Article

Porphyry-Style Alteration and Mineralization of the Middle Eocene to Early Oligocene Andahuaylas-Yauri Belt, Cuzco Region, Peru

December 2003
Economic Geology 98(8):1575-1605

December 2003
98(8):1575-1605

DOI:10.2113/gsecongeo.98.8.1575

Authors:

José Perelló

Víctor Carlotto

Universidad Nacional San Antonio Abad del Cusco, Cusco

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Originally known for its Fe-Cu skarn mineralization, the Andahuaylas-Yauri belt of southeastern Peru is rapidly emerging as an important porphyry copper province. Field work by the authors confirms that mineralization in the belt is spatially and temporally associated with the middle Eocene to early Oligocene (∼48-32 Ma), calc-alkaline Andahuaylas-Yauri batholith, a composite body with an areal extent of ∼300 × 130 km emplaced into clastic and carbonate strata (e.g., Yura Group and Ferrobamba Formation) of Jurassic to Cretaceous age. Batholith emplacement included early-stage, mafic, cumulate gabbro and diorite between ∼48 and 43 Ma, followed by pulses of granodiorite and quartz monzodiorite at ∼40 to 32 Ma. Coeval volcanic rocks make up the middle Eocene to early Oligocene Anta Formation, a sequence of >1,000 m of andesite lava flows and dacite pyroclastic flows with interbedded volcaniclastic conglomerate. Sedimentary rocks include the red beds of the Eocene to early Oligocene San Jerónimo Group and the postmineralization late Oligocene to Miocene Punacancha and Paruro formations. Eocene and Oligocene volcanic and sedimentary rocks are interpreted to have accumulated largely in both transtensional and contractional synorogenic basins. New and previously published K-Ar and Re-Os ages show that much of the porphyry-style alteration and mineralization along the belt took place during the middle Eocene to early Oligocene (∼42-30 Ma). Thus, batholithic magma emplacement, volcanism, and sedimentation are inferred to have accompanied a period of intense deformation, crustal shortening, and regional surface uplift broadly synchronous with the Incaic orogeny. Supergene mineralization is inferred to have been active since the Pliocene on the basis of geomorphologic evidence and a single K-Ar determination (3.3 ± 0.2 Ma) on supergene alunite. The belt is defined by 31 systems with porphyry-style alteration and mineralization, including 19 systems grouped in 5 main clusters plus 12 separate centers, and by hundreds of occurrences of magnetite-rich, skarn-type Fe-Cu mineralization. Porphyry copper stocks are dominated by calc-alkaline, biotite- and amphibole-bearing intrusions of granodioritic composition, but monzogranitic, monzonitic, quartz-monzonitic, and monzodioritic stocks occur locally. Hydrothermal alteration includes sericite-clay-chlorite, and potassic, quartz-sericitic, and propylitic assemblages. Calcic-potassic and advanced argillic alteration associations are locally represented, and calc-silicate assemblages with skarn-type mineralization occur where carbonate country rocks predominate. Porphyry copper deposits and prospects of the belt range from gold-rich, molybdenum-poor examples (Cotabambas), through deposits carrying both gold and molybdenum (Tintaya, Los Chancas), to relatively molybdenum-rich, gold-poor end members (Lahuani). Gold-only porphyry systems are also represented (Morosayhuas). Gold-rich porphyry copper systems are rich in hydrothermal magnetite and display a positive correlation between Cu and Au in potassic alteration. The bulk of the hypogene Cu (-Au, -Mo) mineralization occurs in the form of chalcopyrite and bornite, in intimate association with early-stage potassic alteration which, in many deposits and prospects, is variably overprinted by copper-depleting sericite-clay-chlorite alteration. Most porphyry copper systems of the belt lack economically significant zones of supergene chalcocite enrichment. This is due primarily to their relatively low pyrite contents, the restricted development of quartz-sericitic alteration, and the high neutralization capacities of both potassic alteration zones and carbonate country rocks as well as geomorphologic factors. Leached cappings are irregular, typically goethitic, and contain copper oxide minerals developed by in situ oxidation of low-pyrite, chalcopyrite (-bornite) mineralization.

Andean evolution, orogenic deformation and uplift of the Western Cordillera and Altiplano of southern Peru, northern Bolivia and Chile: Eocene-Oligocene lithospheric delamination

Article

Jun 2023
J S AM EARTH SCI

Chelle Michou EG 2015

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Jun 2021

Cenozoic Tectonics and Porphyry Copper Systems of the Chilean Andes

Chapter

Jan 2012

Boletín de la Sociedad Geológica del Perú Evolución magmática-hidrotermal del sistema pórfido-skarn Paraíso y su relación con la mineralización de Cu

