Analytical and experimental studies on partitioning of elements and diffusion kinetics in some sulfide minerals in ore deposits

本研究期间于1999年引进了用于诱导耦合等离子体质谱仪（ICP-MS）的高性能ArF激光磨光设备，用于覆盖多种地质样品的分析。1)本研究的第一个主题是巴布亚新几内亚马努斯盆地活动维也纳木海底热液矿床的矿物学和结构。在马努斯弧后盆地分布有三个热液点：Pacmanus、Desmos和Vienna Wood。对维也纳木热液区块状硫化物矿石的矿物学特征和形成环境进行了研究。维也纳木热液场为morb型地堑玄武岩赋存。从维也纳木材遗址采集了三种类型的矿石样品：(1)15m高的活性烟囱顶部（IA型），(2)距离大烟囱3米的小活性烟囱（IB型），(3)距离活性烟囱20米的死烟囱（II型）。IA型矿石主要由块状无矿体和浸染状树枝状黄铁矿、闪锌矿和黄铜矿组成。IB型矿石由少量硬石膏、氧化铁、枝晶黄铁矿、半面形黄铁矿、闪锌矿和黄铜矿组成。ⅱ型矿石以树状至自形黄铁矿、枝状黄铁矿、半面形黄铁矿、黄铜矿和闪锌矿为主，少量硬石膏和重晶石。维也纳木矿石总体化学成分显示，IB型锌（16.5 ~ 40.0 wt.%）、Cu （1.0 ~ 2.0 wt.%）和Pb （0.01 ~ 1.7 wt.%）含量高于IA型（Zn = 0.3 ~ 2 wt.%, Cu =< 0.1 wt.%, Pb =< 0.01 wt.%）或II型（Zn = 10 ~ 17 wt.%, Cu =< 1.0wt. %）。%, Pb =<0.4 wt.%)。维也纳森林遗址的矿物学和形成环境与Pacmanus和Desmos遗址中与长英质火山岩相关的活跃形成的多金属硫化物矿床有很大不同。2)第二个目标是塞浦路斯型矿床的地球化学特征。古赞铜铁块状硫化物矿床是阿曼蛇绿岩中典型的塞浦路斯型矿床之一，为研究古海洋地壳地球化学条件提供了独特的机会。研究了Cu、Zn、Co和Ni在片状脉杂岩、蚀变枕状玄武岩和块状硫化物矿石中的垂直分布，阐明了热液循环和硫化物矿物沉淀在海洋地壳中的化学流动性。铜和钴在水热溶液中以黄铜矿和微量元素的形式沉积在黄铁矿中。在循环元素中，锌、氮在蚀变岩中对绿泥石的优先固定是这些金属不沉淀成块状矿石的原因。3)秋田黑子成矿前后沉积岩地球化学特征为第三主题。北陆盆地是15万年前海底热液矿化最著名的黑陆地区。为明确中中新世环境变化，采用ICP-MS分析了黑古前后沉积岩中的微量元素。选择秋田两个地区进行沉积岩地球化学研究。首先是位于日本岛弧东北部山脉西侧的Wagaomono地区。大日农-吉野黑子矿床分布于该区西黑泽组上段。二是位于日本海沿岸地区“秋田油田”的磐城地区。沉积岩中34种元素采用(LA)-ICP-MS测定，碳酸盐岩采用O和C同位素测定。SiO2-Fe2O3系统分析表明，Wagaomono泥岩可能是生物源与酸性凝灰岩混合来源的沉积物。从Nishikurosawa到Onnagawa阶段的Mn/U比率从1200急剧下降到24。这些变化表明沉积环境从氧化态到还原态发生了明显的变化。所有分析样品的球粒陨石归一化稀土模式均显示出明显的Eu负异常。和豪野地区西黑泽期沉积岩的Eu异常大于女川期。岩崎地区碳酸盐结核锰结壳呈现明显的铈负异常。这些数据表明，女川时代的沉积条件及其成岩过程比西黑泽时代的沉积条件和成岩过程要少得多，尽管铁和锰的丰度几乎相同。通过快速LA-ICP-MS分析，细粒沉积岩中微量元素的地球化学信息对沉积环境的讨论是非常有效的。少

High-performance ArF laser abration equipment for induced coupled plasma mass spectrometer (ICP-MS) were introduced in 1999 during this research period for analyses of covering various kinds of geological samples.1)First topics of this study is the mineralogy and textures of active Vienna Wood seafloor hydrothermal deposit, Manus Basin, Papua New Guinea. Three hydrothermal sites are distributed in the Manus Back-arc basin : Pacmanus, Desmos and Vienna Wood sites. The mineralogy and formation environments for the massive sulphide ores from the Vienna Wood hydrothermal site were examined in this study.The Vienna Wood hydrothermal site is hosted by MORB-type basalt in graben morphology. Three types of ore samples were collected from the Vienna Wood site : (1)top of 15m tall active chimneys (type IA), (2)small active chimneys 3 meters away from the big chimneys (type IB) and (3)dead chimneys sampled 20 meters away from the active chimney (type II). The type IA ores consist of massive anhyd … More rite with disseminated dendritic pyrite, sphalerite and chalcopyrite. Type IB ores consist of minor anhydrite, Fe-oxide, dendritic pyrite, subhedral pyrite, sphalerite and chalcopyrite. Type II ores are dominated by framboidal to idiomorphic pyrite, dendritic pyrite, subhedral pyrite, chalcopyrite and sphalerite with minor anhydrite and baryte.Bulk chemical composition of the Vienna Wood ores show high Zn (16.5-40.0 wt.%), Cu (1.0-2.0 wt.%) and Pb (0.01-1.7 wt.%) contents in type IB than type IA (Zn = 0.3-2 wt.%, Cu = <0.1 wt.%, Pb =< 0.01 wt.