Anhydrite-bearing andesite and dacite as a source for sulfur in magmatic-hydrothermal mineral deposits

Chambefort, Isabelle; Dilles, John H.; Kent, Adam J.R.

doi:10.1130/g24920a.1

Cited by 94 publications

(54 citation statements)

References 18 publications

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“…Recently, this paradigm has been challenged by the recognition that ore fluids in sediment-hosted 3-5 , epithermal 6,7 and porphyryrelated [8][9][10] hydrothermal deposits can carry orders of magnitude more metal than previously considered probable, or measured in modern fluid samples. This suggests that our understanding of metal extraction and transport processes is incomplete.Here, this theme is explored by consideration of porphyry ore deposits [11][12][13][14][15] , remarkable geochemical anomalies that can contain up to 1 Gt of sulphur 16 , 200 Mt copper, 2.5 Mt molybdenum and 2600 t gold 17 . The most copper-rich examples include the 4-5 million-year old El Teniente and Rio Blanco-Los Bronces deposits in Central Chile, and the most gold-rich is the 3 million-year old Grasberg deposit in Irian Jaya, Papua New Guinea 17 .…”

mentioning

confidence: 99%

“…Here, this theme is explored by consideration of porphyry ore deposits [11][12][13][14][15] , remarkable geochemical anomalies that can contain up to 1 Gt of sulphur 16 , 200 Mt copper, 2.5 Mt molybdenum and 2600 t gold 17 . The most copper-rich examples include the 4-5 million-year old El Teniente and Rio Blanco-Los Bronces deposits in Central Chile, and the most gold-rich is the 3 million-year old Grasberg deposit in Irian Jaya, Papua New Guinea 17 .…”

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confidence: 99%

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Triggers for the formation of porphyry ore deposits in magmatic arcs

2013

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Porphyry ore deposits source much of the copper, molybdenum, gold and silver utilized by humankind. They typically form in magmatic arcs above subduction zones via a series of linked processes, beginning with magma generation in the mantle and ending with the precipitation of metals from hydrous fluids in the shallow crust. A hierarchy of four key "triggers" involved in the formation of porphyry deposits is outlined. Trigger 1 (10 2 -10 3 km scale) is a process of cyclic refertilization of magmas in the deep crust. Trigger 2 (10 1 -10 2 km scale) is the process of sulfide saturation in magmas that can both enhance and destroy ore-forming potential. Trigger 3 (10 0 -10 1 km scale) relates to the efficient transfer of metals into hydrothermal fluids exsolving from porphyry magmas. Trigger 4 (~10 0 km scale) identifies processes that lead to the final precipitation of ore minerals. Although all processes are required to a greater or lesser degree, it is argued that trigger 3, as an over-riding mechanism, can best explain the restriction of large deposits to specific arc segments and time periods. Consequently, recognition of the fingerprint of sulfide saturation in igneous rocks may help mineral exploration companies to identify parts of magmatic arcs particularly predisposed to ore formation.Ore deposits are scarce. Their discovery consumes considerable time and resources and only about one in every one thousand prospects explored by companies is eventually developed into a mine. Deposits often occur in clusters and formed within specific time intervals. This non-uniform pattern provides keys to understanding how and why metals accumulate in some places and not in others and its explanation is fundamental for mineral exploration.The most important metalliferous ore deposits are hydrothermal deposits, formed from hot waters circulating in Earth's crust. Such deposits represent a highly efficient trap where fluids were focused into a limited volume of rock, became supersaturated and precipitated ore minerals. In theory, this does not require unusual fluid compositions 1,2 as long as fluid focusing, sufficient fluid flux and efficient precipitation conditions can be maintained. Recently, this paradigm has been challenged by the recognition that ore fluids in sediment-hosted 3-5 , epithermal 6,7 and porphyryrelated [8][9][10] hydrothermal deposits can carry orders of magnitude more metal than previously considered probable, or measured in modern fluid samples. This suggests that our understanding of metal extraction and transport processes is incomplete.Here, this theme is explored by consideration of porphyry ore deposits [11][12][13][14][15] , remarkable geochemical anomalies that can contain up to 1 Gt of sulphur 16 , 200 Mt copper, 2.5 Mt molybdenum and 2600 t gold 17 . The most copper-rich examples include the 4-5 million-year old El Teniente and Rio Blanco-Los Bronces deposits in Central Chile, and the most gold-rich is the 3 million-year old Grasberg deposit in Irian Jaya, Papua New Guinea 17 .Porphyry deposits...

