Pumpellyosite alteration in the oceanic crust as marker of chemically evolved hydrothermal discharge and its relation to volcanogenic massive-sulphide (VMS) deposits

2020 ◽  
Author(s):  
Samuel Weber ◽  
Larryn William Diamond
Keyword(s):  
Reactive Transport ◽  
Genetic Model ◽  
Mineral Exploration ◽  
Massive Sulphide ◽  
Source Rocks ◽  
Black Smoker ◽  
Transport Modelling ◽  
Volcanogenic Massive Sulphide ◽  
Vms Deposits ◽  
Semail Ophiolite

<p>Reactions of seawater and fresh basalts below the seafloor are crucial for the formation of black-smoker type volcanogenic massive sulphide (VMS) deposits. Improved understanding of hydrothermal alteration processes can therefore help to improve the genetic model of VMS deposits, facilitating targeting in mineral exploration. Reactions of downwelling seawater with fresh basalts creates Ca-depleted, Mg- and Na- enriched “spilite” alteration (albite+chlorite+hematite+titanite±augite±epidote±quartz±calcite). The fluid in turn becomes enriched in Ca and depleted in Mg and Na. This chemically evolved, upwelling fluid can create Ca-enriched, Mg- and Na-depleted “epidosite” alteration (epidote+quartz+titanite+hematite). Epidosites have often been proposed as being the source-rocks for metals in VMS deposits. The more rarely described “pumpellyosite” alteration (pumpellyite+quartz+titanite) exhibits a very similar metasomatism to epidosite alteration and is assumed to represent the low-T equivalent of epidosite alteration.</p><p>            We recently discovered large, km<sup>2</sup>-sized areas of pumpellyosite alteration in the Semail ophiolite (Oman), allowing us to study the transition from epidosite to pumpellyosite alteration. We use reactive-transport modelling to investigate the mechanism responsible for the change from epidosite to pumpellyosite alteration. Pumpellyosite alteration was observed up to few meters below the palaeo-seafloor, indicating that evolved fluids discharged directly onto the seafloor. However, no sulphide mineralisation was observed on or below the palaeo-seafloor. This observation makes the involvement of pumpellyosite alteration in the VMS-forming system questionable. The metasomatic fingerprint of pumpellyosite alteration also strongly contrasts with the chlorite-quartz alteration typically found below VMS deposits. Since epidosite and pumpellyosite alteration appear to be genetically linked, epidosites may likewise be unrelated to the genesis of VMS deposits.</p>

scholarly journals Subseafloor sulphide deposit formed by pumice replacement mineralisation

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Tatsuo Nozaki ◽  
◽  
Toshiro Nagase ◽  
Yutaro Takaya ◽  
Toru Yamasaki ◽  
...  
Keyword(s):  
Okinawa Trough ◽  
Precious Metals ◽  
Massive Sulphide ◽  
Void Space ◽  
Sulphide Deposit ◽  
Framboidal Pyrite ◽  
Volcanogenic Massive Sulphide ◽  
Vms Deposits ◽  
Hemipelagic Sediment ◽  
Drill Holes

AbstractSeafloor massive sulphide (SMS) deposits, modern analogues of volcanogenic massive sulphide (VMS) deposits on land, represent future resources of base and precious metals. Studies of VMS deposits have proposed two emplacement mechanisms for SMS deposits: exhalative deposition on the seafloor and mineral and void space replacement beneath the seafloor. The details of the latter mechanism are poorly characterised in detail, despite its potentially significant role in global metal cycling throughout Earth’s history, because in-situ studies require costly drilling campaigns to sample SMS deposits. Here, we interpret petrographic, geochemical and geophysical data from drill holes in a modern SMS deposit and demonstrate that it formed via subseafloor replacement of pumice. Samples from the sulphide body and overlying sediment at the Hakurei Site, Izena Hole, middle Okinawa Trough indicate that sulphides initially formed as aggregates of framboidal pyrite and matured into colloform and euhedral pyrite, which were replaced by chalcopyrite, sphalerite and galena. The initial framboidal pyrite is closely associated with altered material derived from pumice, and alternating layers of pumiceous and hemipelagic sediments functioned as a factory of sulphide mineralisation. We infer that anhydrite-rich layers within the hemipelagic sediment forced hydrothermal fluids to flow laterally, controlling precipitation of a sulphide body extending hundreds of meters.

