5:15 PM - 6:30 PM
[SCG44-P07] Microstructures of spherical pyrite in the Kuroko deposits: possible mechanism of pyrite growth on bubble
Keywords:spherical pyrite, Kuroko, bubble surface
The submarine hydrothermal vents are one of the most active sites of mineralization in the Earth. The Kuroko deposits provide the significant insights on the mineralization processes at the active submarine hydrothermal systems. It is known that various forms of pyrite exist within the Kuroko deposits, but the formation mechanism and controlling factor have not been fully understood. In this study, we show the microstructural features of the spherical pyrite of the Kuroko deposits by using the EBSD, EDX and micro X-ray CT analyses, and discuss the formation processes within the hydrothermal vent. The sample was a part of chimney collected from the Kannondo deposit in the Hanaoka mine, NE Japan. The sample show the banded structure mainly composed of pyrite, barite, sphalerite with lessor amount of chalcopyrite and aluminosilicate. The pyrite particles show a spherical shape with 10-100 micrometer in diameter. The spherical pyrite grains often have hollow at the center, and some of them are filled by later minerals (barite and Cu-rich phase). The detailed microstructural analyses revealed that the spherical pyrite is composed of needle-like pyrite crystals, all of which are oriented with <100> direction. The needles are wider outward, suggesting the growth from the center to the margin. These features suggest the growth of pyrite crystals on bubble template as follows. Pyrite nano particles were initially formed in fluids, and they were attracted to a bubble surface by electrostatic double-layer forces and hydrophobic forces in response to specific pH, pS and pFe conditions. The preferential faces were attached on the bubble, and developed their face to grow in <100> direction. Such particle with hollow could have advantages on transport with low particle density.