17:15 〜 19:15
[HRE12-P07] Geochemical and mineralogical characteristics of the Partolang volcanogenic massive sulfide deposit, Wetar Island, Indonesia
キーワード：VHMS, Wetar, Banda Arc, Submarine Vents
The Partolang deposit, situated in the northern coast of Wetar Island within the Inner Banda Arc is a significant example of polymetallic volcanogenic massive sulfide (VMS) deposits within a post collision arc setting. Previous studies on the VMS deposits in Wetar Island have suggested that the polymetallic mineralization exhibits characteristics of a sub-seafloor VMS system with high-sulfidation signature. Despite its proximity to the well-documented Kali Kuning and Lerokis deposits, the Partolang deposit remains less studied. Detailed studies on mineral assemblages, alteration, and fluid evolution of the Partolang deposit have not been sufficiently conducted. This study is aimed at filling the gap by investigating the genetic model of the deposit. Methods employed include petrography, SEM-EDS, EPMA, ICP-MS, and sulfur isotopic analyses.
There are footwall and hanging-wall host rocks that bounds ore horizons in the Partolang deposit. The footwall host rock is rhyodacite lava, while the hanging-wall host rock consists of andesitic pyroclastic breccia and dacite lava. The majority of the host rocks exhibits a calc-alkaline magma affinity, whereas the andesitic pyroclastic breccia is transitional between tholeiitic and calc-alkaline compositions. Trace element data indicate that both the rhyodacite lava and dacite lava are sourced from a continental arc, while the andesitic pyroclastic breccia represents a transitional source between oceanic and continental arcs.
Four distinct ore types were identified such as siliceous sulfide ore, brecciated sulfide ore, massive sulfide ore, and layered barite sand ore. Alteration exhibits spatial distribution of silicification, sericite-dickite±kaolinite alteration, sericite-kaolinite alteration, and propylitic alteration, in order from proximal to distal. Mineralization occurred in four stages, (1) early stage, characterized by pyrite, marcasite, minor chalcopyrite, and bornite, with quartz, sericite, and dickite, (2) main stage dominated by pyrite, enargite, and tennantite-tetrahedrite, with minor chalcopyrite, and barite, (3) late stage comprising pyrite, marcasite, covellite, chalcocite, enargite, tennantite-tetrahedrite, barite, and kaolinite, and (4) supergene stage, featuring secondary chalcocite and minor covellite, with jarosite. Chemical compositions of pyrite indicate two distinct genetic origins. Pyrite in brecciated sulfide ore samples indicates a volcano-exhalative origin, whereas pyrite from siliceous ore and massive sulfide ore samples are predominantly of hydrothermal origin. The deposit aligns closely with bimodal-mafic VMS classification, showing enrichment in Cu with relative depletion in Zn. δ34S values of sulfides in the siliceous ore, brecciated sulfide ore, and massive sulfide ore narrowly range from 9.3 to 9.7 ‰, 7.9 to 8.0 ‰, and 7.9 to 8.1 ‰, respectively. Additionally, one sample of barite from the brecciated sulfide ore yielded a δ34S value of 21.2 ‰. These results indicate that sulfur was sourced from both a magma or volcanic rocks and seawater.
There are footwall and hanging-wall host rocks that bounds ore horizons in the Partolang deposit. The footwall host rock is rhyodacite lava, while the hanging-wall host rock consists of andesitic pyroclastic breccia and dacite lava. The majority of the host rocks exhibits a calc-alkaline magma affinity, whereas the andesitic pyroclastic breccia is transitional between tholeiitic and calc-alkaline compositions. Trace element data indicate that both the rhyodacite lava and dacite lava are sourced from a continental arc, while the andesitic pyroclastic breccia represents a transitional source between oceanic and continental arcs.
Four distinct ore types were identified such as siliceous sulfide ore, brecciated sulfide ore, massive sulfide ore, and layered barite sand ore. Alteration exhibits spatial distribution of silicification, sericite-dickite±kaolinite alteration, sericite-kaolinite alteration, and propylitic alteration, in order from proximal to distal. Mineralization occurred in four stages, (1) early stage, characterized by pyrite, marcasite, minor chalcopyrite, and bornite, with quartz, sericite, and dickite, (2) main stage dominated by pyrite, enargite, and tennantite-tetrahedrite, with minor chalcopyrite, and barite, (3) late stage comprising pyrite, marcasite, covellite, chalcocite, enargite, tennantite-tetrahedrite, barite, and kaolinite, and (4) supergene stage, featuring secondary chalcocite and minor covellite, with jarosite. Chemical compositions of pyrite indicate two distinct genetic origins. Pyrite in brecciated sulfide ore samples indicates a volcano-exhalative origin, whereas pyrite from siliceous ore and massive sulfide ore samples are predominantly of hydrothermal origin. The deposit aligns closely with bimodal-mafic VMS classification, showing enrichment in Cu with relative depletion in Zn. δ34S values of sulfides in the siliceous ore, brecciated sulfide ore, and massive sulfide ore narrowly range from 9.3 to 9.7 ‰, 7.9 to 8.0 ‰, and 7.9 to 8.1 ‰, respectively. Additionally, one sample of barite from the brecciated sulfide ore yielded a δ34S value of 21.2 ‰. These results indicate that sulfur was sourced from both a magma or volcanic rocks and seawater.