A fluid inclusion study of the Little Nahanni LCT-Type Pegmatite Group, NWT Canada: implications for the nature and origin of fluids in LCT-Type Pegmatites and Pegmatite evolution
Bibliographic record
Abstract
The Cretaceous (82 Ma) Little Nahanni Pegmatite Group , Canada, is a 15 km long swarm of \nLCT-type pegmatite dikes that intrude Precambrian to Lower Cambrian siliciclastic metapelites \nand carbonate rocks. The dykes are dominated by a primary assemblage of quartz, spodumene, \nK-feldspar ± muscovite lacking both graphic textures and core zones, but characterized by combtextured spodumene and K-feldspar intergrowths. Varying degrees of albitization and lesser \nphyllic alteration accompany ore-grade oxide enrichment (Ta-Nb and Sn, respectively).A \ncomprehensive fluid inclusion study using a wide variety of methods (petrography , CL, \nmicrothermometry, SEM/EDS evaporate mound analysis, LA ICP-MS, laser Raman \nspectroscopy, δ13C) on minerals (quartz, K-feldspar, albite, spodumene, muscovite, garnet, and \ntourmaline) from barren and mineralized samples indicate the fluid inclusions are secondary and \nappear to post-date pegmatite crystallization. The presence of secondary fluid inclusions may \ninstead represent entrapment during the late-stage (sub-solidus to post crystallization) \nmetasomatic evolution stage of the pegmatites. Three fluid types occur, and listed in paragenetic \norder are: (A) an aqueous-carbonic fluid (≤1 wt. % eq. NaCl) with varying XCO2 (0.1 to 0.78), \npurity (TmCO2= -57o \nto -61oC), and density; (B) a low-salinity (≤2 wt. % eq. NaCl) aqueous \nfluid; and (C) an aqueous-methane-nitrogen fluid. SEM-EDS analysis indicates that the fluids are \nNa (-K) - dominant, but with significant S and enrichment in transition and chalcophile elements. \nFluid inclusion extracts have δ13C values (-9.7 to -27.7‰; n=7) which indicates exchange of the \nfluids with the immediate, carbon-bearing wall rocks occurred. Collectively the data indicate: (1) \nfluids were trapped during the later, metasomatic stage of pegmatite evolution; (2) fluids were \ntrapped at <2.5 kbars and <350°C with pressure fluctuating between lithostatic and hydrostatic; \n(3) variable degrees of fluid:rock interaction occurred with the exocontact zone, resulting in \nvarying XCO2and CO2:CH4 values; and (4) metasomatism and rare metal mineralization \noccurred in the presence of meteoric water. These findings indicate that the LNPG pegmatites \nare not a closed system, some of the carbonic component of H2O-CO2 fluids is exotic, and that \nlow-salinity fluids of meteoric origin infiltrated during the subsolidus stage of pegmatite \nevolution.
Fetched live from OpenAlex and de-inverted. Abstracts are not stored in this database: the inverted indexes are 8.6 GB of the frame’s 9.3 GB of text, and the host has 13 GB free.
How this classification was reachedexpand
Full frame distilled prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.001 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.000 | 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 teacher head, 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".