Re-Os Systematics of Löllingite and Arsenopyrite In Granulite-Facies Garnet Rocks: Insights Into the Metamorphic History and Thermal Evolution of the Broken Hill Block During the Early Mesoproterozoic (New South Wales, Australia)
Bibliographic record
Abstract
Löllingite and arsenopyrite aggregates occur in spessartine-almandine garnet rocks (garnetite) metamorphosed to granulite facies, which are spatially associated with Pb-Zn-Ag mineralization in the giant Broken Hill deposit, southern Curnamona Province, New South Wales, Australia. Sulfarsenide and sulfide minerals comprise löllingite and coexisting arsenopyrite ± galena ± tetrahedrite that occur interstitial to garnet crystals. Löllingite formed first while gold-bearing löllingite, which occurs as rare relicts in arsenopyrite, was destroyed to produce arsenopyrite ± detectable micro-inclusions of invisible gold. Standard mineral separation procedures produced pure separates of löllingite, arsenopyrite, and mixtures of arsenopyrite ± löllingite and löllingite ± arsenopyrite. In a plot of 187Re/188Os versus187Os/188Os, samples of löllingite and löllingite ± arsenopyrite have 187Re/188Os ratios between 6.87 and 7.40 and 187Os/188Os ratios between 0.8506 and 0.8651, whereas arsenopyrite and arsenopyrite ± löllingite samples have higher 187Re/188Os ratios (7.14 to 11.32) and more radiogenic 187Os/188Os ratios (0.8828 to 0.9654). Thirteen analyses of arsenopyrite and arsenopyrite ± löllingite define a Model 1 isochron with an age of 1574 ± 38 Ma (2σ; MSWD = 1.4, initial 187Os/188Os ratio of 0.666 ± 0.006), whereas the five löllingite and löllingite ± arsenopyrite samples define a Model 1 isochron with an age of 1707 ± 290 Ma (2σ; MSWD = 0.32, initial 187Os/188Os ratio of 0.652 ± 0.036) that is indistinguishable from the arsenopyrite age. Rhenium and Os contents are extremely high for löllingite and arsenopyrite (Re = 120–475 ppb; Os = 65–345 ppb), likely as a result of concentration of Re and Os in these minerals during granulite-facies metamorphism from the inferred exhalite protolith. Petrographic observations combined with the Model 1 Re-Os ages and literature SHRIMP U-Pb ages of monazite in garnetite suggest that arsenopyrite formed on the retrograde path at the expense of löllingite. Cooling from peak Olarian P-T conditions (∼800 °C at 1602 Ma) to at least 550 °C (first temperature of stability of arsenopyrite) at ca. 1574 Ma occurred at a rate of ∼9 °C/Myr, which is similar to the rate of cooling determined for previously published SHRIMP U-Pb ages from successive monazite generations (McFarlane & Frost 2009). These results are consistent with the late phase of retrograde metamorphism that began between ca. 1590 and 1575 Ma.
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 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 | 0.001 |
| 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) | 0.001 | 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".