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Geology of giant quartz veins and their host rocks from the Eastern Pyrenees (Southwest Europe)


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Giant Quartz Veins (GQVs) are ubiquitous in different tectonic settings and, besides being often related to hydrothermal ore deposits, also represent large-scale fingerprints of the structural and geochemical history of the rocks in which they are hosted. Here we present detailed geological maps and interpretations of three key areas of the Eastern Pyrenees where GQVs are well exposed. The studied rocks record different styles of deformation and are representative of common settings of the Pyrenees where GQVs are present: pre-Variscan metasedimentary and metavolcanic rocks, late Variscan granitoids, and Mesozoic and Cenozoic sedimentary rocks. GQVs in the study areas formed along pre-existing brittle and ductile structures or at locations with lithological heterogeneities, and have alteration haloes of silicified host rocks. The geological maps and interpretations presented here contribute to gain insights into the formation mechanisms of GQVs and into the structural constraints on fluid flow and mineral reactions at different depths of the Earth's crust.
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Geology of giant quartz veins and their host rocks
from the Eastern Pyrenees (Southwest Europe)
Eloi González-Esvertit, Àngels Canals, Paul D. Bons, Henrique Murta, Josep
Maria Casas & Enrique Gomez-Rivas
To cite this article: Eloi González-Esvertit, Àngels Canals, Paul D. Bons, Henrique Murta,
Josep Maria Casas & Enrique Gomez-Rivas (2022): Geology of giant quartz veins and
their host rocks from the Eastern Pyrenees (Southwest Europe), Journal of Maps, DOI:
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Geology of giant quartz veins and their host rocks from the Eastern Pyrenees
(Southwest Europe)
Eloi González-Esvertit
, Àngels Canals
, Paul D. Bons
, Henrique Murta
, Josep Maria Casas
Enrique Gomez-Rivas
Departament de Mineralogia, Petrologia i Geologia Aplicada, Facultat de Ciències de la Terra , Universitat de Barcelona, Barcelona, Spain;
China University of Geosciences, Beijing, Peoples Republic of China;
Department of Geosciences, Tübingen University Tübingen,
Deep Nature Photography, Belo Horizonte, Brasil;
Departament de Dinàmica de la Terra i lOceà, Facultat de Ciències de la
Terra, Universitat de Barcelona, Barcelona, Spain
Giant Quartz Veins (GQVs) are ubiquitous in dierent tectonic settings and, besides being often
related to hydrothermal ore deposits, also represent large-scale ngerprints of the structural
and geochemical history of the rocks in which they are hosted. Here we present detailed
geological maps and interpretations of three key areas of the Eastern Pyrenees where GQVs
are well exposed. The studied rocks record dierent styles of deformation and are
representative of common settings of the Pyrenees where GQVs are present: pre-Variscan
metasedimentary and metavolcanic rocks, late Variscan granitoids, and Mesozoic and
Cenozoic sedimentary rocks. GQVs in the study areas formed along pre-existing brittle and
ductile structures or at locations with lithological heterogeneities, and have alteration haloes
of silicied host rocks. The geological maps and interpretations presented here contribute to
gain insights into the formation mechanisms of GQVs and into the structural constraints on
uid ow and mineral reactions at dierent depths of the Earths crust.
Received 13 July 2022
Revised 31 August 2022
Accepted 3 October 2022
Giant quartz veins;
geological mapping; Eastern
1. Introduction
Quartz veins with widths that range from metres to
hundreds of metres and lengths from tens of metres
to kilometres, hereafter Giant Quartz Veins (GQVs),
are widespread in various tectonic settings (Main
Map, Map A; Figure 1)(Bons, 2001;Jia & Kerrich,
2000;Lemarchand et al., 2012;Slabunov & Singh,
2022;Yilmaz et al., 2014). These structures can act
as either conduits or barriers to heat and mass
transfer within the Earths crust, can be associated
with hydrothermal ore deposits, and reveal infor-
mation about the deformational and geochemical
history of their host rocks (Amanda et al., 2022;
Bons et al., 2012;Groves et al., 2018;Sharp et al.,
2005;Wagner et al., 2010). However, there still
are several open questions about the origin and sig-
nicance of GQVs: e.g. about the sources of such
large amounts of silica and the tectonic, lithological
and geochemical control(s) on their emplacement.
The decrease in silica solubility and quartz precipi-
tation have been classically linked to temperature
and pressure variations during uid ow (Bons,
2001 and references therein) and, thus,
understanding what drives that uid ow may
reveal the window(Tannock et al., 2020).
In the Alpine fold-and-thrust belt of the Pyrenees
(SW Europe), at least 741 GQVs mappable at the
1:25,000 scale are exposed at dierent structural levels
and emplaced along brittle and ductile structures
(Figure 2)(González-Esvertit et al., 2022a). Here we
present detailed geological maps, descriptions, and
cross-sections of three areas of the Pyrenees in
which GQVs crop out in dierent rock types (Figure
2B, C, D): (1) Upper Neoproterozoic Early Palaeo-
zoic metasediments at the Ger-Gréixer sector (La Cer-
danya area), (2) Lower Permian igneous rocks and
Upper Neoproterozoic Early Palaeozoic metasedi-
ments in the Roses area (Cap de Creus Massif), and
(3) Upper Cretaceous sedimentary rocks at the
Masarac-Vilarnadal area (Roc de Frausa Massif). For
each area, we rst describe the main stratigraphical
and structural features of the host rocks (Figures 3
5) and then examine the occurrence of GQVs based
on their macrostructure, texture, and deformation
structures, in order to address the relationship
between GQVs, host rocks and regional structures
(Figures 6 and 7). The overarching aim of this work
© 2022 The Author(s). Published by Informa UK Limited, trading as Taylor & Francis Group.
This is an Open Access article distributed under the terms of the Creative Commons Attribution License (, which permits unrest-
ricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
CONTACT Eloi González-Esvertit Departament de Mineralogia, Petrologia i Geologia Aplicada, Facultat de Ciències de
la Terra, Universitat de Barcelona, C/Martí i Franquès s/n, Barcelona 08028, Spain
Supplemental data for this article can be accessed online at
is to reveal the dierent structural controls on GQV
emplacement, as well as to update the geology of
three sectors that are key to understand the tectonic
evolution of the Pyrenees.
2. Geological setting
The Pyrenees are an E-W-trending asymmetric
double-verging Alpine fold-and-thrust belt located
at the northern boundary of Iberia (Figure 2A). It
extends from Cap de Creus in the East to the Bay
of Biscay in the West, whilst northwards and south-
wards it is bounded by the Aquitanian and Ebro
foreland basins, respectively. The formation of the
Pyrenees resulted from the collision between the
Iberian and the Eurasian plates from the Late Cre-
taceous to the Miocene (Muñoz, 1992). This collision
produced the exhumation of a pre-Variscan metase-
dimentary succession, late-Neoproterozoic to Car-
boniferous in age, that extensively crops out in the
backbone of the cordillera (Axial Zone) (Figure 2).
