| 莫桑比克含铜锂电气石矿物化学特征与产地示踪 |
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| 关键词:Paraíba tourmaline color origin heat treatment identification origin tracing Cu/(TFe+Ti) ratio electron probe Mozambique |
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| Mineral Chemistry Characteristics and Origin Tracing of Copper-bearing Elbaite Tourmaline from Mozambique |
| Tracing the origin of copper-bearing elbaite tourmaline (commercially known as Paraíba tourmaline) is a critical challenge in gemstone testing; existing discrimination methods mostly rely on LA-ICP-MS, which is difficult to implement in conventional laboratories. In this study, seven copper-bearing elbaite tourmaline samples of different color series from the Alto Ligonha pegmatite belt in Mozambique were systematically investigated using microscopic inclusion observation, EPMA, FTIR, Raman spectroscopy, and UV–Vis spectroscopy. Following the IMA nomenclature, crystal-chemical formulas were calculated and species identification was performed. The samples are water-rich alkaline-group elbaite tourmaline with elbaite indices exceeding 90%, overall characterized by high Li and extremely low Fe–Ti contents. The colors are dominantly controlled by Cu2? and Mn3?: Cu2? d–d transitions (~680 nm broad band) dominate the blue–green hues, with the hue and saturation of the blue series modulated by the Mn3?-related absorption; the green series is genetically divergent, with the electric-green color involving superimposed Mn2?–Ti4? intervalence charge transfer (IVCT) truncation; the Mn3? double peaks at ~500 nm and ~535 nm (Jahn–Teller splitting) for red–purple hues and masks the Cu2?-related blue–green coloration, with the Cu/(Cu+Mn) ratio effectively reflecting the color regulation trend. Based on the Mn3? spectral-retention criteria combined with well-preserved primary inclusions (showing no decrepitation cracks or other thermal-alteration features), four of the seven samples show no obvious heat treatment, one is provisionally assigned as untreated, one remains inconclusive, and one Mn-poor sample is inapplicable to this criterion; however, all samples cannot exclude the possibility of low-temperature treatment without detectable traces. The Cu/(TFe+Ti) ratio, proposed on the basis of the geochemical backgrounds of the three major origins, yields a discrimination agreement rate of approximately 88.9% for the Mozambique samples, far exceeding the 20% obtained with the traditional Zn/Cu criterion applied to EPMA data; EPMA combined with this ratio offers a rapid, preliminary method for origin discrimination of copper-bearing elbaite tourmalines from Mozambique, Brazil, and Nigeria. This study provides a low-cost and accessible technical support for routine testing, heat treatment identification, and geographic origin tracing of copper-bearing elbaite tourmaline. |
| XU Liguo,LYU Linsu,XIONG Jie,ZHOU Zhenhua,ZHANG Yong,XU Mingwang.2026.Mineral Chemistry Characteristics and Origin Tracing of Copper-bearing Elbaite Tourmaline from Mozambique[J].Acta Geoscientica Sinica,47(5):960-970. |
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