scholarly journals Igneous Rock Associations 14. The Volcanic Setting of VMS and SMS Deposits: A Review

2014 ◽  
Vol 41 (3) ◽  
pp. 365 ◽  
Author(s):  
Pierre-Simon Ross ◽  
Patrick Mercier-Langevin
Keyword(s):  
Igneous Rock ◽  
Rock Type ◽  
Massive Sulphide ◽  
Pyroclastic Deposits ◽  
Pyroclastic Rocks ◽  
Rock Types ◽  
Volcanogenic Massive Sulphide ◽  
Vms Deposits ◽  
Volcanic Succession

Volcanogenic massive sulphide (VMS) deposits and seafloor massive sulphide (SMS) deposits have a spatial and genetic connection with contemporaneous volcanism. The control exerted by the volcanic succession (e.g. rock type, architecture and facies) on the nature and style of the ore and alteration (e.g. subsea-floor replacement vs. exhalative, or discordant vs. conformable) is significant, making it imperative to understand the local volcanology in developing better genetic and exploration models. Three VMS deposit groupings collectively represent a high proportion of cases: (1) deposits associated with complexes of submarine felsic domes, cryptodomes, lobe-hyaloclastite flows and/or blocky lavas, and their reworked equivalents; (2) deposits associated with thick piles of pumiceous felsic pyroclastic rocks, suggesting a caldera context; and (3) deposits associated with mafic volcanic footwalls and/or with sedimentary hosts, including significant deposits such as Windy Craggy (~300 Mt) in British Columbia. With regard to number (2) above, demonstrating the presence of a caldera in ancient successions can be difficult because silicic calderas tend to be large and exceed the limits of deposit-scale investigations. Furthermore, there is no consensus regarding what a large submarine caldera should look like, i.e., no accepted facies model exists showing the distribution of rock types. But without thick piles of pumiceous felsic pyroclastic deposits, arguing for a large submarine caldera is a challenge.SOMMAIRELes gisements de sulfures massifs volcanogènes (SMV) et leurs équivalents actuels au fonds des mers ont une connexion spatiale et génétique avec le volcanisme. La succession volcanique – composition, architecture, faciès – exerce un contrôle important sur la nature et le style de minéralisation et d’altération hydrothermale (p. ex. minéralisation mise en place par remplacement sous le fond marin vs. exhalative; altération discordante ou plus concordante). Il est donc impératif de connaître la volcanologie des roches encaissantes pour développer de meilleurs modèles génétiques et d’exploration. Trois groupes de gisements couvrant collectivement une grande proportion des cas sont discutés ici. Premièrement, plusieurs gisements sont associés à des complexes de dômes felsiques sous-marins, des cryptodômes, des coulées de type lobes-hyaloclastite et/ou des laves en blocs, ou leur équivalents resédimentés. Deuxièmement, certains gisements sont associés à d’épaisses séquences de roches pyroclastiques felsiques ponceuses, suggérant un contexte de caldeira. Troisièmement, plusieurs gisements sont associés avec des roches volcaniques mafiques et/ou avec des roches sédimentaires, par exemple l’important dépôt de Windy Craggy (~300 Mt) en Colombie-Britannique. Concernant les contextes de type 2, la démonstration d’une caldeira peut être difficile dans les successions anciennes, car les caldeiras felsiques sont de grandes dimensions, excédant les limites des études à l’échelle du gîte. De plus, il n’existe pas de consensus sur un modèle de faciès pour une grande caldeira sous-marine. Mais sans la présence d’épais empilements de roches pyroclastiques felsiques ponceuses, il est difficile d’argumenter en faveur d’une caldeira sous-marine.

scholarly journals Role of metalliferous mudstones and detrital shales in the localization, genesis, and paleoenvironment of volcanogenic massive sulphide deposits of the Tally Pond volcanic belt, central Newfoundland, Canada

2016 ◽  
Vol 53 (4) ◽  
pp. 387-425 ◽  
Author(s):  
Stefanie Lode ◽  
Stephen J. Piercey ◽  
Gerald C. Squires
Keyword(s):  
Base Metal ◽  
Volcanic Belt ◽  
Hydrothermal Activity ◽  
Black Shales ◽  
Massive Sulphide ◽  
Volcanic Stratigraphy ◽  
Volcanogenic Massive Sulphide ◽  
Vms Deposits ◽  
Oxygenated Water ◽  
Structural Blocks

