Emplacement of the Snap Lake kimberlite intrusion, NW Territories, Arctic Canada
Bibliographic record
Abstract
The Cambrian (523 Ma) Snap Lake hypabyssal kimberlite intrusion, Northwest Territories, Canada, is a complex segmented diamond-bearing ore-body. Detailed geological investigations suggest that the kimberlite is a multi-phase intrusion with at least four different magmatic lithofacies. In particular, olivine-rich (phlogopite-poor) and olivinepoor (phlogopite-rich) varieties of hypabyssal kimberlite have been identified. Key observations are that olivine-rich lithofacies (ORK) has a strong tendency to be located where the intrusion is thickest and that there is a good correlation between intrusion thickness, olivine crystal size and crystal content. The olivine-poor lithofacies (OPK) tends to be most abundant where the intrusion is thinnest. The ORK groundmass is composed of phlogopite (3 -20%), apatite, Cr spinel with Fe-Ti rims and rutile. The OPK groundmass is composed of abundant phlogopite (30 -60%), monazite and rutile and sparse Cr spinel cores and remnants of Fe-Ti rims. The ORK and OPK have a very different mineralogy and geochemistry indicating that they are contrasted magmas with different igneous histories, which have been mixed together in the intrusion. In addition, the ORK and OPK are characterised by different diamond abundances and size distributions. The geometry and distribution of lithofacies points to magmatic co-intrusion, and flow segregation driven by fundamental rheological differences between the ORK and OPK phases. We envisage that the low viscosity OPK magma acted as a lubricant for the highly viscous ORK magma. The presence of such low viscosity, crystal-poor magmas may explain how crystalladen kimberlite magmas (> 60 vol.%) are able to reach the surface and erupt in kimberlite diatremes. We also document the absence of crystal settling and the development of an unusual sub-vertical fabric of elongate olivine crystals, which are explained by rapid degassinginduced quench crystallisation of the magmas during and after intrusion. The igneous events have been followed by multiple stages of metasomatism, including (1) early metasomatism, (2) serpentinization, and (3) alteration by acidic fluids derived from the surrounding granite. The Snap Lake intrusion provides important insights into the architecture and dynamics of magmatic plumbing systems at high crustal levels, particularly in settings where sheet intrusions feed into point-source diatreme-vent systems.
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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 | 0.004 | 0.001 |
| Scholarly communication | 0.002 | 0.000 |
| Open science | 0.000 | 0.001 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.003 | 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".