1?1: Porphyry Cu?Au and epithermal Au?Ag deposits ... - geo.edu.ro

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Box 1-1
1–1: <strong>Porphyry</strong> <strong>Cu</strong>–<strong>Au</strong> <strong>and</strong> <strong>epithermal</strong> <strong>Au</strong>–<strong>Ag</strong> <strong>deposits</strong> in the southern
Apuseni Mountains, Romania
South Apuseni Mountains district: Lat. 46°03’ N, Long. 22°58’ E
K. Kouzmanov a *, P. Ivăşcanu b , G. O’Connor c
a Isotope Geology <strong>and</strong> Mineral Resources, ETH, Sonneggstrasse 5, 8092 Zurich, Switzerl<strong>and</strong>
b Geological Institute of Romania, Caransebes Str.1, 78344 Bucharest, Romania
c Gabriel Resources Ltd, Suite 1501, 110 Yonge St, Toronto, ON, M5C 1T4, Canada
Fig. 1. Geological map of the South Apuseni Mountains
district showing distribution of porphyry <strong>Cu</strong> <strong>and</strong> spatially
related <strong>epithermal</strong> <strong>Au</strong>–<strong>Ag</strong> <strong>deposits</strong>; modified from
Bostinescu (1984).
Producing mining district: mining in the district
has been active for almost 2,000 years <strong>and</strong> is
documented from pre-Roman times Some of the
main <strong>deposits</strong> are: Roşia Montană, Roşia Poieni,
Received 19 November 2004, accepted 1 May 2005
Barza–Musariu (Brad district), Săcărîmb, Deva <strong>and</strong>
Certej (Fig. 1).
Mining: Underground <strong>and</strong> open pits.
Commodities: <strong>Au</strong>, <strong>Ag</strong>, <strong>Cu</strong>, Zn, Pb.
Annual production: exact past <strong>and</strong> present
production figures are impossible to establish.
Resources: Roşia Montană <strong>epithermal</strong> <strong>Au</strong>–<strong>Ag</strong>
deposit (Fig. 2): 400.4 Mt @ 1.3 g/t <strong>Au</strong>, 6 g/t <strong>Ag</strong>;
total resources 16.1 Moz of <strong>Au</strong> <strong>and</strong> 73.3 Moz of <strong>Ag</strong>.
Roşia Poieni porphyry <strong>Cu</strong> deposit: 431 Mt @
0.55%<strong>Cu</strong>, 0.25 g/t <strong>Au</strong>. Bucium–Tarnita porphyry <strong>Cu</strong>
deposit: 335 Mt @ 0.50%<strong>Cu</strong>, 0.36 g/t <strong>Au</strong>. Certej
<strong>epithermal</strong> <strong>Au</strong>–<strong>Ag</strong> deposit: 61.1 Mt @ 1.79 g/t <strong>Au</strong>,
10 g/t <strong>Ag</strong> (3.46 Moz <strong>Au</strong>, 18.2 Moz <strong>Ag</strong>). Rodu–
Frasin <strong>epithermal</strong> <strong>Au</strong>–<strong>Ag</strong> deposit: 35.2 Mt @ 1.12
g/t <strong>Au</strong>, 3 g/t <strong>Ag</strong> (1.22 Moz <strong>Au</strong>, 2.92 Moz <strong>Ag</strong>).
Type: porphyry copper–gold <strong>and</strong> <strong>epithermal</strong> low- to
intermediate-sulphidation <strong>Au</strong>–<strong>Ag</strong>±Te <strong>deposits</strong>.
Morphology: <strong>Porphyry</strong> mineralization is hosted
mainly by subvolcanic <strong>and</strong>esitic bodies <strong>and</strong> forms
stockworks, disseminations <strong>and</strong> impregnations <strong>and</strong>
sometimes occurs as breccia infill (Fig. 3).