%) or type II (Zn = 10-17 wt.%, Cu = <1.0wt.%, Pb =<0.4 wt.%). The mineralogy and formation environment for the Vienna Wood site are quite different from actively forming pollymetallic sulphide deposits associated with felsic volcanic rocks in the Pacmanus and Desmos sites.2)Second target is the geochemical features of Cyprus-type ore deposits. The Ghuzayn Cu-Fe massive sulfide ore deposit is one of the typical Cyprus-type deposits hosted in Oman ophiolite which providing a uniqu opportunity to study geochemical conditions of paleo-oceanic crust. Vertical distribution of Cu, Zn, Co and Ni in sheeted-dike complex, altered pillow basalts and massive sulfide ores were examined to clarify the chemical mobility in oceanic crust because of hydrothermal circulation and precipitation of sulfide minerals.Cu and Co are deposited as chalcopyrite and trace element in pyrite from hydrothermal solution. Among some circulating elements, preferential fixation of Zn and N to chlorite in altered rocks is responsible to the reason that these metals are not precipitated into massive ores.3)Geochemical characteristics of sedimentary rocks of pre-and post-Kuroko mineralization, Akita, is the third topics. The Hokuroku Basin is the most famous Kuroko district for seafloor hydrothermal mineralization around 15 m.y.ago. To clarify the environmental changes of Middle Miocene age, trace elements in sedimentary rocks of pre-and post-Kuroko ages are analyzed by ICP-MS. Two Akita areas are chosen for the geochemical research on sedimentary rocks. First is the Wagaomono area located in the western flank of mountain range of NE Japanese Island-Arc. The Dainihon-Yoshino Kuroko deposit is distributed in the upper Nishikurosawa Formation of this region. Second is the Iwaki area located in "Akita Oil Field" of the coastal district of Japan Sea.(LA)-ICP-MS for 34 elements in the sedimentary rocks and O and C isotope spectrometry for carbonates are employed. Systematics of SiO2-Fe2O3 reveals that the Wagaomono mudstones are likely to be the sediments of the mixed sources between biogenic and acidic tuffs origin. Mn/U ratios from the Nishikurosawa to the Onnagawa stages decrease dramatically from 1,200 to 24. These compositional changes show that sedimentary environments change clearly from oxidation state to reducing condition. Chondrite-normalized REE patterns of sedimentary rocks from all analyzed specimens show clear Eu negative anomalies. These Eu anomalies of sedimentary rocks from the Nishikurosawa Stage are larger than those the Onnagawa Stage in Wagaomono area. Mn crusts of carbonate nodules in the Iwaki area show the distinctive negative anomalies of cerium. Those data could indicate that the sedimentary conditions and their diagenetic processes of the Onnagawa age are much reducing than those of the Nishikurosawa age, in spite of almost the same abundance of Fe and Mn concentration. It is obvious that geochemical information of minor elements in fine-grained sedimentary rocks by rapid LA-ICP-MS analysis is quite effective to discuss the sedimentary environments. Less