Article

Full-text available

Jan 2014

Juan Carlos Cuellar Quispe

The Paraíso porphyry-skarn system is located in southern Peru (Apurímac department, Abancay province, Curahuasi district), 10 km west of the Cotabambas Cu-Au porphyry and 40 km north of the Las Bambas deposit. It is hosted by the Andahuaylas-Yauri Batholith, which elsewhere also hosts Middle Eocene to Early Oligocene porphyry and skarn deposits (~42-30 Ma). The sedimentary rocks in the area belong to a succession that includes siliciclastic deposits (Yura Group) and limestones (Ferrobamba Formation). The local structural system is dominated by two intersecting fault systems, the NW-trending Paraíso system and the NNE-trending Anubia fault system. This study reports mineralogical, petrographic, and geochemical characteristics of several intrusive pulses, to which a series of veins is related. Using paragenetic logging, 15 vein types (type 1 through type 15) were identified on the basis of their mineralogical assemblages. These types were in turn grouped into three main stages: pre-mineralization, main mineralization, and post-mineralization. The precursor plutons consist of the Quartz-Diorite, which does not display veins and appears to have acted as host rock, and the younger Tonalite, which shows quartz veins with halos of K-feldspar. The parental pluton is the Tonalite Porphyry, which presents all vein types and is apparently the intrusion that generated the K-feldspar veins (types 1 to 7). It intruded the limestone succession and generated a skarn assemblage which, following subsequent cooling, developed a typical retrograde assemblage (ep-chl-mag-py-ccp; veins of types 9 to 12). This Tonalite Porphyry yielded a zircon U-Pb age of 34.23 ± 0.20 Ma and is cut by a mineralized magmatic-hydrothermal breccia. The Dacite Porphyry 1, which crystallized at 33.68 ± 0.21 Ma, cuts this breccia and is cut by quartz veins with chalcopyrite sutures (type 13): these veins could represent the distal expression of a mineralized porphyry stock that has not been identified yet, representing a blind exploration target. The younger Dacite Porphyry 2 shows qtz-cal-sph veins (type 15, i.e. the latest type). The last magmatic event is represented by dacitic dikes, one of which crystallized at 33.71 ± 0.36 Ma. The 3 zircon U-Pb ages reported here show that the intrusions related to mineralization crystallized over a very short time span (0.55 ± 0.41 Myr) between at most ~34.5 and ~33.3 Ma, i.e. exactly around the Eocene-Oligocene boundary (~33.9 Ma). Geochemical indicators such as REE and the Sm/Yb ratio indicate that some of the related magmas interacted with a coeval lower crust dominated by amphibole, suggesting that the crust may have been 40-45 km-thick at that time. RESUMEN El sistema pórfido-skarn Paraíso está ubicado en el sur del Perú, departamento de Apurímac, provincia de Abancay, distrito de Curahuasi; a 10 km al oeste del pórfido de Cu-Au de Cotabambas, y 40 km al norte del proyecto Las Bambas, es decir dentro del Batolito Andahuaylas-Yauri, que hospeda yacimientos de tipo pórfido y skarn de edad Eoceno medio a Oligoceno temprano (~42-30 Ma). Las rocas sedimentarias aflorantes pertenecen a la sucesión silicoclástica del Grupo Yura y a las calizas de la Formación Ferrobamba. Estructuralmente, el área está controlada por la intersección del sistema de fallas Paraíso, de orientación NOSE , y del sistema de fallas Anubia, de orientación NNE-SSO.

Exhumation différentielle de la Cordillère Orientale (Déflexion d'Abancay, Pérou): Une syntaxe tectonique andine ?

Thesis

Dec 2019

Benjamin Gérard

Ma thèse se focalise sur la compréhension de la structuration de la bordure nord de l’Altiplano: La Déflexion d’Abancay. Cette région qui marque la segmentation latitudinale des Andes Centrales au Pérou, surprend par son atypisme quant à son anomalie topographique positive et par l’obliquité prononcée des reliefs, des failles et du réseau hydrographique qui la composent. Incisée en profondeur par les rivières Apurimac et Urubamba, elles-mêmes capturées par les systèmes de failles défléchies, la Déflexion d’Abancay présente de nombreux plutons à l’affleurement, idéaux pour investiguer la dynamique des roches en profondeur et comprendre la place de cette région dans la tectonique Andine. Cette dernière, occupe deux ensembles morpho-tectoniques différents : La Cordillère Orientale au nord et l’Altiplano au sud. Ces deux ensembles sont séparés par le système de failles crustales de l’Apurimac. Malgré ses caractéristiques saisissantes, la région d’Abancay est dépourvue d’étude poussée récente à son sujet afin de contraindre sa structuration et son évolution au cours du temps dans le contexte géodynamique andin depuis 40 Ma.J’ai développé une approche pluridisciplinaire basée sur des méthodes de thermochronologie basse-température, de modélisation thermo-cinématique des données obtenues et de géomorphologie quantitative afin de mettre en évidence les vitesses d’exhumation de la région, les mécanismes à l’origine de sa structuration et son évolution morphologique récente pour des échelles spatio-temporelles différentes. Je montre que la Déflexion d’Abancay enregistre dans sa globalité des taux d’exhumation de 0,2±0,1 km/Ma constants et uniformes au cours du temps entre 40 et ∼5 Ma. Cette exhumation est contemporaine au soulèvement des Andes Centrales en conséquence d’un raccourcissement crustal et/ou d’un flux de croûte inférieure à l’échelle des Andes Centrales. Dans ce contexte, La Déflexion d’Abancay s’intégrait dans un paléo-Altiplano partiellement ou totalement endoréique s’étendant bien plus au nord (∼10°S) que son extension septentrionale actuelle (∼14°S). Bien que le nord de la Cordillère Orientale et l’Altiplano conservent des taux d’exhumation identiques après ∼5 Ma, le sud de la Cordillère Orientale enregistre une augmentation abrupte de ces derniers (1,2±0,4 km/Ma) créant un différentiel d’exhumation latitudinal. Cette augmentation locale de l’exhumation s’explique par l’action conjointe de l’incision par capture et érosion régressive du paléo-Altiplano par la rivière Urubamba ainsi qu’un soulèvement tectonique par basculement de la Cordillère Orientale au travers de l’activité en rétrochevauchement du système de failles crustales héritées de l’Apurimac. Compte tenu de ces interprétations, je propose une nouvelle définition géologique de la Déflexion d’Abancay et j’avance l’hypothèse d’une syntaxe tectonique comparable aux syntaxes Himalayennes ou Alaskiennes de par les similitudes morphologiques et tectoniques entre ces régions.

Differential exhumation of the Eastern Cordillera (Abancay Deflection, Peru): An Andean tectonic syntaxis?

