Consorcio Minero Benito Juarez Peña Colorada, S.A. de C.V. ("Peña Colorada") is the operator of Peña Colorada mine. ArcelorMittal holds 50% of Peña Colorada through a joint operation with Ternium S.A. ("Ternium"), who owns the other 50% interest.
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Summary:
Peña Colorada is a complex polyphase iron ore deposit. The iron mineralization at Peña Colorada consists of banded to massive concentrations of magnetite within breccia zones and results from several magmatic, metamorphic and hydrothermal mineralization stages with associated skarns, dykes and late faults sectioning the entire deposit.
The Peña Colorada mineralized area contains several iron oxide-apatite (IOA) deposits around the arguably richest known iron resource in Mexico. The Lower Cretaceous volcano-sedimentary host rock sequence has been subjected to several episodes of hydrothermal alteration, each accompanied by a distinct episode of faulting and intrusion (calc-alkaline to tholeiitic). Faulting is partly associated with the reactivation of cryptic structural corridors in basement rocks.
High-resolution 40Ar/39Ar and apatite fission track (AFT) dating of this deposit and the adjacent Arrayanes prospect reveal the following sequence of events that range from the latest Cretaceous to the earliest Eocene: (1) intrusion of a 67.6 ± 3.5 Ma magnetite-bearing diorite with associated skarn/skarnoid metamorphism that was coeval or predated N-S to NNW-SSE faulting; (2) approximately 63.26 Ma syenite-like potassic alteration with disseminated magnetite, predated by N-S to NNW-SSE faulting and postdated by WNW-ESE faulting; (3) intrusion of 62.0 ± 2.5 Ma diorite and 59.39 ± 0.21 Ma andesite dikes that predate the main mineralization event at 55.72 to 54.84 Ma of large semi-stratabound massive and disseminated bodies; (4) intrusion of a 53.3 ± 3.0 Ma magnetite-bearing gabbro and 53 ± 2 Ma pegmatoid magnetite + fluorapatite veins at the Arrayanes prospect, which overlap the WNW-ESE faulting; (5) 50.70 to 48.18 Ma polymictic magnetite breccia as the last stage of mineralization in the area, predated by E-W faulting; and (6) reactivation of WNW-ESE faults and later NE-SW faults. Therefore, the total age span of the Peña Colorada deposit ranges between approximately 19 and 23 million years.
The closeness in age between intrusions and mineralization in the Arrayanes prospect, their confinement between the WNW-ESE and E-W structural domains, and mingling or mixing structures between gabbro and diorite with an associated magmatic magnetite enrichment support the idea of a close genetic link between such intrusives and IOA hydrothermal mineralization. All mineralization events at Peña Colorada are associated with pervasive potassic to propylitic alteration, whereas at Arrayanes they are associated with dominant sodic alteration instead. Alteration features are suggestive of relatively shallow and deep formation of these deposits, respectively. Event 3 thermally reset fluorapatite in fragments of pegmatoid magnetite + fluorapatite + diopside associations (dated at 59 ± 2 Ma, AFT) within the polymictic breccia, which were sampled from a deep orebody (still to be found) and that would be likely associated with event 1 or 2. Consequently, exploration endeavors at depth at Peña Colorada may be considered promising.
The Peña Colorada iron oxide-apatite (IOA) deposit is located in the northern part of the state of Colima, SW Mexico. The majority of magmatic-hydrothermal iron oxide deposits (or IOCG “clan” deposits) in SW Mexico span Late Cretaceous to Eocene ages (Camprubí, 2009, 2013, 2017; Camprubí and González-Partida, 2017). These are located less than approximately 200 km inland from the paleo-trench in the Pacific margin (Figure 1), not unlike similar deposits in the Andean coastal ranges (Camprubí, 2017; Camprubí and González-Partida, 2017). Their distribution follows that of Late Cretaceous to Eocene magmatism, although the regional tectonomagmatic regime and its evolution are poorly known. Likewise, no clear genetic association between magmatism and such iron deposits has been established.
Mineralogy of the deposits
Peña Colorada The mineralization model of the Peña Colorada deposit is established as a multi-stage, skarn-related, magmatic-hydrothermal iron oxide-apatite (IOA) deposit, and thus it is a part of the IOCG “clan” of ore deposits (Zürcher et al., 2001; Tritlla et al., 2003; Camprubí and Canet, 2009; Camprubí and González-Partida, 2017). This deposit and the neighboring La Fundición prospect are enveloped by widespread potassic alteration, particularly in the lower part of the deposit. Little sodic alteration, and conspicuous propylitic alteration occur in the upper part of the deposit. Potassic alteration is characterized by an assemblage of K-feldspar, ferroan chlorite (chamosite), apatite, magnetite, and accessory titanite, and can be found in other mineralized areas in the region, sometimes in close association with propylitic alteration laterally. Sodic alteration is characterized by the occurrence of actinolite or albite. Propylitic alteration consists of epidote, ferroan chlorite, calcite, analcime, zeolites, and chalcedony or quartz. The various mineralization events in the Peña Colorada deposit display strong textural and structural differences. The most notorious mineralization styles are apparently stratabound massive and disseminated ore bodies that are hosted by the volcano-sedimentary rocks of the Tepalcatepec Formation.