In the Eastern Pyrenees, these rocks record Sardic
(Ordovician), Variscan (Carboniferous-Permian)
and Alpine deformational events, host igneous
bodies of dierent age, extent, and composition,
and were aected by Variscan regional metamorph-
ism (Casas, 2010;Guitard, 1970;Navidad et al.,
2018;Zwart, 1986). The Ger-Gréixer (La Cerdanya;
Figure 2B) and Roses (Cap de Creus; Figure 2D)
study areas are located within this pre-Variscan
basement (Figure 2)(Druguet et al., 2014;Padel
et al., 2018). In contrast, the Mesozoic and Cenozoic
sedimentary rocks that crop out in the South Pyre-
nean Zone (Figure 2A), and in several small areas
of the Axial Zone (as the Masarac-Vilarnadal area
in the Roc de Frausa massif; Figure 2C), have only
been aected by post-Variscan tectonics (Muñoz,
2019;Pujadas et al., 1989).
3. Methods
The study areas were selected considering two pre-
mises: (1) access to outcrops, to ensure that each
area is mapped by eldwork rather than by extrapol-
ation or remote sensing-based interpretations, and
(2) host rock variability, to make sure that each area
is representative of a key tectonic setting in which
GQVs form. The geology of the study areas was
characterised in the eld at the 1:2,500 scale. More
than 2,000 orientation measurements of GQVs, host
rock bedding and cleavage/s, fault structures, fold
axes, and joint sets were collected and georeferenced
in 3D.
In the nal layout, a world map with the location of
GQVs previously reported in the literature (Main
Map, Figure A) is presented together with a geological
Figure 1. Examples of Giant Quartz Veins cropping out in dierent tectonic settings: (A) the Esquerdes de Rojà vein in the Canigó
Massif, pre-Variscan basement of the Pyrenees, SW Europe; (B) the Poolamacca veins in the Broken Hill Inlier, western New South
Wales, Australia (from Bons, 2001); (C) the China Wall vein in the Halls Creek Belt, north Western Australia, Australia; (D) the Castle
Ruin Weissenstein vein in the Bavarian Phal Zone, Bohemian Massif, Central Europe (from the Naturpark Bayerischer Wald admin-
istration); and (E) the Heyuan vein in the Shaowu-Heyuan Fault zone, South China block (from Tannock et al., 2020).
sketch map of the Eastern Pyrenees (Main Map, Figure
B), to provide a general overview of the research topic
and the geological framework of the Pyrenees. The
1:7,500 geological maps of the Ger-Gréixer
(6.5 km
), Roses (5 km
), and Masarac-Vilarnadal
(4.2 km
) sectors are presented over a multidirectional
hillshade (Figures C, D and E of the Main Map).
4. Geology of the study areas
4.1. Ger-Gréixer (La Cerdanya)
The Ger-Gréixer sector is characterised by a low-
grade pre-Variscan metasedimentary succession in
which three stratigraphical units can be distinguished
(Figure 3AD): the Lower Cambrian Err Fm., the
Cambrian-Lower Ordovician Serdinya Fm. (Jujols
Group), and the Upper Ordovician Cava Fm. (see
Main Map, Figure C) (Cavet, 1957;Hartevelt, 1970;
Laumonier, 1988;Padel et al., 2018). These units can
be correlated with those of other sectors of the Eastern
Pyrenees and other regions of the eastern Variscan
Ibero-Armorican Arc, i.e. Montagne Noire and
Sardinia (e.g. Padel et al., 2018).
At the northern sector, the Err Fm. is mainly com-
posed of a rhythmic alternation of mm to cm-thick
dark-blueish shale layers (Figure 3A). Coarse-grained
levels of greywacke and arkose can be found inter-
bedded within monotonous shale-dominant packages.
At the top of the Err Fm., a thin (ca. 25 cm thick) dis-
continuous key level of black shales (Figure 3B), inter-
preted as the Xatard Mb. (Padel et al., 2018), can be
recognised as the boundary with the Serdinya Fm.
The overlying Serdinya Fm. is composed of a rhythmic
alternation of greenish sandstone and shale layers, ca.
0.15 cm-thick (Figure 3C). Coarse-grained cm to
dm-thick sandstone levels are characteristic of this for-
mation. A ca. 10 m-thick package of mm to cm-thick
quartzite layers, attributed to the Font Frède Mb.
(Padel et al., 2018), has also been identied in the
southern sector of the study area (Figure 3D).
An unconformable, scarcely outcropping contact
denes the limit between Serdinya and the overlying
Cava Fm. This intra-Ordovician unconformity was
rst recognised in other sectors of SW Europe
Figure 2. (A) Geological sketch map of the Pyrenees showing the distribution of giant quartz veins and the location of the study
areas located in La Cerdanya (B), Cap de Creus (C), and Roc de Frausa Massifs (D) (orthophotographs from the Institut Cartogràci
Geològic de Catalunya ICGC).
Figure 3. Field photographs of the host rocks from the Ger-Gréixer sector: (A) Typical aspect of the dark-blueish shale layers of the
Err Fm. showing a marked L
intersection lineation; (B) Discontinuous level of black shales that represents the boundary
between the Olette and Serdinya Fms.; (C) Typical example of the greenish sandstone and shale layers of the Serdinya Fm.;
(D) Quartzite layers of the Font Frède Mb. strongly folded in the southern (reverse) limb of a major anticline fold; (E) Cut and
polished sample of the Err Fm. showing the strongly folded bedding surfaces (S
) and a poorly developed slaty cleavage (S
(F) Host rock silicication area linked to one of the south-directed thrusts faults present in the study area, which postdate the
development of the main cleavage S
;(G) Apophysis-like texture (white arrow) and host rock silicication aureole ca. 2 m
away from the giant quartz vein located at the northern sector of the study area; (H) Detail of the GQV boundary showing highly
silicied adjacent host rocks of the Serdinya Fm. (I) Detail of the vein located at the southern sector of the study area, showing host
rock fragments that preserve the original trend of the main S
surfaces and are crosscut by cm-wide veins.
(Teichmüller, 1931), and has been and interpreted as
a result of the Sardic Phase (e.g. Casas, 2010), a Mid
Late Ordovician deformation episode (see review
in Puddu et al., 2019). The overlying Cava Fm. is
composed of feldspar-rich conglomerates and
coarse-grained sandstones with scarce levels of varie-
gated shales and ne-grained sandstones. Neogene
detrital deposits unconformably lie on top of the
pre-Variscan rocks at the southern edge of the
study area.
Slaty cleavage (S
) has only been observed in scarce
outcrops of the Err Fm. as a poorly developed axial pla-
nar cleavage of micro-folds that aect the bedding sur-
faces (Figure 3E). Other deformation mesostructures
associated with this cleavage have not been identied.
