Volcanogenic Massive Sulphide (VMS) Deposits Practice Flashcards

Flashcards covering the definition, tectonic settings, classification, production statistics, and geological attributes of Volcanogenic Massive Sulphide (VMS) deposits based on the lecture notes by Galley, Hannington, and Jonasson.

What are volcanogenic massive sulphide (VMS) deposits and how do they form?

VMS deposits are lenses of polymetallic massive sulphide that form at or near the seafloor in submarine volcanic environments from metal-enriched fluids associated with seafloor hydrothermal convection.

What are the primary and significant secondary metals sourced from VMS deposits?

They are major sources of $Zn$, $Cu$, $Pb$, $Ag$, and $Au$, and significant sources for $Co$, $Sn$, $Se$, $Mn$, $Cd$, $In$, $Bi$, $Te$, $Ga$, and $Ge$.

What common tectonic feature is shared by all VMS deposit types?

VMS deposits are formed in extensional tectonic settings, including oceanic seafloor spreading and arc environments.

What are the two primary physical components of most VMS deposits?

1. A mound-shaped to tabular, stratabound body composed principally of massive ($>40\text{\text{\%}}$) sulphide; 2. Discordant to semi-concordant stockwork vein systems (known as "pipes").

How are VMS deposits classified into groups?

They are classified according to base metal content ($Cu-Zn$, $Zn-Cu$, and $Zn-Pb-Cu$), gold content, or host-rock lithology.

In the classification system by Poulsen and Hannington (1995), how is an "Au-rich" VMS deposit defined?

An "Au-rich" VMS deposit is arbitrarily defined as one in which the abundance of $Au$ in $\text{ppm}$ is numerically greater than the combined base metals ($Zn + Cu + Pb$) in $\text{wt.\text{\%}}$.

What are the six groups of VMS deposits based on host lithology as per Barrie and Hannington (1999) and Franklin et al. (2005)?

Bimodal-mafic, mafic-backarc, pelitic-mafic, bimodal-felsic, felsic-siliciclastic, and hybrid bimodal felsic.

What is the age range of submarine volcanic terranes where VMS deposits are found?

They range in age from $3.4\text{ Ga}$ (Archean Pilbara Block) to modern seafloor environments where deposits are actively forming today.

Which geological province in Canada contains the largest number of VMS deposits?

Quebec ($33\text{\text{\%}}$), followed by Manitoba ($15\text{\text{\%}}$), Newfoundland ($12\text{\text{\%}}$), British Columbia ($10\text{\text{\%}}$), Ontario ($9\text{\text{\%}}$), and New Brunswick ($9\text{\text{\%}}$).

What is the distinction between a "giant" and a "supergiant" VMS deposit?

Giant VMS deposits are the upper $1\text{\text{\%}}$ of the world's VMS deposits in terms of original reserves (over $100\text{ Mt}$); supergiant deposits contain more than $150\text{ Mt}$.

What is the largest known Canadian VMS deposit by tonnage?

The $297\text{ Mt}$ Windy Craggy deposit.

What causes the clustering of VMS deposits into major mining camps?

Clustering is attributed to a common heat source, such as subvolcanic intrusions, that triggers large-scale subseafloor fluid convection systems.

Describe the regional stratified alteration zones from bottom (intrusion contact) to top (seafloor).

1. Amphibolite-facies assemblies ($Fe-Ca$-rich); 2. Na-Ca-rich greenschist-facies; 3. Zeolite-clay and subgreenschist mineral assemblages ($K-Mg$-rich).

What are "exhalites" and how do they form?

Exhalites (ferruginous chemical sediments) are thin, areally extensive units formed from the exhalation of fluids and distribution of hydrothermal particulates on the seafloor.

How does the "zone refining" process internal to a VMS mound work?

Hydrothermal fluid flow through the mound remobilizes metals along a temperature gradient, creating a $chalcopyrite + pyrrhotite$-rich core and a sphalerite + pyrite \text{\textpm} galena-rich outer zone.

What chemical characteristic of felsic volcanics indicates prospective VMS-hosting arc terranes?

They are characterized by low $Zr/Y$ ratios ($< 7$), low $(La/Yb)_N$ ratios ($< 6$), and elevated $Zr$ contents ($> 200\text{ ppm}$).

In upper greenschist-amphibolite metamorphic terranes, what minerals define VMS alteration zones?

Chloritoid, garnet, staurolite, kyanite, andalusite, phlogopite, and gahnite.