Magma mixing responsible for Axi high-Mg andesite, NW China: Mineralogical evidence
Bibliographic record
Abstract
Abstract This contribution presents a case examination of high-Mg andesite formation through magma mixing and its contribution to gold mineralization. The Axi high-Mg andesites from northwest China are host to a large epithermal gold deposit. They are porphyritic, with 15–40 vol% macrocrysts, primarily plagioclase (the dominant phase), along with clinopyroxene, amphibole, and quartz. Textural and compositional analyses of plagioclase macrocrysts reveal a variety of zoning types, including un-zoned, oscillatory-zoned, sieve-zoned, and patchy-zoned textures, often indicative of a multi-stage growth process. Compositions of the plagioclase macrocrysts vary significantly, with anorthite contents ranging from 10% to 78% for plagioclase, while some feldspars exhibit albite contents as high as 95%–99%. Clinopyroxene occurs either as macrocrysts or glomerocrysts, displaying both normal and reverse zoning patterns. Amphibole macrocrystals are found as opacitized grains or pseudomorphed by chloride, quartz, calcite, and Fe-Ti oxide. Quartz macrocrysts occasionally show corroded or embayed boundaries. The occurrence of alkali feldspar macrocrysts is limited, with some being replaced by plagioclase. Taken together, the sieve and patchy zoning in plagioclase, reverse zoning in clinopyroxene, and resorption of quartz macrocrysts suggest open-system processes, likely driven by mafic magma recharge within a silicic magma reservoir. The formation of high-Mg andesite through magma mixing is conducive to gold mineralization, as mafic magma recharge may introduce sulfur and gold into the system.
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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 | 0.001 | 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 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".