DESCRIPTIVE MODEL OF SADO EPITHERMAL VEINS
By Dan L. Mosier, Byron R. Berger, and Donald A. Singer
DESCRIPTION Gold, chalcopyrite, sulfosalts, and argentite in vuggy veins hosted by felsic to intermediate volcanic rocks that overlie older volcanic sequences or igneous intrusions (see fig. 106).
GENERAL REFERENCE Boyle (1979).
Rock Types Host rocks are andesite, dacite, quartz latite, rhyodacite, rhyolite, and associated sedimentary rocks. Mineralization related to calc-alkaline or bimodal volcanism.
Age Range Mainly Tertiary (most are 38-5 m.y.).
Depositional Environment Calc-alkaline and bimodal volcanism and associated intrusive activity over basement rocks composed of thick, older volcanic sequences or igneous intrusives (batholiths). Volcanic-related geothermal systems lack access to saline fluids from basement sources.
Tectonic Setting(s) Through-going fracture systems, major normal faults, fractures related to doming, ring fracture zones, joints.
Associated Deposit Types Placer gold and quartz-alunite Au.
Mineralogy Gold ± argentite + electrum + chalcopyrite. Sulfosalts and tellurides are moderate, galena and sphalerite are sparse. Gangue minerals are quartz ± pyrite ± adularia ± calcite. Chalcedony, adularia, kaolinite, rhodochrosite, chlorite, sericite, and barite are moderate to sparse.
Texture/Structure Banded veins, open space filling, lamellar quartz, stockwork, breccia pipes.
Alteration Silicification zoned by quartz + kaolinite + montmorillonite ± alunite; may have pervasive propylitic alteration of chlorite + calcite.
Ore Controls Through-going fracture systems; major normal faults, fractures related to doming, ring fractures, joints.
Weathering Bleached country rock, limonite, hematite, goethite, jarosite, alunite; argillization with kaolinite.
Geochemical Signature Au + Ag; Au + Ag + Cu.
Takeno, JAPN (Soeda and Watanabe, 1981)