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.

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.

scholarly journals Selenium and tellurium resources in Kisgruva Proterozoic volcanogenic massive sulphide deposit (Norway)

2018 ◽  
Vol 99 ◽  
pp. 411-424 ◽  
Author(s):  
Liam A. Bullock ◽  
Magali Perez ◽  
Joseph G. Armstrong ◽  
John Parnell ◽  
John Still ◽  
...  
Keyword(s):  
Massive Sulphide ◽  
Massive Sulphide Deposit ◽  
Sulphide Deposit ◽  
Volcanogenic Massive Sulphide

Silver and silver-bearing minerals at the Um Samiuki volcanogenic massive sulphide deposit, Eastern Desert, Egypt

2004 ◽  
Vol 39 (5-6) ◽  
pp. 608-621 ◽  
Author(s):  
Ibrahim M. Shalaby ◽  
Eugen Stumpfl ◽  
Hassan M. Helmy ◽  
Mahmoud M. El Mahallawi ◽  
Omar A. Kamel
Keyword(s):  
Eastern Desert ◽  
Massive Sulphide ◽  
Massive Sulphide Deposit ◽  
Sulphide Deposit ◽  
Volcanogenic Massive Sulphide

Alteration and ore-forming processes at Mattagami Lake Mine, Quebec

1978 ◽  
Vol 15 (1) ◽  
pp. 1-21 ◽  
Author(s):  
R. Gwilym Roberts ◽  
Eric J. Reardon
Keyword(s):  
Water Flux ◽  
High Water ◽  
Massive Sulphide ◽  
Sulphide Deposit ◽  
Seawater Chemistry ◽  
Thermally Induced ◽  
Volcanic Material ◽  
Volcanogenic Massive Sulphide ◽  
Significant Chemical ◽  
Chemical Sediments

The altered rocks of the Mattagami Lake Mine, a stratabound, volcanogenic, massive sulphide deposit, were examined using whole rock analyses and electron microprobe studies of the constituent minerals. The significant chemical and mineralogical transformations involved in the progressive alteration of the footwall, vitroclastic tuff of rhyodacitic composition, are: (1) the removal of alkalies (sodium followed by potassium), and the addition of magnesium and iron during initial chloritization; (2) substantial removal of silica by the solution of quartz, to produce a chlorite-rich rock, and (3) gradual removal of aluminum and the transformation of chlorite (Mg2.5 Fe2.5Al2Si3O10(OH)8) to talc (MG2.5FE0.5Si4O10(OH)2 to produce units of talc–actinolite schist. The reaction: 3 chlorite + 10H2S(g) + 2.5 O2 + 11,H4SiO4 + 5Mg2+ = 5talc + 5pyrite + [Formula: see text] + 19H2O + 16H+ (log K, 25 °C = +145; log K, 100 °C = +102; log K, 250 °C = +68.2) is favoured by high temperature and Mg2+ activity, and low activity of aluminum.The alteration pipe zone immediately beneath the orebody is assumed to have been the discharge site of a thermally induced, convective flow system. The upper part of the system would have been characterized by the movement of seawater, of comparatively short residence time in the rocks, to areas of discharge. Under conditions of high permeability and high water flux in these zones, bulk seawater composition of comparatively high magnesium and low aluminum concentrations would ultimately control the composition of the volcanic material by the formation of alteration products in equilibrium with it, rather than the volcanic material significantly affecting the seawater chemistry. This would ensure the early development of magnesian chlorite in the vitric tuff. The transformation chlorite to talc took place at discharge sites, the locations of highest surface temperatures, under hydrologic conditions such that the flux rate was sufficiently high to remove the comparatively immobile aluminum.The massive sulphide units were emplaced in association with the development of talc. Layered pyrite–sphalerite, overlying and extending beyond talc units are chemical sediments.

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