Lead-Zinc Mineralization of the Toyoha Mine, with Special Reference to the Nature and Occurrence of Sphalerite and the Behaviour of Silver

Abstract

Two sets of epithermal vein fissures of the Toyoha mine are distinguished; the one is E-W shear veins composing of two linking champion veins; and the other NW-SE tension veins cross-cutting obliquely the former.
The early-stage mineralization occurred in the E-W fissures and deposited sphalerite, galena, pyrite, hematite and small amount of chalcopyrite in the abundant gangue quartz. On the other hand, the late-stage mineralization filled the NW-SE fissures with banded ores of galena, sphalerite and pyrite with or without rhodochrocite and manganiferous calcite.
Lattice constants of sphalerite specimens from different localities were measured by X-ray diffraction method. They were correlated with the powder-colors, and with the iron contents as follows.
Sphalerites of the early-stage mineralization have generally lighter color, and the smaller lattice constant, while sphalerites of the later stage mineralization have the opposite characters, similarly different characters were recognized on the sphalerite in or out of the ore shoot.
Although silver and silver minerals are mainly native silver, argentite, and pyrargyrite, silver is concentrated in the banded ore of the sulphides, especially in galena of later mineralization. Hairly native silver was found in druses. The silver content of the crude ore is about 130 g/t in average. It attains, however, up to several thousands g/t in the silver rich parts.