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Late Miocene magmatic-hydrothermal system and related Cu mineralization of the Arakawa area, Akita, Japan
Resource Geology ( IF 1.4 ) Pub Date : 2022-02-07 , DOI: 10.1111/rge.12284 Shota Satori 1, 2 , Yasushi Watanabe 1 , Takeyuki Ogata 3 , Yasutaka Hayasaka 4
Resource Geology ( IF 1.4 ) Pub Date : 2022-02-07 , DOI: 10.1111/rge.12284 Shota Satori 1, 2 , Yasushi Watanabe 1 , Takeyuki Ogata 3 , Yasutaka Hayasaka 4
Affiliation
The Northeast Japan arc hosts a number of hydrothermal vein-type copper deposits associated with Neogene felsic intrusions. The Arakawa area is underlain by Cretaceous granites and Tertiary sedimentary rocks, which were intruded by the Miocene Ushizawamata dacite. Zircon grains from the dacite intrusion yield a 206Pb/238U intercept age (laser ablation inductively coupled plasma mass spectrometry) of 8.10 ± 0.30 Ma, consistent with a previously reported K-Ar illite age (8.1 ± 0.4 Ma) of the Ushizawamata lead and zinc prospect in the Arakawa area. The dacite intrusion and the surrounding Miocene sedimentary rocks were altered by hydrothermal activity on the surface, classified into four alteration zones: (1) biotite-chlorite, (2) illite, (3) chlorite and (4) smectite, centered on the intrusion. About 20 major vertical sub-parallel copper-bearing quartz veins occur in the chlorite alteration zone on the west side of the dacite. The first vein stage is composed of chalcopyrite and chamosite with a minor amount of quartz in brecciated wall rocks, and the second-stage is characterized by the presence of hematite in addition to the first-stage mineral assemblage. The third-stage consists of comb-shaped quartz veins with a minor amount of chalcopyrite, sphalerite, galena and pyrite, and the fourth-stage of barite and apatite present in druse in the third-stage veins. Primary fluid inclusions in quartz of the first- and third-stages are all liquid-rich and two-phase. Homogenization temperature and salinity of first-stage quartz are 263–277°C and 5.7–7.5 wt% NaCl equivalent (eq.); in quartz of the third-stage, 251–270°C and 2.7–4.2 wt% in the inner zone and 207–250°C and 2.7–3.7 wt% in comb-shaped quartz on the vein margin. The fluid inclusions in quartz phenocrysts of the Ushizawamata dacite show two distinct assemblages, halite-bearing polyphase inclusions that coexist with vapor-phase inclusions and/or vapor-rich two-phase inclusions, and liquid-rich two-phase inclusions. Homogenization temperature and salinity of the polyphase inclusions are higher than 401°C and 46.7 wt%, respectively, and those of the vapor-rich two-phase inclusions report 393–419°C and 2.6–3.7 wt% NaCl, whereas