Publications by authors named "Adam C Simon"

4 Publications

  • Page 1 of 1

Thermal evolution of Andean iron oxide-apatite (IOA) deposits as revealed by magnetite thermometry.

Sci Rep 2021 Sep 16;11(1):18424. Epub 2021 Sep 16.

Department of Earth and Environmental Sciences, University of Michigan, 1100 North University Ave, Ann Arbor, MI, USA.

Magnetite is the main constituent of iron oxide-apatite (IOA) deposits, which are a globally important source of Fe and other elements such as P and REE, critical for modern technologies. Geochemical studies of magnetite from IOA deposits have provided key insights into the ore-forming processes and source of mineralizing fluids. However, to date, only qualitative estimations have been obtained for one of the key controlling physico-chemical parameters, i.e., the temperature of magnetite formation. Here we reconstruct the thermal evolution of Andean IOA deposits by using magnetite thermometry. Our study comprised a > 3000 point geochemical dataset of magnetite from several IOA deposits within the Early Cretaceous Chilean Iron Belt, as well as from the Pliocene El Laco IOA deposit in the Chilean Altiplano. Thermometry data reveal that the deposits formed under a wide range of temperatures, from purely magmatic (~ 1000 to 800 °C), to late magmatic or magmatic-hydrothermal (~ 800 to 600 °C), to purely hydrothermal (< 600 °C) conditions. Magnetite cooling trends are consistent with genetic models invoking a combined igneous and magmatic-hydrothermal origin that involve Fe-rich fluids sourced from intermediate silicate magmas. The data demonstrate the potential of magnetite thermometry to better constrain the thermal evolution of IOA systems worldwide, and help refine the geological models used to find new resources.
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http://dx.doi.org/10.1038/s41598-021-97883-3DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8445919PMC
September 2021

Oxidized sulfur-rich arc magmas formed porphyry Cu deposits by 1.88 Ga.

Nat Commun 2021 Apr 13;12(1):2189. Epub 2021 Apr 13.

Canadian Centre for Isotopic Microanalysis, University of Alberta, Edmonton, AB, Canada.

Most known porphyry Cu deposits formed in the Phanerozoic and are exclusively associated with moderately oxidized, sulfur-rich, hydrous arc-related magmas derived from partial melting of the asthenospheric mantle metasomatized by slab-derived fluids. Yet, whether similar metallogenic processes also operated in the Precambrian remains obscure. Here we address the issue by investigating the origin, fO, and S contents of calc-alkaline plutonic rocks associated with the Haib porphyry Cu deposit in the Paleoproterozoic Richtersveld Magmatic Arc (southern Namibia), an interpreted mature island-arc setting. We show that the ca. 1886-1881 Ma ore-forming magmas, originated from a mantle-dominated source with minor crustal contributions, were relatively oxidized (1‒2 log units above the fayalite-magnetite-quartz redox buffer) and sulfur-rich. These results indicate that moderately oxidized, sulfur-rich arc magma associated with porphyry Cu mineralization already existed in the late Paleoproterozoic, probably as a result of recycling of sulfate-rich seawater or sediments from the subducted oceanic lithosphere at that time.
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http://dx.doi.org/10.1038/s41467-021-22349-zDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8044198PMC
April 2021

Accumulation of magnetite by flotation on bubbles during decompression of silicate magma.

Sci Rep 2019 Mar 7;9(1):3852. Epub 2019 Mar 7.

Institut für Mineralogie, Leibniz Universität Hannover, Callinstraße 3, 30167, Hannover, Germany.

Magnetite (FeO) is an iron ore mineral that is globally mined especially for steel production. It is denser (5.15 g/cm) than Earth's crust (~2.7 g/cm) and is expected to accumulate at the bottom of melt-rich magma reservoirs. However, recent studies revealed heterogeneous fluid bubble nucleation on oxide minerals such as magnetite during fluid degassing in volcanic systems. To test if the attachment on fluid bubbles is strong enough to efficiently float magnetite in silicate magma, decompression experiments were conducted at geologically relevant magmatic conditions with subsequent annealing to simulate re-equilibration after decompression. The results demonstrate that magnetite-bubble pairs do ascend in silicate melt, accumulating in an upper layer that grows during re-equilibration. This outcome contradicts the paradigm that magnetite must settle gravitationally in silicate melt.
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http://dx.doi.org/10.1038/s41598-019-40376-1DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6405838PMC
March 2019

Formation of massive iron deposits linked to explosive volcanic eruptions.

Sci Rep 2018 Oct 5;8(1):14855. Epub 2018 Oct 5.

Department of Geology and Andean Geothermal Center of Excellence (CEGA), FCFM, Universidad de Chile, Plaza Ercilla 803, Santiago, Chile.

The genetic link between magmas and ore deposit formation is well documented by studies of fossil hydrothermal systems associated with magmatic intrusions at depth. However, the role of explosive volcanic processes as active agents of mineralization remains unexplored owing to the fact that metals and volatiles are released into the atmosphere during the eruption of arc volcanoes. Here, we draw on observations of the uniquely preserved El Laco iron deposit in the Central Andes to shed new light on the metallogenic role of explosive volcanism that operates on a global scale. The massive magnetite (FeO) ore bodies at El Laco have surface structures remarkably similar to basaltic lava flows, stimulating controversy about their origin. A long-standing debate has endured because all proposed models were constructed based exclusively on samples collected from surface outcrops representing the uppermost and most altered portion of the deposit. We overcome this sampling bias by studying samples retrieved from several drill cores and surface outcrops. Our results reveal complex lithological, textural and geochemical variations characterized by magmatic-like features and, most notably, a systematic increase in titanium concentration of magnetite with depth that account for an evolving system transitioning from purely magmatic to magmatic-hydrothermal conditions. We conclude that El Laco, and similar deposits worldwide, formed by a synergistic combination of common magmatic processes enhanced during the evolution of caldera-related explosive volcanic systems.
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http://dx.doi.org/10.1038/s41598-018-33206-3DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6173703PMC
October 2018
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