Subseafloor sulphide deposit formed by pumice replacement mineralisation

Abstract

Seafloor 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.

Mineralogy and mineral chemistry of the ABM replacement-style volcanogenic massive sulfide deposit, Finlayson Lake district, Yukon, Canada

“…In replacement-style deposits, metal zonation follows the same sequence as in exhalative- and mound-style deposits with interiors dominated by Cu and exterior portions of the lenses being enriched in Zn, Pb, and Ba (Knuckey et al 1983 ; Lydon 1988 ), albeit with different geometries that reflect the porosity and permeability of the host rocks that controlled the subsurface hydrothermal fluid flow. In particular, the metal zonation is more pronounced laterally than vertically in replacement-style mineralization (Bradshaw et al 2008; Piercey et al 2014 ; Nozaki et al 2021 ). The metal distribution within the massive sulfide mineralization in the ABM zone has Cu-rich zones at the center of the mineralized lenses, overlapping with Zn-rich zones at the margins of the lenses (Figs.…”

Tidally modulated temperature observed atop a drillsite at the Noho hydrothermal site, mid-Okinawa Trough

“…Trough (e.g., Glasby and Notsu, 2003;Halbach et al, 1989;Ishibashi & Urabe, 1995;Ishibashi et al, 2015;Kawagucci et al, 2010;Kimura et al, 1988;Kinoshita & Yamano, 1997;Kinoshita et al, 1990;Nozaki et al, 2021aNozaki et al, , 2021cSakai et al, 1990;Takai et al, 2011Takai et al, , 2012Yamano et al, 1989). According to Masaki et al (2011), who analyzed heat flow data from 78 sites in the manuscript submitted to Journal of Geophysical Research: Solid Earth Iheya-North hydrothermal field in the mid-Okinawa Trough obtained by remotely operated vehicle (ROV) dive surveys, heat flow within the active hydrothermal area varies greatly from 0.01 to 10 W/m 2 whereas heat flow on the eastern sedimented slope is 0.1-1 W/m 2 .…”

Automated Detection of Hydrothermal Emission Signatures From Multibeam Echo Sounder Images Using Deep Learning

“…deposits are rich in various base, precious, and critical metals [1, 2, 7−9], they have attracted attention as potential sources of minerals that are essential for sustainable society in the future [2,10,11]. Moreover, seafloor massive sulfide deposits also attract attention as an analogue of metal deposits on land that formed over a geological time scale of hundreds of millions of years [7]. Thus, the study of submarine hydrothermal deposits is important both to thoroughly understand the resources that humankind utilizes at present and to secure resources that humankind will require in the future.…”