Supergene Turquoise and Associated Phosphate Minerals of the Porphyry-Lode System at Butte, Montana, USA
Bibliographic record
Abstract
ABSTRACT Weathering processes superimposed onto exhumed hydrothermal ore deposits in western North America have developed secondary mineral assemblages that inform the near-surface evolution of these systems within the context of Basin and Range extension. The occurrence of the secondary phosphate mineral turquoise [CuAl6(PO4)4(OH)8·4H2O] in the weathering profile of Laramide porphyry copper deposits is widely documented, although previous studies on the composition and distribution of turquoise are largely restricted to the archaeological literature. In this study, we use the world-class Butte porphyry-epithermal system to study the occurrence, paragenesis, and mineral chemistry of turquoise and related phosphates in the weathering profile of the deposit. Field observations, mineral textures by optical microscopy, electron microprobe analyses, and geochemical modeling show that blue, Al-endmember turquoise formed exclusively at or immediately below the pre-mining water table, within the chalcocite enrichment blanket and in the absence of significant FeIII. At higher structural levels above the pre-mining water table, green FeIII-bearing turquoise [Cu(Al,FeIII)6(PO4)4(OH)8·4H2O] is commonly intergrown with jarosite and/or tinticite at the micron scale. We show that jarosite, tinticite, and FeIII-bearing turquoise formed at the expense of pre-existing, Al-endmember turquoise after extensional faulting caused a relative lowering of the water table in the eastern fault block of the deposit. The low solubility of the FeIII-phosphates tinticite and strengite in the leach cap environment suggests that it is unlikely that these minerals formed directly from oxidized meteoric water. Electron probe microanalysis documented the presence of As and F in blue Al-endmember turquoise and Cl in green FeIII-bearing turquoise. The presence of Cl in FeIII-bearing turquoise may represent an evaporitic signal associated with basin development as the Butte district was exhumed. The paragenesis of Cu- and Fe-phosphate minerals provides another tool with which to interrogate spatial and temporal relationships in the near-surface evolution of porphyry copper systems.
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 | 0.001 | 0.001 |
| Science and technology studies | 0.001 | 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".