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Triggers for the formation of porphyry ore deposits in magmatic arcs

2013

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“…These are very scattered and seem unlikely to reflect very high melt sulfur concentrations, as the oxidized dacitic melt would be anhydrite saturated at few hundred ppm of S (certainly less than 500 ppm S; Baker and Moretti 2011). Similar S-rich apatites (SO 3 > 0.5 wt%) have been reported in a number of natural systems (Streck and Dilles 1998;Parat et al 2002Parat et al , 2011aStreck et al 2007;Chambefort et al 2008;Van Hoose et al 2013), but could not be synthesized experimentally and remain enigmatic. Their common association with anhydrite-saturated magmas suggests that they might have crystallized from abnormally S-enriched melt pockets (Parat et al 2011a, b).…”

Section: S-rich Apatite Domainsmentioning

confidence: 86%

Amphibole and apatite insights into the evolution and mass balance of Cl and S in magmas associated with porphyry copper deposits

Chelle-Michou

Chiaradia

2017

Contrib Mineral Petrol

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Chlorine and sulfur are of paramount importance for supporting the transport and deposition of ore metals at magmatichydrothermal systems such as the Coroccohuayco Fe-Cu-Au porphyry-skarn deposit, Peru. Here, we used recent partitioning models to determine the Cl and S concentration of the melts from the Coroccohuayco magmatic suite using apatite and amphibole chemical analyses. The pre-mineralization gabbrodiorite complex hosts S-poor apatite, while the syn-and post-ore dacitic porphyries host S-rich apatite. Our apatite data on the Coroccohuayco magmatic suite are consistent with an increasing oxygen fugacity (from the gabbrodiorite complex to the porphyries) causing the dominant sulfur species to shift from S 2− to S 6+ at upper crustal pressure where the magmas were emplaced. We suggest that this change in sulfur speciation could have favored S degassing, rather than its sequestration in magmatic sulfides. Using available partitioning models for apatite from the porphyries, pre-degassing S melt concentration was 20-200 ppm. Estimates of absolute magmatic Cl concentrations using amphibole and apatite gave highly contrasting results. Cl melt concentrations obtained from apatite (0.60 wt% for the gabbrodiorite complex; 0.2-0.3 wt% for the porphyries) seems much more reasonable than those obtained from amphibole which are very low (0.37 wt% for the gabbrodiorite complex; 0.10 wt% for the porphyries). In turn, relative variations of the Cl melt concentrations obtained from amphibole during magma cooling are compatible with previous petrological constraints on the Coroccohuayco magmatic suite. This confirms that the gabbrodioritic magma was initially fluid undersaturated upon emplacement, and that magmatic fluid exsolution of the gabbrodiorite and the pluton rooting the porphyry stocks and dikes were emplaced and degassed at 100-200 MPa. Finally, mass balance constraints on S, Cu and Cl were used to estimate the minimum volume of magma required to form the Coroccohuayco deposit. These three estimates are remarkably consistent among each other (ca. 100 km 3 ) and suggest that the Cl melt concentration is at least as critical as that of Cu and S to form an economic mineralization.

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“…However, titanite is not uncommon in dacites and rhyolites in western North America and the Andes, areas where voluminous high-silica rhyolites are abundant (Ewart 1979;Thompson et al 1986;Best et al 1989;Warren et al 1989;Nakada 1991;Wark 1991;de Silva et al 1994;Chambefort et al 2008). This suggests that Fish Canyon-type magmas, with both titanite and a relatively large liquid fraction, are not uncommon.…”

Section: The Titanite Problemmentioning

confidence: 95%

The Volcanic-Plutonic Connection

Glazner¹,

Coleman²,

Mills³

2015

Advances in Volcanology

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One way to frame the debate about the relationships between volcanic and plutonic rocks is this: are plutons samples of magma that passed through the crust, or residues left behind by extraction of erupted liquids? In the former case plutons are compositionally equivalent to cogenetic volcanic rocks, barring biases introduced by passing through the crustal filter; in the latter they are cumulates, having lost liquid to eruption. These hypotheses make specific predictions about trace-element variations, which we test using global geochemical databases for circum-Pacific convergent margins and western North America. Volcanic rocks are far more abundant in these datasets than plutonic rocks and are biased to more mafic compositions. After subsampling the volcanic dataset to match the plutonic dataset, we find little evidence for significant loss of liquid from plutons. Rather, plutonic and volcanic trace-element patterns are generally indistinguishable. Where distinctions do occur, they are backwards; for example, a higher proportion of plutonic rocks has low Eu, Zr, and Ba, features of fractionated liquids, than volcanic rocks. These observations support the hypothesis that liquids fractionated from crystal-rich magmas are of small volume and are relatively immobile (e.g., aplites). These conclusions, derived from bulk-rock geochemistry, are supported by U-Pb zircon geochronology and field and textural observation. These data support the view that plutonic rocks are texturally modified samples of the same magmas that erupt. Partial melting provides an alternative to crystal fractionation for the origin of high-silica volcanic rocks.

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Anhydrite-bearing andesite and dacite as a source for sulfur in magmatic-hydrothermal mineral deposits

Cited by 94 publications

References 18 publications

Triggers for the formation of porphyry ore deposits in magmatic arcs

Triggers for the formation of porphyry ore deposits in magmatic arcs

Amphibole and apatite insights into the evolution and mass balance of Cl and S in magmas associated with porphyry copper deposits

The Volcanic-Plutonic Connection

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