Lay summary
The combination of near-infrared (NIR) microscopy and microthermometry and laser-ablation inductively coupled plasma mass-spectrometry (LA-ICP-MS) techniques makes possible to progress in the analysis of real ore-precipitating fluids. Combining these techniques enables successful analysis of individual fluid inclusions hosted by opaque to the visible light but transparent to the NIR radiation ore minerals. Joining this novel analytical approach and the standard microthermometry on transparent gangue minerals offers new opportunities to compare the chemistry and P-T conditions of entrapment of fluids in texturally co-genetic ore and gangue minerals from different ore deposits styles. This project aims to: i) perform test runs on several gangue/ore mineral pairs from a variety of hydrothermal environments in order to better evaluate the potential application of the methodology to study different ore deposit types and to develop, if necessary, the established analytical protocols; ii) apply the new methodology and undertake a detailed ore minerals-oriented fluid inclusion study on the Butte polymetallic district, Montana, and the Madan polymetallic district, Bulgaria; iii) study the chemistry (by LA-ICP-MS) and stable (oxygen and hydrogen) isotopic composition of enargite-hosted fluid inclusions from the Lepanto epithermal high-sulfidation deposit, Philippines. The three districts offer the possibility to work on fluids trapped in large temperature range - from temperatures as high as >400°C (porphyry environment at Butte and skarn environment at Madan), intermediate temperatures (300-200°C, corresponding roughly to the temperatures of the main polymetallic stage mineralization in the three districts), down to low-temperatures (~100°C). Thus, NIR experiments will cover a temperature range, which is typical for most of the known hydrothermal ore deposits and can be used to assess the applicability of this technique to other ore deposit types.The acquired new results and interpretations will be combined with previous geological, fluid inclusion and stable isotope data on the studied deposits to develop models for fluid processes which govern ore-precipitation mechanisms at the porphyry-epithermal interface (Butte and Lepanto) or in an epithermal environment without direct link with a deeper porphyry system (Madan). Such results would have implications also for general understanding of the mechanisms of hydrothermal ore-formation.