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Figure 1 - Reflected light photomicrographs of typical ore
assemblages at the Canahuire Au-(Cu-Ag) deposit. A) Spongy pyrite
(Py I) grain with chalcopyrite (Cp) rimmed with sphalerite (Sph)and
cut by thin veinlets of tennantite-tetrahedrite (Tn-Th). B)
Intergrowth of marcasite (Mrc) and
polygonal pyrite (Py II) together with chalcopyrite (Cp) grains
in the matrix. C) Arsenopyrite(Apy) with inclusions of native gold
(Au). D) Galena (Gn) in contact with intergrowth of pyrite I(Py I)
and pyrite II (Py II).
Figure 2 - A) Backscattered electron image showing the
intergrowth of pyrite I (Py I) and pyriteII (Py II). The yellow
circles are the points analysed on the electron microprobe. Points
1 to 4 arewithin pyrite spongy I (Py I) and points 5 to 8 are
within pyrite II (Py II). Polygonal pyrite (PyII) contains minor
amounts of AsAuAg.
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13o Simpsio de Geologia da Amaznia
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PRELIMINARY CONCLUSIONS
The change in ore paragenesis from stage I, with pyrite I,
pyrrhotite, arsenopyrite andmagnetite, to stage II with
arsenopyrite chalcopyrite tennantite tetrahedrite
-stibiobismuthinite marks a hydrothermal system evolving from low
to intermediate sulphidationstate fluids (see Fig. 1 in Einaudi et
al. 2003).
Collectively, 13
C and 18
O values from calcite veinlets are comparable with
marinelimestone values and may reflect fluids in equilibrium with
the Gramadal Formation limestone,under low fluid/rock ratios, in
distal zones from the mineralization. The marked shift to
slightlymore depleted 13C values and much lower 18O values, as
observed in siderite replacementzones towards the mineralization,
suggests that the Canahuire hydrothermal system evolvedthrough
varying degrees of interaction of the Gramadal limestone with
magmatic and meteoricfluids. This interaction may have probably
promoted the change from low to intermediatesulphidation state of
the fluids and gold deposition.
ACKNOWLEDGEMENTSThis research project is part of a M.Sc.
dissertation under progress at the Institute of
Geosciences of the University of Campinas and with support from
Gold Fields Exploration.Special acknowledgements are due to Dr.
Erika Tonetto (SEMUNICAMP), Profs. Alcides Sialand Valderez
Ferreira (NEG LABISE UFPE) and Nilson Botelho (electron microprobe
UNB).
REFERENCESBAUMGARTNER R. & FONTBOT L. Mineral Zoning and
Geochemistry of Epithermal
Polymetallic Zn-Pb-Ag-Cu-Bi Mineralization at Cerro de Pasco,
Peru. In: ECONOMICGEOLOGY, 2008. v.103, p.493537
BENEDEZ R., FONTOBT L. Cordilleran epithermal Cu-Zn-Pb-(Au-Ag)
mineralization inthe Colquijirca district, central Peru:
Deposit-scale mineralogical patterns. In:ECONOMIC GEOLOGY, 2009.
v.104, p.905-944.
EINAUDI M., HEDENQUIST J., INAN E. Sulfidation state of fluids
in active and extincthydrothermal systems: transition from porphyry
to epithermal environments. In:ECONOMIC GEOLOGY SPECIAL
PUBLICATION, 2003. v.10, p.285-313
SANTOS A., BAUMGARTNER R., GAIBOR A., DUSCI M., AZEVEDO F.,
GRADIM R.,DUNKLEY P., DENBOER D., VALER R. 2011. Geology and
mineralisation of the Au-Cu-Ag Canahuire epithermal deposit,
Chucapaca Project, Southern Peru. In: SGA, TheBiennial SGA
Conference, 11, Proceedings, Antofagasta (Chile) available
on:https://www.e-sga.org/index.php?id=228&tx_commerce_pi1%5BshowUid%5D=1903&tx_commerce_pi
1%5BcatUid%5D=2&cHash=03f281e3a8
