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Trace elements in Cu-Fe sulfides from the Mantoverde IOCG deposit
Conference proceeding

Trace elements in Cu-Fe sulfides from the Mantoverde IOCG deposit

Cinthia Johansson, Fernando Barra, Martin Reich, Artur P. Deditius, Adam C. Simon, Paula Rojas, Mauricio Arce-Salazar and Anonymous
Actas - Congreso Geologico Chileno, Vol.15, pp.479-479
XV Congreso Geologico Chileno (Universidad de Concepción, Concepción, Chile, 18/11/2018–23/11/2018)
2018
url
https://congresogeologicochileno.cl/wp-content/uploads/2018/12/Libro-de-Actas-XVCongresoGeologicoChileno2018-2.pdfView
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Abstract

Atacama Chile brecciation chalcopyrite Chile Chilean Iron Belt copper copper ores detection Economic geology, geology of ore deposits endogene processes gold ores IOCG deposits iron Mantoverde Deposit metal ores metals mineral deposits, genesis mineralization pyrite rare earths recrystallization silver ores South America sulfides trace elements
IOCG deposits are an important source of Cu and other critical elements such Au, Ag, REE, U, P and Co. However, regardless of their economic significance, their origin remains controversial. In this study, we focus on the chemistry of sulfides from the Mantoverde IOCG deposit located in the northern section of the Chilean Iron Belt (CIB). Our purpose is to characterize pyrite and chalcopyrite samples collected from drill cores, and compare their chemistry with sulfides from iron oxide-apatite (IOA) deposits from the CIB in order to elucidate/evaluate the genetic links between these two styles of mineralization. EMPA and wavelength dispersive spectrometry (WDS) X-ray mapping performed on hypogene sulfides revealed very complex chemical zoning of Ni and Co in pyrite. The sectoral and oscillatory zoning, overprinted by brecciation and recrystallization of Co-rich pyrite confirms the presence of multiple pulses of cryptic mineralization. In general, pyrite has Co and Cu concentrations of up to 2.8 and 1.4 wt.%, respectively, whereas Ni can reach hundreds to thousands ppm. Three types of pyrite are recognized based on their Co/Ni ratios, i.e., Co/Ni<1, Co/Ni=1-20, and Co/Ni>90. Pyrite grains from the upper sections of the deposit have a Co/Ni<1, whereas pyrite grains with a Co/Ni>90 correspond to samples from the deeper sections of the deposit. The high Co/Ni ratio in some pyrites is consistent with a magmatic-hydrothermal origin associated with a mafic source. The concentration of other metals (e.g., Au, Ag, Pb, Cd, Zn, Bi) are usually low, with Ag reaching a maximum of 230 ppm. Concentration of metalloids (e.g., As, Sb) and Hg is generally below detection limit; however, some analyses indicate thousands of ppm As, Sb, Hg, suggesting the presence of micro to nano-sized inclusions. On the other hand, chalcopyrite has very low concentrations of the aforementioned trace elements; although As, Zn and Bi can locally reach up to 170 ppm. The EMPA-WDS results show that the concentrations of trace elements vary significantly in sulfides at Mantoverde (especially in pyrite), and their incorporation depends on the physicochemical conditions of the mineralizing fluid(s) of each stage. Furthermore, the geochemical characteristics of Mantoverde pyrite, including the high Co concentration, are remarkably similar to those reported for pyrite from Los Colorados and El Romeral IOA deposits in northern Chile, supporting a link between Andean IOA and IOCG deposits.

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