A well-developed NW-SE-trending and roughly mod-
erately-to-subvertical NE-dipping cleavage (S
) is the
most recognisable structure in the pre-Variscan rocks
(Figure 3A, D, F). Bedding (S
) planes and S
dene a well-developed intersection lineation (L
(Figure 3A, C). S
and S
dip attitudes dene an anti-
form-synform fold sequence in the northern sector of
the study area (Figure 7A). These folds present SSW-
verging axial planes parallel to the S
surfaces, are
open to tight, and have a wavelength ranging between
metres and hundreds of metres. S
indicate repetitive variations of the rocks, from reverse
to normal arrangement fold limbs (Figure 7A). Further
south, S
surfaces dip moderately towards the NNE and
form the normal limb of a meso-scale overturned anti-
cline located in the central sector of the study area
(Figure 7A). The reverse limb of this fold is character-
ised by sub-vertical NNE-dipping S
surfaces that
become moderately NNE-dipping southwards. The
contact between the Err Fm. and the Serdinya Fm.
crops out along this southern reverse fold limb,
where S
surfaces exhibit a moderate to subvertical
NNE dip (Figure 7A). Cm to m-scale second-order
folds, with axial planes parallel to the S
cleavage, are
also common in the study area (Figure 3D). They
verge to the SSW with a Zasymmetry when located
in reverse fold limbs and to the NNE with an Sasym-
metry when located in normal fold limbs. A set of ve
E-W-trending south-directed thrusts was identied
(Figure 3F). They postdate folding and the S
and are spatially related to silicication areas (Figure
3F, G, H). Southwards displacement cannot be quan-
tied due to the lithological similarities between the
various rock units involved. An Alpine age has been
proposed for the southernmost thrust on the basis of
their geometry and orientation (González-Esvertit
et al., 2022b).
Two thrust-related parallel GQVs are present in
the study area (Figures 6A and 7A). They are mainly
composed of massive milky quartz with variable
amounts of silicied host rock fragments (535%),
0.525 cm in size (Figure 3H, I). The number of
these fragments increases notably (up to 80%)
towards the edges of the main bodies, dening a pro-
gressive and diuse vein-host rock contact. S
and S
surfaces observed within these host rock fragments
show, as in the Roc de Frausa and Cap de Creus
areas (see sections 4.2 and 4.3), the same orientation
as in the rocks located in the outer part of the
GQVs. This fact is dicult to explain by uid-assisted
fracturing and entrapment of host rock fragments
within the main quartz mass (e.g. by hydraulic brec-
ciation), which would involve transport (and hence
misorientation) of the host rock fragments (Figures
3I, 4I, J, 5H, I, J). Silicication aureolesof ca. 5
30 m width can be observed in those rocks adjacent
to the GQVs (Figures 3G, H and 7A). The GQVs, sili-
cication aureoles, and undisturbed host rocks are
crosscut by anastomosing 110 cm thick quartz vein-
lets (Figure 3C, G, H), that occasionally have void
cavities of ca.14cm
partially lled by euhedral pris-
matic quartz crystals.
4.2. Roses (Cap de Creus massif)
In the Roses sector, pre-Variscan ne to coarse-
grained low-grade metasedimentary and metavolcanic
rocks, as well as the late-Variscan Roses granodiorite,
constitute the main host rocks of GQVs (see Main
Map, Figure D; Figure 4AE). Fine-grained metasedi-
mentary rocks, muscovite-rich greyish-blueish slate
and alternating shale layers (Figure 4A) are the strati-
graphically lowermost unit. A ca. 80 m-thick level of
black slates is found at the top of this unit. The ne-
grained unit is attributed to the Upper Neoproterozoic
Lower Series (i.e. Cadaqués and Montjoi Series) (e.g.
Druguet & Carreras, 2019), which crops out along
the central and northern areas of the Cap de Creus
Massif. A ca. 30 m-thick unit of acid volcanic rocks
(Figure 4B) is interbedded within this unit (Mas de
la Torre acid metatus, 558 ± 3 Ma; Casas et al.,
2015). Volcanic rocks show porphyritic textures on
which mm to sub-mm-sized plagioclase and, predo-
minantly, potassium feldspar crystals are embedded in
ane-grained matrix (Figure 4B). The overlying
coarse-grained unit is made up of cm-thick layers of
dark greenish-yellowish sandstone and greywacke
(Figure 4C, D) and is attributed to the Lower Cam-
brian Upper Series (i.e. Norfeu Series). The uppermost
part of this unit is composed of greyish-blackish
banded limestones that crop out in the northern sector
of the study area. The sheet-shaped Roses granodiorite
(290.8 ± 2.9 Ma; Druguet et al., 2014)(Figure 4E) con-
stitutes a ca. 3 × 4 km late-Variscan igneous body
mainly composed of feldspar, quartz, biotite, and
hornblende. This intrusion produced a contact meta-
morphic aureole of highly variable width (from 5 to
100 m) recognisable as spotted phyllites and horn-
felses (Carreras et al., 2004;Carreras & Losantos,
1982). Aplite and leucogranite dykes, 1 cm to 2 m
wide, often crosscut the granodiorite.
Bedding surfaces of the pre-Variscan metasedimen-
tary rocks (S
) are often dicult to recognise in the
Roses area due to the complex deformational history.
When present, S
surfaces are moderately to steeply
dipping and show a highly variable trend due to late
folding (Figures 4A, C, D). A large NW-SE-trending
Figure 4. Field photographs of the host rocks from the Roses sector: (A) Strongly folded bedding surfaces of the ne-grained
metasedimentary rocks; (B) metavolcanic rocks intercalated within ne-grained metasediments crosscut by pinch-and-swell
(occasionally boudinated) quartz veins; (D) Coarse-grained metasediments showing a NW-SE-oriented main cleavage (S
) and
a SW-NE-oriented crenulation cleavage (S
); (E) Roses granodiorite showing 2 cm-wide shear bands parallel to the main cleavage
; gneissic foliation); (F) Zone of major deformation within the silicication area of the NW segment of the Roses giant quartz
vein, showing deformed quartz veins that crosscut the coarse-grained metasediments; (G) Silicied and sheared quartz-schist
band located a few metres away from the NW segment of the Roses giant quartz vein; (H) Giant quartz vein-host rock contact
zone showing cm-wide quartz veins with apophysis-like textures; (I) and (J) Host rock fragments within the main quartz mass
preserving the orientation of the main cleavage (S
); (K) Vein-parallel stylolite networks (red arrows) and highly-silicied host
rocks at the contact zone between the SE segment of the Roses vein and the ne-grained metasediments; (L) Detail of the SE
segment of the Roses vein showing a network of cm-wide crack-seal veins crosscutting a blueish-greyish quartz mass that records
traces of the original fabric of the metasedimentary host rocks.