The Cambrian Tally Pond volcanic belt in central Newfoundland contains numerous volcanogenic massive sulphide (VMS) deposits and prospects associated with exhalative metalliferous mudstones. Deposits in the belt are bimodal felsic VMS deposits that are both base metal bearing (e.g., Duck Pond – Boundary), and base metal and precious metal bearing (Lemarchant). At the Lemarchant deposit, metalliferous mudstones are stratigraphically and genetically associated with mineralization. In the remainder of the Tally Pond belt, detrital shales occur predominantly in the northeastern part of the belt (mostly as unrelated mid-Ordovician structural blocks) in the upper sections of the Cambrian volcanic stratigraphy, but locally also are intercalated with metalliferous mudstones. Their relationships to massive sulphides are less obvious, with many spatially, but not necessarily genetically, related to mineralization. Upper Cambrian to Lower Ordovician black shales from Bell Island, which represent pelagic sedimentation not associated with hydrothermal activity and volcanism, are compared with the Tally Pond belt mudstones and shales. Exhalative mudstones, like those at Lemarchant, have elevated Fe/Al and base-metal values, and have shale-normalized negative Ce and positive Eu anomalies, indicative of deposition from high-temperature (>250 °C) hydrothermal fluids within an oxygenated water column. Mudstones and shales sampled from other Tally Pond prospects have more variable signatures, ranging from hydrothermal to nonhydrothermal black shales (no positive Eu anomalies, flat rare earth element patterns, low Fe/Al and base-metal contents), to those that have mixed signatures. Accordingly, mudstones from areas with a Lemarchant-like hydrothermal and vent-proximal character are more attractive exploration targets than mudstones and shales with predominantly detrital signatures.

Geology, mineralogy, S and Sr isotope geochemistry, and fluid inclusion analysis of barite associated with the Lemarchant Zn–Pb–Cu–Ag–Au-rich volcanogenic massive sulphide deposit, Newfoundland, Canada

2020 ◽  
Vol 57 (1) ◽  
pp. 133-166
Author(s):  
Marie-Ève Lajoie ◽  
Stephen J. Piercey ◽  
James Conliffe ◽  
Daniel Layton-Matthews
Keyword(s):  
Fluid Inclusion ◽  
Isotope Geochemistry ◽  
Regional Metamorphism ◽  
Massive Sulphide ◽  
Sr Isotope ◽  
Sulphide Deposit ◽  
Sulphur Isotope ◽  
Volcanogenic Massive Sulphide ◽  
Vms Deposits ◽  
Mineral Scale

Barite in the approximately 513 Ma Lemarchant volcanogenic massive sulphide (VMS) deposit, Newfoundland, consists of granular and bladed barite intimately associated with mineralization. Regardless of type, the composition of barite is homogeneous at bulk rock and mineral scale containing predominantly Ba, S, and Sr, with minor Ca and Na. The barite has homogeneous sulphur isotope compositions (δ34Smean = 27‰), similar to Cambrian seawater sulphate (25–35‰) and Sr isotope compositions (87Sr/86Sr = 0.706905 to 0.707485). These results are consistent with barite having formed from fluid–fluid mixing between Cambrian seawater and VMS-related hydrothermal fluids. The 87Sr/86Sr values in the barite are lower than mid-Cambrian seawater, which suggests that some of the Sr was derived from the underlying Neoproterozoic basement. Fluid inclusions in bladed barite are low-salinity, CO2-rich inclusions with homogenization temperatures between 245°–250 °C, and average salinity of 1.2 wt.% NaCl equivalent. Estimated minimum trapping pressures of between 1.7 to 2.0 kbars were calculated from aqueous–carbonic fluid inclusion assemblages. The fluid inclusion results reflect regional metamorphic reequilibration during younger Silurian regional metamorphism, rather than primary fluid signatures, despite the preservation of primary barite and fluid inclusion textures. These results illustrate that barite in VMS deposits records the physicochemical processes associated with VMS formation and the sources of fluids in ancient VMS deposits, as well as seawater sulphate and basement isotopic compositions. The results herein are not only relevant for the Lemarchant deposit but also for other barite-rich VMS deposits globally.