Thesis

Full-text available

Jan 2020

Benjamin Gérard

I focus my thesis on the understanding of the structuration of the Altiplano northern edge : the Abancay Deflection. This region marks abruptly the latitudinal segmentation of the Peruvian Central Andes and presents striking features such as a positive topographic anomaly in comparison of its surroundings, relief obliquity, faults et rivers deviations. Numerous plutons, deeply incised by the Apurimac and Urubamba Rivers, outcrop in the core of the Abancay Deflection. This is a key that permits us to quantify the rock kinetics at depth in this region. The Abancay Deflection is located over two morpho- tectonic areas : The Eastern Cordillera northward and the Altiplano to the south. The crustal-scale Apurimac fault system separates these two regions. Despite these significant characteristics, the Abancay Deflection is poorly documented and no recent study deals about its long-lived structuration in the Andean geodynamic context since 40 Ma. I developed a multidisciplinary approach based on low-temperature thermochrono- logy, thermo-kinematics modeling and quantitative geomorphology to determine exhu- mation rates in the studied area, to unravel the mechanisms behind its structuration and to define its recent morphological evolution for different spatial and temporal scales. I demonstrate that the Abancay Deflection registered globally steady and uniforms ex- humation rates of 0.2±0.1 km/m.y. between 40 and ∼5 Ma, contemporary to the Central Andes surface uplift. This exhumation pattern marks a large-scale tectonic shortening and/or a lower crustal flow. In this context, the Abancay Deflexion was an integrant part of a paleo-Altiplano extending northward (∼10◦S vs. ∼14◦S nowadays) partially or to- tally internally drained. Although the northern Eastern Cordillera and the Altiplano kept identical exhumation rates after ∼5 Ma, the southern Eastern Cordillera experienced a rapid increase of these ones (1.2±0.4 km/m.y.) creating a latitudinal differential exhuma- tion pattern. I explain this very sharp and local increase of exhumation by the common work of the incision by capturing via regressive erosion the paleo-Altiplano through the Urubamba River together with a tectonic uplift tilting the Eastern Cordillera through the backthrusting activity of the inherited crustal-scale Apurimac fault system. Accor- ding to these interpretations, and regarding the morphological and tectonics similarities, I propose a new geological definition for the Abancay Deflection implying that this area is a tectonic syntaxis similar to the Himalayan or Alaskan syntaxes.

Antilla: a supergene enriched porphyry copper deposit in the Andahuaylas-Yauri belt, Peru

Conference Paper

Nov 2019

Andean Copper Province: Tectonomagmatic Settings, Deposit Types, Metallogeny, Exploration, and Discovery

Chapter

Jan 2005

Geologic Controls on Hypogene Mineralization at the Zaldívar Porphyry Copper-Gold-Molybdenum Deposit, Escondida District, Northern Chile

Chapter

Jan 2018

The porphyry copper mineralization at the Zaldívar deposit is confined to a NE-striking corridor of early- and late-intermineral granodioritic and dacitic porphyry intrusions and associated magmatic-hydrothermal breccia bodies. Country rocks comprise Early Permian rhyolite and andesite of La Tabla Formation plus comagmatic granitoids and Late Triassic andesite dikes. Middle Eocene andesitic rocks are common but of ill-defined distribution. Hydrothermal alteration consists of centrally located, magnetite-bearing potassic assemblages that are partially to completely overprinted by chlorite-epidote and sericitic alteration zones. The bulk of the hypogene metal resource was introduced synchronously with potassic alteration and A- and B-type veinlets during emplacement and evolution of multiple centers of biotite-bearing, early-intermineral porphyry and breccia bodies. Late-intermineral, hornblende-bearing dacite porphyry phases and associated breccia centers were emplaced later than the A- and B-veinlets but prior to multiple D-type veinlet generations and contributed additional, although lower grade, mineralization. Late-mineral dacite dikes are barren. Extensions to the east and northeast connect Zaldívar with Escondida Norte, and both can be considered as separate, coalescing porphyry copper deposits. Two discrete porphyry copper systems coexist at Zaldívar: Early Permian and late Eocene. The minor, copper-only Early Permian event (~290–285 Ma) was associated with an evolved, end-stage rhyolite porphyry phase of the La Tabla magmatism. The major late Eocene event (38.6–36.1 Ma) produced copper in addition to gold, molybdenum, and silver. Protracted Eocene porphyry copper alteration and mineralization, over ~2.5 m.y. as constrained by numerous U-Pb (zircon) and Re-Os (molybdenite) ages, was coincident with the high rates of uplift and denudation synchronous with contractional Incaic deformation. Earliest-stage porphyry intrusions at 39–38 Ma were probably associated with the terminal stages of a volcanic edifice, likely a dome complex, whose erosion products were deposited in contiguous, synorogenic basins. District-wide precursor magmatism of intermediate composition was active between 45 and 41 Ma. Oxidation and enrichment were active between ~17 and 15 Ma (supergene alunite), consistent with the chronology of supergene activity throughout the district and wider region.

