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Geological Society, London, Special Publications
doi: 10.1144/SP402.2
 2014, v.402;Geological Society, London, Special Publications
Evandro L. Klein
sources, and mechanisms of Au transport and
Brazil: a review of the physico-chemical properties, 
Ore fluids of orogenic gold deposits of the Gurupi Belt,
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© The Geological Society of London 2014
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Ore fluids of orogenic gold deposits of the Gurupi Belt, Brazil: a
review of the physico-chemical properties, sources, and
mechanisms of Au transport and deposition
CPRM/Geological Survey of Brazil. Av. Dr. Freitas, 3645, Belém, State of Pará,
Brazil, CEP: 66095-110 (e-mail: evandro.klein@cprm.gov.br)
Abstract: The Neoproterozoic Gurupi Belt in northern Brazil developed at the southwestern
margin of the Palaeoproterozoic São Luı́s-West Africa Craton. Orogenic gold deposits of this
belt are hosted in Palaeoproterozoic (2160–2147 Ma) metavolcano-sedimentary and calc-alkaline
granitoid rocks formed in arc and/or back-arc settings during a protracted Rhyacian orogeny
(2240–2080 Ma). These host rock assemblages were tectonically and isotopically reworked
during the Neoproterozoic and represent the reworked margin of the craton, that is, the external
domain of the Neoproterozoic (Brasiliano-Pan African) orogen. The location of the gold deposits
is controlled by the Tentugal shear zone, which represents the tectonic boundary between craton
and the Gurupi Belt, and its subsidiary structures. Gold occurs in veins and in association with
pyrite, and subordinately arsenopyrite and chalcopyrite, in strongly altered and variable deformed
host rocks. Geological characteristics, petrographic, fluid inclusion, and isotopic evidence indicate
near-neutral, reduced aqueous-carbonic metamorphic fluids, with local contributions from host
rocks at the deposit site. Ore deposition occurred at about 300–370 8C and up to 3 kbars in
response to fluid immiscibility and fluid-rock reactions (sulphidation, desulphidation, carbonatiza-
tion, CO2 removal) and local fluid mixing and oxidation.
The Gurupi Belt is a Neoproterozoic mobile belt
developed at the southwestern margin of the São
Luı́s-West African Craton (Fig. 1) during the
Brasiliano-Pan African cycle of orogenesis (see
Klein & Moura 2008 for a review). Gold is the
main known mineral resource in this belt, and the
metal has intermittently been mined by artisanal
miners since the 17th century. There is no official
historical record on the artisanal production, but
unofficial data indicate over 16 t of gold has been
extracted from Chega Tudo, Serrinha, and Cacho-
eira. To date, more than 120 gold occurrences are
reported, in addition to more developed deposits
(Klein & Lopes 2011). The known gold resources
of four deposits are equal to about 120 t Au
(Table 1), which will be mined in open pit. The
opening of the first organized, industrial operation
is planned to occur at Cipoeiro.
In the last decade efforts have been made to
improve the understanding of the geological evol-
ution of the Gurupi Belt (Ribeiro 2002; Klein
et al. 2005b; Teixeira et al. 2007; Klein & Lopes
2009, 2011; Palheta et al. 2009) and of individual
deposits (Torresini 2000; Ribeiro 2002; Yamaguti
& Villas 2003; Klein et al. 2005a, 2006, 2007,
2008b). Results provided constraints on: (1) the
nature and age of the host rocks; (2) the nature of
the hosting structures; (3) the composition of the
ore fluids; and (4) the T–P conditions of ore depo-
sition. An integration of these studies is presented
in this review, which attempts to link geological
processes documented at the provincial scale with
those documented in individual deposits. Special
attention will be given to the circulation of fluids
that have led to the formation of the deposits, espe-
cially the evaluation of the mechanisms of gold
transport and deposition. Other parameters that are
critical for the development of genetic models
have not yet been determined. Such parameters are
mostly dependent on the absolute age of gold depo-
sition, and also include the tectonic setting of ore
formation. A brief discussion of these issues is
addressed throughout the review.
Geological overview
São Luı́s cratonic fragment
Considering that a significant part of the Gurupi
Belt is made of reworked units of the São Luı́s
cratonic fragment (Fig. 1), the geology and evol-
ution of this cratonic fragment is briefly outlined
here (based on Klein et al. 2008a, 2009, 2012;
Palheta et al. 2009). Three main stratigraphic units
crop out in the cratonic area (Fig. 1a). The oldest
rocks known in the São Luı́s cratonic fragment
belong to the Aurizona Group, which is an island
arc-related metavolcano-sedimentary sequence of
2240 + 5 Ma that was intruded by shallow grano-
phyric rocks at 2214 + 3 Ma and by the juvenile,
From: Garofalo, P. S. & Ridley, J. R. (eds) 2014. Gold-Transporting Hydrothermal Fluids in the Earth’s Crust.
Geological Society, London, Special Publications, 402, 121–145.
First published online March 19, 2014, http://dx.doi.org/10.1144/SP402.2
# The Geological Society of London 2014. Publishing disclaimer: www.geolsoc.org.uk/pub_ethics
 by guest on August 7, 2014http://sp.lyellcollection.org/Downloaded from 
Fig. 1. (a) Location of the São Luı́s cratonic fragment and Gurupi Belt (hatched). For the sake of scale, only the major
rock units of the São Luı́s cratonic fragment are considered here. (b) Simplified geological map of the Gurupi Belt
showing the main gold deposits and showings.
E. L. KLEIN122
 by guest on August 7, 2014http://sp.lyellcollection.org/Downloaded from 
subduction-related, metaluminous to slightly pera-
luminous calc-alkaline granitoids developed in an
island arc between 2168 and 2147 Ma. These gran-
itoids form batholiths and stocks that are included
in the Tromaı́ Intrusive Suite, which comprise
mainly tonalites and granodiorites and subordi-
nated quartz-diorite, monzogranite, and syenogra-
nite. Minor units, which do not appear in the scale
used in Figure 1a, include andesites, dacites, felsic
tuffs, and subordinately basic volcanic rocks depos-
ited over the Aurizona Group and the Tromaı́ Suite
at 2164–2160 Ma. These volcanic associations
have metaluminous to peraluminous, high-K calc-
alkaline to tholeiitic signature and have been inter-
preted to have formed in mature or transitional
arc with minor back-arc component and active
continental margin, respectively. Peraluminous,
collision-type granites of c. 2100 Ma belong to the
Tracuateua Intrusive Suite, crop out in the western
portion of the cratonic area and are covered by Pha-
nerozoic sequences. Late- to post-orogenic small
plutons of highly evolved/shoshonitic granite of
2056–2076 Ma and are the youngest rocks known
so far in the São Luı́s cratonic fragment.
Based on rock association, geochronology, and
on geochemical and Nd isotope signatures, these
Palaeoproterozoic associations of the São Luı́s cra-
tonic fragment are interpreted as a section of the
Rhyacian orogen, which records an accretionary
stage at 2240–2150 Ma and a collisional stage at
c. 2100 Ma (Klein et al. 2008a, 2009, 2012). This
scenario correlates with what is described for
similar successions of the Eburnean-Birimian ter-
ranes of the West-African Craton (Klein & Moura
2008 and references