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.

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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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