hydrothermal veins, porphyry geochemistry and

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.

ddfa

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.