Decoding magma plumbing and geochemical evolution beneath the Lastarria volcanic complex (Northern Chile)—Evidence for multiple magma storage regions

Abstract The El Volcán gold project (8.9 Moz Au @ 0.71 g/t Au) is located in the Maricunga gold belt in northern Chile, on the flank of the large Cenozoic Copiapó Volcanic Complex. Precious metal mineralization is hosted in two zones (Dorado and Ojo de Agua) of (pervasively) altered Miocene porphyry intrusions and lava flows of andesitic to rhyolitic composition, and in breccias. The ore zones reflect an evolving magmatic-hydrothermal system with mineral assemblages of magnetite-ilmenite-pyrite-molybdenite (early), bornite-chalcopyrite-pyrite-rutile (stage I), chalcocite-chalcopyrite-enargite-fahlore-pyrite (stage II), and chalcopyrite-covellite-pyrite (stage III). Alteration is dominantly of Maricunga-style (illite-smectite-chlorite ± kaolinite), partly obscured by quartz-kaolinite-alunite ± illite ± smectite alteration. Powdery quartz-alunite-kaolinite alteration with native sulfur and cinnabar forms shallow steam-heated zones. Early K-feldspar ± biotite alteration is preserved only in small porphyry cores and in deep drill holes. Most gold is submicrometer size and is in banded quartz veinlets, which are characteristic of the Maricunga gold belt. However, some gold is disseminated in zones of pervasive quartz-kaolinite-alunite alteration, with and without banded quartz veinlets. Minor visible gold is related to disseminated chalcocite-chalcopyrite-enargite-fahlore-pyrite. The lithogeochemical database identifies a pronounced Au-Te-Re signature (>100× bulk crust) of the hydrothermal system. Molybdenum-rich bulk rock (100–400 ppm Mo) has an Re-Os age of 10.94 ± 0.17 Ma (2σ). 40Ar-39Ar ages on deep K-feldspar alteration and on alunite altered rock have the same age within error and yield a combined age of 11.20 ± 0.25 Ma (2σ). The formation of the El Volcán gold deposit took place during the establishment of the Chilean flat-slab setting in a time of increasing crustal thickness when hydrous magmas were formed in a mature arc setting. The vigorous nature of the hydrothermal system is expressed by abundant one-phase vapor fluid inclusions recording magmatic vapor streaming through a large rock column with a vertical extent of ≥1,500 m.

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Geochemical evolution of a shallow magma plumbing system during the last 500 years, Miyakejima volcano, Japan: Constraints from 238U–230Th–226Ra systematics

Geochimica et Cosmochimica Acta ◽

10.1016/j.gca.2006.02.027 ◽

2006 ◽

Vol 70 (11) ◽

pp. 2885-2901 ◽

Cited By ~ 28

Author(s):

Tetsuya Yokoyama ◽

Takeshi Kuritani ◽

Katsura Kobayashi ◽

Eizo Nakamura

Keyword(s):

Geochemical Evolution ◽

Plumbing System ◽

Magma Plumbing System ◽

Miyakejima Volcano ◽

Magma Plumbing

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Piton de la Fournaise, elasto-plastic models of stresses and deformation accounting for the topographic load and a magmatic injection

10.5194/egusphere-egu2020-11571 ◽

2020 ◽

Author(s):

Muriel Gerbault ◽

Fabrice Fontaine ◽

Aline Peltier ◽

Lydie Gailler ◽

Riad Hassani ◽

...

Keyword(s):

Large Scale ◽

Numerical Models ◽

Three Dimensions ◽

Stress Fields ◽

Volcanic Complex ◽

Test Cases ◽

Magma Storage ◽

Arbitrary Geometry ◽

Piton De La Fournaise ◽

Central Cone

Building on previous work aimed at identifying and characterizing the potential mechanical trigger controlling eruptions and destabilization at Piton de la Fournaise, we study the mechanical behavior of the volcanic edifice on a crustal scale. Do the recurrent earthquake pattern correspond to a destabilization structure, precursor of a large-scale flank sliding? Or instead to a reactivated area of magma storage (partially crystallized &#8220;sill&#8221;)? To answer these questions, we design numerical models which estimate the stress field associated with the volcanic complex. We use the ADELI finite element method in three dimensions, which handles elasto-visco-plastic rheologies. In these models, we take into account 1) the topographic load, 2) the major density and resistance heterogeneities within the volcano obtained from previous studies, and 3) the overpressure induced by the intrusion of a dike of arbitrary geometry. The modeled dike injection generates deformation and stress fields such that their isocontours highlight an ellipsoidal cup structure extending from the central cone to a depth close to 0 and reaching the ends of the eastern flank. This zone could be assimilated to the zone of seismicity observed and described previously. Together with several systematic test cases, we will discuss the significance of these results, such as whether it reveals a rheological delimitation zone of the hydrothermalized bedrock, resulting from the combined influence of the topographic load and that of a magmatic injection.

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Geomorphology, lithofacies, and block characteristics to determine the origin, and mobility, of a debris avalanche deposit at Apacheta-Aguilucho Volcanic Complex (AAVC), northern Chile

Journal of Volcanology and Geothermal Research ◽

10.1016/j.jvolgeores.2017.09.008 ◽

2017 ◽

Vol 347 ◽

pp. 136-148 ◽

Cited By ~ 9

Author(s):

Benigno Godoy ◽

Inés Rodríguez ◽

Marcela Pizarro ◽

Germain Rivera

Keyword(s):

Debris Avalanche ◽

Volcanic Complex ◽

Northern Chile ◽

Debris Avalanche Deposit

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Warm storage for arc magmas

Proceedings of the National Academy of Sciences ◽

10.1073/pnas.1616129113 ◽

2016 ◽

Vol 113 (49) ◽

pp. 13959-13964 ◽

Cited By ~ 46

Author(s):

Mélanie Barboni ◽

Patrick Boehnke ◽

Axel K. Schmitt ◽

T. Mark Harrison ◽

Phil Shane ◽

...

Keyword(s):

Human Life ◽

Volcanic Complex ◽

Magma Storage ◽

Storage Model ◽

Arc Magmas ◽

Physical Conditions ◽

Show Evidence ◽

History Of ◽

Chemical History ◽

Volcanic Reservoirs

Felsic magmatic systems represent the vast majority of volcanic activity that poses a threat to human life. The tempo and magnitude of these eruptions depends on the physical conditions under which magmas are retained within the crust. Recently the case has been made that volcanic reservoirs are rarely molten and only capable of eruption for durations as brief as 1,000 years following magma recharge. If the “cold storage” model is generally applicable, then geophysical detection of melt beneath volcanoes is likely a sign of imminent eruption. However, some arc volcanic centers have been active for tens of thousands of years and show evidence for the continual presence of melt. To address this seeming paradox, zircon geochronology and geochemistry from both the frozen lava and the cogenetic enclaves they host from the Soufrière Volcanic Center (SVC), a long-lived volcanic complex in the Lesser Antilles arc, were integrated to track the preeruptive thermal and chemical history of the magma reservoir. Our results show that the SVC reservoir was likely eruptible for periods of several tens of thousands of years or more with punctuated eruptions during these periods. These conclusions are consistent with results from other arc volcanic reservoirs and suggest that arc magmas are generally stored warm. Thus, the presence of intracrustal melt alone is insufficient as an indicator of imminent eruption, but instead represents the normal state of magma storage underneath dormant volcanoes.

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