hydrothermal veins, porphyry geochemistry and
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Cu > 0.7 wt%
Mo > 125 ppm
?
200 m
200
m
Low gradeK-altered “barren” core
SECTION 1900NW, Haquira-EastLooking NorthwestMolybdenum grade
SW NE
Porphyries
Siltstones
Quartzites
Quartzites (Soraya Fm.)
Siltstones (Soraya and Mara Fm.)
Haquira stock porphyries
Lahuani sills
Geoc
hem
istry
Soil and gravels
Mo > 125 ppm
Mo < 125 ppm
AHAD-143
AHAD
-176
AHAD
-117
AHAD
-185AH
AD-097
AHAD
-98A
AHAD
-225
AHAD
-091
AHAD
-102
AHAD
-105
AHAD-237
AHAD-248
1006 m
1026 m
1117 m
1087 m
784 m
558m
513 m
417 m
614m
801m
153m
253m
Figure 5: Table of cross-cutting relationships of veins and representative photos from Haquira-East.
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Location and Geology:
Hydrothermal veins, porphyry geochemistry and mineralization zonation of the
Haquira-East porphyry Cu-Mo Deposit, Perú
Modi�ed from Mamani et al. 2010
PerúHaquira
N
100 km
Nazca
Lima Perú
Bolivia
Chile
Nazca Ridge
13º S
17º S
75ºW 70ºW
Andahuaylas-Anta arc (45 - 30 Ma)
Trench
Haquira
Cuzco
Arequipa
Wall-rock compositional control of the Cu & Mo shells:
Federico Cernuschi*, Marco Einaudi, John Dilles, Kevin Heather & Neil Barr*cernuscf@geo.oregonstate.edu
Haquira-East is a well defined and relatively high-grade porphyry Cu-Mo deposit (660 MT @ 0.56% Cu and 0.3% Cu cutoff and ~ 160 ppm Mo) hosted in a porphyry stock intruded in a compressionally deformed se-quence of Mesozoic quartzite, meta-siltstone and minor limestone. Haquira-East is part of the Eocene (ca. 43-31 Ma) Andahuaylas-Yauri porphyry belt of southern Perú. New core-logging observations and whole-rock major and trace element data are presented here.
633 rock pulp samples from sections 1900NW and 2100NW (1m sample every 10 m) were analyzed by ICP-MS after four acid digestion and used to delineate the copper and molybdenum grade distribu-tion and study the dispersion of trace elements in the wall-rock proximal to the high grade ore.
Because of the compositional contrast between the meta-sedimentary wall-rock and the HP-stock wall-rock, the Fe-Cu sulfides tend to precipitate principally in the more reactive intrusive rocks. Mafic minerals in the intrusive rocks release Fe after reacting with the Cu-rich hydrothermal fluids, enabling the precipitation of Fe-Cu sulfides. The sedimentary wall-rock, mainly quartzites, lucks Fe-bearing min-erals, therefore Fe-Cu sulfides are not precipitated (see insert in figure below). This phenomenon pro-duces only a “half ” Cu-ore shell in the HP-stock that disappears abruptly in the contact with the quartz-ites. However, molybdenite precipitation is not restricted by the protolith composition, and a more continuous inverted-cup shaped, Mo-ore shell is observed. Because of the shape of the Cu- and the Mo-shells in the 1900NW section, the main channel of mineralizing fluid flow can be inferred to be located close to the contact of the HP-stock with the meta-sedimentary wall-rock.
Figure 6: Cross-section 1900NW showing copper and molybdenum grade. Geology modified from Gans P., Heather, K., Einaudi, M. and the Antares-FQM geology team.
Molybdenite precipitation: Mo(OH)4 + 2H2S = MoS2 + 4H2O
Mo-shell
Cu-shell Haquira-stock / Quartzite contact
Mo-shell
Haquira Stock
Haquira-stock / Quartzite contact
Cu-ShellCu-shell
Porphyries: Intrusions can be divided into four groups based on cross-cutting age relationships.
1) Early Lahuani sills and dikes (Pre-Mineralization) quartz monzodiorite to granodiorite intruding the sedimentary wall-rocks and moderately deformed with these wall rocks
2) Haquira stock porphyries (Pre- to Syn-Mineralization) (Hp stock) granodiorite, main host of Cu-mineralization
3) Haquira porphyry dikes (Syn-Mineralization) (Hp dikes) narrow sub-vertical dikes similar in composition to the Hp stock but cross-cut it
4) Late Pararani porphyry dikes (Post-Mineralization) (Pp dikes) quartz monzodiorite to granodiorite cut previous the intrusions and the Cu-Mo mineralization.
The Hp stock, Hp dikes and Pp dikes are characterized by low Y and high Sr/Y (~60 to a 100) compositions that have been observed in other mineralization related intrusions from Cu-Mo-porphyry districts globally.
