Abstract
The Arinem deposit is an epithermal–type, gold–silver–base metal mineralization, hosted by the Arinem vein system which cross–cut volcanic rocks of Oligocene to Miocene age. There are three main stages (I to III) of ore mineralization in quartz–illite–calcite veining. The physico–chemical conditions and the origin of the hydrothermal fluids in the Arinem deposit are examined. We find the fS2 to have decreased from ~ 10−8 to 10−16 atm and the fTe2 to have increased from ~ 10−15 to 10−8 atm with decreasing temperature of ore fluids during mineralization. Oxygen (δ18O), hydrogen (δD), and sulfur (δ34S) isotopic values as derived from quartz, fluid inclusions, and sulfides in the mineralized veins range −6.0 to −1.7‰, −66 to −34‰, and −3.6 to −1.8‰, respectively. The sulfur isotope values indicate that sulfur was mostly derived from a magmatic source, whereas the oxygen and hydrogen isotope values suggest an influx of meteoric water into the hydrothermal system. As a consequence of the mixing of magmatic and meteoric waters and changes in the physico–chemical conditions of the ore fluids (i.e., ore fluid temperature and chemistry), higher temperature mineralization was triggered during stage I, followed by lower temperature mineralization during stage II. Continued influx of meteoric water may have caused the ore fluids to become oversaturated, resulting in the precipitation of unmineralized stage III veins.
