5:15 PM - 6:45 PM
[HRE13-P07] Cathodoluminescence and trace element composition of the ore-bearing crustiform veins in the Hokuryu Ag-Au deposit, Hokkaido, Japan
Keywords:Hokuryu, epithermal, quartz texture, electrum, hessite, cathodoluminescence
The Hokuryu deposit was one of the largest producers of silver and gold in Omu, Hokkaido, Japan. Its ores are characterized by Ag- and Au-rich crustiform veins of low-sulfidation epithermal mineralization. A detailed characterization of the occurrence of Au-Ag bearing minerals is currently warranted as this would aid the ongoing exploration work in the deposit. Presented here therefore are the detailed characterization of the ore-bearing crustiform veins with particular attention to their cathodoluminescence (CL) characteristics.
The Au-Ag bearing minerals in the crustiform veins are mainly electrum and hessite, which show distinct mode of occurrence. Electrum is hosted within a quartz textural sequence composed of colloform, ghost-sphere and pseudo-bladed. Meanwhile, hessite is hosted within microcrystalline quartz-adularia wherein quartz exhibits an apparent microspherical texture with 5-10 µm diameter and adularia displays rhombic habit. Electrum grains are anhedral with sizes of 20-50 µm and are occasionally intergrown with naumannite-aguilarite solid solution and sulfides such as pyrite, sphalerite, and chalcopyrite. Hessite is usually intergrown with chalcopyrite, sphalerite, galena and pyrite, and they collectively show skeletal habit.
In CL images, the electrum-bearing colloform quartz is composed of alternating non-luminescent and blue-luminescent bands; the ghost-sphere quartz is composed of a set of non-luminescent spheres (20-200 µm diameter) in a blue-luminescent fibrous to massive matrix; and pseudo-bladed quartz is composed of blue-luminescent quartz intergrown with anhedral adularia. Electrum grains are commonly encapsulated within the non-luminescent bands of the colloform texture and the non-luminescent spheres of the ghost-sphere texture. CL images of the hessite-bearing microcrystalline quartz that exhibits microspherical texture generally display blue-luminescence. CL spectra of the blue-luminescent quartz in all textures consistently show a main peak at ~400 nm. The blue-luminescent quartz has higher Al concentration (ave. 3245 ppm) compared to the non-luminescent quartz (ave. 1440 ppm). In conclusion, electrum is mostly associated with the non-luminescent, relatively low Al quartz, whereas hessite is more associated with blue-luminescent quartz that has higher Al concentration.
The Au-Ag bearing minerals in the crustiform veins are mainly electrum and hessite, which show distinct mode of occurrence. Electrum is hosted within a quartz textural sequence composed of colloform, ghost-sphere and pseudo-bladed. Meanwhile, hessite is hosted within microcrystalline quartz-adularia wherein quartz exhibits an apparent microspherical texture with 5-10 µm diameter and adularia displays rhombic habit. Electrum grains are anhedral with sizes of 20-50 µm and are occasionally intergrown with naumannite-aguilarite solid solution and sulfides such as pyrite, sphalerite, and chalcopyrite. Hessite is usually intergrown with chalcopyrite, sphalerite, galena and pyrite, and they collectively show skeletal habit.
In CL images, the electrum-bearing colloform quartz is composed of alternating non-luminescent and blue-luminescent bands; the ghost-sphere quartz is composed of a set of non-luminescent spheres (20-200 µm diameter) in a blue-luminescent fibrous to massive matrix; and pseudo-bladed quartz is composed of blue-luminescent quartz intergrown with anhedral adularia. Electrum grains are commonly encapsulated within the non-luminescent bands of the colloform texture and the non-luminescent spheres of the ghost-sphere texture. CL images of the hessite-bearing microcrystalline quartz that exhibits microspherical texture generally display blue-luminescence. CL spectra of the blue-luminescent quartz in all textures consistently show a main peak at ~400 nm. The blue-luminescent quartz has higher Al concentration (ave. 3245 ppm) compared to the non-luminescent quartz (ave. 1440 ppm). In conclusion, electrum is mostly associated with the non-luminescent, relatively low Al quartz, whereas hessite is more associated with blue-luminescent quartz that has higher Al concentration.