antiform-synform pair was identied from the map
analysis (Figure 7B). A bedding-parallel cleavage (S
is the most recognisable structure within the metasedi-
ments (Figures 4A, C, D). S
surfaces consist of 0.2
3 cm thick shallow-dipping layers, broadly N-S to
NW-SE-trending, that are dened by the orientation
of ne-grained phyllosilicates. They can be dened
as a slaty cleavage when present in the ne-grained
unit, or as an anastomosing spaced cleavage when
identied in the coarse-grained unit. S
surfaces con-
sist of a NE-SW-trending and moderately SE or
NW-dipping crenulation cleavage (Figures 4C, D). S
is heterogeneously developed through the study area
and show mm to cm-thick layers interpreted as the
axial planar cleavage of cm-scale folds aecting the
surfaces (Figure 4C). In the Roses granodiorite
(Figure 4D), a NW-SE-trending and mostly SE-dip-
ping gneissic foliation dened by biotite crystals ana-
stomosing around mm-cm sized feldspar crystals
) is present (Figures 4E and 7B). Deformation local-
isation along cm-wide mylonitic bands that follow the
main trend of the S
surfaces can occasionally be
identied (Figure 4E). According to regional compari-
sons (e.g. Druguet, 1997;Llorens et al., 2013), S
tures correspond to the oldest D
deformation phase
that occurred prior to the metamorphic peak. The S
crenulation cleavage can be attributed to the hetero-
geneous D
deformation event that led to the folding
of S
and S
layers, whilst S
surfaces can be attributed
to the multiphase post-magmatic D
event widely recognised in the Cap de Creus area,
which is responsible for the formation of the main
shear zones in this massif.
In addition, the study area exhibits high-strain
zones where a strong NW-SE-oriented and moder-
ately-to-strongly SW-dipping mylonitic/phyllonitic
foliation developed (Figures 4F, G and 7B). These
zones mostly aect both the Roses GQV and the sili-
cied quartz-schists that occur close to it in the NW
sector of the study area (Figure 4G). A second NE-
SW-oriented sub-horizontal or slightly NW-dipping
mylonitic foliation has also been identied in the
Roses granodiorite and the GQV (Figure 7B). It
denes cm to m-wide high-strain bands that post-
date both the formation of the GQV and the develop-
ment of the NW-SE mylonitic/phyllonitic foliation.
Latequartz veins, with a width of 15 cm, are
often emplaced parallel to these mylonitic/phyllonitic
foliation, showing pinch-and-swell (occasionally bou-
dinage) structures (Figure 4B).
The Roses GQV (Figures 4HLand 6B, C) is
dened by several NW-SE-trending aligned discon-
tinuous quartz bodies with heterogeneous internal
structure in terms of grain size, crystal transparency
and nite strain. Two main outcropping domains
can be distinguished according to the GQV main
trend and the deformation style: the NW (Figures
6B and 7B) and SE (Figure 6C) domains. The
main quartz bodies exhibit a gentle strike variation,
from NW-SE (ca. N135°) in the NW segment to
WNW-ESE (ca. N120°) in the SE segment. On
the NW segment (Figure 6B) nite strain is higher
and the quartz bodies follow the main trend of the
silicied sheared quartz-schist with variable contents
of muscovite and chlorite (Figures 4G and 7B).
Contrarily, quartz bodies of the SE segment of the
GQV (Figure 6C) are emplaced following a
WNW-ESE-trending and NNE-directed thrust.
This fault separates the volcanic breccias, in the
hanging wall, and the black slates that are at the
top of the ne-grained unit.
The host rocks immediately adjacent to the GQV
have a 220 m wide silicication halo. Within the
main quartz bodies, greyish quartz aggregates with
variable phyllosilicate and oxide content and highly
silicied fragments of the metasedimentary rocks
are common (Figure 4HK). In some cases, clea-
vage surfaces present in host rock fragments iso-
lated within the main quartz bodies show the
same structural attitude as those rocks located
immediately outside the GQV (Figure 4I, J). As in
the La Cerdanya area (see section 4.1), this suggests
that host rock silicication by replacement was an
important quartz precipitation mechanism during
the formation of this GQV, which left remnants
of the original fabric and the unreplaced host
rock fragments in their original position. Beyond
silicication and replacement, quartz fabrics also
point to other formation processes. For example,
cm-thick veins that crosscut and postdate the
highly-silicied host rocks exhibit vein-parallel sty-
lolites suggesting host rock pressure-solution related
to the opening of cm-wide veins (Figure 4K). The
aggregation of many of these smaller veins, simi-
larly to a crack-seal system (Ramsay, 1980), could
also give rise to substantial accumulations of quartz
(Figure 4H, L).
4.3. Vilarnadal-Masarac (Roc de Frausa Massif)
The Vilarnadal-Masarac study area represents the
southeasternmost portion of the late-Variscan Sant
Llorenç-La Jonquera pluton, which is unconformably
overlain by Triassic, Cretaceous, and Palaeocene sedi-
mentary rocks. The Sant Llorenç-La Jonquera pluton
crops out extensively along the NW sector of the
study area and consists of a biotite and hornblende
rich granodiorite (Figure 5A) crosscut by leucogra-
nite and granite porphyry dykes and cm-wide quartz
veins (see Main Map, Figure E) (Autran et al., 1970;
Liesa, 1988). Occasionally, the granodiorite is altered
into an orange-pink quartz-feldspar rock, from which
biotite and hornblende crystals have been completely
removed (Figure 5B). This alteration style is similar
to the quartz-feldspar gneisses that formed by biotite
dehydration in South Australia (see Weisheit et al.,
2013). The granodiorite is unconformably overlain
by Lower Triassic Buntsandstein facies, consisting
of SW-NE-trending beds, ca. 80 m-thick, of an
alternation of reddish claystone mm to cm
thick beds and ne-grained sandstone. Occasionally,
210 cm thick conglomerate levels with a reddish
matrix were found within this unit. Above, a ca.
50 m-thick greyish unit of laminated limestones,
Figure 5. Field photographs of the host rocks from the Masarac-Vilarnadal sector: (A) unaltered granodiorite from the St. Llorenç-
La Jonquera pluton; (B) altered granodiorite that is crosscut by 2 cm-wide quartz veins; (C) micritic limestone of the Mid Triassic
lower Muschelkalk facies; (D) calcite vein networks close to the hinge zone of a NW-SE-oriented anticline in the Mid Triassic lower
Muschelkalk facies; (E) SW-NE-oriented bedding surface of the Upper Cretaceous conglomerates showing a NW-SE-oriented sub-
vertical cleavage; (F) silicication area with cm-wide quartz veins within the Upper Cretaceous-Paleocene lower Garumnian facies;
(G) Syncline-anticline NW-SE-oriented folds aecting the Upper Cretaceous ochre limestones; (H) Embryonic replacement textures
of host rocks in the Upper Cretaceous conglomerates close to the giant quartz vein (see location on Figure 6D); (I) and (J) detail of
a giant quartz vein with visible remnants of the replaced conglomerate fabric (see location on J).
marly limestones and dolostones, corresponding to
the Mid Triassic lower Muschelkalk facies, crops
out with the same SW-NE trend (Figure 5C). Lami-
nated limestones show 0.22 cm-thick micritic layers
and are the most abundant lithology. Calcite vein net-
works linked to high deformation zones are abundant
in (and restricted to) this carbonate unit (Figure 5D).
