Petrogenetic and Metallogenetic Relationships in the Eastern Cordillera Occidental of Central Peru
Bibliographic record
Abstract
Ore deposits spatially and temporally related to high‐K calc‐alkaline intrusions or domes are widespread in the central Peruvian Cordillera Occidental. Geochronology and petrochemistry of intrusive rocks associated with mineralization reveal that most ore deposits (1) were emplaced in the late Middle to early late Miocene and (2) are related to calc‐alkaline igneous rocks of granodioritic composition with $$\mathrm{Sm}\,/ \mathrm{Yb}\,> 3$$ , $$\mathrm{Sr}\,/ \mathrm{Y}\,> 40$$ , and $$\mathrm{Y}\,/ \mathrm{Th}\,< 1.5$$ . The largest deposits are associated with intrusions with $$\mathrm{Sm}\,/ \mathrm{Yb}\,> 4$$ . Strontium isotopic compositions of the igneous rocks vary from $$^{87}\mathrm{Sr}\,/{}^{86}\mathrm{Sr}\,=0\mathrm{.}\,7038$$ to 0.7089, but the $$^{87}\mathrm{Sr}\,/ {}^{86}\mathrm{Sr}\,$$ ratio values exhibit only a poorly defined overall trend toward increased crustal contamination through time. Lead isotopic ratios generally correlate with the Sr isotopes and range from $$^{206}\mathrm{Pb}\,/ {}^{204}\mathrm{Pb}\,=18.64$$ to 18.91, from $$^{207}\mathrm{Pb}\,/ {}^{204}\mathrm{Pb}\,=15.58$$ to 15.66, and from $$^{208}\mathrm{Pb}\,/ {}^{204}\mathrm{Pb}\,=38.60$$ to 39.06. The overall Sr and Pb isotopic compositions of the igneous rocks indicate a generally moderate crustal assimilation of ancient radiogenic rocks. The Pb isotopic composition of sulfides from 14 polymetallic ore deposits in the study area lie on parallel arrays between the Pb isotopic compositions of spatially related igneous rocks and higher $$^{208}\mathrm{Pb}\,/ {}^{204}\mathrm{Pb}\,$$ and $$^{207}\mathrm{Pb}\,/ {}^{204}\mathrm{Pb}\,$$ sources such as Paleozoic and Mesozoic siliciclastic sedimentary rocks or the Carboniferous and older crystalline basement. The trace element and radiogenic isotope signature of igneous rocks related to mineralization indicates that these rocks have undergone limited midcrustal and shallow crustal assimilation and reflect melt equilibration in the lower crust at a crustal thickness of more than 40–45 km under conditions where hornblende and garnet were stable in the basaltic lower crustal residuum. Mineralization was favored by a change from normal to flat subduction, resulting in crustal thickening as well as broadening and subsequent cessation of the magmatic arc. However, some igneous rocks apparently unrelated to mineralization have high Sm/Yb and Sr/Y ratios as well. Petrographic and Pb isotopic evidence indicates that for some of these rocks, these trace element ratios may be better explained by shallow crustal hornblende fractionation or assimilation of pelitic material.
Fetched live from OpenAlex and de-inverted. Abstracts are not stored in this database: the inverted indexes are 8.6 GB of the frame’s 9.3 GB of text, and the host has 13 GB free.
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 | 0.001 | 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".