Structural Evolution of the Rio Blanco-Los Bronces District, Andes of Central Chile: Controls on Stratigraphy, Magmatism, and Mineralization

Piquer, J; Skarmeta, Jorge; Cooke, David R.

doi:10.2113/econgeo.110.8.1995

Cited by 52 publications

(39 citation statements)

References 58 publications

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“…These transverse structures have been recognized as (1) NW striking major magnetic and gravimetric anomalies [ Yañez et al ., ], (2) NW and NE striking long‐lived faults spatially and genetically associated with porphyry copper deposits [ Mpodozis and Cornejo , ; Piquer et al ., ], (3) ENE and NW trending alignments of major stratovolcanoes and minor eruptive vents within the intra‐arc [e.g., Cembrano and Moreno , ; López‐Escobar et al ., ], and (4) NW striking faults in the fore arc that recent structural and seismological data have associated with neotectonic activity [e.g., Haberland et al ., ; Farías et al ., ].…”

Section: Introductionmentioning

confidence: 99%

Tectonic role of margin-parallel and margin-transverse faults during oblique subduction in the Southern Volcanic Zone of the Andes: Insights from Boundary Element Modeling

et al. 2016

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Obliquely convergent subduction margins develop trench‐parallel faults shaping the regional architecture of orogenic belts and partitioning intraplate deformation. However, transverse faults also are common along most orogenic belts and have been largely neglected in slip partitioning analysis. Here we constrain the sense of slip and slip rates of differently oriented faults to assess whether and how transverse faults accommodate plate‐margin slip arising from oblique subduction. We implement a forward 3‐D boundary element method model of subduction at the Chilean margin evaluating the elastic response of intra‐arc faults during different stages of the Andean subduction seismic cycle (SSC). Our model results show that the margin‐parallel, NNE striking Liquiñe‐Ofqui Fault System accommodates dextral‐reverse slip during the interseismic period of the SSC, with oblique slip rates ranging between 1 and 7 mm/yr. NW striking faults exhibit sinistral‐reverse slip during the interseismic phase of the SSC, displaying a maximum oblique slip of 1.4 mm/yr. ENE striking faults display dextral strike slip, with a slip rate of 0.85 mm/yr. During the SSC coseismic phase, all modeled faults switch their kinematics: NE striking fault become sinistral, whereas NW striking faults are normal dextral. Because coseismic tensile stress changes on NW faults reach 0.6 MPa at 10–15 km depth, it is likely that they can serve as transient magma pathways during this phase of the SSC. Our model challenges the existing paradigm wherein only margin‐parallel faults account for slip partitioning: transverse faults are also capable of accommodating a significant amount of plate‐boundary slip arising from oblique convergence.

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Section: Introductionmentioning

confidence: 99%

Tectonic role of margin-parallel and margin-transverse faults during oblique subduction in the Southern Volcanic Zone of the Andes: Insights from Boundary Element Modeling

et al. 2016

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“…In this portion of the magmatic arc, oblique (~78°) plate convergence at rates of ~8 cm/yr has resulted in EW to ENE‐directed crustal shortening since the middle Miocene (Angermann et al, ; Marrett & Strecker, ; Pardo‐Casas & Molnar, ). The Miocene crustal shortening is recorded by NS to NNW‐striking, reverse faults and folds tens of km long, located immediately west of the volcanic chain (Astaburuaga, ; Piquer et al, ; Rojas Vera et al, ; Figure b). Present crustal shortening at rates of 10 −7 yr −1 is recorded by interseismic ENE‐oriented Global Positioning System (GPS) velocities that decrease in magnitude away from the trench toward the magmatic arc (Ruegg et al, ).…”

Section: Geologic Settingmentioning

confidence: 99%

Interpreting Granitic Fabrics in Terms of Rhyolitic Melt Segregation, Accumulation, and Escape Via Tectonic Filter Pressing in the Huemul Pluton, Chile

