The evolution of the hydrothermal IOCG system in the Mantoverde district, northern Chile: new evidence from microthermometry and stable isotope geochemistry

Abstract

New microthermometric data combined with stable isotope geochemistry and paragenetic relationships support a previously suggested cooling-mixing model for the iron oxide-copper-gold mineralization in the Mantoverde district. Fluid inclusions show characteristics of a CO 2 -bearing aqueous NaCl±CaCl 2 salt system. The evolution of the Mantoverde hydrothermal system is characterized by (1) an early hypersaline, high to moderate temperature fluid; (2) a moderate saline, moderate temperature fluid; and (3) a low saline, moderate to low temperature fluid. Early magnetite formation took place at median temperatures of 435.0°C, whereas hematite formed at median temperatures of 334.4°C. The main sulfide mineralization texturally post-dates the iron oxides and occurred before late-stage calcite, which developed at a median temperature of 244.8°C. Boiling occurs only locally and is of no relevance for the ore formation. The microthermometric and stable isotope data are supportive for a fluid cooling and mixing model, and suggestive for a predominantly magmatic-hydrothermal fluid component during the iron oxide and main sulfide mineralization. Thereafter, the incursion of a nonmagmatic fluid of ultimately meteoric or seawater gains more importance.

Unraveling the origin of the Andean IOCG clan: A Re-Os isotope approach

“…In Chile, several IOCG deposits have been found during the last decade such as Casualidad (Rivera et al, 2009;Kovacic et al, 2012), Diego de Almagro (Herrera et al, 2008;Loyola et al, 2015), Barreal Seco/Teresa de Colmo (Correa, 2000;Hopper and Correa, 2000), Santo Domingo Sur (Daroch, 2011), El Espino (Correa, 2003;Lopez et al, 2014), and Dominga (Veloso et al, 2016). However, only two large IOCG deposits are currently mined, the Candelaria deposit with estimated total reserves of 408 Mt with Cu grades of 0.6 % and 0.1 g/ton Au (http://www.lundinmining.com/s/Candelaria.asp), and Mantoverde with 42.7 Mt averaging 0.58 % Cu in oxides and about 440 Mt at 0.56 % Cu, and 0.12 g/t Au in sulfides (Rieger et al 2012).…”

Mineralogical and sulfur isotopic evidence for the incursion of evaporites in the Jinshandian skarn Fe deposit, Edong district, Eastern China

“…Stable isotopes of H, O and S provide important constraints on the provenance and timing of external fluid, including evaporites, involvement in the magmatic-hydrothermal system (Ohmoto, 1972(Ohmoto, , 1986Johnson, 1996, 2000;Benavides et al, 2007;Rieger et al, 2012). Sulfur isotope of pyrite from the early and late stage at Jinshandian are obviously different from that of sulfides formed in magmatic-hydrothermal fluid (Ohmoto, 1986;Hoefs, 2009), and the sulfur isotope values of anhydrite and gypsum from late retrograde stage are similar to that of the Triassic sedimentary anhydrite of the MLYRMB ($28‰, Chen et al, 1986;Hou et al, 2004), (Fig.…”

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

“…The silician magnetite of the Copiapó Nordeste could be the first documented occurrence in Chilean IOCG-type deposits. Similar to the porphyry-and skarn-type deposits, these types of deposits are generally regarded to also be related to high-temperature and hypersaline fluid-related hydrothermal systems, particularly in the earlier iron-oxide stage (e.g., [12,31]). It is well known that saline fluids increase the solubility of quartz at high temperatures above~300 • C, changing the retrograde solubility of quartz at the approximate temperature range of 375-550 • C [32][33][34].…”