Preliminary trace element modelling sug-gests that fractionation of an oxydized and water rich magma in a shallow crust reservoir with periodic mafic recharge from a deep crustal garnet-bearing source, is a plausible genetic mechanism for these rocks.
Porphyry chemistry:
Hydrothermal veins:
Ap
Qtz-vein
Qtz-vein
A-vein
Qtz-vein
AB-vein
A-vein
These veins are cut:
VEINS
Aplites
Quartz-‐K-‐feldspar
veins ± anhydrite (no
sulfides)
Biotite
microbreccias/veins
Actinolite veins with
plagioclase haloes
and epidote veins
Dark and pale
micaceous (EDM,
PGS) halos with
chalcopyrite-‐bornite
A-‐quartz veins with
bornite-‐chalco
pyrite
Quartz-‐molybdenite
veins
B-‐quartz -‐bornite-‐
chalcopyrite
Chalcopyrite-‐bornite
only veins
D-‐quartz veins with
pyrite-‐chalcopyrite
and sericitic h
alos
Pyrite±quartz veins
with sm
ectite-‐
chlorite halos
Aplites 2 1Quartz-‐K-‐feldspar veins ±anhydrite (no sulfides) 24 3Biotite microbreccias/veins 5Actinolite veins with plagioclase haloes and epidote veins 2Dark and pale micaceous (EDM, PGS) halos with chalcopyrite-‐bornite 4 3A-‐quartz veins with bornite-‐chalcopyrite 21 2 3 4 3Quartz-‐molybdenite veins 5 3 1B-‐quartz -‐bornite-‐chalcopyrite 8 6 2 3 11 5 9 3Chalcopyrite-‐bornite only veins 10 6 4 3D-‐quartz veins with pyrite-‐chalcopyrite and sericitic halos 3 2 1 5 1Pyrite±quartz veins with smectite-‐chlorite halos 3
Qtz-vein + Anh.
Act-v
eins
Bt-mxAp
Ap
A-vein
EDM
Ap
B-vein
PGS
PGS
B-veinCpy BnQtz
Banded moly vein
A-veins
Band
ed m
oly
vein
Band
ed m
oly
vein
B-ve
in
D-vein D-vein
“green-sericite”
“white-sericite”
EDM
Ap
Ap
D-vein
Int.
Argillic
haloInt.
Argillic
halo
B-veinCpy Bn
Qtz
Low grade core
Lima, Perú 2012
Cu > 0.7 wt%
200 m
200
m
Low gradeK-altered “barren” core
SECTION 1900NW, Haquira-EastLooking Northwest
Copper grade
Porphyries
Cu > 0.7 wt%
Cu < 0.7 wt%
Siltstones
Quartzites
Quartzites (Soraya Fm.)
Siltstones (Soraya and Mara Fm.)
Haquira stock porphyries
Lahuani sills
Geoc
hem
istry
Soil and gravels
SW NE
AHAD-143
AHAD
-176
AHAD
-117
AHAD
-185AH
AD-097
AHAD
-98A
AHAD
-225
AHAD
-091
AHAD
-102
AHAD
-105
AHAD-237
AHAD-248
1006 m
1026 m
1117 m
1087 m
784 m
558m
513 m
417 m
614m
801m
153m
253m
Chalcopyrite precipitation: Cu+ + Fe2+ + 2H2S + 0.25 O2 = CuFeS2 + 3H+ + 0.5 H2O
Cu(HS)2- + Fe2+ + 0.25 O2=
CuFeS2 + H+ + 0.5 H2O
Figure 7: 3D Leapfrog modelling of Haquira stock porphyries (brown), Cu-ore shell (red) and Mo-ore shell (blue)
Figure 3: Oblique view over Haquira-East looking south: A-Aerial photo, B-Geology map draped a top of Google Earth image.
Figure 1: Location of Haquira and tectonic setting. Figure 2: Geologic map of Haquira and surroundings.
Figure 8: Trace element ratio plot and preliminar fractionation model.
Chalcobamba
Ferrobamba
Haquira EastHaquira
West
Cristo de los Andes
3 km
N
Chuquibambilla Fm.(Sandstones-Siltsones-Shales)
Soraya Fm.(Quartzites)
Mara Fm.(Sandstones-Siltstones)
Ferrobamba Fm. (Limestones)
Andahuaylas -Yauri batholithand porphyry-related intrusion, dikes and sills
Pyroclastic rocks (Tu�s)
Mid
dle
Jura
ssic
to
uppe
r Cre
tace
ous
EoceneOligocene
NeogeneSecti
on 1900NW
Sect
ion
1900
NW
Inferred Haquira stockbelow cover
A B
Section 1900NW
Figure 4: Photographs of representative igneous rocks from Haquira-East.
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