A Model for the Lithospheric Architecture of the Central Andes and the Localization of Giant Porphyry Copper Deposit Clusters

Article

Aug 2023
ECON GEOL

In the central Andes, giant porphyry copper deposits of similar ages group into discrete geographic clusters that are regularly spaced and aligned within orogen-parallel belts. This clustering highlights how exceptional geologic processes affected localized regions of the lithosphere during mineralization and that the spatial and temporal distribution of giant porphyry deposits is non-random. Development of favorable regions of lithosphere for significant metal concentration are linked to the overlap of structural pathways that focus fluid and magma flow from the mantle to upper crust during high horizontal compressive strain events. These structural pathways are notoriously difficult to identify in the field due to their often-subtle surficial manifestations and continental scale. Field mapping at multiple scales in northwest Argentina and southern Peru, as well as regional structural traverses throughout the central Andes, indicate the presence of regional-scale structural corridors 5 – 25 km wide and hundreds of kilometers long that consist of myriad fault planes. The variable width and diffuse surface expression of these corridors is interpreted to reflect the upward propagation of underlying zones of basement weakness through younger supracrustal sequences in the over-riding plate. Such structural corridors are: (i) apparent at multiple scales of investigation; (ii) long-lived; (iii) preferentially reactivated though time; and (iv) evident in geophysical datasets. This structural architecture formed in response to the interplay of pre-Cenozoic tectonics and the orientation of inherited structural weaknesses. These fault systems persist in the upper crust as steep zones of enhanced permeability that can preferentially reactivate as pathways for ascending hydrous magmas and fluids during major deformation events. Linear orogen-parallel structural belts cogenetic with the magmatic arc, provide the first order control to giant porphyry copper deposit distribution. The second order control is the intersection of orogen-oblique structural corridors with the orogen parallel belts, localizing deposit clusters at these intersections. Such regions are inferred to have been zones of deep permeability, with vertical translithospheric pathways activated during high strain tectonic events that affected the intra-arc stress field.

Differential exhumation of the Eastern Cordillera in the Central Andes

Article

Apr 2021

Basin evolution in response to flat-subduction in the Altiplano

Article

Full-text available

Oct 2021

This paper assesses models for basin formation in the Altiplano. New magnetostratigraphy, palynology, and 40Ar/39Ar and U–Pb geochronology from the central Corque Syncline show that the 7.4 km thick section was deposited between 36.7 and 18.7 Ma. The base of the section post-dates exhumation in both the Western and Eastern cordilleras, precluding deposition in a classic retroarc foreland basin setting. Rotated palaeomagnetic vectors indicate counterclockwise rotation of 0.8 (myr)−1 since the early Oligocene. Detrital zircon provenance data confirm previous interpretations of Eocene– early Oligocene derivation from the Western Cordillera and a subsequent switch to an Eastern Cordilleran source. Flexural modelling indicates that loads consistent with palaeoelevation estimates cannot account for all the subsidence. Rather, the timing and magnitude of subsidence is consistent with Eocene emplacement and Oligocene–early Miocene re-steepening of a flat slab. Integration of the magmatic, basin and deformation history provides a coherent model of the effects of flat-slab subduction on the overriding plate. In this model, basin formation in the upper platewas controlled by flat-slab subduction, with subsidence enhanced in front of the zone of flat-slab subduction, but reduced over the crest of the flat slab. We conclude that the Altiplano was conditioned for plateau formation by Eocene–Oligocene flat-slab subduction. Supplementary material: https://doi.org/10.6084/m9.figshare.c.5664345

Differential Exhumation of the Eastern Cordillera in the Central Andes: Evidence for South‐Verging Backthrusting (Abancay Deflection, Peru)

Article

Full-text available

Apr 2021
TECTONICS

Located at the northern tip of the Altiplano, the Abancay Deflection marks abruptly the latitudinal segmentation of the Central Andes spreading over the Altiplano to the south and the Eastern Cordillera northward. The striking morphological contrast between the low‐relief Altiplano and the high‐relief Eastern Cordillera makes this area a well‐suited place to determine spatiotemporal variations in surface and/or rock uplift and discuss the latest phase of the formation of the Central Andes. Here, we aim to quantify exhumation and uplift patterns in the Abancay Deflection since 40 Ma and present new apatite (U–Th)/He and fission track data from four altitudinal profiles and additional individual samples. Age–elevation relationships and thermal modeling both document that the Abancay Deflection experienced a moderate, spatially uniform, and steady exhumation at 0.2 ± 0.1 km/Myr between 40 and ∼5 Ma implying common large‐scale exhumation mechanism(s). From ∼5 Ma, while the northern part of the Eastern Cordillera and the Altiplano registered similar ongoing slow exhumation, the southern part of the Eastern Cordillera experienced one order‐of‐magnitude of exhumation acceleration (1.2 ± 0.4 km/Myr). This differential exhumation since ∼5 Ma implies active tectonics, river capture, and incision affecting the southern Eastern Cordillera. 3D thermokinematic modeling favors a tectonic decoupling between the Altiplano and the Eastern Cordillera through backthrusting activity of the Apurimac fault. We speculate that the Abancay Deflection, with its “bulls‐eye” structure and significant exhumation rate since 5 Ma, may represent an Andean protosyntaxis, similar to the syntaxes described in the Himalaya or Alaska.

Características Metalogenéticas de los Depósitos Tipo Pórfidos y Epitermales de las Franjas XV, XXIII, XXI-A y XXI-C del Sur del Perú.

Preprint

Full-text available

Mar 2021

Resumen: Importantes yacimientos minerales como Arcata, el Zafranal, Las Bambas, Trapiche, Orcopampa, entre otros; se emplazan en la Cordillera Occidental de los Andes del Sur del Peru, espáticamente en las franjas metalogenéticas X, XV, XX-A y XXIII. El presente trabajo se ha desarrollado en base a la información recolectada en campo, así como los datos geoquímicos, isotópicos y dataciones geocronológicas de los principales yacimientos, recopilados de los distintos trabajos de multiples autores, con la que se ha determinado que las principales épocas metalogenéticas, entre los 5 y 6 Ma (Franja XXIII), entre los 18-10 Ma (franja XXI-A) y 40-36 Ma (Franja XV), asociadas a las unidades tectonoestratigráficas, Plutonismo de Arco Magmático Eoceno Oligoceno y al Arco magmático del Mioceno. Palabras clave: Metalogenia, unidades tectonoestratigráficas, geocronología, franjas metalogenéticas.

