Experimental and fluid inclusion constraints on the ore metal content and origin of volatiles associated with large NI-CU--PGE deposits
Bibliographic record
Abstract
Microanalyses of synthetic fluid inclusions containing a S-free, NaCl brine (20-70 wt% eq. NaCl) that was reacted with silicate melt and Pt and Au metal at T=600-800°C, P=1.5 kbar show that both metals are significantly soluble (Cfluidmetal 1-103 ppm) at moderately oxidizing (Ni-NiO) conditions, and partition strongly into the fluid phase (Dfluid/meltmetal = 102-103). Maximum dissolved Pt and Au concentrations decrease by sim;2 log units with increasing salinity from 20 to 70 wt% eq. NaCl. Maximum dissolved Au concentrations increase approximately sim;1 log unit for every 100°C increase in brine temperature. The negative correlation between trapped metal concentration and salinity may be the result of the "salting-out" of neutral metal complexes [e.g., aqueous PtCl3H or Pt(OH)2-(H2On) as the NaCl0 content increases in the fluid and free H2O is consumed. Due most likely to slow metal-fluid-melt equilibrium, microanalysis of fluids trapped using synthetic fluid inclusion methods allows only semi-quantitative estimation of minimum (non-equilibrium) precious metal solubility. Microanalyses of fluid inclusions from the footwall Cu-Ni-PGE systems at Sudbury, Canada, and pegmatites and cumulate rocks below the J-M reef in the Stillwater Complex, U.S.A. show that Na-Ca-K-Fe-Mn-Ba-Pb-Sr-Zn-rich brines ( sim;30-80 wt% eq. NaCl) and non-aqueous volatiles (CH4 vapour; liquid/supercritical CO2; halide melt) carried ppm concentrations of precious/accessory metals (Pt, Pd, Au, Ag, Sn, Ag, Bi) and up to wt% concentrations of base metals (Cu) at the time of their entrapment. Volatile P-T-X characteristics show major similarities at Sudbury and Stillwater, notably evidence for carbonic fluid-brine immiscibility and the selective partitioning of ore metals into the carbonic fluid phase. Inclusion assemblages record a prolonged evolution of volatiles. At near-solidus conditions, inclusions trapped C and Cl-rich volatiles that exsolved from and coexisted with a high Cl/H2O residual silicate liquid or fractionated sulfide liquid at sim;700-800°C. At post-cumulus conditions, inclusions trapped hybrid fluid compositions derived by the interaction of magmatic brines with crystalline wall-rocks, sulfides, or groundwater, and later modified by carbonic fluid-brine immiscibility and metal reprecipitation. Ore metals in the volatiles were derived through interaction with PGE-bearing sulfide assemblages or possibly by the partitioning of ore metals from sulfide liquid.
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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 | 0.001 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.001 |
| Scholarly communication | 0.000 | 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".