Lithogeochemical constraints on the host rock, hydrothermal alteration and weathering of the Groundrush gold deposit
Bibliographic record
Abstract
Lithogeochemical research at the Groundrush gold deposit, Tanami region, Northern Territory, has identified new lithologies and provides a new understanding of the hydrothermal alteration, metamorphism and weathering processes that have affected the suite of metamorphosed igneous host rocks. Metamorphosed hornblende–chlorite–plagioclase-bearing mafic–intermediate intrusive rocks were classified, using conserved constituents, as dolerite and previously unrecognized basaltic andesite and diorite, the last of which hosts Au mineralization. The diorite forms a steeply dipping dyke, whereas the dolerites are sills intruding clastic sedimentary rocks. Major element geochemical variation in dolerite is consistent with the fractionation of plagioclase and pyroxene, whereas diorite is more chemically homogenous and does not exhibit evidence of fractional crystallization. Hydrothermal alteration, principally developed within the diorite, was accompanied by addition of S and carbonate, and the loss of Ca and Na, giving rise to a propylitic hydrothermal alteration assemblage of chlorite, albite, carbonate and pyrite. A regolith profile of c. 40 m thickness overlies these rocks. If originally present, Fe-rich upper units have been removed. The major weathering processes observed in the regolith profile are: (1) sulphur oxidation and (in diorite), calcite dissolution at 40 m depth; (2) ferrolysis (Fe oxidation) and the production of smectite, goethite and quartz from chlorite and hornblende at 20 m depth; (3) breakdown of albite to kaolinite, breakdown of apatite, and deposition of secondary carbonate in the top 5 to 15 m. No evidence for significant near-surface gold depletion is evident, suggesting that regolith processes remobilizing gold were generally not operating to any significant extent. However, gold was leached from a metre-scale quartz vein, possibly as thiosulphate complexes formed from pyrrhotite oxidation in a relatively low-oxygen environment.
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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 | 0.000 | 0.001 |
| 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".