Triassic rocks are unconformably overlain by a ca.
60 m-thick Upper Cretaceous unit composed of
ochre limestones interbedded with siltstone levels
(Figure 5G), ne to coarse-grained yellowish-red-
dish sandstones, and matrix-supported, polymictic
and heterometric conglomerates (Figure 5E, H).
Ochre limestones and siltstones are only present at
the base of this unit and form ca. 210 m-thick dis-
continuous levels (Figure 5G), whilst sandstone layers
of variable thickness (115 m) are the most abundant
rock type within this unit. Furthermore, a ca. 10
15 m-thick conglomerate key level that follows the
main trend of the post-Variscan rocks can be ident-
ied at the map scale (Figure 5E). The conformably
overlying Cenozoic succession crops out in the SE
sector of the study area and is attributed to the
Upper Cretaceous Lower Paleocene Garumnian
facies (Cirés et al., 1994). The lowermost unit of
this succession is composed of a ca. 30 m-thick
monotonous alternation of mm-cm-thick reddish
claystone layers, occasionally crosscut by cm-wide
quartz veins (Figure 5F). It is conformably topped
by an intermediate package of greyish-blueish micri-
tic limestones, ca. 50 m-thick, and an uppermost unit
of reddish and ochre claystones intercalated with
some small lenses (0.51 m thick) of conglomerates
and coarse-grained sandstones.
A map-scale interference between two fold systems
is the most striking feature of the Vilarnadal-Masarac
area. Together with the Sant Climent (ca. 3 km north-
wards) and Montpedrós (ca. 2 km southeastwards)
areas, they represent three km-scale isolated remnants
of synform-shaped post-Variscan rocks (e.g. Cirés
et al., 1994). Part of the Montpedrós syncline structure
can be observed in the Garumnian succession crop-
ping out at the southeasternmost sector of the study
area. The major synclines in the Sant Climent and
Montpedrós areas are NW-SE-oriented (calculated
fold axes of ca. 36/134), whilst the arrangement of
the post-Variscan rocks in the Vilarnadal-Masarac
area depicts a SW-NE-oriented syncline (calculated
Figure 6. (A) The giant quartz vein located at the northern sector of the Ger-Gréixer area, emplaced along a ca. 50° N-dipping
thrust fault; (B) UAV (Unnamed Aerial Vehicle) aerial photograph of the NW segment of the Roses vein, where it was emplaced
along a ca. 5070° SW-dipping silicied and sheared quartz-schist band; (C) The SE segment of the Roses vein, where it was
emplaced along a ca. 4055° SW-dipping thrust fault; (D) Digital Elevation Model coupled with aerial photographs acquired
using an UAV of a giant quartz vein (white arrows) from the Vilarnadal-Masarac area.
fold axis of ca. 040/20). Furthermore, a well-exposed
anticline-syncline sequence of NW-SE-oriented
minor folds can be identied at both the outcrop
and map scales (Figure 5G) in the Vilarnadal-Masarac
area. These folds are related to the major NW-SE-
oriented major synclines of the Sant Climent and
Montpedrós areas and form an angle of ca. 90° to
the main trend of the SW-NE syncline (measured
fold axes from Figure 5G of ca. 42/124). Anticlines
are tight, regularly spaced, and their limbs dip moder-
ately-to-strongly towards the SW and NE (occasion-
ally in a reverse way) in the immediately adjacent areas
(ca. 510 m) of their axial plane (Figure 5G). Folds
have only been identied aecting Triassic and Cre-
taceous rocks in the NW limb of the major syncline,
although a well-developed and sub-vertical dipping
axial-planar cleavage is present throughout the rest
of the study area following the main fold trends
(Figure 5E). In the central sector of the study area, a
SW-NE-oriented normal fault denes the contact
between the granodiorite and the moderately SE-
dipping Buntsandstein, Muschelkalk and Upper
Cretaceous successions (Figure 7C). This sequence
progressively dips less towards the SE and becomes
moderately-to-strongly NW-dipping in the southern-
most sector of the study area, where it is truncated
by a WSW-ENE-oriented normal fault that
denes the southern contact with the granodiorite
(Figure 7C).
GQVs of the Masarac-Vilarnadal area are hosted
either in the granodiorite or in the Upper Cretaceous
conglomerates and sandstones (Figures 5I, J and 6D).
They are in all cases associated with intense silicica-
tion, and no previous fractures along which the
GQVs could have been emplaced have been identied.
Irregular and diuse boundaries and the presence of
remnants of the replaced fabric within the veins
(Figure 5H, I), suggest that the main formation mech-
anism of these GQVs was the replacement of the pre-
existing rocks rather than lling of fracture porosity
with quartz precipitates. For example, when hosted
in Upper Cretaceous sandstones and conglomerates,
the GQVs record the former clast distribution patterns
and show embryonic replacement textures at their
boundaries (Figure 5H, I) that become dominant
towards their core zone (Figure 5J). Silicication
areas not related to GQVs have also been identied
(Figure 5F). The orientation of GQVs ranges from
NW-SE near the Vilarnadal village to SW-NE close
to the Masarac village, where they follow the main
trend of an Upper Cretaceous conglomerate key
level. Contrarily, GQVs located at the southern contact
between the Upper Cretaceous rocks and the Sant Llor-
enç-La Jonquera granodiorite (Figure 6D) are W-E to
Figure 7. Representative cross sections of the Ger-Gréixer (A), Roses (B) and Vilarnadal-Masarac (C) sectors. See Main Map, Figures
C, D and E for location.
WSW-ENE-oriented (Figure 7C). These latter veins
show the most intense wall rock alteration.
5. Concluding remarks
The geological maps presented in this work are
representative of the three key tectonic settings in
the Pyrenees in which GQVs are present. In the
Ger-Gréixer sector, GQVs follow south-directed
thrusts, probably Alpine, that were emplaced along
major fold limbs that postdate the development of
the main S
cleavage. In the Roses area, the age of
the GQVs is not constrained and could be related
to either Variscan or Alpine deformational events,
although they postdate the development of S
and S
cleavages and predate the NW-SE mylonitic/
phyllonitic foliation. Quartz bodies that crop out in
the SE sector of the Roses area were emplaced
along a NE-directed thrust, whilst the NW segment
of the Roses GQV follows the main trend of a
sheared quartz-schist. GQVs of the Vilarnadal-
Masarac area are post-Variscan and mostly hosted
in Upper Cretaceous sedimentary rocks, following
the main trend of an Upper Cretaceous conglomerate
level and the fold limbs of a major SW-NE-oriented
syncline. Rocks of this area show an Alpine fold
interference pattern and a NW-SE-oriented fold-
related Alpine cleavage.