Metallogenic aspects of giant porphyry systems of the Andes

Conference Paper

Jan 2004

Aplicación de los algoritmos de machine learning e innovaciones estadísticas en nuevas metodologías para la prospección geoquímica del departamento de Puno

Conference Paper

Full-text available

Sep 2023

Luis Alberto Tupa Coila

El Perú es un país minero donde se hospedan gran cantidad de yacimientos que están en operación, ¿Qué haremos cuando estas reservas se acaben? Encontrar nuevos yacimientos se vuelve cada vez un reto mayor, por ello necesitamos plantear nuevos métodos de exploración, el presente trabajo propone el uso de Machine Learning e innovaciones estadísticas para identificar nuevas zonas geoquímicamente prospectables en el departamento de Puno, para lo cual se evaluaron muestras de sedimentos publicados en el INGEMMET. La evaluación consistió en reconocer anomalías de los elementos indicadores y pathfinders en dominios geoquímicos identificados a partir de los algoritmos de clustering como K-means y T-SNE aplicados a elementos litófilos y siderófilos, tratando de no omitir anomalías por el tamaño de escala en el análisis se optó en identificar anomalías locales con grado de confianza mediante una variante del índice de enriquecimiento relativo local; en el análisis multivariado se recurrió a los algoritmos de scoring y clustering para comparar relaciones respecto a un elemento de interés. Finalmente se integró las capas generadas a partir del análisis Fuzzy y las redes neuronales artificiales en los mapas autoorganizados de Kohonen, los resultados mostraron una buena validación con los depósitos conocidos, mostrando nuevas áreas con alto grado de prospectividad. La metodología propuesta en el análisis univariado y multivariado permitieron extraer la mayor cantidad de información de las muestras, analizándolo y representándolo de distintas formas y escalas. Palabras clave: Clasificación mineral, dominios geoquímicos, máxima entropía, machine learning.

Aplicación de los algoritmos de Machine Learning e innovaciones estadísticas en nuevas metodologías para la prospección geoquímica del departamento de Puno.

Conference Paper

Sep 2023

Luis Alberto Tupa Coila

Influence of different tectonic settings on fracture formation and fluid flow around upper-crustal magmatic intrusion: insights from numerical modelling

Article

Full-text available

Mar 2024

Large porphyry Cu and epithermal Au deposits tend to form in distinct tectonic, porphyry and high-sulfidation epithermal deposits in compressional settings, and low-sulfidation epithermal deposits in extensional settings. Given that the analysis of the shallow metallogenic dynamic processes at the upper-crust scale is insufficient, especially the ore-bearing fracture formation and fluid-focusing mechanism around the mineralizing magmatic intrusion under different tectonic backgrounds, we aimed to study how tectonic settings influence fracture formation and fluid hydrodynamics in and around a hot intrusion. We developed a finite element model coupling thermal-hydrological-mechanical processes to simulate the fracture formation, evolution of fluid velocities, and accumulation of water-rock interactions. The model results show that tectonic compression increases the degree of fracturing, hydrothermal fluid velocities, and water-rock interaction within and laterally around the intrusion; tectonic extension enhances fracturing, hydrothermal fluid velocities, and water-rock interaction at shallow depth. These results confirm that tectonic compression may promote the formation of porphyry Cu deposits, while tectonic extension may promote the formation of shallow hydrothermal deposits. Our model explains the effects of tectonic activity on fracture formation and fluid flow around hot magmatic intrusions in upper crust and deepens our understanding of the relationship between tectonic activity and deposit formation there.

Geochemical prospectivity of Au mineralization through Concentration-Number fractal modelling and Prediction-Area plot: a case study in the east of Iran

Article

Full-text available

Feb 2024

Capitana mine, Tignamar district, a unique tin – bismuth concentration in the Chilean Central Andes, 250 km west of the Bolivian Tin Belt: Link to the Proterozoic-Paleozoic basement Belen inlier and the Arequipa-Antofalla terrane, a probable remnant of Laurentia

Article

Dec 2023
J S AM EARTH SCI

The dogma is that there are NO TIN deposits in the Chilean Andes; tin deposits would exist only some 250 km to the east in the Bolivian Tin Belt. We describe here a small but metallogenetically significant epithermal tin system with bismuth, silver, copper, and antimony-arsenic in a belt otherwise characterized by porphyry copper and epithermal gold deposits in the high Andes of Arica, northernmost Chile. Its lead isotopes are different from porphyry copper deposits and have affinity to the Proterozoic-Paleozoic metamorphic basement, represented locally by the Belen-Tignamar Metamorphic Complex, considered to be part of a “Grenville age” remnant of North America left behind before rifting and dismembering of the ancient mega continent of Rodinia. Surprisingly, the ca. 220°C hydrothermal mineralization is evidently younger than the adjacent 17 Ma old Tignamar porphyry copper system, and appears to have been formed from fluids expelled during post Miocene compressive thrusting and thickening of the crust to more than 80 km.

