Acid-sulphate type alteration and mineralization in the Desmos Caldera, Manus back-arc basin, Papua New Guinea

Saved in:
Authors:Gena, Kaul; Mizuta, Toshio; Ishiyama, Daizo; Urabe, Tetsuro
Author Affiliations:Primary:
Akita University, Institute of Applied Earth Science, Akita, Japan
Other:
University of Tokyo, Japan
Volume Title:Resource Geology (Tokyo 1998)
Source:Resource Geology (Tokyo 1998), 51(1), p.31-44. Publisher: Society of Resource Geology, Tokyo, Japan. ISSN: 1344-1698
Publication Date:2001
Note:In English. 35 refs.; illus., incl. 4 tables
Summary:The Onsen acid-sulphate type of mineralization is located in the Desmos caldera, Manus back-arc basin. Hydrothermal precipitates, fresh and altered basaltic andesite collected from the Desmos caldera were studied to determine mineralization and mobility of elements under seawater dominated condition of hydrothermal alteration. The mineralization is characterized by three stages of advanced argillic alteration. Alteration stage I is characterized by coarse subhedral pyrophyllite with disseminated anhedral pyrite and enargite which were formed in the temperature range of 260-340°C. Alteration stage II which overprinted alteration stage I was formed in the temperature range of 270-310°C and is characterized by euhedral pyrite, quartz, natroalunite, cristobalite and mixed layer minerals of smectite and mica with 14-15 Å XRD peak. Alteration stage III is characterized by amorphous silica, native sulphur, covellite, marcasite and euhedral pyrite, which has overprinted alteration stages I and II. Relative to the fresh basaltic andesite samples, the rims and cores of the partly altered basaltic andesite samples have very low major, minor and rare earth elements content except for SiO2 which is much higher (58-78 wt%) than SiO2 content of the fresh basaltic andesite (55 wt%). REE patterns of the partly altered basaltic andesite specimens are variably depleted in LREE and have pronounced negative Eu anomalies. Normalization of major, minor and REE content of the partly altered basaltic andesites to the fresh basaltic andesite indicates that all the elements except for SiO2 in the partly altered basaltic andesite are strongly lost (e.g. Al2O3 = -8.3 to -10.9 g/100 cm3, Ba = -2.2 to -5.6 mg/100 cm3, La = -130 to -200 µg/100 cm3) during the alteration process. Abnormal depletion of MgO, total Fe as Fe2O3, LREE especially Eu and enrichment of SiO2 in the altered basaltic andesites from the Desmos caldera seafloor is caused by interaction of hot acidic hydrothermal fluid, which originates from a mixing of magmatic fluid and seawater.
Sections:Geochemistry; Petrology
Subsections:Hydrogeochemistry; Metamorphism: thermal, metasomatic; Minerals and ores; Oceanic petrology
Subjects:Acidic composition; Andesites; Back-arc basins; Basins; Hydrothermal alteration; Igneous rocks; Metal ores; Metallogeny; Metasomatism; Mineral deposits, genesis; Mineralization; Ore-forming fluids; Sulfates; Volcanic rocks; Australasia; Bismarck Sea; Manus Basin; Pacific Ocean; Papua; Papua New Guinea; South Pacific; Southwest Pacific; West Pacific; Desmos Caldera
Coordinates:S034300 S034100 E1515300 E1515100
Abstract Numbers:05M/1098
Record ID:2001065596
Copyright Information:GeoRef, Copyright 2019 American Geosciences Institute.
Tags: Add Tag
No Tags, Be the first to tag this record!
LEADER 04920naaaa2200673zu 4500
001 2001065596
003 ViAlAGI
005 20190221173854.0
008 190110s2001 ja a 0 0 eng d
034 0 |a a  |d E1515100  |e E1515300  |f S034100  |g S034300 
040 |a ViAlAGI  |c ViAlAGI 
072 7 |a 27A  |2 georeft 
100 1 |a Gena, Kaul  |e analytic author  |u Akita University, Institute of Applied Earth Science, Akita 
245 1 0 |a Acid-sulphate type alteration and mineralization in the Desmos Caldera, Manus back-arc basin, Papua New Guinea 
300 |a p. 31-44 
500 |a In English. 35 refs. 