the liquid-rich two-phase inclusions returned 344–403°C and 8.0–9.3 wt%, respectively. These results indicate that the ore forming fluid was slightly cooler and lower in salinity than the late-stage hydrothermal fluid in the Ushizawamata intrusion. The spatial and temporal proximity between the Ushizawamata dacite and the hydrothermal veins indicates that the dacitic magma was genetically related to the vein copper mineralization in the Arakawa area.
中文翻译:
日本秋田县荒川地区晚中新世岩浆热液系统及相关铜矿化
日本东北弧拥有许多与新近纪长英质侵入体相关的热液脉型铜矿床。荒川地区下伏白垩纪花岗岩和第三纪沉积岩,中新世牛泽又英安岩侵入。来自英安岩侵入体的锆石晶粒产生 206 Pb / 238U 截距年龄(激光烧蚀电感耦合等离子体质谱法)为 8.10 ± 0.30 Ma,与先前报道的荒川地区 Ushizawamata 铅和锌勘探区的 K-Ar illite 年龄(8.1 ± 0.4 Ma)一致。英安岩侵入体和周围的中新世沉积岩受到地表热液活动的改变,分为四个蚀变带:(1)黑云母-绿泥石,(2)伊利石,(3)绿泥石和(4)绿土,以侵入体为中心. 在英安岩西侧的绿泥石蚀变带中出现了约20个主要的垂直亚平行含铜石英脉。第一脉阶段由黄铜矿和水辉石组成,角砾岩围岩中含有少量石英,第二阶段的特征是除第一阶段矿物组合外还存在赤铁矿。第三期为梳状石英脉,含少量黄铜矿、闪锌矿、方铅矿和黄铁矿,第四期重晶石和磷灰石在第三期脉中以粗晶状体存在。一、三期石英中的原生流体包裹体均为富液两相。第一阶段石英的均化温度和盐度为 263–277°C 和 5.7–7.5 wt% NaCl 当量(eq.);第三阶段石英中,251~270℃,2.7~4.2 wt%为内层,207~250℃,2.7~3.7 wt%为脉缘梳状石英。Ushizawata英安岩石英斑晶中的流体包裹体显示出两种不同的组合,即与气相包裹体和/或富含蒸气的两相包裹体共存的含岩盐的多相包裹体,以及富含液体的两相包裹体。多相包裹体的均质化温度和盐度分别高于 401°C 和 46.7 wt%,富含蒸汽的两相包裹体报告 393-419°C 和 2.6-3.7 wt% NaCl,而液态-丰富的两相包裹体分别返回 344–403°C 和 8.0–9.3 wt%。这些结果表明,与牛沢侵入体后期的热液相比,成矿流体的温度略低,矿化度也较低。牛泽又英安岩与热液脉在空间和时间上的接近性表明,英安岩岩浆与荒川地区的脉铜矿化有成因相关。而富含液体的两相包裹体分别返回 344-403°C 和 8.0-9.3 wt%。这些结果表明,与牛沢侵入体后期的热液相比,成矿流体的温度略低,矿化度也较低。牛泽又英安岩与热液脉在空间和时间上的接近性表明,英安岩岩浆与荒川地区的脉铜矿化有成因相关。而富含液体的两相包裹体分别返回 344-403°C 和 8.0-9.3 wt%。这些结果表明,与牛沢侵入体后期的热液相比,成矿流体的温度略低,矿化度也较低。牛泽又英安岩与热液脉在空间和时间上的接近性表明,英安岩岩浆与荒川地区的脉铜矿化有成因相关。
更新日期:2022-02-07
中文翻译:
日本秋田县荒川地区晚中新世岩浆热液系统及相关铜矿化
日本东北弧拥有许多与新近纪长英质侵入体相关的热液脉型铜矿床。荒川地区下伏白垩纪花岗岩和第三纪沉积岩,中新世牛泽又英安岩侵入。来自英安岩侵入体的锆石晶粒产生 206 Pb / 238U 截距年龄(激光烧蚀电感耦合等离子体质谱法)为 8.10 ± 0.30 Ma,与先前报道的荒川地区 Ushizawamata 铅和锌勘探区的 K-Ar illite 年龄(8.1 ± 0.4 Ma)一致。英安岩侵入体和周围的中新世沉积岩受到地表热液活动的改变,分为四个蚀变带:(1)黑云母-绿泥石,(2)伊利石,(3)绿泥石和(4)绿土,以侵入体为中心. 在英安岩西侧的绿泥石蚀变带中出现了约20个主要的垂直亚平行含铜石英脉。第一脉阶段由黄铜矿和水辉石组成,角砾岩围岩中含有少量石英,第二阶段的特征是除第一阶段矿物组合外还存在赤铁矿。第三期为梳状石英脉,含少量黄铜矿、闪锌矿、方铅矿和黄铁矿,第四期重晶石和磷灰石在第三期脉中以粗晶状体存在。一、三期石英中的原生流体包裹体均为富液两相。第一阶段石英的均化温度和盐度为 263–277°C 和 5.7–7.5 wt% NaCl 当量(eq.);第三阶段石英中,251~270℃,2.7~4.2 wt%为内层,207~250℃,2.7~3.7 wt%为脉缘梳状石英。Ushizawata英安岩石英斑晶中的流体包裹体显示出两种不同的组合,即与气相包裹体和/或富含蒸气的两相包裹体共存的含岩盐的多相包裹体,以及富含液体的两相包裹体。多相包裹体的均质化温度和盐度分别高于 401°C 和 46.7 wt%,富含蒸汽的两相包裹体报告 393-419°C 和 2.6-3.7 wt% NaCl,而液态-丰富的两相包裹体分别返回 344–403°C 和 8.0–9.3 wt%。这些结果表明,与牛沢侵入体后期的热液相比,成矿流体的温度略低,矿化度也较低。牛泽又英安岩与热液脉在空间和时间上的接近性表明,英安岩岩浆与荒川地区的脉铜矿化有成因相关。而富含液体的两相包裹体分别返回 344-403°C 和 8.0-9.3 wt%。这些结果表明,与牛沢侵入体后期的热液相比,成矿流体的温度略低,矿化度也较低。牛泽又英安岩与热液脉在空间和时间上的接近性表明,英安岩岩浆与荒川地区的脉铜矿化有成因相关。而富含液体的两相包裹体分别返回 344-403°C 和 8.0-9.3 wt%。这些结果表明,与牛沢侵入体后期的热液相比,成矿流体的温度略低,矿化度也较低。牛泽又英安岩与热液脉在空间和时间上的接近性表明,英安岩岩浆与荒川地区的脉铜矿化有成因相关。