The contact metasomatic magnetite deposits of southwestern British Columbia
Bibliographic record
Abstract
Ore zones, skarn, host rocks, and associated intrusions of 12 magnetite deposits were studied in both field and laboratory to determine their mineralogical and geochemical characteristics, origin of the iron, and factors controlling emplacement of iron-bearing minerals. This study seeks a better understanding of the origin and mode of occurrence of contact metasomatic magnetite deposits which in turn may provide better guides to their exploration and evaluation. Local folds and faults are important factors in the explacement of magnetite in volcanic rocks and limestone of the Vancouver group. Adjacent stocks are of intermediate composition. Post-ore leucodiorite dykes are common in many orebodies . The author proposes that the process by which skarn is formed be called skarnification i.e. the replacement by, conversion into, or introduction of skarn. The term would include all processes by which skarn may be formed such as contact metamorphism, contact metasomatism, or regional metamorphism. Skarn in the coastal British Columbia region is composed mainly of garnet (andradite-grossularite), pyroxene (diopside-hedenbergite), epidote, and magnetite. Conformity to Gibbs Phase Rule and the non-appearance of incompatible phases is strong evidence that equilibrium was attained during skarnification. Magnetite is the major metallic mineral, but chalcopyrite, pyrite, pyrrhotite, and arsenopyrite are locally abundant. The temperature of intrusion is estimated to be in the range 800-900°C and stability relations of coexisting minerals indicate a temperature of 700- 550°C daring skarnification. The pyrite-pyrrhotite geothermometer applied to eight specimens shows that ore deposition, took place within the temperature range 400-550°C. The composition of arsenopyrite coexisting with pyrite and pyrrbotite in one orebody indicates a confining pressure of 2600± 1,000 bars during ore formation. The immediate source of iron in these deposits is believed to be nearby intrusions. The ultimate source, however, is very probably underlying volcanic rocks which have been assimilated, in part, by an advancing pluton. Iron is considered to have been derived from plutons adjacent to the orebodies and to have been carried to the sites of deposition as aqueous supercritical solutions of iron chloride. Magnetite was precipitated from the ore-forming fluid by an increase in pH brought about by reaction with limestone. Changes in the chemical and physical nature of the ore-forming fluid during ore deposition are discussed in terms of temperature, density, pH, partial pressures of oxygen and sulphur, and composition. Hydrothermal processes operative in formation of the deposits were solvate opposition, metasomatism, and cavity filling
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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 | 0.002 | 0.000 |
| Scholarly communication | 0.001 | 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".