Alvo 118

Para, Brazil

Main commodities: Cu Au
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The Alvo 118 iron oxide copper gold (IOCG) deposit is located some 12 km west of the Sossego deposit and 40 km to the south of the Carajás townsite in the state of Para, Brazil.

This deposit is hosted by the Archaean (2.76 to 2.73 Ga) metavolcano-sedimentary Itacaiúnas Supergroup and lies on a steeply-dipping, WNW-ESE-striking, 60 km-long shear zone, close to the contact between the Itacaiúnas Supergroup and the basement ~3.0 Ga Xingu Complex. The Sossego and Cristalino IOCG deposits lie along the same structure, 12 and 55 km to the east respectively. Along this structure, mafic and felsic meta-volcanic rocks of the Grão Pará Group (Itacaiúnas Supergroup), together with granite, gabbro and porphyry dyke intrusions, comprise the main hosts to the copper-gold mineralisation. The ages of crystallisation of the granite intrusion and the porphyry dykes have been estimated at 2743±3 Ma and at 2654±9 Ma, respectively, via SHRIMP II 207Pb-206Pb ages from zircon grains. These rocks have been subjected to an early sodic (albite and scapolite) alteration, followed by more pervasive and widespread potassium and chloritic, silicic, carbonate, and minor epidote alteration. Potassic alteration is accompanied of magnetite formation, mainly represented by biotite in the mafic volcanic and intrusive rocks, while K feldspar (microcline) is dominant in the felsic volcanic and intrusive host rocks.

The copper-gold mineralisation is closely associated with brittle deformation in the form of breccias and vein stockworks, with open-space filling textures composed of quartz, calcite, fluorite, apatite, allanite and Y-bearing phosphates (e.g., britholite and xenotime). The ore assemblage is generally composed of chalcopyrite (80 vol%), bornite (5 vol%), hematite (10 vol%), magnetite (5 vol%) and very much subordinate amounts of native gold, chalcocite, galena, sphalerite, cassiterite and Bi-Te-Au-Ag minerals (e.g., stutzite and petzite).

The felsic and mafic meta-volcanic and intrusive rocks have been subjected an inward progression of alteration, towards the ore zones of:  i). an early, but restricted, sodic (albite and scapolite) phase;  ii). a potassic assemblage, dominantly biotite or microcline, accompanied by magnetite;  iii). pervasive and widespread chlorite alteration, spatially associated with the copper-gold mineralisation; and  iv). local post-ore quartz-sericite alteration.

The mineralisation and alteration styles and stable isotope data suggest that both were linked to a similar hydrothermal system, with Alvo 118 possibly formed at shallower crustal levels, associated to brittle structures and a major circulation of meteoric oxidised fluids. The geochemical signature of the Alvo 118 ore is characterised by Fe-Cu-Au-(Te-Ag-Pb-Sn)-P-F-ETR, and differs from Sossego in the absence of Co-Ni-Pd-bearing phases and the presence of F. In addition, unlike the other IOCG deposits of the Carajás Mineral Province, Alvo 118 is enriched in HREEs, which are concentrated in apatite and in an Al-poor, Be-B-HREE silicates of the gadolinite group.

The quoted resource at Alvo 118 (Torresi, 2008) is:   170 Mt @ 1.0% Cu, 0.3 g/t Au

The most recent source geological information used to prepare this summary was dated: 2010.    
This description is a summary from published sources, the chief of which are listed below.
© Copyright Porter GeoConsultancy Pty Ltd.   Unauthorised copying, reproduction, storage or dissemination prohibited.

  References & Additional Information
   Selected References:
Pollard, P.J., Taylor, R.G., Peters, L., Matos, F., Freitas, C., Saboia, L. and Huhn, S.,  2019 - 40Ar-39Ar dating of Archean iron oxide Cu-Au and Paleoproterozoic granite-related Cu-Au deposits in the Carajas Mineral Province, Brazil: implications for genetic models: in    Mineralium Deposita   v.54, pp. 329-346.
Torresi I, Xavier R P, Bortholoto D F A and Monteiro L V S,  2012 - Hydrothermal alteration, fluid inclusions and stable isotope systematics of the Alvo 118 iron oxide–copper–gold deposit, Carajas Mineral Province (Brazil): Implications for ore genesis: in    Mineralium Deposita   v.47 pp. 299-323
Xavier R P, Monteiro L V S, Souza Filho C R, Torresi I, Carvalho E R, Dreher A M, Wiedenbeck M, Trumbull R B, Pestilho A L S and Moreto C P N,  2010 - The Iron Oxide Copper-Gold Deposits of the Carajas Mineral Province, Brazil: an Updated and Critical Review: in Porter T M, (Ed),  2010 Hydrothermal Iron Oxide Copper-Gold and Related Deposits: A Global Perspective PGC Publishing, Adelaide   v.3 pp. 285-306
Xavier, R.P., Monteiro, L.V.S., Moreto, C.P.N., Pestilho, A.L.S., de Melho, G.H.C., Delinardo da Silva, M.A., Aires, B., Ribeiro, C. and Freitas e Silva, F.H.,  2012 - The Iron Oxide Copper-Gold Systems of the Carajás Mineral Province, Brazil: in    Society of Economic Geologists,   Special Publication 16, Chapter 17, pp. 433-454.

Porter GeoConsultancy Pty Ltd (PorterGeo) provides access to this database at no charge.   It is largely based on scientific papers and reports in the public domain, and was current when the sources consulted were published.   While PorterGeo endeavour to ensure the information was accurate at the time of compilation and subsequent updating, PorterGeo takes no responsibility what-so-ever for inaccurate or out of date data, information or interpretations.

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