Silician Magnetite from the Copiapó Nordeste Prospect of Northern Chile and Its Implication for Ore-Forming Conditions of Iron Oxide–Copper–Gold Deposits

Silica-bearing magnetite was recognized in the Copiap&#243; Nordeste prospect as the first documented occurrence in Chilean iron oxide&#8315;copper&#8315;gold (IOCG) deposits. The SiO<sub>2</sub>-rich magnetite termed silician magnetite occurs in early calcic to potassic alte...

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Main Authors: Elías González, Shoji Kojima, Yoshihiko Ichii, Takayuki Tanaka, Yoshikazu Fujimoto, Takeyuki Ogata
Format: Article
Language:English
Published: MDPI AG 2018-11-01
Series:Minerals
Subjects:
Online Access:https://www.mdpi.com/2075-163X/8/11/529
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spelling doaj-b57c226575994125a4fbc54399e44d622020-11-25T00:50:08ZengMDPI AGMinerals2075-163X2018-11-0181152910.3390/min8110529min8110529Silician Magnetite from the Copiapó Nordeste Prospect of Northern Chile and Its Implication for Ore-Forming Conditions of Iron Oxide–Copper–Gold DepositsElías González0Shoji Kojima1Yoshihiko Ichii2Takayuki Tanaka3Yoshikazu Fujimoto4Takeyuki Ogata5Departamento de Ciencias Geológicas, Universidad Católica del Norte, Av. Angamos 0610, Antofagasta, ChileDepartamento de Ciencias Geológicas, Universidad Católica del Norte, Av. Angamos 0610, Antofagasta, ChileNittetsu Mining Consultants Co. Ltd., 2-3, Shiba 4-Chome, Minato-ku, Tokyo 108-0014, JapanMinera Nittetsu Chile Ltda., O´Higgins 744, Oficina 607, Copiapó, ChileMinera Nittetsu Chile Ltda., O´Higgins 744, Oficina 607, Copiapó, ChileInternational Center for Research &amp; Education on Mineral &amp; Energy Resources, Akita University, 1-1 Tegata-Gakuen Machi, Akita 010-8502, JapanSilica-bearing magnetite was recognized in the Copiap&#243; Nordeste prospect as the first documented occurrence in Chilean iron oxide&#8315;copper&#8315;gold (IOCG) deposits. The SiO<sub>2</sub>-rich magnetite termed silician magnetite occurs in early calcic to potassic alteration zones as orderly oscillatory layers in polyhedral magnetite and as isolated discrete grains, displaying perceptible optical differences in color and reflectance compared to normal magnetite. Micro-X-ray fluorescence and electron microprobe analyses reveal that silician magnetite has a significant SiO<sub>2</sub> content with small amounts of other &#8220;impure&#8222; components, such as Al<sub>2</sub>O<sub>3</sub>, CaO, MgO, TiO<sub>2</sub>, and MnO. The oscillatory-zoned magnetite is generally enriched in SiO<sub>2</sub> (up to 7.5 wt %) compared to the discrete grains. The formation of silician magnetite is explained by the exchange reactions between 2Fe (III) and Si (IV) + Fe (II), with the subordinate reactions between Fe (III) and Al (III) and between 2Fe (II) and Ca (II) + Mg (II). Silician magnetite with high concentrations of SiO<sub>2</sub> (3.8&#8315;8.9 wt %) was similarly noted in intrusion-related magmatic&#8315;hydrothermal deposits including porphyry- and skarn-type deposits. This characteristic suggests that a hydrothermal system of relatively high-temperature and hypersaline fluids could be a substantial factor in the formation of silician magnetite with high SiO<sub>2</sub> contents.https://www.mdpi.com/2075-163X/8/11/529silician magnetiteCopiapó Nordesteiron oxide–copper–gold depositmicro-X-ray fluorescenceelectron probe microanalysis
collection DOAJ
language English
format Article
sources DOAJ
author Elías González
Shoji Kojima
Yoshihiko Ichii
Takayuki Tanaka
Yoshikazu Fujimoto
Takeyuki Ogata
spellingShingle Elías González
Shoji Kojima
Yoshihiko Ichii
Takayuki Tanaka
Yoshikazu Fujimoto
Takeyuki Ogata
Silician Magnetite from the Copiapó Nordeste Prospect of Northern Chile and Its Implication for Ore-Forming Conditions of Iron Oxide–Copper–Gold Deposits
Minerals
silician magnetite
Copiapó Nordeste
iron oxide–copper–gold deposit
micro-X-ray fluorescence
electron probe microanalysis
author_facet Elías González
Shoji Kojima
Yoshihiko Ichii
Takayuki Tanaka
Yoshikazu Fujimoto
Takeyuki Ogata
author_sort Elías González
title Silician Magnetite from the Copiapó Nordeste Prospect of Northern Chile and Its Implication for Ore-Forming Conditions of Iron Oxide–Copper–Gold Deposits
title_short Silician Magnetite from the Copiapó Nordeste Prospect of Northern Chile and Its Implication for Ore-Forming Conditions of Iron Oxide–Copper–Gold Deposits
title_full Silician Magnetite from the Copiapó Nordeste Prospect of Northern Chile and Its Implication for Ore-Forming Conditions of Iron Oxide–Copper–Gold Deposits
title_fullStr Silician Magnetite from the Copiapó Nordeste Prospect of Northern Chile and Its Implication for Ore-Forming Conditions of Iron Oxide–Copper–Gold Deposits
title_full_unstemmed Silician Magnetite from the Copiapó Nordeste Prospect of Northern Chile and Its Implication for Ore-Forming Conditions of Iron Oxide–Copper–Gold Deposits
title_sort silician magnetite from the copiapó nordeste prospect of northern chile and its implication for ore-forming conditions of iron oxide–copper–gold deposits
publisher MDPI AG
series Minerals
issn 2075-163X
publishDate 2018-11-01
description Silica-bearing magnetite was recognized in the Copiap&#243; Nordeste prospect as the first documented occurrence in Chilean iron oxide&#8315;copper&#8315;gold (IOCG) deposits. The SiO<sub>2</sub>-rich magnetite termed silician magnetite occurs in early calcic to potassic alteration zones as orderly oscillatory layers in polyhedral magnetite and as isolated discrete grains, displaying perceptible optical differences in color and reflectance compared to normal magnetite. Micro-X-ray fluorescence and electron microprobe analyses reveal that silician magnetite has a significant SiO<sub>2</sub> content with small amounts of other &#8220;impure&#8222; components, such as Al<sub>2</sub>O<sub>3</sub>, CaO, MgO, TiO<sub>2</sub>, and MnO. The oscillatory-zoned magnetite is generally enriched in SiO<sub>2</sub> (up to 7.5 wt %) compared to the discrete grains. The formation of silician magnetite is explained by the exchange reactions between 2Fe (III) and Si (IV) + Fe (II), with the subordinate reactions between Fe (III) and Al (III) and between 2Fe (II) and Ca (II) + Mg (II). Silician magnetite with high concentrations of SiO<sub>2</sub> (3.8&#8315;8.9 wt %) was similarly noted in intrusion-related magmatic&#8315;hydrothermal deposits including porphyry- and skarn-type deposits. This characteristic suggests that a hydrothermal system of relatively high-temperature and hypersaline fluids could be a substantial factor in the formation of silician magnetite with high SiO<sub>2</sub> contents.
topic silician magnetite
Copiapó Nordeste
iron oxide–copper–gold deposit
micro-X-ray fluorescence
electron probe microanalysis
url https://www.mdpi.com/2075-163X/8/11/529
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