3:30 PM - 5:00 PM
[SCG48-P01] Characterization of Various Polycyclic Aromatic Hydrocarbon Minerals Found in Hokkaido
Keywords:Organic Minerals, Polycyclic aromatic hydrocarbon, Hokkaidoite, Carpatite, Analytical Method
Organic minerals are crystalline organic compounds of geological origin. Among them, seven polycyclic aromatic hydrocarbon (PAH) minerals have also been approved, but there are some unclear points about their crystallization process and formation mechanisms of these organic molecules. Although the analysis of PAH minerals has been established by Wise et al. (1986), it is important to determine the optimal methods for the target organic compounds and characterize the compounds using various analytical techniques for organic substance. Recently, we have discovered PAH minerals at two sites in Hokkaido, Japan. In this study, the organic chemical analysis method was applied to these PAHs to identify the organic components and to investigate the properties of the organic minerals. In this poster, we will also report on the formation mechanism of organic minerals.
PAHs from two sites in Hokkaido (Aibetsu and Shikaribetsu) are both associated with epithermal silica vein. These are hydrothermal cinnabar quartz veins (Aibetsu) and opal precipitated by paleosprings (Shikaribetsu). The organic matter content was 1.5 wt% (max.) in Shikaribetsu, and less than 0.1 wt% in Aibetsu. PAHs are characterized by strong emission (yellow to yellow-green to blue-green, orange under long-wave UV irradiation), and this fluorescence was used as an indicator of PAH presence.
The crystalline fluorescent samples obtained in both regions were analyzed by high-performance liquid chromatography (HPLC). HPLC analysis showed that there are two kind of crystalline minerals, benzo[ghi]perylene (BPer) and coronene (Cor, carpathite). The former was a new mineral and was approved as hokkaidoite. These crystalline minerals exhibit broad emission bands at 450-700 nm in the solid-state fluorescence spectrum, and are indistinguishable in solid state. In addition, all organic minerals showed blue fluorescence in solution. In micro-Raman (excitation wavelength 633 nm) spectrum, few peaks attributed to stretching and angular vibrations of C-C and C-H bonds were observed, which were in good agreement with the authentic sample.
In Shikaribetsu, orange-fluorescent opal is often found, which is due to the amorphous bitumen contained within it. Gas chromatography-mass spectrometry (GC-MS) of the bitumen showed that bitumen is mainly composed of BPer (m/z 276) and Cor (m/z 300). HPLC analysis of bitumen revealed that it contained BPer and Cor as well as PAHs with molecular weights of about 150-400. In the 1H NMR spectrum, a signal in the aromatic proton region at 7.4-9.2 ppm and weak signals in other regions were detected. These indicated that the Shikaribetsu bitumen is a mixture of PAHs, predominantly containing BPer and Cor. This may be due to the solidification of dissolved organic matter in the hot water by rapid cooling.
The PAHs in this study were considered to be produced by thermal- and/or hydrothermal alteration of bioorganic matter. At both sites, not only known Cor, but also by smaller PAH that are thought to be produced under lower temperature conditions. This is expected to provide some information on the thermal history of hydrothermal transformation of organic matter and its molecular formation in nature.
This survey was conducted based on permission from the Ministry of the Environment.
References.
Wise et al. (1986) Chem. Geol. 54, 339-357.
PAHs from two sites in Hokkaido (Aibetsu and Shikaribetsu) are both associated with epithermal silica vein. These are hydrothermal cinnabar quartz veins (Aibetsu) and opal precipitated by paleosprings (Shikaribetsu). The organic matter content was 1.5 wt% (max.) in Shikaribetsu, and less than 0.1 wt% in Aibetsu. PAHs are characterized by strong emission (yellow to yellow-green to blue-green, orange under long-wave UV irradiation), and this fluorescence was used as an indicator of PAH presence.
The crystalline fluorescent samples obtained in both regions were analyzed by high-performance liquid chromatography (HPLC). HPLC analysis showed that there are two kind of crystalline minerals, benzo[ghi]perylene (BPer) and coronene (Cor, carpathite). The former was a new mineral and was approved as hokkaidoite. These crystalline minerals exhibit broad emission bands at 450-700 nm in the solid-state fluorescence spectrum, and are indistinguishable in solid state. In addition, all organic minerals showed blue fluorescence in solution. In micro-Raman (excitation wavelength 633 nm) spectrum, few peaks attributed to stretching and angular vibrations of C-C and C-H bonds were observed, which were in good agreement with the authentic sample.
In Shikaribetsu, orange-fluorescent opal is often found, which is due to the amorphous bitumen contained within it. Gas chromatography-mass spectrometry (GC-MS) of the bitumen showed that bitumen is mainly composed of BPer (m/z 276) and Cor (m/z 300). HPLC analysis of bitumen revealed that it contained BPer and Cor as well as PAHs with molecular weights of about 150-400. In the 1H NMR spectrum, a signal in the aromatic proton region at 7.4-9.2 ppm and weak signals in other regions were detected. These indicated that the Shikaribetsu bitumen is a mixture of PAHs, predominantly containing BPer and Cor. This may be due to the solidification of dissolved organic matter in the hot water by rapid cooling.
The PAHs in this study were considered to be produced by thermal- and/or hydrothermal alteration of bioorganic matter. At both sites, not only known Cor, but also by smaller PAH that are thought to be produced under lower temperature conditions. This is expected to provide some information on the thermal history of hydrothermal transformation of organic matter and its molecular formation in nature.
This survey was conducted based on permission from the Ministry of the Environment.
References.
Wise et al. (1986) Chem. Geol. 54, 339-357.