mount Pleasant, and Kedron granites show the highest fluorine contents, ranging from 4.5 wt.% to 6.5 wt.%. Trace element changes within the biotite lattice were measured using LA-ICP-MS. Interestingly, almost all of studied grains show Cs, Ba, and Rb zoning relative to K. These patterns were followed by Co, Cu, K, Li, Be, Sn, W, Ti, Sc, Ni, B, and V. Large ionic charge and radius make it difficult for elements to join or leave any crystalline structure; therefore, any Cs or Ba zoning could be of an igneous origin. As a result, any other elemental pattern following those could be a result of magmatic evolution, which has been recorded by the biotite crystal growth. Based on the results of this project, the concept of using biotite composition to help identify fertile Acadian magma systems has been established; however, more work needs to be done to define characteristics of different magmatic processes.
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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 | 0.004 | 0.004 |
| Science and technology studies | 0.002 | 0.001 |
| Scholarly communication | 0.001 | 0.000 |
| Open science | 0.001 | 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".