Arizona Geological Society
2026 Speaker Series
Tuesday, 1 September2026 | 5:30 - 8:00 PM
Location: Hexagon Mining Division Office
40 East Congress Street, Suite 150, Tucson, Arizona 85701
Parking: On the street or parking garage (Old Pueblo Parking)
Social Hour - Sandwiches from Beyond Bread (5:30-6:20 PM MST), Presentation (6:25 PM MST)
AGS and SEG Publications will be available
for sale at the meeting.
Will need cash or check (no credit cards)
For those planning to attend the event, please register by 6:00 PM on Sunday, August 30, 2026. Please register early so we have an accurate number of attendees to order the right amount of food.
The Arizona Geological Society thanks Hexagon
for generously providing the venue and drinks
The Northern Filo del Sol Porphyry-Epithermal Cu-Au-Ag System: Argentina: Opportunities for Expanding a Giant into a Behemothian
Guido Merino1 and Herve Rezeau2
1Dept. of Geosciences, Univ. of Arizona, Tucson, AZ USA
2Earth Res. Lab, Dept. of Earth, Atmos., & Planetary Sci., Massachusetts Inst. of Tech., Cambridge, MA, USA
Abstract: The Filo del Sol (FDS) deposit is recognized as one of the world’s premier porphyry-epithermal Cu-Au-Ag discoveries. The mineralized system extends for approximately 8.5 km along a N- to NE-trending corridor that straddles the Argentina–Chile border in the southern Central Andes. Recent resource estimates demonstrate that FDS is a giant porphyry–epithermal system comprising several mineralized areas, including the Aurora–Filo zones to the south and the Refugio, Bonita, and Maranceles zones to the north. However, the limits of mineralization remain unconstrained to the north and east, highlighting the potential for significant resource expansion. Unlocking the district-scale potential of FDS, and assessing whether it could evolve from a giant to a behemothian deposit, requires a better understanding of its underexplored northern extension.
Aerial View of Filo del Sol Porphyry-Epithermal System
In this presentation, I will integrate field observations with detailed petrography, mineral chemistry, sulfur isotope geochemistry, and geochronology from the Refugio, Bonita, and Maranceles areas to reconstruct the spatiotemporal evolution of the northern FDS magmatic-hydrothermal system and evaluate its implications for resource expansion. New 40Ar/39Ar ages of hydrothermal biotite, sericite, and alunite indicate that the northern FDS magmatic-hydrothermal system developed over a prolonged period (14.3-11.0 Ma), overlapping temporally with mineralization in the main Aurora-Filo zone to the south. The Refugio and Bonita areas are characterized by porphyry-style mineralization with potassic and dominant phyllic alteration, overlain by shallower epithermal mineralization with advanced argillic to argillic alteration and marked lateral ore and alteration zoning. Petrography and ore mineral trace element chemistry indicate that Refugio and Western Bonita record a transition from high- to intermediate-sulfidation epithermal mineralization, whereas Eastern Bonita is dominated by intermediate-sulfidation epithermal mineralization. In contrast, the northernmost Maranceles area hosts high-sulfidation epithermal veins associated with advanced argillic and argillic alteration and exhibits ore mineral chemistry that is inconsistent with derivation from the Refugio-Bonita magmatic-hydrothermal system. Sulfur isotopes indicate a magma-derived sulfur source (d34S = +5‰), where porphyry mineralization formed at relatively high temperatures (400–530°C) under highly oxidized conditions, whereas epithermal mineralization formed at lower temperatures (200–300°C) and records fluctuations in fluid redox conditions that reflect increasing fluid-rock interaction, although mixing with meteoric fluids and/or magmatic fluid immiscibility cannot be excluded.
3-D Section of Filo del Sol Porphyry-Epithermal System
We propose that Refugio and Bonita are likely part of the same magmatic-hydrothermal system, centered beneath Refugio and Western Bonita, with Eastern Bonita representing its lateral and more distal expression. Although coeval and sharing similar characteristics, Maranceles is interpreted to represent a distinct magmatic-hydrothermal center. These results suggest that the northern FDS district was constructed by multiple overlapping magmatic-hydrothermal centers rather than representing a simple northward continuation of the Aurora-Filo system, highlighting substantial potential for future resource expansion.
Bio: Guido is an exploration geologist who has just finished his MS in the Department of Geosciences at the University of Arizona, working under the supervision of Dr. Hervé Rezeau (MIT Earth Resources Laboratory, and former Lundin chair in Economic Geology at the University of Arizona). He obtained his Honor’s Bachelor’s Degree in Geological Sciences at the University of Buenos Aires (2017) and has worked nearly six years with the Lundin Group, exploring for porphyry and epithermal deposits in the Central Andes. He was part of the team that discovered the Filo del Sol Cu-Au-Ag epithermal-porphyry deposit, also contributing to its first scientific publication.
His academic interests include economic geology, with a big emphasis on field geology as well as geochemistry and mineralogy. His research focuses on characterizing the ore distribution of the Filo del Sol deposit particularly its northern area, which holds a big potential to expand the limits of the mineralization and resource. To address this matter at Filo del Sol, he carried on several techniques including field mapping and core logging, petrography, mineral and isotopic chemistry, and geochronology.
Hexagon Mining Division Office - 40 East Congress Street,
Suite 150, Tucson, Arizona 85701
