The Pefka Cu-Au-Te In Se and nearby St Philippos Pb-Zn-Bi-Sn-Ge-Ga-In
vein- and breccia-type deposits in western Thrace, Greece, display
strong similarities, but also differences in terms of mineralization
style, ore mineralogy, and chemistry, and host rock compositions. The
Pefka mineralization consists of two crosscutting vein systems with high
sulfidation (HS)- and intermediate-sulfidation (IS) assemblages hosted
by andesitic lavas and is unusually enriched in In (up to 700 ppm), Te
(>1000 ppm), Se (>100 ppm), and Cu (>1 wt%). The main In-carriers are
roquesite (CuInS2) and In-bearing “tennantite-(Cu)” and Cu-rich
“tennantite-(In)” which contains up to 6.5 wt% In, substituting
into the C site. Roquesite is associated with enargite and
arsenosulvanite/colusite, as part of the HS assemblage at Pefka.
Selenium-bearing galena and a large suite of tellurides including
calaverite, sylvanite, petzite, hessite, kostovite, empressite,
tellurantimony, and coloradoite, in addition to native tellurium,
account for the marked tellurium and selenium enrichment in the ores
from Pefka. Tellurides and native gold at Pefka accompany the
precipitation of Te-bearing minerals of the tetrahedrite group, such as
“stibiogoldfieldite” and “arsenogoldfieldite”, and Cu-excess
varieties of tetrahedrite and tennantite. However, the bulk of telluride
deposition is associated with normal, fully substituted
tetrahedrite-tennantite varieties.
The St Philippos deposit is associated with a brecciated fault zone
hosted by Eocene sandstones and Oligocene quartz-feldspar porphyry
dikes. It is enriched in a large suite of incompatible elements,
including Bi (>2000 ppm), Sn (>100 ppm), U (up to 200 ppm), Pb (>1
wt%), Zn (>1 wt%), Mo (up to 62 ppm), Ge (>100 ppm), Ga (up to 466
ppm) and In (up to 222 ppm), contrasting with the element suite defining
the nearby Pefka deposit. The main carrier of In, Ga, and Ge is
sphalerite (and wurtzite) with In-rich zones in sphalerite containing up
to 6.1. wt% In. Germanium and Ga in sphalerite reach concentrations of
up to 0.27 and 0.32 wt%, respectively. Sphalerite from the St Philippos
deposit is extremely Fe-poor (<0.04 wt%), and is associated with an
unusual suite of Sn-bearing sulfosalts (kesterite-stannite, Mn-bearing
kesterite, unnamed Cu2MnSnS4), and enargite, marking an early HS event.
Kesterite also hosts indium (up to 0.6 wt% In). Mn-bearing varieties of
tennantite host inclusions of minor tellurides (e.g., hessite, altaite,
and tsumoite) and formed later in the paragenetic sequence under
transitional HS-IS and IS conditions.
Both deposits are characterized by early high-temperature (>300 degrees
C) and HS fluid conditions, followed by IS assemblages as temperatures
waned. Rhyolitic oxidized magmas are considered to be the sources of
metals in the St Philippos deposit; however, their anomalous W, Sn, U,
and Bi contents suggest a contamination by crustal rocks. The Cu-Au-Te
signature of the Pefka deposit is compatible with a genetic relationship
to less fractionated andesitic magmas, although a possible contribution
of In from rhyolitic magmas could explain the high In contents of the
ore. However, other factors, as for example different metal-deposition
mechanisms resulting in metal zonation around causative porphyry centers
at depth, may also account for the observed metal endowment in these two
deposits. The Sn-Te-In-(Ge-Ga) element association at Pefka and St
Philippos is unusual in that it has been previously reported from only a
few other places in the world (e.g., Capillitas deposit, Argentina, and
the Kawazu deposit, Japan). We conclude based on this exotic
mineralization-style that the northeastern part of Greece represents an
area of great potential for the exploitation of critical metals and
metalloids.
(EN)
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