Musings on Future Exploration Targets and Strategies in the Andes

Chapter

Jan 2005

Richard H Sillitoe

A variety of metals and deposit types define the metallogeny of the Andes from Colombia through Ecuador, Peru, and Bolivia to Argentina and Chile, although porphyry copper and epithermal gold deposits undoubtedly predominate and will continue to do so. Discoveries over the last 30 yrs or so, predominantly in the central Andes and especially Chile, have been made using routine, field-based geologic and complementary geochemical methods, a situation that is considered unlikely to change radically in the foreseeable future. The only clearcut evolutionary change is the increased number of deposits being discovered beneath pre- and postmineral cover. The predictive capacity of conceptual geology has had minimal impact on the Andean discovery record but is thought to offer much promise for the future. This introductory article selects mineralization styles and relationships as well as some broader metallogenic parameters as simple examples of geologic concepts that may assist exploration. Emphasis is placed on porphyry copper ± molybdenum ± gold and high-, intermediate-, and lowsulfidation epithermal gold ± silver deposits, although reference is also made to several carbonate rock-hosted precious and base metal deposit types and styles as well as subvolcanic tin, volcanogenic massive sulfide, and slate-belt and intrusion-related gold deposits. Particular emphasis is placed on the potential for exceptionally high grade porphyry copper, porphyry gold, epithermal gold, and subvolcanic tin deposits. Deposits resulting from the oxidation, enrichment, and chemical transport of copper and zinc and mechanical transport of gold and silver during supergene weathering are also briefly highlighted. Si bien la metalogenia de los Andes de Colombia, Ecuador, Perú, Bolivia y Chile se encuentra definida por una gama de metales y estilos de mineralización, son los depósitos tipo pórfido de cobre y epitermal de oro los que dominan en el presente y continuarán prevaleciendo en el futuro. Los descubrimientos de los últimos 30 años, predominantemente en los Andes centrales y especialmente en Chile, han sido realizados mediante métodos geológicos rutinarios de campo, generalmente complementados satisfactoriamente por métodos geoquímicos. Se estima que esta situación difícilmente experimentará variaciones radicales en un futuro cercano. El único cambio destacable en esta historia evolutiva está dado por el aumento apreciable de descubrimientos de depósitos cubiertos, bajo cobertura pre o postmineral. A nivel andino, la capacidad predictiva de la geología conceptual ha tenido un impacto mínimo en el número total de descubrimientos, aunque se piensa que su uso debiera garantizar buenas perspectivas futuras. El presente artículo

Discovery and Geology of the Esperanza Porphyry Copper-Gold Deposit, Antofagasta Region, Northern Chile

Chapter

Jan 2005

Geoquímica de sedimentos en las subcuencas Ichu, Hornillos Alto, Molloco, Alto Camaná, San Gabán Alto, Antauta y Grande, sur del Perú

Technical Report

Full-text available

Nov 2022

Gerardo Trelles

Local knowledge and imperial art: A preliminary LA-ICP-MS analysis of clay preference and ceramic production practices in ancient Cuzco (ca. 1100–1550 CE)

Article

Apr 2023
JASR

Arc magmatic evolution and porphyry copper deposit formation under compressional regime: A geochemical perspective from the Toquepala arc in Southern Peru

Article

Mar 2023
EARTH-SCI REV

The Paleocene–Eocene southern Peru metallogenic belt contains numerous very large to supergiant porphyry Cu‒Mo deposits. The deposits were dated previously as coeval with the Incaic I orogeny at ca. 60 Ma. However, tectono-magmatic processes during the formation of the deposits are poorly constrained. Here, we integrate published geochronological, geochemical, and mineralogical data from barren and ore-related granitoids in the region. The syn-orogenic unit (60–53 Ma) has significantly higher average ratios of Sr/Y (104.4), La/Yb (29.6), Dy/Yb (1.9), and EuN/Eu* (1.07) than the pre-orogenic unit (69–60 Ma; Sr/Y = 18.6, La/Yb = 11.5, Dy/Yb = 1.7, and EuN/Eu* = 0.66). The syn-orogenic unit exhibits high Dy/Yb ratios in relatively primitive rocks and has a lower average Dy/Yb(zircon) ratio (0.23) and higher EuN/Eu*(zircon) ratio (0.43) than the pre-orogenic unit (Dy/Yb(zircon) = 0.29 and EuN/Eu*(zircon) = 0.21). These integrated data suggest that the syn-orogenic magmas underwent high-pressure, garnet-dominated fractionation prior to amphibole-dominated fractionation, distinct from the pre-orogenic magmas which underwent low-pressure, plagioclase-dominated fractionation. Comprehensive investigation of the geological background suggests that the geochemical variations between pre- and syn-orogenic units were caused by the long-term evolution of mantle-derived magmas at the crust‒mantle boundary during arc compression, instead of crustal thickening. Fractionation of ferric iron-depleted minerals (e.g., garnet and amphibole) in the mantle-derived basaltic magmas probably has positive effects on magmatic fertility. The dataset presented highlights the critical role of high-pressure differentiation, thus providing an insight into the relationship between the arc compressional regime and giant porphyry Cu deposit formation in the Andes. Zircon trace elements can be useful indicators for porphyry deposit exploration in the Toquepala arc in southern Peru. However, the regional tectonic settings of the Andean arcs should be studied thoroughly before applying these indicators.

Investigation of geochemical characteristics and hydrothermal alteration zone mapping supported by remote sensing of a porphyry-copper prospect, southeastern Iran: integrated applications to exploration

Article

Jul 2022

This exploration methodology case study is situated along the Sistan Suture Zone where the granitoid suite is a mantle-derived multiphase intrusive complex. One of the characteristics of this region is the presence of large areas of sulfide-bearing, quartz-rich stockwork and pyritic veins. Geochemical findings show it is limited to the calc-alkaline to shoshonitic series intrusions and is associated with a volcanic arc (I-type) formed within an active continental margin subduction setting. The associated intrusive complex has characteristics consistent with Cu productive porphyries, supported by high K-adakitic Sr/Y, La/Yb, Y, and Al 2 O 3 /TiO 2 geochemical signatures. The stockwork mineralization includes the hypogene (chalcopyrite and bornite), with locally superimposed supergene (covellite, malachite, goethite, and hematite) zones. The Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) images (visible-near infrared (VNIR) and shortwave infrared (SWIR) bands) and Mixture Tuned Matched Filtering (MTMF) algorithm, enable identification of each hydrothermal alteration type, especially where pictures were innovatively classified by a concentration-number (C-N) fractal method. Four alteration types are evident, i.e. phyllic, argillic, and propylitic, as well as secondary (supergene) jarositethat are associated with gossans, which are an indicator of the hypogene pyritic shell. The propylitic alteration envelopes the phyllic and argillic varieties, forming a belt around the pyritic shell; alteration assemblages were confirmed by XRD analysis. Finally, all results show a mineralization-alteration pattern within this case study region that is similar to those of known porphyry copper and associated molybdenum- and gold-bearing systems in this region of Iran and worldwide.

