Thursday, September 13, 2018 - USGS Luncheon
The Proterozoic Vazante – Paracatu carbonate-hosted zinc district, Minas Gerais, Brazil: Siliciclastic rocks and their relationship with carbonate-hosted Zn-silicate and Zn-sulphide mineralizations
Time: 11:30 am - 1:00 pm
The Proterozoic Upper Vazante Sequence (≈ 1300 – 1100 Ma) in Minas Gerais, Brazil is a mixed carbonate-siliciclastic succession that contains a number of hypogene Zn-silicate and Zn-sulphide deposits along a 250 km – long Vazante Belt (Monteiro et al. 2006; Olivo et al. 2018). Host rocks in the mineral deposits include a variety of dolomitic rocks within a shallow water carbonate succession belonging to the Vazante Group (Dardenne 2000). The Zn deposits and their contained resources (data from Nexa Resources, personal communication; Olivo et al., 2018) include: 1. The Vazante – North Extension Zn silicate mines (combined resources of 37.6Mt @ 19.78% Zn, 0.48% Pb, 29.94g/t Ag) located in the southern part of the district, 2. The Morro Agudo Zn – Pb sulphide mine (resource of 20Mt @ 5% Zn, 2% Pb) located in the central-north part of the district, and 3. The Fagundes – Ambrosia Zn – Pb sulphide deposits located in the northern part of the district (No current published resource). It is thought that the majority of the carbonate-hosted Zn mineralization was formed during the Brasiliano Orogeny (≈ 650 Ma; Dn; Dardenne and Freitas-Silva 1999; Misi et al. 2014). However, little is known about the sources of metals.
The Serra do Garrote Formation is a thick (500+ m) meta-siliciclastic package dominated by phyllites, carbonaceous phyllites (≥1 wt.% TOC) and minor coarse rock types, and it underlies all the known dolostone-hosted Zn-deposits and the Serra do Garrote Formation The lithologies are made up of muscovite- and chlorite-bearing rocks that contain variable amounts of quartz, albite, titanite and organic matter. These rocks can be subdivided into three distinct subunits/protoliths (SG1, SG2, SG3) on the basis of immobile elements, specifically whole-rock Al/Ti ratios. Whole-rock geochemical analyses of these shows that they are enriched in Zn (up to 0.46% Zn), and that SG1 (mean 550 ppm Zn) and SG2 (mean 360 ppm Zn) contain higher Zn compared to the SG3 subunit (mean 125 ppm Zn).
Zn-enrichment is associated with various generations of hydrothermal sphalerite and pyrite that formed prior to the Brasiliano Orogeny. Whole-rock element correlation matrices provide a geochemical signature of Zn-enrichment, which is associated with Cd, Cu, Hg, In, V ± Sb, Se, Mo and Re in the SG1 and SG2 subunits. This signature is similar to that documented in the dolostone-hosted Zn deposits (Olivo et al. 2018; Slezak et al. 2014; Monteiro et al. 2007). Hydrothermal sulphides were at least partially remobilized during orogenesis, suggesting that the siliciclastic rocks of the Serra do Garrote Formation could have been the source of Zn and other ore-related elements in the dolostone-hosted Zn deposits.
Neil A. Fernandes, Queen’s University, Ontario, Canada
Neil Fernandes is a Ph.D. candidate at the Department of Geological Sciences and Geological Engineering, Queen’s University, Canada. He is currently in the final year of his studies working with Dr. Gema Olivo and Dr. Dan Layton-Matthews. The H.C. Morris Fellowship is sponsoring a self-designed experiential learning program (ELP) that is allowing him to explore his interest in sediment-hosted mineral deposits in Canada, U.S.A, Australia, Namibia, Ireland, Sweden, Peru and Brazil by funding visits to government geological surveys, mining companies and mines, and universities in all these countries. The objective of his ELP is to gain expertise in all facets of these mineral systems, from exploration to remediation. Prior to his Ph.D. studies, he worked in Chile for Barrick Gold exploration. He holds a M.Sc. from the University of Alberta, and a B.Sc. (Honours) from the University of Toronto.
Tuesday, September 18, 2018 - AGS Luncheon Lecture
Eruption response and preliminary observations of the 2018 eruption of Kilaueavolcano, Hawaii
Noon Luncheon 11:30-1:00 pm
The 2018 eruption of Kīlauea Volcano is an unprecedented event in the historical record at one of the most active volcanoes in the world. With two simultaneous eruption sites, one at the volcano’s summit and one on the lower East Rift Zone, the event has produced a range of volcanic hazards from lava inundation to earthquakes that have affected local communities. New eruptive activity began with magma intrusion and eruption of lava on Kīlauea’s lower East Rift Zone on May 3, 2018. More than 0.5 km3 of lava has erupted from a 6.8-km-long fissure system and destroyed multiple residential areas, infrastructure, and local landmarks. Eruption of lava in the lower East Rift Zone was accompanied by withdrawal of magma from the volcano’s summit reservoir, resulting in draining of the summit lava lake, followed by a number of ash-producing explosions and caldera collapse. The dynamics of the eruption were documented in detail by the USGS Hawaiian Volcano Observatory (with support from staff at other observatories, including the Alaska Volcano Observatory) with geophysical monitoring equipment, ground-based observations, helicopter and unmanned aircraft systems (UAS) mapping, and satellite remote sensing. Monitoring 24/7 allowed for rapid analysis and alerts of activity by volcano observatory staff in close communication with local, state, and federal emergency managers. This talk will provide an overview of eruptive activity with photos and videos of the eruption from the ground and the air (UAS), as well as a discussion of the eruption response.
Hannah Dietterich, USGS Alaska Volcano Observatory, Anchorage
Hannah Dietterich is a Research Geophysicist at the U.S. Geological Survey Alaska Volcano Observatory. Her work focuses on the physics of volcanic processes, remote sensing of volcanic activity, numerical modeling of volcanic hazards, and probabilistic volcanic hazard assessment. She integrates geologic mapping, physical volcanology, remote sensing, and numerical modeling with observations of ongoing eruptions to advance our understanding of volcanic hazards.