马达加斯加南部安帕尼希地区古生代锰质成岩的沉积环境和热液蚀变作用

IF 3.4 2区 地球科学 Q1 GEOCHEMISTRY & GEOPHYSICS
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引用次数: 0

摘要

众所周知,古近纪有大量沉积锰矿沉积在近克拉通地区。尽管沉积环境、锰的来源和盆地的几何形状是了解这些战略资源来源的关键因素,但人们对这些因素的了解往往很少。我们对 Ampanihy 地区(马达加斯加南部)的富锰石墨基岩进行了调查,以确定沉积条件的特征并识别潜在的热液蚀变。研究结果表明,矿石主要由硅酸锰矿(锰锰矿、菱锰矿)组成,在靠近安帕尼希剪切带的地方还伴生有富含锌的黝帘石和焦锰矿。地球化学数据表明,与该地区西部(沃希德拉基齐、贝基利)的沉积物相比,该地区东部(安卡拉)的矿源物质更多来源于地壳。安卡拉矿床的化学特征与许多其他古生代锰矿床相近,可以认为是相对未改变的矿床,符合戊新模式。安帕尼希地区西域显示出强烈的热液叠印,锌、钡和锑含量显著富集,这是由于沿原安帕尼希剪切带的沉积后热液蚀变所致。这一事件发生在沉积物沉积(约 1.9-1.7 Ga)与 Vohibory 域和 Androyen 域缝合(约 0.63-0.60 Ma)之间的某个阶段。根据我们的数据,我们提出了一个新的判别图,即(La/Lu)PAAS vs Zn/Ni,它有助于确定沉积物来源和识别热液叠印。
本文章由计算机程序翻译,如有差异,请以英文原文为准。
Depositional setting and hydrothermal alteration of Paleoproterozoic manganiferous metasedimentary rocks in the Ampanihy district (Southern Madagascar)

The Paleoproterozoic is known to host significant sedimentary manganese accumulations deposited in peri-cratonic areas. The depositional environments, the source of Mn and the geometry of the basins are often poorly understood, although they are key aspects in understanding the origin of these strategic resources. We investigate the Mn-rich graphitic metasediments of the Ampanihy district (South Madagascar) to characterize depositional conditions and to identify potential hydrothermal alteration. The results show that the ore is predominantly composed of Mn silicates (spessartine, rhodonite) with accessory jacobsite and pyrophanite varieties rich in Zn close to the Ampanihy shear zone. Geochemical data suggest that the source material in the eastern domain (Ankara) of the district is more crustal in origin than sediments in the western part of the district (Vohidrakitsy, Bekily). The Ankara deposits have chemical characteristics that are close to many other Paleoproterozoic Mn deposits and can be considered as relatively unaltered and fits with the euxinic model. The western domain of the Ampanihy district shows strong hydrothermal overprinting, with significant enrichment in Zn, Ba and Sb, resulting from post-depositional hydrothermal alteration along the proto-Ampanihy shear zone. This event took place at some stage between the deposition of the sediments (c. 1.9‐1.7 Ga) and the suture of the Vohibory and Androyen domains (c. 0.63–0.60 Ma). Based on our data, we propose a new discrimination plot, (La/Lu)PAAS vs Zn/Ni, which helps in the identification of sediment sources and the recognition of hydrothermal overprinting.

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来源期刊
Journal of Geochemical Exploration
Journal of Geochemical Exploration 地学-地球化学与地球物理
CiteScore
7.40
自引率
7.70%
发文量
148
审稿时长
8.1 months
期刊介绍: Journal of Geochemical Exploration is mostly dedicated to publication of original studies in exploration and environmental geochemistry and related topics. Contributions considered of prevalent interest for the journal include researches based on the application of innovative methods to: define the genesis and the evolution of mineral deposits including transfer of elements in large-scale mineralized areas. analyze complex systems at the boundaries between bio-geochemistry, metal transport and mineral accumulation. evaluate effects of historical mining activities on the surface environment. trace pollutant sources and define their fate and transport models in the near-surface and surface environments involving solid, fluid and aerial matrices. assess and quantify natural and technogenic radioactivity in the environment. determine geochemical anomalies and set baseline reference values using compositional data analysis, multivariate statistics and geo-spatial analysis. assess the impacts of anthropogenic contamination on ecosystems and human health at local and regional scale to prioritize and classify risks through deterministic and stochastic approaches. Papers dedicated to the presentation of newly developed methods in analytical geochemistry to be applied in the field or in laboratory are also within the topics of interest for the journal.
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