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Cristalino

Para, Brazil

Main commodities: Cu Au
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The Cristalino IOCG deposit is located some 40 km to the east of Sossego in a bifurcation of the major regional Carajás Fault in the Carajás district of Para State, Brazil.

Basement in the area is represented by the Xingu Complex which is >2.86 Ga in age and is composed of a variety of rocks, including the ~3.0 Ga Pium Complex and 2.9 Ga Greenstones.   These are overlain by the 2.76 Ga Grão Para Group of volcanics and sediments, cut by the 2.5 Ga Estrella Granite and subsequently by 1.9 Ga granites but is overlain by the un-metamorphosed 2.7 to 2.6 Ga Águas Claras marine sandstones.

Cristalino is hosted by volcanics of the Grão Para Group composed of orange dacite and green andesite with minor basalt and in association with hydrothermally altered and disrupted banded iron formations within this same sequence.   These iron formations have been upgraded nearby where they constitute part of the Carajás Iron Resources.

Mineralisation is concentrated in a NW-SE trending, sinsitral transpressive zone of shearing over a drilled length of 2200 m and thickness ranging from 10's of metres to 500 m.   The shear zone is several hundreds of metres in width and is a splay of the Carajás Fault.   The ore zone is generally brecciated and is found in the volcanics below the iron formation and in the lower sections of the iron formation itself.   In general the iron formation forms the upper limit to ore and may have acted as a capping.   The hydrothermally altered breccia is composed of 5 to 50% sub-angular to sub-rounded fragments.

Mineralisation is associated with the emplacement of 2.7 Ga diorite to quartz-diorite intrusions into the volcano-sedimentary sequence and iron formation.

There are two styles of mineralisation:  (i). 60% of which is crosscutting stockwork veins and veinlets, and  (ii). 40% breccia ore where the breccia fragments are surrounded by sulphide veins and a sulphide matrix.   Mineralisation is also accompanied by magnetite and associated amphibole alteration.   The principal sulphides are chalcopyrite and pyrite in a 2:1 to 3:1 ratio.   The Copper was introduced after the magnetite and amphibolite alteration, although the highest grades are associated with the amphibole zones.   The iron alteration where it affects the iron formation represents addition, not remobilisation of iron.

Hydrothermal alteration progressed from:  (i). early widespread actinolite-albite; to  (ii). biotite with scapolite and magnetite; to  (iii). amphibole with magnetite as hastingsite, grunerite, actinolite and cummingtonite; to  (iv). chlorite with albite, magnetite and hematite; to  (v). chlorite and carbonate; to  (vi). muscovite and carbonate.

The average 3-5% sulphide mineralisation is associated with the last three overlapping phases of alteration and comprise chalcopyrite, pyrite and lesser arsenopyrite with trace Ni-Co sulphides.   The gold is in the pyrite.

Indications of Cu mineralisation were first noted in the area in the late 60's to early 70's.   Grid geochemistry and geophysics from 1984-87 led to 2 anomalies being drilled in 1988 with some 13 holes in two prospects.   The second phase of work was commenced in 1997-98 with more grid mapping, geochemistry and geophysics, culminating in a drill intersection of 38 m @ 1.4% Cu, 0.25 g/t Au between 76 and 114 m depth.

The resultant approximate resource from the subsequent drilling to 2001 amounted to 500 Mt @ 1.0% Cu, 0.2-0.3 g/t Au. According to CVRD, the reserves amount to 261 Mt @ 0.73% Cu.

The most recent source geological information used to prepare this summary was dated: 2001.    
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.
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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