On Some Gold-silver Ores from Taio Mine
1953 Volume 3 Issue 8 Pages 79-86
Details
1953 Volume 3 Issue 8 Pages 79-86
The ore deposits of Taio mine are typical epithermal gold-silver veins in Tertiary apo-andesite. In rich ores of the No.3 and No.4 Veins, the most productive lodes of this mine, the black crustified bands or patches called "Ginguro" (silver black) are commonly found. From microscopic observations, it is known that the textural and mineralogical characters, and the mode of occurrence of gold in the ore differ remarkably in these two veins.
The ore consists essentially of common ore minerals, such as pyrite, chalcopyrite, galena and sphalerite, with quartz, chalcedony and calcite. Sphalerite, a principal constituent, amounts to about 70 percent of all ore minerals. Polybasite occurs as the only sulphosalt mineral in the No.4 Vein, but is present in a very small amount. Argentite is commonly found in the No.4 Vein, but is relatively rare in the No.3 Vein.
Gold, as electrum, is concentrated in the Ginguro. From observation on 2000 gold particles under the microscope, the mode of occurrence of gold was revealed as follows:
I. No.3 Vein.
1) Gold particles are generally granular and about 90 percent of the particles are intimately associated with sulphide minerals such as galena and chalcopyrite, and especially with sphalerite. But some particles are associated with argentite and pyrite. Gold which is not enclosed in sulphide minerals is about 3 percent.
2) The grain size of the gold particles ranges from 0.5 to 85 microns, and grains from 3 to 10 microns in size are most predominant.
II. No.4 Vein.
1) Most of the gold particles are not enclosed by the sulphide minerals but filling the interstices of quartz crystals. These free particles amount to 44 percent of all. Grains which are associated with galena, chalcopyrite and sphalerite are about 30 percent. Grains associated with pyrite and argentite are notably greater in number than in the No.3 Vein.
2) It is revealed that the size of the gold particles of this vein is finer than that of No.3 Vein and the peak of the size frequency curve is between 3 to 7 microns. The size are widely distributed ranging from 0.3 to 400 micrns.
