The hypogene iron oxide copper-gold mineralization in the Mantoverde District, Northern Chile


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The hypogene iron oxide copper-gold mineralization in the Mantoverde District, Northern Chile
Economic Geology
Rieger A.A., Marschik R., Diaz M., Hoelzl S., Chiaradia M., Akker B., Spangenberg J.E.
Statut éditorial
Date de publication
The Mantoverde iron oxide copper-gold (IOCC) district, northern Chile,
is known for its Cu production from supergene ores. Recently,
exploration outlined an additional hypogene ore resource of 440 Mt with
0.56 percent Cu, and 0.12 g/t An. The hypogene sulfide mineralization
occurs mainly as chalcopyrite and pyrite, typically in specularite or
magnetite-cemented breccias and associated stockworks. The host rocks
underwent variably intense K feldspar alteration, chloritization,
sericitization, silicification, and/or carbonatization. A district scale
Na(-Ca) alteration is absent. The IOCC mineralization in the district
shows a strong tectonic control by northwest- to
north-northwest-trending brittle structures. Large Cu sulfide-rich veins
or Cu sulfide-cemented breccias are absent. Therefore, head grades of 4
percent Cu are an exception. There is a positive correlation between Cu
and An grades. Gold is probably contained mostly in chalcopyrite and
pyrite. Elevated concentrations of light rare-earth elements (LREE)
occur locally but are attributed to redistribution of LREE within the
deposits rather than to derivation from external sources. The Cu-Au ores
in the Mantoverde district are low in and have relatively low contents
in heavy metals that are potentially hazardous to the environment, such
as As (avg 14 ppm), Hg (<5 ppm), or Cd (<0.2 ppm). The sulfur isotope
ratios of chalcopyrite from the IOCC deposits lie between -5.6 and 8.9
per mil delta(34)S(VCDT). They show systematic variations within the
district, which are interpreted to reflect relative distance to inferred
fluid conduits and the level of deposition within the hydrothermal
system. Most initial (87)Sr/(86)Sr values of altered volcanic rocks and
hydrothermal calcite from the Mantoverde district are between 0.7031 and
0.7060 and are similar to those of the igneous rocks of the region. Lead
isotope ratios of chalcopyrite are consistent with Pb (and by inference
Cu) derived from Early Cretaceous magmatism. The sulfur, strontium, and
lead isotope data of chalcopyrite, calcite gangue, or altered host
rocks, respectively, are compatible with a genetic model that involves
cooling of metal and sulfur-bearing magmatic-hydrothermal fluids that
mix with meteoric waters or seawater at relatively shallow crustal
levels. An additional exotic sulfur input is likely, though not
required, for the copper mineralization. Apart from the IOCC. deposits,
there are a number of smaller magnetite(-apatite) bodies in the
district. These are geologically similar to the Cu-Au-bearing magnetite
bodies, but are related to splays of the north-south-trending Atacama
fault zone and differ in alteration and texture.
Création de la notice
26/09/2012 15:11
Dernière modification de la notice
03/03/2018 16:38
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