Despite being hosted in dierent host rocks and
emplaced along distinct structures, the GQVs share
various strikingly similar features (Figures 37): (1)
the development of silicication halosin either sedi-
mentary, igneous, or metamorphic host rocks; (2)
evidences of dierent mechanisms of quartz growth
through host rock replacement, host rock pressure-
dissolution and stylolite formation simultaneous to
the opening of cm-wide veins, and aggregation of
multiple latecrack-seal veins with dierent orien-
tations; and (3) a strong structural control rep-
resented by zones of localised deformation (e.g.
normal faults, thrusts, shear zones, and fold axes or
fold axial planes) or lithological contrast levels (e.g.
conglomerate units) that vary even within hundreds
of metres.
Fieldwork was carried out using the FieldMove® (Pet-
roleum Experts) application running on a high-per-
formance tablet connected to a Garmin® GPSMAP
66ST device. Accuracy of positioning (±3 to ±8 m)
was continuously checked with high-resolution ortho-
photographs and LiDAR-derived Digital Elevation
Models from ICGC (Institut Cartogràc i Geològic
de Catalunya; Geological boundaries
and dip data collected on the eld were imported to
the 3D software MOVE® (Petroleum Experts), where
representative cross-sections of the study areas were
built by projecting orientation data through calculated
vectors into the cross-section lines.
When necessary, aerial photographs and elevation
models were acquired using UAVs (Unnamed Aerial
Vehicles) DJI Mavic Air 2 and DJI Mini Pro equipped
with a 12 MP camera. The mapping accuracy of geo-
logical boundaries was further improved using high-
resolution orthophotographs from PNOA-IGN (Plan
Nacional de Ortofotografía Aérea Instituto Geo-
gráco Nacional; and the ICGC (Institut
Cartogràc i Geològic de Catalunya;
The Main Map was designed with the software QGIS
( using a 1:50,000 scale geological
map base from the ICGC. Dip symbols were designed
according to the standard geological representation in
an SVG editor and exported as an SVG library. Accu-
racy and truthfulness of the cross-sections were
checked through extra eldwork in each study area.
Open Scholarship
We are grateful to Heike Apps (Geoscience Australia), Leo
Afraneo Hartmann (Universidade Federal do Rio Grande do
Sul) and Carlos Galé (Universidad de Zaragoza) for their use-
ful and constructive revisions, and to Jordi Cirés for introdu-
cing us to some outcrops of the Vilarnadal-Masarac area.
Claudia Prieto-Torrell and Daniel Martí Tubau are gratefully
acknowledged for their eldwork assistance. EGE acknowl-
edges the funding provided by the Geological Society of
London (GSL) Student Research Grants 2022.
Disclosure statement
No potential conict of interest was reported by the author(s).
This work is a contribution to the Geologia Sedimentaria
(2017SGR-824) Research Group and to research projects
DGICYT CGL2017-87631-P, PGC2018-093903-B-C22 and
PID2020-118999GB-I00, funded by the Spanish Ministry
of Science and Innovation (MCIN)/State Research Agency
of Spain (AEI)/10.13039/501100011033. EGE acknowledges
the funding provided by the Geological Society of London
(GSL) Student Research Grants 2022. The PhD grant of
EGE is funded by the Generalitat de Catalunya and the
European Social Fund (2021 FI_B 00165 and 2022 FI_B1
00043). EGR acknowledges the Ramón y Cajalfellowship
RYC2018-026335-I, funded by the Spanish Ministry of
Science and Innovation (MCIN)/State Research Agency of
Spain (AEI)/European Regional Development Fund
(ERDF)/10.13039/501100011033; Ministerio de Ciencia,
Innovación y UniversidadesAgència de Gestió dAjuts Uni-
versitaris i de Recerca.
DATA availability statement
The authors conrm that the data supporting the ndings of
this study are available within the article and its supplemen-
tary materials.
Eloi González-Esvertit
Àngels Canals
Paul D. Bons
Josep Maria Casas
Enrique Gomez-Rivas
Amanda, F. F., Tsuchiya, N., Alviani, V. N., Uno, M.,
Yamada, R., Shimizu, S., & Oyanagi, R. (2022). High-temp-
erature silicied zones as potential caprocks of supercriti-
cal geothermal reservoirs. Geothermics,105, 102475.
Autran, A., Fonteilles, M., & Guitard, G. (1970). Relations
entre les intrusions de granitoides, lanatexie et le meta-
morphisme regional considerees principalement du
point de vue du role de leau; cas de la chaine hercynienne
des Pyrenees orientales. Bulletin de la Société Géologique
de France,S7-XII(4), 673731.
Bons, P. D. (2001). The formation of large quartz veins by
rapid ascent of uids in mobile hydrofractures. 17.
Bons, P. D., Elburg, M. A., & Gomez-Rivas, E. (2012). A
review of the formation of tectonic veins and their micro-
structures. Journal of Structural Geology,43,3362.
Carreras, J., Druguet, E., Griera, A., & Soldevila, J. (2004).
Strain and deformation history in a syntectonic pluton.
The case of the Roses granodiorite (Cap de Creus,
Eastern Pyrenees). Geological Society, London, Special
Publications,224(1), 307319.
Carreras, J., & Losantos, M. (1982). Geological setting of the
Roses gtanodiorite (E-Pyrenees. Spain).Acta Geologica
Hispanica,4, 211217.
Casas, J. M. (2010). Ordovician deformations in the
Pyrenees: New insights into the signicance of pre-
Variscan (sardic) tectonics. Geological Magazine,147
(5), 674689.
Casas, J. M., Navidad, M., Castiñeiras, P., Liesa, M., Aguilar,
C., Carreras, J., Hofmann, M., Gärtner, A., & Linnemann,
U. (2015). The Late Neoproterozoic magmatism in the
Ediacaran series of the Eastern Pyrenees: new ages and
isotope geochemistry. International Journal of Earth
Sciences,104(4), 909925.
Cavet, P. (1957). Le Paléozoïque de la zone axiale des
Pyrénées orientales françaises entre le Roussillon et
lAndorre. Bulletin Service Carte Géologique France,55,
Cirés, J., Morales, V., Liesa, M., Carreras, J., Escuer, J., &
Pujadas, J. (1994). Mapa geológico y Memoria de la
Hoja n
220 (La Jonquera). Mapa Geológico de España
E. 1:200.000 IGME.
Druguet, E. (1997). The structure of the NE Cap de creus
peninsula relationships with metamorphism and magma-
tism. Doctoral dissertation. Universitat Autònoma de
Barcelona, Unpublished.
Druguet, E., & Carreras, J. (2019). Folds and Shear Zones at
Cap de Creus. Field Trip Guide XXXI Reunión de La
Comisión de Tectónica SGE 27.
Druguet, E., Castro, A., Chichorro, M., Pereira, M. F., &
Fernández, C. (2014). Zircon geochronology of intrusive
rocks from Cap de Creus, Eastern Pyrenees. Geological
Magazine,151(6), 10951114.
