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Near-infrared and Visible Light Microthermometry of Fluid Inclusions in Sphalerite from a Possible Southeast Extension of the Toyoha Polymetallic Deposit, Japan |
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| Authors: | Toru Shimizu Masahiro Aoki Taro Kabashima |
| Institution: | Micro-scale Isotope Geochemistry Group, Institute of Geoscience, Geological Survey of Japan/AIST, Central 7, Higashi 1–1–1, Tsukuba 305–8567, Japan [e-mail: ];Geological Museum, Geological Survey of Japan/AIST, Central 7, Higashi 1–1–1, Tsukuba 305–8567, Japan;Global Minerals Exploration Group, Metal Mining Agency of Japan, Tokiwa Bldg., 1–24–14, Toranomon, Minato-ku, Tokyo 105–0001, Japan |
| Abstract: | Abstract. Near-infrared (NIR) and visible light microthermometry was applied to the fluid inclusions in sphalerite from a possible southeast extension of the Toyoha polymetallic deposit. Sphalerite occurs as euhedral-subhedral crystals or collo-form aggregates with a variety of color, which contain a well-developed growth banding. Combined with morphological observations, fluid inclusions in dark-colored sphalerite were examined using a near-infrared light microscopic technique, whereas those in light-colored sphalerite and quartz were examined by a conventional visible light microscopy. Salinities of fluid inclusions in dark-colored sphalerite have a wide variation (1.0–10.3 wt % NaCl equiv.) compared to that in light-colored sphalerite and quartz (0.0–3.4 wt % NaCl equiv.). These variations suggest that the conventional microthermometric data from light-colored sphalerite and quartz were inadequate to interpret the ore formation process. Dark-colored colloform sphalerite and a dark core of subhedral sphalerite formed from high-salinity fluids (6.5–10.3 wt % NaCl equiv.) under highly supersaturated conditions with respect to sphalerite. The NIR and visible light microthermometry of fluid inclusions in sphalerite combined with its morphological observations is an invaluable method to infer the formation conditions of sphalerite. The NIR and visible light microthermometry is useful to reveal how the nature of ore fluids changed with time. |
| Keywords: | near-infrared microthermometry sphalerite fluid inclusions Toyoha |