Magmatic-Hydrothermal Events, Mineralogy and Geochemistry of Tourmaline Breccia in the Giant Río Blanco – Los Bronces Porphyry Copper Deposit, Central Chile

The Río Blanco–Los Bronces (Chile) is one of the richest endowed porphyry copper-molybdenum districts worldwide, where about 20% of the known mineralization is hosted by tourmaline-cemented hydrothermal breccia. This work seeks: (1) to find a relationship between tourmaline chemical and/or isotopic composition and the degree of mineralization in the breccia, (2) to constrain the source of the mineralizing fluid in the breccia, and (3) to determine of the composition and age of intrusive units in three new exploration projects and correlate them with the known intrusive rocks of the mine areas. Tourmaline from mineralized and barren breccias has similar boron isotopic compositions but differences in Mg/(Mg+Fe) ratios, Al-contents and Al-Fe correlation, which may have exploration value. Boron and sulfur isotopes results are consistent with a magmatic source of hydrothermal fluids. Results of whole rock geochemistry and U-Pb and 40Ar/39Ar geochronology of intrusive units, breccia and late-stage veins are combined with previous U-Pb, Ar/Ar and Re-Os ages to elucidate the magmatic and hydrothermal history of the district.:1 Introduction 1.1 Motivation of the study and statement of research questions 1.2 Scope of the study 2 Porphyry copper deposits (PCDs) 2.1 Introduction 2.1.1 Global copper inventory 2.1.2 Definition and classification of PCDs 2.2 Regional scale characteristics of PCDs 2.2.1 Tectonic setting 2.2.2 Space and time distribution 2.2.3 Porphyry stocks and their pluton and volcanic connections 2.2.4 Wall-rock Influence 2.3 Deposit-scale characteristics 2.3.1 Porphyry stocks and dikes 2.3.2 Hydrothermal breccia 2.3.3 Alteration-mineralization zoning 2.4 Processes of PCD formation 2.4.1 Arc magmatism 2.4.2 Magmatic volatiles 2.4.3 Genetic models 3 Regional setting of the study area 3.1 Tectono-magmatic setting 3.2 Metallogenic belts 4 Río Blanco – Los Bronces mining district 4.1 Mining history 4.2 District geology 4.2.1 Stratified rocks 4.2.2 Plutonic and hypabyssal intrusions 4.2.3 Structures 4.2.4 Alteration and mineralization 4.2.1 Geochronology database 5 Results 5.1 Plutonic units 5.1.1 Petrography 5.1.2 Whole rock (WR) geochemistry 5.1.3 Geochronology 5.2 Mineralization 5.2.1 Petrography 5.2.2 Tourmaline occurrence and composition 5.2.3 Sulfides and sulfates 6 Discussion 6.1 Time-space relationships of intrusion, brecciation and hydrothermal alteration 6.2 Stable isotope constraints on fluid source and evolution 6.2.1 Oxygen, hydrogen and sulfur isotopes 6.2.2 Boron isotopes 6.3 Tourmaline as a redox indicator and significance for exploration 7 Summary and conclusions 8 References Digital supplement Appendix (Methods) 9 Appendix Methods 9.1 Optical microscopy (OM) 9.2 Scanning electron microscope (SEM) and energy-dispersive X-ray spectroscopy (EDS) 9.3 Whole rock chemical analysis 9.4 Electron microprobe analyses (EMPA) 9.5 Boron isotopes 9.6 Sulfur isotopes 9.7 40Ar/39Ar dating 9.8 Zircon separation and characterization 9.9 U-Pb zircon LA-ICP-MS dating 9.10 U-Pb zircon CA-ID-TIMS dating 9.11 Single zircon evaporation as screening metho