González-Esvertit, E., Gomez-Rivas, E., Canals, A., Bons,
P. D., & Casas, J. M. (2022a). Compiling regional struc-
tures in geological databases: the Giant Quartz Veins of
the Pyrenees as a case study. Journal of Structural
Geology,163, 104705.
González-Esvertit, E., Molins-Vigatà, J., Canals, À., & Casas,
J. M. (2022b) The geology of the Gréixer area (La
Cerdanya, Eastern Pyrenees): Sardic, Variscan, and
Alpine imprints. Trabajos de Geología, in press.
Groves, D. I., Santosh, M., Goldfarb, R. J., & Zhang, L.
(2018). Structural geometry of orogenic gold deposits:
Implications for exploration of world-class and giant
deposits. Geoscience Frontiers,9(4), 11631177. https://
Guitard, G. (1970). Le métamorphisme hercynien
mésozonal et les gneiss oeillés du massif du Canigou
(Pyrénées orientales). Mémoires Du Bureau de
Recherches Géologiques et Minières (BRGM),63, 353.
Hartevelt, J. A. A. (1970). Geology of the upper Segre and
Valira valleys, central Pyrenees. Andorra/Spain. Leidse
Geologische Mededelingen,45, 167236.
Jia, Y., & Kerrich, R. (2000). Giant quartz vein systems in
accretionary orogenic belts: the evidence for a meta-
morphic £uid origin from N15N and N13C studies.
Earth and Planetary Science Letters,14.
Laumonier, B. (1988). Les groupes de Canaveilles et de
Jujols (‘“Paléozoïque inférieur”’) des Pyrénées orientales
arguments en faveur de lâge essentiellement Cambrien
de ces séries. Hercynica,4,2538.
Lemarchand, J., Boulvais, P., Gaboriau, M., Boiron, M.-C.,
Tartèse, R., Cokkinos, M., Bonnet, S., & Jégouzo, P.
(2012). Giant quartz vein formation and high-elevation
meteoric uid inltration into the South Armorican
Shear Zone: geological, uid inclusion and stable isotope
evidence. Journal of the Geological Society,169(1), 1727.
Liesa, M. (1988). El metamorsme del vessant sud del
Massís del Roc de Frausa (Pirineus Orientals) (Doctoral
dissertation). Universitat de Barcelona, Unpublished,
Llorens, M.-G., Bons, P. D., Griera, A., & Gomez-Rivas, E.
(2013). When do folds unfold during progressive shear?
Geology,41(5), 563566.
Muñoz, J. A. (1992). Evolution of a continental collision
belt: ECORS-Pyrenees crustal balanced cross-section. In
K. R. McClay (Ed.), Thrust tectonics (pp. 235246).
Dordrecht: Springer Netherlands.
Muñoz, J. A. (2019). Alpine orogeny: Deformation and
structure in the northern Iberian margin (Pyrenees s.l.).
In C. Quesada & J. T. Oliveira (Eds.), The geology of
Iberia: A geodynamic approach, regional geology reviews
(pp. 433451). Springer International Publishing.
Navidad, M., Castiñeiras, P., Casas, J. M., Liesa, M.,
Belousova, E., Proenza, J., & Aiglsperger, T. (2018).
Ordovician magmatism in the Eastern Pyrenees:
Implications for the geodynamic evolution of northern
Gondwana. Lithos,314-315, 479496.
Padel, M., Clausen, S., Álvaro, J. J., & Casas, J. M. (2018).
Review of the Ediacaran-Lower Ordovician (pre-Sardic)
stratigraphic framework of the Eastern Pyrenees, south-
western Europe. Geologica Acta,16, 339365.
Puddu, C., Álvaro, J. J., Carrera, N., & Casas, J. M. (2019).
Deciphering the Sardic (Ordovician) and Variscan defor-
mations in the Eastern Pyrenees, SW Europe. Journal of
the Geological Society,176(6), 11911206. https://doi.
Pujadas, J., Maria Casas, J., Anton Muñoz, J., & Sabat, F.
(1989). Thrust tectonics and paleogene syntectonic sedi-
mentation in the Empordà area, southeastern Pyrenees.
Geodinamica Acta,3(3), 195206.
Ramsay, J. G. (1980). The crackseal mechanism of rock
deformation. Nature,284(5752), 135139. https://doi.
Sharp, Z. D., Masson, H., & Lucchini, R. (2005). Stable iso-
tope geochemistry and formation mechanisms of quartz
veins; extreme paleoaltitudes of the Central Alps in the
Neogene. American Journal of Science,305(3), 187219.
Slabunov, A. I., & Singh, V. K. (2022). Giant quartz veins of
the Bundelkhand craton, Indian shield: New geological
data and U-Th-Pb age. Minerals,12(2), 168. https://doi.
Tannock, L., Herwegh, M., Berger, A., Liu, J., Lanari, P., &
Regenauer-Lieb, K. (2020). Microstructural analyses of
a giant quartz reef in south China reveal episodic
brittle-ductile uid transfer. Journal of Structural
Geology,130, 103911.
Teichmüller, R. (1931). Zur Geologie des Yhyrrenisbebietes,
Teil1: Alte und junge Krustenbewegungen im südlinchen
Dardinien. Abhandlungen Der Gesellschaft (Akademie)
Der Wissenschaften, Gottingen,3, 857950.
Wagner, T., Boyce, A. J., & Erzinger, J. (2010). Fluid-rock
interaction during formation of metamorphic quartz
veins: A REE and stable isotope study from the Rhenish
Massif, Germany. American Journal of Science,310(7),
Weisheit, A., Bons, P. D., & Elburg, M. A. (2013). Long-lived
crustal-scale uid ow: The hydrothermal mega-breccia
of Hidden Valley, Mt. Painter Inlier, South Australia.
International Journal of Earth Sciences,102(5), 1219
Yilmaz, T. I., Prosser, G., Liotta, D., Kruhl, J. H., & Gilg, H.
A. (2014). Repeated hydrothermal quartz crystallization
and cataclasis in the Bavarian Pfahl shear zone
(Germany). Journal of Structural Geology,68, 158174.
Zwart, H. J. (1986). The variscan geology of the Pyrenees.
Tectonophysics,129(14), 927.
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The Ediacaran-Lower Ordovician successions exposed in the Eastern Pyrenees are updated and revised based on recent U-Pb zircon radiometric ages, intertonguing relationships of carbonate-dominated strata, and onlapping patterns marking the top of volcano-sedimentary complexes. A stratigraphic comparison with neighbouring pre-Variscan outcrops from the Montagne Noire (southern French Massif Central) and Sardinia is related to i) the absence of Cadomian deformation close to the Ediacaran-Cambrian boundary interval; ii) the presence of an episodic, Cadomian-related, acidic-dominant volcanism related to carbonate production punctuating the Ediacaran-Cambrian transition, similar to that recorded in the northern Montagne Noire; and iii) the lack of Guzhangian (Cambrian Epoch 3) regressive shoal complexes present in the Montagne Noire and probably in Sardinia.