Rapid transition to fertile magma and promotion of porphyry mineralization: A case study from the Don Javier deposit

Article

Full-text available

Jun 2022
ORE GEOL REV

The Don Javier porphyry Cu–Mo deposit formed contemporaneously with the Incaic I orogeny (∼60 Ma) in southern Peru. The causative dacite porphyry is hosted by the Yarabamba Superunit, which is the youngest batholithic unit in the Toquepala arc. In this study, we conducted elemental and isotopic analyses on samples from the dacite porphyry and Yarabamba Superunit in an effort to clarify the origins and formation mechanism of the deposit. Zircon U–Pb dating shows that the young part of the Yarabamba Superunit was emplaced at 65.4 ± 0.7 to 63.5 ± 0.8 Ma, and the causative dacite porphyry was emplaced at Don Javier between 59.2 ± 1.1 and 59.9 ± 0.4 Ma. The Yarabamba Superunit and dacite porphyry have similar εHf(t) and δ¹⁸O isotope values, ranging from –4.6 to +1.9 and 5.1‰ to 6.4‰, respectively. The Yarabamba Superunit has initial Sr and Nd isotope values of 0.7053–0.7058 and 0.51242–0.51244, respectively. Isotopic data suggest that the Yarabamba Superunit and dacite porphyry evolved from an isotopically homogeneous magma reservoir with minor crustal assimilation. However, the dacite porphyry has whole-rock and zircon Eu/Eu* values of 0.9 and 0.34, respectively, higher than those of the Yarabamba Superunit (0.6 and 0.13). Additionally, the dacite porphyry has significantly higher apatite S content (0.07) and XCl values (0.21) than those of the Yarabamba Superunit (apatite S: 0.04; XCl values: 0.15). The calculated magmatic oxidation state shows that the dacite porphyry has a significantly higher magmatic oxygen fugacity (ΔFMQ +1.1) than the Yarabamba Superunit (ΔFMQ –0.5). Together, the data suggest that the magmas that formed the Yarabamba Superunit and causative dacite porphyry are characteristics of distinct tectonic regimes. The magma of the Yarabamba Superunit was generated during normal subduction and underwent low-pressure, H2O-poor, plagioclase-dominated fractionation while the magma of the dacite porphyry was generated during arc compression and underwent high-pressure, H2O-rich, amphibole-(garnet) dominated fractionation, which led to a high oxidation state and volatile-rich magma that promoted porphyry mineralization at Don Javier. This rapid elevation of the magmatic oxidation state and volatile content occurred synchronously with the Incaic I orogeny (∼60 Ma), which indicates that this orogeny had a significant impact on the formation of the very large–giant porphyry ore systems in southern Peru.

Geology and Geochronology of the Miocene Rio Blanco Porphyry Cu-Mo Deposit, Northern Peru

Article

Mar 2022

The Rio Blanco porphyry Cu-Mo deposit occurs at the north end of the Miocene metallogenic belt of northern Peru. It has a thick supergene enrichment blanket; while normal for hyperarid Chile, this is unusual in mountainous, cloud forest terrain. Rio Blanco is hosted by the Portachuela batholith. Zircon U-Pb dating shows that the youngest part of the batholith was emplaced at 12.43 ± 0.13 Ma. The deposit formed during three magmatic-hydrothermal cycles. Cycle 1, by far the most important, occurred at 11.50 ± 0.17 to 10.92 ± 0.14 Ma (zircon U-Pb). Two intermineralization intrusions caused early potassic and propylitic alteration. This was then overprinted by a blanket of quartz-sericite, grading down into sericite-chlo-rite alteration. Cycle 1 was finally cut by a quartz-sericite–cemented breccia, which contains the highest-grade hypogene Cu-Mo grades. A cycle 1 molybdenite-bearing vein has a molybdenite Re-Os model age of 11.43 ± 0.16 Ma. Molybdenite Re-Os dating of the quartz-sericite–cemented breccias shows brecciation occurred at 11.28 ± 0.24 to 11.11 ± 0.18 Ma. Cycle 2 was restricted to the east side, where narrow porphyritic dacite 1 dikes (dated by zircon U-Pb at 10.62 ± 0.16 Ma) show biotite alteration and economic copper. Cycle 3, at 10.02 ± 0.12 to 9.06 ± 0.09 Ma (zircon U-Pb), was triggered by a swarm of NE-striking quartz-plagioclase porphyry and porphyritic dacite 2 dikes. Alteration was milder, and this cycle did not introduce economic copper. Nonmineralized pebble dikes cut the system, emanating from a major diatreme, about 3 × 1.3 km in size, on the north side of the deposit. The magmatic-hydrothermal history spanned about 2.5 m.y., with economic mineralization over about 1.48 m.y. However, metals were mostly introduced during cycle 1, which lasted approximately 0.58 m.y. Our work shows that while multiple magmatic-hydrothermal cycles produced Rio Blanco, sufficient metals were introduced to form a giant porphyry deposit within a single magmatic-hydrothermal cycle.

