High cerium anomalies in zircon from intrusions associated with porphyry copper mineralization in the Gibraltar deposit, south-central British Columbia
Bibliographic record
Abstract
The Gibraltar porphyry-Cu deposit in the Quesnel Terrane in south-central British Columbia is hosted by the Late Triassic to Early Jurassic Granite Mountain Batholith (GMB). The GMB has been classified into four phases of tonalitic rocks with minor quartz diorite. The rocks of the Mine Phase, host of the Cu mineralization, are foliated tonalite and are extensively altered to form K-feldspar, white mica, epidote and pyrite. All zircon grains examined from the GMB are magmatic with Th/U ranging from 0.15 to 1.44 and low Nd/Yb ratios below 0.01. U-Pb dating of zircons reveals three Cu-mineralized intrusions within the Mine Phase ranging from 201 to 218 Ma. The age gaps between the mineralized intrusions are larger than the uncertainty of the age data. Zircons from the oldest Cu- mineralized intrusion (218.9±3.1 Ma) in the Mine Phase record the highest Ce4+/Ce3+ (680± 180 (1 sigma), n=14). Zircons from the two other groups of Cu-mineralized intrusions in the Mine Phase show lower Ce4+/Ce3+ (214± 64 (1 sigma), n=43) and those from the unmineralized Border and Granite Mountain phases of the GMB show even lower Ce4+/Ce3+ (128± 35 (1 sigma), n=108). Zircons from the Cretaceous Sheridan Creek Stock, south of the GMB, show low Ce4+/Ce3+ (203± 60 (1 sigma), n=28). The data suggest multiple pulses of intrusions and mineralization in the Mine Phase, which is supported by Re-Os ages of molybdenite which are similar to the second and third pulses of intrusions. Ages and Ce4+/Ce3+ values for zircons from Cu-mineralized rocks in the Mine Phase are similar to the values for intrusions associated with the Highland Valley porphyry Cu deposit in the Guichon Creek Batholith. The ratios Ce/Nd and Ce/Ce* from the measured concentrations of Ce, Nd, and Sm correlate well with Ce4+/Ce3+, based on the compositions of zircon and bulk rocks. This suggests that the compositions of detrital zircons in glacial sediments and streams may be used in mineral exploration to detect intrusions with affinity to host porphyry Cu mineralization.
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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 | 0.002 | 0.002 |
| Science and technology studies | 0.001 | 0.001 |
| Scholarly communication | 0.001 | 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".