Features of Large Magmatic–Hydrothermal Systems in Japan: Characteristics Similar to the Tops of Porphyry Copper Deposits
Bibliographic record
Abstract
Abstract Volcanic complexes in Japan such as Kusatsu Shirane, Honshu, and Kuju‐Hatchobaru and Kirishima, Kyushu, host active magmatic–hydrothermal systems that are several kilometers in diameter and typically asymmetric to the intrusive center. Their heat flow is driven by multiple intrusions at <5–10 km depth over a period on the order of ~105 years. These hydrothermal systems consist of advecting fluids of magmatic origin (either vapor with acidic components condensed into meteoric water, or a subsequent liquid of varying reactivity) that interact with convecting meteoric water. The amount of the magmatic component depends on location relative to the intrusive center, local controls on permeability, and the temporal evolution of the intrusions. The proportion of meteoric water diluent typically increases from proximal to distal locations (over several kilometer distance), and with time after intrusion (> several thousands of years). Some of the neutral pH solutions in these large hydrothermal systems, up to ~5 km from volcanic vents, support geothermal energy developments, with strong structural control on fluid flow. Near active volcanic vents, the magmatic vapor component of hydrothermal systems can form acidic condensates (pH ~ 1.5) that are responsible for strong alteration of the host rock. The resulting residual quartz and advanced argillic minerals are typical of shallow‐formed lithocap alteration that is associated with deeper porphyry copper deposits in similar arc‐hosted volcanic settings. Around the world, this near‐surface lithocap alteration, influenced by structures as well as lithology, may be barren in metals, even where associated with mineralized porphyry intrusions at depth. Such intrusion‐proximal alteration is widespread in both active and extinct settings in Japan. In addition, distal geothermal hot springs typically have a magmatic water component, albeit minor, with a pH that varies from ~3 to near‐neutral; deep alteration intersected in drill holes is characterized by alunite–dickite–pyrophyllite or chlorite–wairakite, respectively. These alteration assemblages are typical of their extinct equivalents, intermediate sulfidation epithermal veins, with mineralogical complexities caused by temporal evolution as well as spatial variation (e.g. along different structures). Such active and extinct magmatic–hydrothermal systems signify the presence of shallow degassing or degassed intrusions, respectively. Where similar intrusions in volcanic arcs around the world are eroded to ~1 to 2 km depth, the tops of porphyry copper deposits are commonly exposed, marked by a transition of white mica upward to pyrophyllite‐dominant alteration. Active magmatic–hydrothermal systems on the flanks of arc volcanoes in Japan are dynamic – both cycling as well as evolving – and share characteristics with extinct systems that host epithermal and porphyry ore deposits.
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 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 | 0.003 | 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) | 0.002 | 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".