500 |a Abstract number: 05M/1098 
500 |a Category Section: Geochemistry 
500 |a Category Section: Petrology 
500 |a Category Subsection: Hydrogeochemistry 
500 |a Category Subsection: Metamorphism: thermal, metasomatic 
500 |a Category Subsection: Minerals and ores 
500 |a Category Subsection: Oceanic petrology 
500 |a Affiliation: Akita University, Institute of Applied Earth Science; Akita; JPN; Japan 
500 |a Affiliation: University of Tokyo; ; JPN; Japan 
500 |a Key title: Resource Geology (Tokyo 1998) 
500 |a Source note: Resource Geology (Tokyo 1998), 51(1), p.31-44. Publisher: Society of Resource Geology, Tokyo, Japan. ISSN: 1344-1698 
500 |a Publication type: journal article 
504 |b 35 refs. 
510 3 |a GeoRef, Copyright 2019 American Geosciences Institute. 
520 |a The Onsen acid-sulphate type of mineralization is located in the Desmos caldera, Manus back-arc basin. Hydrothermal precipitates, fresh and altered basaltic andesite collected from the Desmos caldera were studied to determine mineralization and mobility of elements under seawater dominated condition of hydrothermal alteration. The mineralization is characterized by three stages of advanced argillic alteration. Alteration stage I is characterized by coarse subhedral pyrophyllite with disseminated anhedral pyrite and enargite which were formed in the temperature range of 260-340°C. Alteration stage II which overprinted alteration stage I was formed in the temperature range of 270-310°C and is characterized by euhedral pyrite, quartz, natroalunite, cristobalite and mixed layer minerals of smectite and mica with 14-15 Å XRD peak. Alteration stage III is characterized by amorphous silica, native sulphur, covellite, marcasite and euhedral pyrite, which has overprinted alteration stages I and II. Relative to the fresh basaltic andesite samples, the rims and cores of the partly altered basaltic andesite samples have very low major, minor and rare earth elements content except for SiO<2` which is much higher (58-78 wt%) than SiO<2` content of the fresh basaltic andesite (55 wt%). REE patterns of the partly altered basaltic andesite specimens are variably depleted in LREE and have pronounced negative Eu anomalies. Normalization of major, minor and REE content of the partly altered basaltic andesites to the fresh basaltic andesite indicates that all the elements except for SiO<2` in the partly altered basaltic andesite are strongly lost (e.g. Al<2`O<3` = -8.3 to -10.9 g/100 cm>3`, Ba = -2.2 to -5.6 mg/100 cm>3`, La = -130 to -200 µg/100 cm>3`) during the alteration process. Abnormal depletion of MgO, total Fe as Fe<2`O<3`, LREE especially Eu and enrichment of SiO<2` in the altered basaltic andesites from the Desmos caldera seafloor is caused by interaction of hot acidic hydrothermal fluid, which originates from a mixing of magmatic fluid and seawater. 
650 7 |a Acidic composition  |2 georeft 
650 7 |a Andesites  |2 georeft 
650 7 |a Back-arc basins  |2 georeft 
650 7 |a Basins  |2 georeft 
650 7 |a Hydrothermal alteration  |2 georeft 
650 7 |a Igneous rocks  |2 georeft 
650 7 |a Metal ores  |2 georeft 
650 7 |a Metallogeny  |2 georeft 
650 7 |a Metasomatism  |2 georeft 
650 7 |a Mineral deposits, genesis  |2 georeft 
650 7 |a Mineralization  |2 georeft 
650 7 |a Ore-forming fluids  |2 georeft 
650 7 |a Sulfates  |2 georeft 
650 7 |a Volcanic rocks  |2 georeft 
651 7 |a Australasia  |2 georeft 
651 7 |a Bismarck Sea  |2 georeft 
651 7 |a Manus Basin  |2 georeft 
651 7 |a Pacific Ocean  |2 georeft 
651 7 |a Papua  |2 georeft 
651 7 |a Papua New Guinea  |2 georeft 
651 7 |a South Pacific  |2 georeft 
651 7 |a Southwest Pacific  |2 georeft 
651 7 |a West Pacific  |2 georeft 
653 |a Desmos Caldera 
700 1 |a Mizuta, Toshio,  |e analytic author 
700 1 |a Ishiyama, Daizo,  |e analytic author 
700 1 |a Urabe, Tetsuro,  |e analytic author 
773 0 |t Resource Geology (Tokyo 1998)  |d Tokyo : Society of Resource Geology, 2001  |x 1344-1698  |n Resource Geology (Tokyo 1998), 51(1), p.31-44. Publisher: Society of Resource Geology, Tokyo, Japan. ISSN: 1344-1698 Publication type: journal article  |g Vol. 51, no. 1  |h illus., incl. 4 tables