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Hydrothermal Alteration and Fluid Evolution of the Deep Grasberg Porphyry System, Papua, Indonesia
https://doi.org/10.20569/00006110
https://doi.org/10.20569/00006110f93ae0fa-0a42-4308-9803-aabff9ee68eb
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内容要旨及び審査結果要旨 (205.5 kB)
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本文 (20.2 MB)
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| Item type | 学位論文 / Thesis or Dissertation(1) | |||||
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| 公開日 | 2022-12-06 | |||||
| タイトル | ||||||
| タイトル | Hydrothermal Alteration and Fluid Evolution of the Deep Grasberg Porphyry System, Papua, Indonesia | |||||
| 言語 | ||||||
| 言語 | eng | |||||
| 資源タイプ | ||||||
| 資源タイプ識別子 | http://purl.org/coar/resource_type/c_db06 | |||||
| 資源タイプ | doctoral thesis | |||||
| ID登録 | ||||||
| ID登録 | 10.20569/00006110 | |||||
| ID登録タイプ | JaLC | |||||
| アクセス権 | ||||||
| アクセス権 | open access | |||||
| アクセス権URI | http://purl.org/coar/access_right/c_abf2 | |||||
| 別タイトル | ||||||
| その他のタイトル | インドネシア，パプアにおける深部グラズベルグ斑岩システムの熱水変質および流体の進化 | |||||
| 作成者 |
Reza, Al Furqan
× Reza, Al Furqan |
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| 内容記述（抄録） | ||||||
| 内容記述タイプ | Other | |||||
| 内容記述 | The giant Grasberg Cu-Au-(Mo) deposit is one of the world’s largest porphyry Cu deposit located in Indonesia, which hosts 32 million metric tons of copper and 96 million ounces of gold. The deposit is contained in two overlapping porphyry systems: Gajah Tidur Cu-Mo-(Au) and Main Grasberg Cu-Au. The Grasberg Block Cave reserve that lies beneath the Grasberg open pit has recently been associated with the Gajah Tidur (GT) porphyry that is older than the shallower Main Grasberg (MG) porphyry system. This study is intended to confirm and delineate the existence of GT porphyry in the Grasberg Cu-Au-(Mo) deposit, decipher the hydrothermal fluid evolution, and optimize the wholerock geochemistry as well as chemical variation of GT porphyry white micas to develop exploration vectoring tools for the deep-seated porphyry Cu deposits. Dating of hydrothermal biotite and muscovite by K-Ar method revealed that the GT porphyry system is ~300 k.y. older than the shallower MG porphyry system, which formed at 3.1 ± 0.05 Ma. The age-depth relationships between the GT and MG porphyry systems suggest there was an accumulation of volcanic rocks in between the two porphyry events, associated with growth of a ~0.5 to 1 km high stratovolcano prior the formation of MG porphyry system. The configuration of alteration patterns and associated mineralization, supported by hydrothermal biotite and muscovite ages, indicates that all white mica assemblages and more than 70% of Cu, Mo, and Au contained in the Grasberg Block Cave reserve are associated with the GT porphyry system. Sulfur isotope study shows that the evolution of GT hydrothermal fluid is initiated by the formation of K-feldspar-biotite at a temperature as high as 590 °C. Cooling of this fluid from ~460° to ~370 °C allowed the formation of white mica-dominated alteration, which is associated with various amounts of anhydrite, chlorite, chalcopyrite, and pyrite. Based on the anhydrite and chlorite abundances, this white mica assemblage can be subdivided into muscovite-anhydrite-chlorite and muscovite-chlorite-anhydrite, both of which contain remnant hydrothermal biotite. The muscovite-quartz ± pyrophyllite assemblage associated with covellite-pyrite mineralization formed in the outer part of the muscovite-anhydrite-chlorite alteration zone at a lower temperature range (340-280 °C). Based on mineral chemistry and infrared spectroscopy analysis, the muscoviteanhydrite- chlorite white micas are characterized by high Na, Fe, Ti, and V concentrations, and mainly display short-wave infrared Al-OH absorption wavelengths of 2,203-2,208 nm. The muscovite-chlorite-anhydrite white micas have distinctly higher Mg content than the other two GT white mica assemblages but similar Al-OH absorption wavelengths to the muscovite-anhydrite-chlorite white micas. The muscovite-quartz ± pyrophyllite white micas have low Na, Fe, Mg, and Ti, but relatively high Si, Al, and F, and Al-OH absorption wavelengths are largely shorter than 2,202 nm. The amounts of Si and Al contained in the GT white micas allow occupancy of other cations, particularly Fe and Mg in octahedral lattice sites and cause variations in their short-wave infrared Al-OH absorption wavelengths. Three decades of exploration and geologic studies of the giant Grasberg Cu-Au-(Mo) deposit provide information that is relevant to porphyry exploration globally. The existence of GT porphyry below the shallower MG porphyry system reveals that there is potential for nearby porphyry deposits at depth beneath the already discovered porphyry Cu districts. Taking an example from the deep-seated GT porphyry system, the wholerock geochemical anomaly of F, V, W, and Sn, and the white mica short-wave infrared Al-OH wavelength lie in between ~2,200 and ~2,215 nm can be integrated with other geological and geophysical information to locate the centre of porphyry Cu systems. |
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| 著者版フラグ | ||||||
| 出版タイプ | VoR | |||||
| 出版タイプResource | http://purl.org/coar/version/c_970fb48d4fbd8a85 | |||||
| 書誌情報 | 発行日 2022-09-29 | |||||
| 出版者 | ||||||
| 出版者 | 秋田大学 | |||||
| 学位名 | ||||||
| 学位名 | 博士（理学） | |||||
| 学位授与機関 | ||||||
| 学位授与機関識別子Scheme | kakenhi | |||||
| 学位授与機関識別子 | 11401 | |||||
| 学位授与機関名 | 秋田大学 | |||||
| 学位授与年月日 | ||||||
| 学位授与年月日 | 2022-09-29 | |||||
| 学位授与番号 | ||||||
| 学位授与番号 | 甲第1438号 | |||||