et al. 2018

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The physical process of rhyolite segregation from crystal mushes remains elusive as microstructural evidence of conventional segregation mechanisms is not available. This study provides direct fabric evidence for deformation‐assisted segregation of eruptible rhyolite in the Chilean Andean arc. The shallow (<7 km), 6.4–6.2 Ma Huemul pluton comprises domains of quartz monzonite, granite, and high‐silica granite. Compositional modeling shows that rhyolitic melt (high‐silica granite) was extracted from a granitic parent, leaving behind silicic cumulates (quartz monzonite). To understand mechanisms of rhyolite segregation, we investigate magmatic fabrics in the pluton. Anisotropy of Magnetic Susceptibility analyses reveal oblate magnetic fabrics and NNW‐striking, subvertical magnetic foliations throughout Huemul. Within the high‐silica granite, magnetic lineations are subvertical and parallel to elongate miarolitic cavities. Magnetic lineations in the quartz monzonite plunge moderately to the NNW, away from the high‐silica granite. In the quartz monzonite, the Shape‐Preferred Orientation of early feldspars is parallel to the magnetic lineation and developed while suspended in melt. Estimations of early feldspar clustering and crystallinity yield ~38% of interstitial volume loss in the quartz monzonite and no volume loss in the granite. These fabric data suggest ENE tectonic shortening coeval with rhyolite extraction. We explain these observations with a model of tectonic filter pressing in which shortening is accommodated by interstitial melt flow at slow (10−5 km3/yr) rates, segregating moderate volumes of rhyolite in Myr time scales. These interactions link plutonism, tectonic deformation, and upward mobility of eruptible rhyolite in tectonically active margins.

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“…The "Los Bronces-Río Blanco" porphyry Cu-Mo deposit is emplaced in the Miocene to early Pliocene Andean magmatic arc and is developed in the frontal cordillera of the Central Andes of Chile in South America (Figure 2a) [12,14,15,26]. It is exploited in two neighbor mining operations (Figure 2b), namely the Los Bronces Mine, which is managed by the Anglo American Company and the Andina Mine, managed by CODELCO (Corporación Nacional de Cobre, Santiago, Chile).…”

Section: The Case Of Study: Main Mineralogical Features Of the Los Brmentioning

confidence: 99%

“…It is exploited in two neighbor mining operations (Figure 2b), namely the Los Bronces Mine, which is managed by the Anglo American Company and the Andina Mine, managed by CODELCO (Corporación Nacional de Cobre, Santiago, Chile). Recent discoveries by Anglo American have determined that this porphyry deposit is one of the largest world class metal districts [12,14,15,26]. In the Los Bronces Mine, extraction is developed at ~4000 m above mean sea level (a.m.s.l.…”

Section: The Case Of Study: Main Mineralogical Features Of the Los Brmentioning

confidence: 99%

“…This pattern has a hybrid kinematics evidenced by strike-slip displacement and hydrothermal filling [28,31,32]. The vein-fault pattern cuts the entire bedrock system including a folded volcanoclastic sequence of the Farellones Formation, the granitoid rocks of San Francisco Batholith, minor intrusions and the mineralized hydrothermal breccias [26,28,31] ( Figure 5b). The kinematic model of the district (Figure 5c; [31]) explains the relationship between the regional and mine scale structural patterns.…”

Section: Without-arsenic Structural Modelmentioning

confidence: 99%

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The Arsenic Fault-Pathfinder: A Complementary Tool to Improve Structural Models in Mining

2018

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In a mining operation, the structural model is considered as a first-order data required for planning. During the start-up and in-depth expansion of an operation, whether the case is open-pit or underground, the structural model must be systematically updated because most common failure mechanisms of a rock mass are generally controlled by geological discontinuities. This update represents one of the main responsibilities for structural geologists and mine engineers. For that purpose, our study presents a geochemically-developed tool based on the tridimensional (3-D) distribution of arsenic concentrations, which have been quantified with a very high-density of blast-holes sampling points throughout an open pit operation. Our results show that the arsenic spatial distribution clearly denotes alignments that match with faults that were previously recognized by classical direct mapping techniques. Consequently, the 3-D arsenic distribution can be used to endorse the existence and even more the real persistence of structures as well as the cross-cutting relationships between faults. In conclusion, by linking the arsenic fault-pathfinder tool to direct on field fault mapping, it is possible to improve structural models at mine scale, focusing on geotechnical design and management, with a direct impact in the generation of safety mining activities.

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Structural Evolution of the Rio Blanco-Los Bronces District, Andes of Central Chile: Controls on Stratigraphy, Magmatism, and Mineralization

Cited by 52 publications

References 58 publications

Tectonic role of margin-parallel and margin-transverse faults during oblique subduction in the Southern Volcanic Zone of the Andes: Insights from Boundary Element Modeling

Tectonic role of margin-parallel and margin-transverse faults during oblique subduction in the Southern Volcanic Zone of the Andes: Insights from Boundary Element Modeling

Interpreting Granitic Fabrics in Terms of Rhyolitic Melt Segregation, Accumulation, and Escape Via Tectonic Filter Pressing in the Huemul Pluton, Chile

The Arsenic Fault-Pathfinder: A Complementary Tool to Improve Structural Models in Mining

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