Hydrothermal Deposits - Metals and Society: An Introduction to Economic Geology - page 86

Table 4.2 Different types of VMS deposits
Type Lithological

association

Tectonic setting Metals Examples

Bimodal-
mafic

Dominantly mafic
volcanic but with
up to 25%felsic
volcanic stata

Volcanic arcs
(rifted) above
intra-oceanic
subduction zones

Cu-Zn Noranda, Abitibi

belt, Canada -
Archean; Flin-
Flon, Canada -
Proterozoic; mid
and south Urals,
Russia -
Phanerozoic

Mafic Ophiolite sections of

basaltic lavas
with minor
boninite, cherts
and mafic tuffs

Mature intra-oceanic
back-arcs

Cu- (Zn) Southern Urals;

Newfoundland;
Troodos in
Cyprus

Pelitic-
mafic

Basaltic lavas and
sills and equal or
greater amounts
of pelitic
sedimenary rocks

Mature, juvenile and
accreted backarc

Cu-Zn-Pb Outokumpo, Finland

- Proterozoic;
Windy Craggy,
Canada -
Paleozoic;
Besshi, Japan -
Mesozoic

Bimodal-
felsic

Felsic volcanic and
terrigenous
sedimentary
rocks in near-
equal proportions

Continental margin
arcs and related
backarcs

Cu-Zn-Pb Bergslagen, Sweden -

Proterozoic;
Tasman orogen,
Australia -
Paleozoic

Siliciclastic-
felsic

Felsic volcanoclastic
rocks and high-
level intrusions;
minor mafic lavas
and chemical
sediments

Mature
epicontinental
backarcs

Cu-Zn-Pb Golden Grove,

Australia -
Archean; Iberian
pyrite belt, Spain
and Portugal;
Bathurst, Canada

cold seawater, which drastically decreases the metal solubility, leading to the
precipitation of metal sulfides, together with barite, anhydrite and silica. Some of
the sulfides accrete around the hydrothermal vents to build chimneys that reach 10's
of metres high before they crash down to form a layer of sulfide debris mixed with
precipitated chemical sediment on the seafloor. This layer has low permeability and
hinders the ascent of fluid to the surface; the trapped fluid accumulates beneath the
seafloor where it mixes with seawater and precipitates more sulfide. In this manner
the main tabular or lens-shaped body of massive sulfide is built up. Some of the
fluid escapes to form a hydrothermal plume that ascends many hundreds of metres
around the black smoker and precipitates sulfide particles that settle out to form
bedded “exhalative” sediments around the site. The stockwork beneath the ore body
forms as high-temperature hydrothermal fluid interacts with wallrocks and seawater
in the conduits that transfer the fluid to the surface.