Syenite mapping and prediction of geochemical Na versus K signatures: A novel remote sensing approach and implications for mineral resources

IF 3.4 2区 地球科学 Q1 GEOCHEMISTRY & GEOPHYSICS
Youssef Ahechach , Otmane Raji , Muhammad Ouabid , Cheikh-Elwali Malainine , Jean-Louis Bodinier , Fleurice Parat , Hicham El Messbahi , Oussama Khadiri-Yazami , Essaid Jourani , Jean-Marie Dautria
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引用次数: 0

Abstract

Syenites are highly valued for economic and strategic exploration programs worldwide, along with associated rocks (e.g., carbonatites), as a primary source for several industrial minerals and strategic elements, such as phosphate, potash, rare earth elements (REE), and Nb. Rapid identification and mapping of syenite outcrops and their major geochemical signatures (i.e. potassic and sodic) over vast areas are crucial for exploration programs aimed at identifying new economic deposits. For this, remote sensing provides an interesting way to delineate these alkaline igneous rocks and predicts their mineralogical and geochemical characteristics. In the literature, few remote sensing studies have been devoted to syenite outcrops, and an effective predictive tool for their mapping and mineralogical-geochemical classification remains to be done. Accordingly, we explore in the present study the potential of using ASTER thermal emissivity data for prospectivity mapping and predicting the main alkaline mineralogical and geochemical affinities of syenite rocks. This approach was applied to the Moroccan High-Atlas Mountains (area ∼ 42,000 km2), known for the presence of several alkaline intrusions hosting different alkali-syenites. Hence, a spectral syenite index [SyI = (B10/B11 * B10/B13 * B14/B13)] without the use of in-situ field data, was suggested in the first stage to quickly highlight potential areas, reducing the initial exploration zone to only ∼1000 km2/42000 km2 that include all well-known syenites in the studied area. Subsequently, several in-situ field missions were conducted in the identified zones to sample and obtain precise GPS points of well-exposed syenitic outcrops. For discrimination of mineralogical and geochemical endmembers (Na vs. K) of syenites, two new spectral indices were proposed [SpI-A = (B14-B12)/(B14 + B12) for K syenite signature and SpI-B = (B10-B11)/(B10 + B11) for Na syenite signature]. These indices highlight the two major geochemical affinities in the High-Atlas Mountains: the potassic syenite character (K-feldspar- and nepheline-rich) in the Midelt-Tamazeght Cenozoic complex and the sodic syenite character (albite-rich) in the Imilchil Mesozoic massifs. The results have significant implications for early exploration programs, aiming to cost-effectively discover favorable areas of alkali syenites, potassic against sodic affinities, and optimize fieldwork as well as preliminarily mineralogical and geochemical characterization.

辉绿岩地图绘制和 Na 与 K 地球化学特征预测:新型遥感方法及其对矿产资源的影响
正长岩及其伴生岩(如碳酸盐岩)是多种工业矿物和战略元素(如磷酸盐、钾盐、稀土元素 (REE) 和铌元素)的主要来源,在全世界的经济和战略勘探计划中具有很高的价值。在广大地区快速识别和绘制正长岩露头及其主要地球化学特征(即钾盐和钠盐)对于旨在识别新经济矿床的勘探计划至关重要。为此,遥感提供了一种有趣的方法来划分这些碱性火成岩,并预测其矿物学和地球化学特征。在文献中,很少有专门针对正长岩露头的遥感研究,对其绘图和矿物地球化学分类的有效预测工具仍有待开发。因此,我们在本研究中探讨了利用 ASTER 热发射率数据绘制前景图和预测正长岩主要碱性矿物学和地球化学亲缘关系的潜力。这一方法被应用于摩洛哥高阿特拉斯山脉(面积为 42,000 平方公里),该山脉因存在多个碱性侵入体而闻名,其中孕育着不同的碱性正长岩。因此,在第一阶段,在不使用原位实地数据的情况下,建议使用光谱正长岩指数[SyI = (B10/B11 * B10/B13 * B14/B13)]来快速突出潜在区域,将最初的勘探区域缩小到只有 1000 平方公里/42000 平方公里,其中包括研究区域内所有著名的正长岩。随后,在确定的区域内进行了多次现场实地考察,对出露良好的正长岩露头进行取样并获得精确的 GPS 点。为了区分正长岩的矿物学和地球化学内含物(Na 与 K),提出了两个新的光谱指数[SpI-A = (B14-B12)/(B14 + B12) 表示 K 正长岩特征,SpI-B = (B10-B11)/(B10 + B11) 表示 Na 正长岩特征]。这些指数凸显了高阿特拉斯山脉的两大地球化学特征:米德尔特-塔马泽格特新生代复合体的钾长岩特征(富含钾长石和霞石)和伊米尔基尔中生代地块的钠长岩特征(富含白云石)。这些结果对早期勘探计划具有重要意义,旨在以具有成本效益的方式发现碱长岩、钾长岩和钠长岩亲缘关系的有利区域,并优化野外工作以及初步矿物学和地球化学特征描述。
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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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