Precious metal enrichment processes in volcanogenic massive sulphide deposits - a summary of key features, with an emphasis on TGI-4 research contributions
Bibliographic record
Abstract
Volcanogenic massive sulphide deposits contain precious metals (Au, Ag) that can be present in high to low grades and total amounts; depending on tonnage and/or precious metal grade, such deposits can represent desirable exploration targets. Globally, deposits with >3.46 g/t Au are considered "auriferous", those with >-31 t of contained Au are "anomalous", and those with both large tonnage (>-31 t Au) and high gold grade (>3.46 g/t Au) are considered "Au-rich". There are still no clear statistical criteria to determine thresholds that would define "anomalous" Ag grades and/or total amount of Ag in volcanogenic massive sulphide deposits, as grades vary widely depending on the nature of the host succession. Two general requisites may explain anomalous primary precious metal budgets in volcanogenic massive sulphide deposits: 1) inherently Au- and/or Ag-enriched source rocks and fluids due to a specific geodynamic setting or heritage and/or to magmatic input, and 2) efficient transport (favourable ligands) and precipitation (e.g. boiling/phase separation, zone refining). These two requisites, which are of different scales, may or may not be mutually exclusive. Late or "secondary" Au- and/or Ag-enrichment in volcanogenic massive sulphide deposits can be due to the superposition of mineralizing systems of a different style (e.g. epithermal, intrusion-related, orogenic, etc.). Weathering processes (e.g. supergene enrichment) on the seafloor or on land can also significantly modify the distributions of precious metals in a volcanogenic massive sulphide deposit. Volcanogenic massive sulphide deposits in volcanic belts that formed in pericratonic settings or on older crust basement in the early stages of rifting are commonly slightly better endowed in precious metals than those formed in belts or settings with no or limited basement influence. Gold-rich and auriferous VMS are preferentially associated with calc-alkaline or transitional magmatic successions, with andesite-dacite-rhyodacite- rhyolite magmatic suites and with thick (10s to 100s of m) felsic volcanic packages. Evidence for a magmatic input and of deposition in response to boiling/phase separation include the presence of complex mineral assemblages comprising sulphosalts, sulphides, native elements, and anomalous trace element signatures (e.g. enrichment in the "epithermal suite" of elements Au-As-Sb-Ag-Hg and/or in felsic magmaassociated elements Bi-W-Te-In-Sn). A laterally extensive sericitic (phyllic) }siliceous alteration halo, a zone of intense aluminous (argillic to advanced argillic-style) alteration, and heterogeneous Au and Ag distributions and mineralogical residence sites within or near the sulphide bodies are also indicators of a possible magmatic contribution of Au, Ag, and other metals, such as Te and Bi, or metal deposition due to boiling in VMS systems.
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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) | 0.001 | 0.000 |
| Meta-epidemiology (broad) | 0.001 | 0.001 |
| Bibliometrics | 0.003 | 0.002 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.002 | 0.001 |
| Open science | 0.000 | 0.001 |
| Research integrity | 0.001 | 0.001 |
| Insufficient payload (model declined to judge) | 0.002 | 0.001 |
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".