Substitution mechanism controls on compositional variations and spectral responses of white micas in major hydrothermal systems

IF 5.3 2区 地球科学 Q2 CHEMISTRY, PHYSICAL
Junfeng Zhao , Huayong Chen , Bing Xiao , Yabo Zhu , Hao Wang
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Abstract

Whether the shorter or longer wavelengths of diagnostic absorption features of white mica serve as a better vector to mineralization remains controversial. This uncertainty stems from a limited understanding of the compositional substitution mechanisms that control spectral variations. This study compiled published datasets of white mica with both available composition and spectroscopy data from five major hydrothermal systems, including porphyry, epithermal, skarn, orogenic, and volcanogenic massive sulfides (VMS) deposits. Three types of white micas, each dominated by distinct substitution mechanisms—interlayer-dominated (Na+ ↔ K+, and Ca2+, Ba2+ ↔ 2 K+), Tschermak-dominated (VIAl3+ + IVAl3+VIFe2+, VIMg2+ + IVSi4+), and illitic-dominated (K+ + IVAl3+IVSi4+ + []interlayer)—have been identified, accounting for the observed inconsistencies in spectral responses. The interlayer substitution is associated with shorter absorption feature (< 2195 nm) arising from the combination of high-frequency Al2OH stretching (ν) vibration and bending (δ) vibration. Interlayer-dominated white mica is predominantly found in orogenic deposits, where its presence typically indicates proximal mineralization. Tschermak substitution induces continuous wavelength shifts (2195–2215 nm) in the mid-frequency ν region combined with δ vibration. A high-level of Tschermak reaction stimulates low-frequency ν vibration, producing specific longer absorption feature (> 2215 nm) with δ vibration. Tschermak-dominated white mica is the most widespread among diverse systems. Illitic substitution, however, leads to compositional changes that are not detectable in shortwave infrared (SWIR, 1300–2500 nm) regions, thus rarely providing vectoring indicators. This study suggests that data from white mica characterized by different dominant substitution mechanisms should be distinctly evaluated, thereby enhancing the efficacy of SWIR spectroscopy for mineral exploration.

Abstract Image

取代机制控制了主要热液体系中白色云母的成分变化和光谱响应
白云母的诊断吸收特征的短波长还是短波长作为更好的矿化载体仍然存在争议。这种不确定性源于对控制光谱变化的成分替代机制的有限理解。本研究收集了来自五个主要热液系统(斑岩、浅成热液、夕卡岩、造山岩和火山块状硫化物)的白色云母的已发表的数据集,包括可用的成分和光谱数据。三种类型的白色云母,每一种都有不同的替代机制:层间主导(Na+↔K+,和Ca2+, Ba2+↔2k +), tschermakk主导(VIAl3+ + IVAl3+↔VIFe2+, VIMg2+ + IVSi4+)和illit主导(K+ + IVAl3+↔IVSi4+[]层间),这说明了光谱反应中观察到的不一致。层间取代与较短的吸收特征(<;2195 nm),由高频Al2OH拉伸振动(ν)和弯曲振动(δ)共同产生。层间占主导地位的白色云母主要存在于造山矿床中,其存在通常表明近端矿化。Tschermak取代在δ振动的中频ν区引起连续的波长位移(2195 ~ 2215 nm)。高强度的切尔马克反应刺激低频ν振动,产生特定的长吸收特征(>;2215 nm), δ振动。以切尔马克为主的白色云母在不同的体系中分布最广。然而,非晶取代会导致在短波红外(SWIR, 1300-2500 nm)区域无法检测到的成分变化,因此很少提供矢量指标。研究表明,不同优势取代机制的白云母数据应进行明确的评价,从而提高SWIR光谱在矿产勘查中的效果。
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来源期刊
Applied Clay Science
Applied Clay Science 地学-矿物学
CiteScore
10.30
自引率
10.70%
发文量
289
审稿时长
39 days
期刊介绍: Applied Clay Science aims to be an international journal attracting high quality scientific papers on clays and clay minerals, including research papers, reviews, and technical notes. The journal covers typical subjects of Fundamental and Applied Clay Science such as: • Synthesis and purification • Structural, crystallographic and mineralogical properties of clays and clay minerals • Thermal properties of clays and clay minerals • Physico-chemical properties including i) surface and interface properties; ii) thermodynamic properties; iii) mechanical properties • Interaction with water, with polar and apolar molecules • Colloidal properties and rheology • Adsorption, Intercalation, Ionic exchange • Genesis and deposits of clay minerals • Geology and geochemistry of clays • Modification of clays and clay minerals properties by thermal and physical treatments • Modification by chemical treatments with organic and inorganic molecules(organoclays, pillared clays) • Modification by biological microorganisms. etc...
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