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With very few exceptions, orogenic gold deposits formed in subduction-related tectonic settings in accretionary to collisional orogenic belts from Archean to Tertiary times. Their genesis, including metal and fluid source, fluid pathways, depositional mechanisms, and timing relative to regional structural and metamorphic events, continues to be controversial. However, there is now general agreement that these deposits formed from metamorphic fluids, either from metamorphism of intra-basinal rock sequences or de-volatilization of a subducted sediment wedge, during a change from a compressional to transpressional, less commonly transtensional, stress regime, prior to orogenic collapse. In the case of Archean and Paleoproterozoic deposits, the formation of orogenic gold deposits was one of the last events prior to cratonization. The late timing of orogenic gold deposits within the structural evolution of the host orogen implies that any earlier structures may be mineralized and that the current structural geometry of the gold deposits is equivalent to that at the time of their formation provided that there has been no significant post-gold orogenic overprint. Within the host volcano-sedimentary sequences at the province scale, world-class orogenic gold deposits are most commonly located in second-order structures adjacent to crustal scale faults and shear zones, representing the first-order ore-forming fluid pathways, and whose deep lithospheric connection is marked by lamprophyre intrusions which, however, have no direct genetic association with gold deposition. More specifically, the gold deposits are located adjacent to ∼10°–25° district-scale jogs in these crustal-scale faults. These jogs are commonly the site of arrays of ∼70° cross faults that accommodate the bending of the more rigid components, for example volcanic rocks and intrusive sills, of the host belts. Rotation of blocks between these accommodation faults causes failure of more competent units and/or reactivation and dilation of pre-existing structures, leading to deposit-scale focussing of ore-fluid and gold deposition. Anticlinal or antiformal fold hinges, particularly those of ‘locked-up’ folds with ∼ 30° apical angles and overturned back limbs, represent sites of brittle-ductile rock failure and provide one of the more robust parameters for location of orogenic gold deposits. In orogenic belts with abundant pre-gold granitic intrusions, particularly Precambrian granite-greenstone terranes, the boundaries between the rigid granitic bodies and more ductile greenstone sequences are commonly sites of heterogeneous stress and inhomogeneous strain. Thus, contacts between granitic intrusions and volcano-sedimentary sequences are common sites of ore-fluid infiltration and gold deposition. For orogenic gold deposits at deeper crustal levels, ore-forming fluids are commonly focused along strain gradients between more compressional zones where volcano-sedimentary sequences are thinned and relatively more extensional zones where they are thickened. World-class orogenic gold deposits are commonly located in the deformed volcano-sedimentary sequences in such strain gradients adjacent to triple-point junctions defined by the granitic intrusions, or along the zones of assembly of micro-blocks on a regional scale. These repetitive province to district-scale geometrical patterns of structures within the orogenic belts are clearly critical parameters in geology-based exploration targeting for orogenic gold deposits.
We examined the silicification zone in a granite-porphyry system in order to investigate the caprocks in a supercritical geothermal system. At the top of the granite intrusion, a high-temperature silicification zone contains three generations of quartz. The earliest generation formed at higher temperatures and has bright luminescence and high Ti contents. This quartz is the phenocryst that formed in the granitic magma. The second and third generations formed at lower temperatures and have weak to dark luminescence and low Ti contents. This quartz is formed as replacement and in microfractures and cavities in the earlier quartz, suggesting it is a caprock for a supercritical geothermal reservoir.
A long-lived hydrothermal system at the Heyuan fault, South China, has led to the development of a giant quartz reef, now partially exhumed along its length for more than 40 km. Systematic analyses and focused microstructural studies have been undertaken to unravel a complex formation history of repeated fracturing, hydrothermal fluid flow and sealing cycles, resulting in a dynamic permeability across the fault zone. The change in morphology and decreasing grain size with time further indicates the move from slow ductile opening to fast seismic events. Quartz-reef formation has been estimated to occur within a range of ~200–350 °C, based on evaluation of (i) quartz deformation microstructures; (ii) chlorite and mica geothermometry; and (iii) review of comparable quartz-reef studies. Additionally, a set of physico-chemical formation conditions have been identified which compose the ‘quartz-reef window’. These are: (i) significant volume of fluid; (ii) fluid sources from meteoric, metamorphic and/or from mantle origin; (iii) considerable Time-Integrated Fluid Fluxes; (iv) SiO2 oversaturation due to (a) temperature change, (b) sudden pressure drop, or (c) chemical change e.g. fluid mixing; (v) accommodation space to ‘grow’ the reef; (vi) channel permeability; and (vii) cap rock/seal to trap the fluid flow. The mechanism of quartz-reef growth is here interpreted as the brittle-ductile analogue of the brittle fault-valve model.
The Pyrenean Orogenic system formed by the contractional deformation of the North Iberian margin from late Santonian to Middle Miocene times as a result of the collision between the Iberian and European plates. The Iberian lithosphere subducted underneath the European one. The structural style of the Pyrenees has been mainly controlled by the reactivation of the segmented rift system that formed at Late Jurassic-Early Cretaceous times connecting the Atlantic with the Alpine Tethys along the Bay of Biscay and Pyrenean domains, as well as by the distribution of the Triassic salt. Preserved syntectonic sediments in the adjacent foreland basins and piggy-back basins combined with thermochronological data allow constraining the evolution of the orogen.
New data on the geochemistry and geochronology of different felsic gneisses and metabasites from the Variscan massifs of Eastern Pyrenees have allowed us to shed some light on the Ordovician magmatic evolution in northern Gondwana during the opening of the Rheic Ocean. According to these data, the Ordovician magmatism represents a continuous event of anatectic melting, with limited mantle influence, that lasted 20 m.y., from Early to Late Ordovician. In the Canigó massif, peraluminous monzogranitic and granodioritic metaigneous rocks intruded a late Ediacaran-early Cambrian sequence at 464.3 ± 1.6 Ma and 461.6 ± 1.5 Ma, respectively, and leucogranitic gneisses intruded at 457.4 ± 1.6 Ma. Whole-rock geochemistry of the felsic rocks (plutonic and subvolcanic) points to a volcanic arc setting. However, the geological context and the geochemistry of the coeval metabasites are incompatible with this tectonic setting and point out to the inception of an extensional margin. Sm-Nd isotopic data suggest that the felsic rocks are derived from the anatexis of juvenile igneous rocks (probably Cadomian), mixed with older crustal components present in a late Neoproterozoic crust. We interpret that the Ordovician magmas inherited the geochemical signature of the rocks formed at the former Cadomian convergent margin. The variation of the εNd values from −2 to −4 in the Lower Ordovician rocks, to −5 in the Upper Ordovician rocks suggests a greater implication of the older component in a within-plate geodynamic context, coeval with the evolution of an extensional marginal basin linked to the opening of the Rheic Ocean. A similar isotopic evolution, more depleted first and with a greater implication of the crust in the younger sample, is shown by the studied metabasites.