Deciphering the evolution of ore fluids at the Batu Hijau copper-gold porphyry deposit, Sumbawa, Indonesia

Fluid inclusions contained within quartz veins from the Batu Hijau Cu-Au porphyry deposit in Indonesia were analyzed to track the evolution of fluid temperature, pressure, and composition during the formation of the deposit to better understand the formation of this and other Cu-Au porphyry deposits in order aid future exploration. A combination of petrography, microthermometry, synchrotron x-ray fluorescence, and laser ablation-inductively coupled plasma-mass spectrometry were used to determine the temperature, pressure, and compositional aspects of the deposit.;Four types of fluid inclusions were recognized at Batu Hijau based on the volume percent of the vapor bubble; inclusions were classified as VB35, VB20H, VB60, and VB85 type inclusions. A high temperature, non-reactive fluid trapped in VB60 inclusions was introduced to the system first, was associated with only minor ore mineral precipitation, and was likely linked to high temperature alteration. A second, lower temperature, highly reactive fluid trapped in VB35 inclusions was then introduced to the system and was likely responsible for the majority of ore mineral precipitation as well as lower temperature alteration assemblages. This second fluid became immiscible during its ascent to the surface, forming a highly reactive brine and a non-reactive vapor, trapped in VB20H and VB85 inclusions, respectively.;While these two fluids seem temporally distinct, future studies investigating the exact timing of ore fluid introduction, and the association of ore fluids pulses to magmatic intrusions is required to full understand the temporal relationships of fluids at Batu Hijau. If fluid inclusions can be petrographically linked to distinct intrusion events, a complete four-dimensional model for fluid evolution can be completed, providing a valuable new tool to aid in the exploration of Cu-Au porphyry deposits.