Geologic structure and mineralization of the xenothermal vein-type deposits in Japan

• DOI: 10.2113/gsecongeo.70.4.647
• Publication Date: 2009-04-03T13:27:25Z
• Authors: H. Imai; Min Sung Lee; K. Iida; Y. Fujiki; S. Takenouchi
• Keywords: Arsenopyrite; Cassiterite; Wolframite; Hypogene

Sn-W-Cu-Zn-Pb-Ag vein deposits in Japan, belonging to xenothermal class, occur or close proximity regions of rhyolitic (and andesitic) rocks intruded by granitic rocks. The are products the same igneous activities as intrusives. geologic age is late Cretaceous early Tertiary. Akenobe, Ikuno, and Tada mines western Japan Ashio mine eastern belong class.The fissures containing materials strike-slip faults tension cracks formed lateral pressure which caused folded structures each region. They also normal due upheaval withdrawal (including cauldron subsidence) magma.The at Akenobe follows: Ore minerals: cassiterite, wolframite, scheelite, magnetite (lamellar magnetite), arsenopyrite, molybdenite, pyrite, native bismuth, bismuthinite, chalcopyrite, stannite, sphalerite, galena, primary bornite, stannoidite (hexastannite), mawsonite, tennantite, chalcocite, roquesite, silver, argentite, polybasite, stephanite, etc. Gangue minerals quartz, topaz, apatite, fluorite, orthoclase, chlorite, calcite, rhodochrosite, Indium selenium relatively concentrated ores from this type deposit.Similar paragenesis observed Tada, mines. At Ikuno mine, distribution shows a remarkable zoning. There zones, vertically lower higher horizontally center margin, (1) tin-tungsten, (2) tin-copper, (3) copper-zinc, (4) zinc-lead, (5) silver. zones generally coincides with zoning described Emmons (1924). As whole it belongs monoascendant similar recognized. It inferred that mineralizing fluid may have ascended along flowed into cracks. silver stromeyerite characteristically recognized zone deposit. These latest stage mineralization.At reverse recognized, i.e., tin-tungsten occurs level copper zinc exist below zone.From inclusion studies, decrepitation temperatures determined be 355 degrees 155 C. inclusions quartz two-phased (liquid vapor). homogenization filling heating microscope, NaCl equivalent concentration cooling 350 200 C 0 9 percent, respectively. In some cases, under microscope crystal veins predominating liquid phase coexists one vapor phase. This indicates boiling phenomenon ore-forming has occurred course mineralization.In areas composed Permo-Carboniferous sedimentary Early Tertiary period adjacent above ore deposits, there hypothermal tungsten tin veins, mesothermal chalcopyrite pyrrhotite deposits. stannoidite, mawsonite lacking, found type. type, cubanite (mackinawite) pyrrhotite, often types, not following succession Cu-Fe-Sn-S mineralization recognized: Pyrite, Chalcopyrite --> Chalcopyrite, Stannite Stannoidite Bornite, Mawsonite. From hydrothermal experiments apparently stable conditions sulfur fugacity temperature than assemblage bornite + chalcopyrite. Similarly, would stannite sequence thus proceeds toward temperatures, depositing stage.