Characteristics and Behavior of Hydrothermal Fluids for Gold Mineralization at the Hishikari Deposits, Kyushu, Japan
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Résumé
Abstract The Hishikari gold–silver deposits in southern Kyushu, Japan, are low‐sulfidation vein‐type epithermal deposits. Bulk composition analysis, fluid inclusion microthermometry and quantitative gas composition analysis on the basis of the crush‐fast scan (CFS) method were conducted to elucidate characteristics and behavior of hydrothermal fluids responsible for the gold mineralization of the Hishikari deposits. Quartz vein samples were collected from widely scattered locations of ore veins: Zuisen‐6, ‐3, ‐1 (Main deposit), Keisen‐2 and Shosen‐5 (Sanjin deposit), and Seisen‐8 (Yamada deposit) between −70 and 64 ML (mine meter level). The samples are composed mainly of quartz and adularia, and ore minerals of electrum, pyrargyrite, pyrite and/or stibnite, having an average bulk Ag/Au weight ratio of 0.54. Fluid inclusions in quartz and adularia are two‐phase liquid–vapor, and their trapping temperatures and salinities are ca. 190–220 °C and 1.5–2.7 wt.% NaCl eq., respectively. The salinity is highest with an average 2.4 wt.% NaCl eq. of the fluid inclusions from the deepest level (Zuisen‐6 vein at −70 ML), while the fluid inclusion salinities from other samples are relatively low less than ca. 2.0 wt.% NaCl eq. Parallel‐ and lattice‐bladed quartz occur in a number of veins, suggesting fluid boiling during the vein formation. Gases of fluid inclusions are composed mainly of H 2 O (93.4–99.8 mol%) and CO 2 (0.15–6.2 mol%), N 2 (0.007–0.96 mol%), Ar (0.0001–0.0047 mol%), CH 4 (0.002–0.048 mol%), H 2 S (0.0004–0.0028 mol%), H 2 (0–0.074 mol%) and He (0.0002–0.0011 mol%). CO 2 , N 2 and Ar contents of the fluid inclusions are elevated in the samples collected from deep levels, while H 2 O, H 2 S and He contents are elevated in those from shallow levels. The Ar/He, CO 2 /CH 4 and N 2 /Ar ratios of fluid inclusion gas indicate a systematic transition from magmatic to meteoric signatures in order from deep to shallow levels. The CO 2 /N 2 ratio and volatiles contents are positively correlated suggesting condensation in relatively high Au‐grade quartz vein samples (19.5–27.7 ppm Au), while negative correlations suggest boiling with volatile contents less than 1% are indicative of low Au‐grade quartz vein samples (0.14 to 0.18 ppm Au). The elevated CO 2 contents observed in the Zuisen veins are signatures of the deeply circulating hydrothermal fluid with a magmatic contribution. Due to intermittent boiling of hydrothermal fluid, CO 2 and H 2 S were partitioned into the vapor phase in deeper portions and condensed into the steam‐heated meteoric water in shallower portions. The signatures of both meteoric and magmatic fluids in fluid inclusion gas compositions were detected in the samples collected near the unconformity between Shimanto Supergroup (shale and sandstone) and Hishikari Lower Andesite. This suggests that a mixing of the deeply circulating hydrothermal fluids with the steam‐heated meteoric water took place near the unconformity, and it was one of the mechanisms to have precipitated gold.
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Imitation des enseignantsNi prévalence calibrée, ni vérité terrain. Validation humaine à venir. Apprise à partir de 10 348 étiquettes directes de Codex et de 10 348 étiquettes directes de Gemma. Le mode candidate est l'union des têtes enseignantes seuillées; le consensus est leur intersection. Ces sorties portent le statut machine_predicted_unvalidated et ne sont ni des étiquettes humaines ni des étiquettes directes de modèles de pointe.
Scores Codex et Gemma par catégorie
| Catégorie | Codex | Gemma |
|---|---|---|
| Métarecherche | 0,000 | 0,000 |
| Méta-épidémiologie (sens strict) | 0,000 | 0,000 |
| Méta-épidémiologie (sens large) | 0,000 | 0,000 |
| Bibliométrie | 0,000 | 0,000 |
| Études des sciences et des technologies | 0,000 | 0,000 |
| Communication savante | 0,000 | 0,000 |
| Science ouverte | 0,000 | 0,000 |
| Intégrité de la recherche | 0,000 | 0,000 |
| Charge utile insuffisante (le modèle a refusé de juger) | 0,001 | 0,000 |
Scores machine (provisoires)
Les deux têtes enseignantes du modèle étudiant, lues sur ce travail. Un score ordonne la base pour la relecture; il n'affirme jamais une catégorie, et le statut de validation accompagne chaque rangée tel quel.
Scores de référence d'un modèle non mature (critères de maturité non atteints, 7 itérations). Un score ordonne; il n'affirme jamais une catégorie.
score_only:v0-immature-baseline · tel quel depuis la passe de notation : score_only signifie que le nombre peut ordonner les travaux, et qu'aucune étiquette de catégorie n'en découle