Zone refinement related to the mineralization process as evidenced by mineralogy and element geochemistry in a chimney fragment from the Southwest Indian Ridge at 49.6°E

Investigation of the Internal Structure of a Modern Seafloor Hydrothermal Chimney With a Combination of EBSD, EPMA, and XRD

“…The columnar growth evident in this phase in Figure 12b indicates directional crystallization from edge to center (Kurz & Fisher, 1998). It is possible that this phase has precipitated from a supersaturated solution after dissolution of the sulfide matrix in the manner suggested by Yuan et al (2018). By contrast, the chalcopyrite grains (e.g., Figure 11) do not seem to show the same columnar growth.…”

“…This grain shows columnar growth from the edge of the grain to the center which would seem to suggest that this grain has formed after the sphalerite. The process where solid areas that have already precipitated are subject to dissolution by hot hydrothermal fluids and subsequent precipitation of new phases such as pyrite and chalcopyrite has been documented in the literature (Yuan et al, 2018). The columnar growth evident in this phase in Figure 12b indicates directional crystallization from edge to center (Kurz & Fisher, 1998).…”

“…Prior to 2002, they provided 22% of its Zn, 6% of its Cu, 9.7% of its Pb, and 8.7% of its Ag (Galley et al, 2007). While it is known that these deposits form originally from hydrothermal activity on the sea floor (Herzig & Hannington, 1995; Galley et al, 2007; Shanks & Thurston, 2012; Boschen et al, 2013; Yuan et al, 2018), the precise details of the original structure and ore-forming processes of the ore body are sometimes difficult to understand since these have been obscured by metamorphism, hydrothermal alteration, and significant tectonic upheaval over millions of years since their formation (Herzig & Hannington, 1995; Perfit et al, 1999; Shanks & Thurston, 2012). Understanding the ore-forming processes is important since this helps identify mineral associations for the ore body which can, in turn, assist in the search for new deposits.…”

“…It has been postulated that modern, active, sea floor hydrothermal vents, also known as black smokers when actively venting (Hu et al, 2019), are modern analogs of the ancient deposits. By understanding how these vents and their associated chimneys form, their mineralogy, their associations with particular hydrothermal vent types, and their respective geological settings, we can begin to reconstruct the original ore-forming processes of ancient VMS deposits (Herzig & Hannington, 1995; Humphris et al, 1995; Shanks & Thurston, 2012; Yuan et al, 2018).…”

He–Ar–S Isotopic Compositions of Polymetallic Sulphides from Hydrothermal Vent Fields along the Ultraslow-Spreading Southwest Indian Ridge and Their Geological Implications

“…In particular, because of their remote locations, ancient and active hydrothermal systems on the ultraslow-spreading Southwest Indian Ridge (SWIR) have been much less extensively explored until recently [19][20][21][22][23][24][25], when compared to those well-investigated vent sites located along the fast-spreading East Pacific Rise (EPR), and the slow-spreading Mid-Atlantic Ridge (MAR) [1][2][3][4]. Although preliminary geochemical analyses of sulphide samples and the sporadic occurrence of gold have been reported in several newly discovered hydrothermal fields near the SWIR 49 • -51 • E region [26][27][28][29][30], there is only little data on the physicochemical properties of local vent fluids which may be distinct from other categories of ocean ridges [31]. Furthermore, what was the source of ore-forming fluids in such a unique geologic setting, and how did the fluids evolve through multiple stages of hydrothermal circulation, remain poorly understood.…”