Structural evolution of the Agnew–Wiluna greenstone belt, Eastern Yilgarn Craton and implications for komatiite-hosted Ni sulfide exploration
Bibliographic record
Abstract
The Agnew–Wiluna greenstone belt in the Yilgarn Craton of Western Australia is a narrow package of complexly deformed Archean supracrustal rocks that hosts two of the world's largest komatiite-hosted nickel sulfide deposits, the Mt Keith and Perseverance deposits. These deposits and several others in the belt are centred on thick lenses of adcumulate-textured komatiite interpreted to represent areas of channelised magma flow. The large nickel sulfide deposits are located in parts of the belt associated with ca 2720 to 2700 Ma felsic volcanism (e.g. the Leinster and Mt Keith nickel camps). In these areas, felsic to intermediate volcanic rocks are intercalated with syn-volcanic massive sulfides of inferred exhalative origin. While these primary magmatic features are clearly first-order controls on the distribution of Ni sulfide deposits in the belt, several regional-scale deformation events have significantly complicated the interpretation of primary stratigraphic relationships. The earliest recorded deformation events (D1,2,3) resulted in an east–west trending greenstone belt with recumbent isoclinal folds and ductile shear zones. Subsequent west-southwest–east-southeast shortening during the D4 event at ca 2666 Ma involved the refolding of the tectono-stratigraphy to produce belt-scale, north- to north-northwest-trending upright folds, a pervasive axial planar schistosity in all rocks, and the present-day steeply dipping, overturned supracrustal sequences, and emplacement of granitoids in major antiformal fold hinges. Polyphase folding of supracrustal rocks produced Type 2 fold interference patterns with multiple facing reversals at various scales across the belt. West-southwest–east-southeast extension during the D5 event at ca 2665 Ma triggered the development of terrestrial basins (i.e. Scotty Creek and Jones Creek) in areas flanking major antiforms, resulting in the deposition of the Jones Creek Conglomerate. Subsequent west-southwest–east-southeast shortening during the D6 event resulted in the folding of the Jones Creek Conglomerate and formation of gold-bearing veins in the Agnew gold camp. Belt-wide relaxation in east–west shortening during the D7 event caused open, recumbent F7 folding of the steeply dipping stratigraphy. Broadly east–west shortening during the D8 to D10 events resulted in the tightening of existing fold hinges, the dismemberment and displacement of panels of supracrustal rocks by sinistral (e.g. Perseverance shear zone) and then dextral (Waroonga) shear zones. The Agnew–Wiluna belt displays (para)autochthonous associations within the belt, with district-scale heterogeneities caused by primary volcano-sedimentary facies changes combined with polyphase deformation. Importantly, nickel sulfide-bearing sequences identified in nickel camps can potentially be traced to different parts of the belt by unravelling the effects of polyphase deformation.
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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 | 0.001 |
| 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) | 0.002 | 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".