Role of colloidal transport in the formation of high-grade gold veins at Brucejack, British Columbia
Bibliographic record
Abstract
Low solubility of Au in hydrothermal fluids at epithermal pressures and temperatures make it difficult to reconcile extremely localized, very high Au grades in epithermal vein deposits. Au has been known to form colloidal suspensions (sols) of nanoparticles when it is super-saturated within solution. Drop in temperature and/or pressure of hydrothermal fluids causing super-saturation of Au is also known to saturate a fluid with respect to silica leading to the precipitation of silica nanoparticles. Au can adhere to silica nanoparticles causing the stability of Au within suspension to be greatly enhanced increasing transport distance. A silica-protected Au sol allows a much higher flux of Au through a hydrothermal system and deposition of very concentrated Au grades within an epithermal vein system. Depressurization caused by fracture and fault-slip within the epithermal environment commonly causes supersaturation of silica leading to sudden precipitation of amorphous silica phases such as opal, which traps any suspended Au nanoparticles. Subsequent recrystallization of amorphous silica alters depositional textures by forcing nanoparticles to quartz grain boundaries. Deformation and metamorphism will further recrystallize quartz, obscuring evidence of this process. This thesis presents structural data, and detailed optical and electron microscopy observations of epithermal quartz-carbonate vein stockwork systems at Brucejack, British Columbia and Dixie Valley, Nevada that are used to test a colloidal Au transport model. At the Jurassic aged Brucejack Au-Ag deposit, very high grades up to 41 582 ppm Au are reported within electrum that is hosted within metamorphosed and deformed quartz-carbonate stockwork. I show that initial stockwork development occurred during north-south extension and formation of mode 1 fractures with continued stockwork development within major normal fault zones. Electrum mineralization within these veins is shown to consist of an amalgamation of nanoparticles. Observations made on quartz formed within the recently active Stillwater fault zone at Dixie Valley, Nevada show that quartz here has recrystallized from an amorphous silica phase. Using these observations for comparison, quartz associated with nanoparticulate electrum at the much older Brucejack deposit is shown to also have recrystallized from an amorphous phase. The association between amorphous silica and nanoparticulate electrum indicates a colloidal origin for high-grade Au at the Brucejack deposit.
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How this classification was reachedexpand
Full frame distilled prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| 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 | 0.000 |
| 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 teacher head, 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".