Epithermal mineralization is developed mainly as
steeply dipping veins or hydrothermal breccia zones
crosscutting basement rocks, <strong>and</strong>esitic lavas,
subvolcanic intrusions <strong>and</strong> Cretaceous or Tertiary
sediments. Minerals in <strong>epithermal</strong> veins occur in
open-space filling <strong>and</strong> crustiform textures.
Telescoping of porphyry <strong>and</strong> <strong>epithermal</strong>
mineralization is common.
<strong>Ag</strong>e of mineralization: porphyry mineralization is
contemporaneous with associated Miocene
magmatism (see below); <strong>epithermal</strong> mineralization
post-dates the porphyry-type ore formation.
Ore minerals: chalcopyrite, gold, electrum ±
sphalerite, galena, tellurides in the <strong>epithermal</strong>
<strong>deposits</strong>; bornite in the porphyry-type <strong>deposits</strong>.
Alteration: potassic, phyllic to argillic in the
porphyry copper <strong>deposits</strong>; propylitic, quartz–
* corresponding author: e-mail kouzmanov@erdw.ethz.ch
0169-1368/$ - see front matter D 2005 Elsevier B.V. All rights reserved.
doi:10.1016/j.ore<strong>geo</strong>rev.2005.07.030

Box 1-1 47
Fig. 2. E–W cross-section through the diatreme-hosted Roşia Montană <strong>Au</strong>–<strong>Ag</strong> deposit (from O’Connor et al., 2003).
Mineralization occurs within an intermediate-sulphidation style <strong>epithermal</strong> mineralized system, hosted by dacitic intrusions
<strong>and</strong> associated phreato-magmatic breccias.
Fig. 3. NE–SW cross-section through the Deva porphyry
<strong>Cu</strong>–<strong>Au</strong> deposit, consisting of cylindrical 0.5 km diameter
breccia-hosted subvolcanic stock. Mineralization consists
of bornite–chalcopyrite–magnetite stringers <strong>and</strong>
impregnations, producing ore grade up to 2%<strong>Cu</strong>.
adularia–illite to argillic in the <strong>epithermal</strong> <strong>deposits</strong>.
<strong>Ag</strong>e of host rocks: Miocene, 14.7 to 7.4 Ma, based
on K–Ar dating on whole rock (Roşu et al., 2004).
Nature of host rocks: calc-alkaline <strong>and</strong>esites to
dacites, mainly <strong>and</strong>esites, with subordinate
occurrences of alkaline affinity. Existing stable
isotope analyses (O, H, S, C; Alderton <strong>and</strong> Fallick,
2000), combined with recent LA–ICP–MS analyses
of fluid inclusions from porphyry <strong>and</strong> <strong>epithermal</strong>
systems in the southern Apuseni Mountains, support
the concept of a dominant magmatic component in
the hydrothermal fluids of both deposit types.
References
Alderton, D.H.M., Fallick, A.E., 2000. The nature <strong>and</strong>
genesis of gold–silver–tellurium mineralization in the
Metaliferi Mountains of western Romania: Economic
Geology 95, 495–515.
Bostinescu, S., 1984. <strong>Porphyry</strong> copper systems in the
South Apuseni Mountains, Romania. Annuaire de
l'Institut de Géologie et Géophysique 64, 163–174.
O’Connor, G.V., Minut, A., Leary, S.F., 2003. The
<strong>geo</strong>logy <strong>and</strong> exploration of the Roşia Montană gold
deposit, Roşia Montană, Transylvania, Romania. In:
Eliopoulos, D.G. et al. (Eds.), Mineral Exploration <strong>and</strong>
Sustainable Development. Millpress, Rotterdam 2, pp.
1213–1216.
Roşu, E., Seghedi, I., Downes, H., Alderton, D.H.M.,
Szakacs, A., Pecskay, Z., Panaiotu, C., Panaiotu, C.E.,
Nedelcu, L. 2004. Extension-related Miocene calcalkaline
magmatism in the Apuseni Mountains,
Romania: Origin of magmas. Schweizerische
Mineralogische und Petrographische Mitteilungen 84,
153–172.