Characterization and origin of dunitic rocks in the Ni-Cu-(PGE) sulfide ore-bearing Kevitsa intrusion, northern Finland: whole-rock and mineral chemical constraints
Bibliographic record
Abstract
The ca. 2.06 Ga Kevitsa intrusion is one of the ore-bearing mafic-ultramafic igneous bodies in the Central Lapland greenstone belt.A large disseminated Ni-Cu-(PGE) sulfide ore deposit is hosted by olivine-pyroxene cumulates in the lower ultramafic part of the intrusion, indicating involvement of a multiply saturated magma in the ore formation.There are also various dunitic rocks, which occur as numerous inclusions within the Kevitsa intrusion, most commonly in the economic resource area.On textural basis, two distinct types of inclusions are recognized: i) cumulate-textured (Kevitsa Dunite) and ii) recrystallized ultramafic inclusions.In addition, there also exists a separate dunitic body (Central Dunite) with a suface area of 0.6 x 1.0 km, cropping out in the central part of the intrusion.The Central Dunite and Kevitsa Dunite are similar olivine-chromite cumulates and with comparable whole-rock and mineral compositions, suggesting that they are cogenetic.A magmatic, rather than replacement origin for the dunitic cumulates is evidenced by their systematic mineral compositional trends consistent with magmatic fractionation.Wholerock major and trace element and mineral compositional data of the dunitic cumulates and Kevitsa olivine pyroxenites fall on the same linear trends and record similar REE characteristics indicating a genetic link between these two.The parental magmas for the dunitic cumulates were probably picritic and related to the picritic and basaltic volcanic rocks in the area.The high Fo content of olivine (up to ~89 mol.%) is consistent with a high-Mg parental melt.The recrystallized ultramafic inclusions are fine-grained and show a granoblastic/interlobate textures indicative for thermal textural readjustment.Two subgroups are identified: Group 1 shows a chemical affinity towards the dunitic cumulates and are interpreted as their recrystallized clasts.The Group 2 inclusions are compositionally comparable to the ~2.06Ga komatiitic volcanic rocks in the area and are considered as dehydrated metavolcanic xenoliths.A decrease in the flow rate of the Kevitsa magmas due to entrapment of a high number of inclusions is proposed as a mechanism to promote settling of sulfides, contributing to the formation of the Ni-Cu-(PGE) ore.
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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 | 0.002 | 0.001 |
| 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".