Evolution of the Paleoproterozoic Snow Lake arc assemblage and geodynamic setting for associated volcanic-hosted massive sulphide deposits, Flin Flon Belt, Manitoba, Canada

1999 ◽  
Vol 36 (11) ◽  
pp. 1789-1805 ◽  
Author(s):  
Alan H Bailes ◽  
Alan G Galley
Keyword(s):  
High Heat ◽  
Massive Sulphide ◽  
Geodynamic Setting ◽  
Hydrous Melting ◽  
Volcanogenic Massive Sulphide ◽  
Vms Deposits ◽  
Mantle Sources ◽  
Flin Flon ◽  
East End ◽  
Fault Scarps

The majority of volcanogenic massive sulphide (VMS) deposits at the east end of the Paleoproterozoic Flin Flon "greenstone" belt occur in the 1.89 Ga Snow Lake arc assemblage. VMS deposits in this isotopically juvenile oceanic arc sequence are hosted within a 6 km thick monoclinal section that records in its stratigraphy and geochemistry a temporal evolution in arc development from primitive, through mature, to arc rift. VMS deposits occur in both the primitive and mature arc sequences and are interpreted to be products of arc extension and accompanying anomolously high heat flow, fracturing, and fluid circulation. Boninites, low-Ti tholeiites, and isotopically juvenile rhyolite flows, a rock association that has been attributed in both modern and Phanerozoic arcs to high-temperature hydrous melting of refractory mantle sources in an extensional and (or) proto-arc environment, forms the primitive arc. Indication that the mature arc also underwent extension includes voluminous volcaniclastic detritus (from fault scarps?), prominent synvolcanic dykes, isotopically juvenile rhyolite flows, and the fact that the mature arc is stratigraphically overlain by arc-rift basalts with MORB-like geochemistry. Interpretation of VMS deposits at Snow Lake as products of an extensional geodynamic setting suggests that the traditional Flin Flon Belt exploration model, invoking "pluton-generated" convective seawater, be augmented by the search for evidence of rifting. Economically significant rock associations at Snow Lake include geochemically primitive refractory mafic magmas (e.g., boninites), isotopically juvenile felsic magmas, bimodal basalt-rhyolite sequences, and arc-rift basalts.

scholarly journals Gold and gold-bearing volcanogenic massive sulphide deposits of the Central Cuba

2021 ◽  
pp. 27-37
Author(s):  
D. De la Nuez Colon ◽  
M. Santa Cruz Pacheco
Keyword(s):  
Gold Deposits ◽  
Massive Sulphide ◽  
The West ◽  
Massive Sulphide Deposits ◽  
Volcanogenic Massive Sulphide ◽  
Vms Deposits ◽  
Gold Silver ◽  
San Fernando ◽  
Copper Zinc ◽  
Sulphide Deposits

Background. Volcanogenic massive sulphide deposits (VMS) are the most important sources of Cu and Zn; they account for a large share of the world production of Pb, Ag, Au, Se, Te, Bi and Sb, as well as small amounts of many other metals. The polymetallic VMS deposits of economic value of varying degrees are known in the rocks of the Los Pasos Cretaceous Formation, Cuba.Aim. To show the potential of the Cretaceous volcanic deposits of Central Cuba for gold, silver, copper, zinc and lead deposit prospecting.Materials and methods. The study characterises the San Fernando, Independencia, Antonio, Los Cerros VMS deposits and the Boca del Toro and El Sol ore occurrences located in the Los Pasos Formation. The similarities and differences in the mineral and elemental composition and structures of the ores of these objects are described, which underlie the assessment of their economic importance.Results. The latitudinal zoning of VMS and noble metal mineralisation of the Central Cuban ore region is outlined. In the west, copper-VMS deposits with accompanying gold ore objects prevail. In the east, copper-zinc VMS deposits with barite and gold-silver objects are widespread.Conclusions. It is necessary to assume the different erosional sections corresponding to the blocks of the Cretaceous volcanic arc of Central Cuba, which is larger in the west and smaller in the east. Proceeding from the presence of veinlet gold ores, their confinement to tectonic zones and the lack of correlation between noble and chalcophile metals at the San Fernando deposit, as well as significantly different gold-silver ratios in the considered ore objects, it could be assumed that some of the gold-silver ores were formed after VMS. The obtained Au/Ag ratios are close to the ores of the high sulphidation type (high sulphide ores) from similar ore regions of Venezuela and the Kur-il island arc. In this regard, one can expect hidden gold deposits in the west and gold-silver deposits in the east of the studied area.

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