Are Alkalic Porphyry Deposits Overlain by Advanced Argillic Lithocaps?
Bibliographic record
Abstract
Abstract A commonly highlighted feature that distinguishes alkalic porphyry deposits from those associated with calc-alkaline magmatism is a paucity of the advanced argillic alteration that can form shallow-level lithocaps. This scarcity has been attributed to either the inability of alkalic systems to generate the necessary hyperacidic fluids or erosional removal. Here, it is concluded that erosional removal is responsible, as supported by the following four lines of evidence: Alkaline stratovolcanoes at convergent margins emit as much SO2—the principal ingredient for hyperacidic fluid formation—as those in calc-alkaline arcs;At least one example of recently formed lithocap alteration in an alkaline volcano (Vulcano, Italy) is known;Remnants of advanced argillic lithocaps are present in several alkalic porphyry systems, but only those of Cenozoic age, whereas Paleozoic and Mesozoic deposits, including those in the Macquarie arc of New South Wales, Australia, and the Intermontane belt of British Columbia, Canada, appear to lack them; andAvailable fluid inclusion pressure estimates for alkalic porphyry deposits show paleodepths of at least 1.5 km, possibly up to several kilometers, for deposits lacking lithocaps, consistent with their erosional removal. Therefore, it is concluded that preservation potential, influenced to a significant degree by formational age, is a fundamental control on the presence or absence of lithocaps above alkalic porphyry deposits—as, of course, it is in porphyry systems hosted by calc-alkaline intrusions. Thus, the presence of lithocaps in association with both alkaline and calc-alkaline igneous centers is evidence for concealed shallow intrusions and potential porphyry-type 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 | 0.001 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.002 | 0.001 |
| Science and technology studies | 0.000 | 0.001 |
| Scholarly communication | 0.001 | 0.001 |
| Open science | 0.000 | 0.001 |
| Research integrity | 0.001 | 0.000 |
| Insufficient payload (model declined to judge) | 0.003 | 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".