Diamond potential of metamorphic rocks in the Kokchetav Massif, northern Kazakhstan
Bibliographic record
Abstract
There are two known diamondiferous bodies in Kazakhstan, the Kumdy-Kol deposit and the Barchi-Kol occurrence. Both are located within the western part of a metamorphic belt that outcrops at the central part of the Kokchetav Massif. The metamorphic belt is interpreted as a mega-melange that comprises structural units underlain by HP and UHP rocks. Diamondiferous varieties of the UHP rocks within the Kumdy-Kol deposit form a narrow (~1 km thick), NE-trending band; they comprise less than one percent of the total UHP rock volume. The economically important diamondiferous zone consists of variegated rocks, from silicate to essentially carbonate varieties with a wide spectrum of mineral assemblages. Garnet-biotite gneiss makes about 80 % of the diamondiferous zone. Certain regularity is discernable in spatial distribution of diamonds: linear diamond-rich zones alternate with barren ones. The diamond grade ranges from several carats per ton (cpt) to several hundreds cpt. Different morphological varieties are present among the diamonds: octahedra, cubes, cube-octahedron combination forms, skeletal and spheroid crystals. A wide range of δ 13 C (−8.9‰ through −27 ‰) and δ 15 N (+5.3 ‰ through +25 ‰) values have been measured. Diamonds from different rock types differ in their carbon isotopic pattern: diamonds from gneiss have ‘lighter’ isotopic compositions relative to those of pyroxene-carbonate and garnet-pyroxene rocks. Graphite, coesite, clinopyroxene, rutile, titanite, kyanite, K-feldspar, biotite, phengite, quartz, phlogopite, albite, apatite, chlorite and carbonates are minerals forming intergrowths with diamonds. The most frequent combination is graphite +diamond. We conclude that the model of crustal fluid-metasomatic formation of diamonds in metamorphic rocks reflects the observed regularities best. The morphology of diamondiferous bodies favors the notion of their formation from a carbon-bearing fluid. The micrometer size of the diamonds, along with isotopic signatures, hint at their formation under metastable crustal conditions. This model presumes that the formative process occurred at relatively low temperature and pressure within an open disequilibrium catalytic system. It does not exclude an UHP episode in the geological history of the metamorphic rocks.
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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 | 0.003 | 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".