Locating the “Missing Half” of the Giant Chuquicamata Porphyry Copper Deposit, Chile
Bibliographic record
Abstract
Abstract The supergiant Chuquicamata porphyry Cu-Mo deposit in northern Chile is truncated on its west side by a N-S-trending regional fault (the West fault), juxtaposing its ore to a relatively barren granodiorite (Fortuna Igneous Complex). There has been much speculation about the fate of, and extensive exploration for, the “missing half” of the deposit. It has been proposed that the west side of the fault hides the ore at depth, or that it was uplifted and the ore eroded; however, regional geologic mapping suggests that the West fault had a postore left-lateral strike-slip displacement of ca. 35 km. Accordingly, exploration, so far unsuccessful, has been focused in an area 35 km south near the Loa River and the city of Calama. In 1989, the Mina Ministro Hales (MMH) deposit was unexpectedly discovered west of the fault, under thick gravels, only 7 km south of the main mine. A previous study at MMH had suggested that mineralization was as old as 39 Ma, hence its ores were correlated with deposits of that age near Calama. Our recent U-Pb and Re-Os dating indicates that MMH mineralization was formed between 35 and 31 Ma, thus concurrently with Chuqui. The geochemistry of host Triassic and Eocene porphyry intrusions, ore mineralogy, and common Pb isotope ratios of hypogene sulfides at MMH and Chuqui proper are indistinguishable. Fluid inclusion data for paragenetically early porphyry assemblages at MMH closely mimic Th-salinity data from earlier studies at Chuqui, showing little or no evidence of boiling but indicating widely fluctuating confining pressures, compatible with hydraulic fracturing and fault movement during and after mineralization at a minimum initial lithostatic constraint of 5- to 8-km depth. We propose that MMH is a sheared-off portion of Chuqui, wedged in a fault cymoid loop and spared the full 35-km displacement of the West fault.
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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 | 0.001 | 0.001 |
| 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) | 0.002 | 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".