Geology and Geochronology of the Don Javier Cu-Mo Porphyry Deposit, Southern Peru

Article

Full-text available

Feb 2022
ORE GEOL REV

The Don Javier porphyry Cu-Mo deposit is located in the Yarabamba district of the Arequipa region, Peru, which represents the northwestern end of the Paleocene-early Eocene Cu belt of the central Andes, extending from northern Chile into southwestern Peru. The deposit occurs around the contacts of a dacite porphyry stock emplaced into the pre-mineralization and Yarabamba granodiorite batholith. The intrusions display a telescoped sequence of alteration, from shallow sericitic to deeper chloritic-sericitic, with minor remnant potassic assemblages, which are surrounded by propylitic zones. EB-, M-, EQ-, SQ-, and D-type veinlets occur in all alteration zones. The higher Cu and Mo grades are mainly associated with the widely distributed sulfide-quartz veinlets within the potassic and chlorite-sericite overlapping zones. The mineralized zone measures ∼500 m in width (NE-SW) by ∼ 800 m in length (NW-SE). Uranium-Pb zircon ages show that the Yarabamba granodiorite plutons were emplaced at ∼64.6 Ma and subsequently intruded by the inter-mineralization dacite porphyry intrusions at ∼59.9 to 59.5 Ma. Molybdenite Re-Os ages indicate that the deposit formed between ∼60.5 and 59.6 Ma. Younger molybdenite Re-Os ages (∼45.4 to 44.4 Ma) obtained in the deep parts of the altered rocks suggest that the deposit might have been overprinted by later hydrothermal activity in the Eocene. The success of exploration at Don Javier emphasizes that traditional methods such as geologic and geophysical mapping followed by timely drilling tests can still be effective in a mature metallogenic belt.

Timing and Nature of Mineralization and Associated Hydrothermal Alteration at the Öksüt High-Sulfidation Epithermal Au-Cu Deposit (Kayseri Province, Central Anatolia)

Chapter

Full-text available

Sep 2021

Öksüt is a breccia-hosted high-sulfidation epithermal gold-copper deposit, situated within the Develidag Volcanic Complex in south-central Anatolia. The volcanic complex, exposed on the northern edge of the Tauride range, is largely made up of late Miocene andesitic to dacitic porphyries, covered by a succession of Pliocene basalts and basaltic andesites. A series of N-S- to NNW-trending faults of the regional central Anatolian fault zone partly cut and border the volcanic complex to the east and west. Mineralization at Öksüt follows a predominant north-northwest trend that correlates well with the regional stress regime. The bulk of the mineralization occurs in two domains, the Keltepe and Güneytepe orebodies, where steeply dipping and pervasively supergene oxidized breccia zones exploited funnel-shaped diatreme conduits within pyroxene andesite porphyry. Emplacement of these phreatomagmatic breccias was largely controlled by vertical to subvertical faults with dominant normal-slip components. Mineralized breccias comprise a central zone of residual vuggy to massive silica alteration, laterally and vertically grading into zones of quartz-alunite and quartz-alunite-clay alteration. These silica-altered breccias contain relatively high gold grades, whereas significant mineralization was also encountered in quartz-alunite-clay alteration. In the oxide zone, gold occurs in native form, whereas in the hypogene zone it occurs both as native gold or within pyrite-enargite accompanied by marcasite, and rare chalcopyrite and tetrahedrite. To the west of Keltepe and in Güneytepe, at depth, the altered and mineralized breccias pass into barren zones of argillic and then into biotite-magnetite ± K-feldspar ± anhdyrite alteration, the latter typical of porphyry-type systems. Sporadic zones of calc-silicate alteration, represented by grossularite, diopside, and vesuvianite, are also present. Three 40Ar/39Ar ages obtained from alunite and illite range between 5.7 to 5.5 Ma and are concordant with previously reported U-Pb and 40Ar/39Ar ages (~6–5.5 Ma) from host pyroxene andesite porphyry. This suggests that high-sulfidation alteration and mineralization developed contemporaneously with postsubduction magmatism at the Develidag Volcanic Complex, in relationship to regional E-W directed extension that commenced at ~6 Ma. Our new ages also confirm Öksüt as the youngest epithermal gold deposit discovered to date in Anatolia, and possibly in the entire Western Tethyan metallogenic belt. The topographic prominence of the volcanic edifice combined with high permeability of the breccias favored deep supergene sulfide oxidation, thereby rendering Öksüt economically viable. Gold encapsulated in hypogene sulfides was liberated during the oxidation, whereas the copper was leached to produce a discontinuous chalcocite- and covellite-dominated enrichment zone, up to 50 m thick, at the base of oxidation.

Provenance of the Middle Jurassic-Cretaceous sedimentary rocks of the Arequipa Basin (South Peru) and implications for the geodynamic evolution of the Central Andes

Article

Jul 2021
GONDWANA RES

The provenance of Middle Jurassic-Cretaceous sedimentary rocks deposited in the southern Peruvian Arequipa Basin has been investigated based on the measurement of 41 Sr-Sm-Nd isotopic compositions of sedimentary rocks, 993 U-Pb zircons ages, and 202 Lu-Hf zircon isotope data. The Middle Jurassic units are dominated by Brazilian/Pampean and Grenville/Sunsas and have juvenile to evolved Hf isotopic compositions of Permian zircons. These are consistent with an Eastern Cordillera (EC) provenance. In contrast, the Late Jurassic Labra Formation presents the first appearance of Triassic-Jurassic zircons and an increase in Famatinian zircons thus suggesting a mixed provenance from the EC and/or Altiplano and the Coastal Cordillera (CC). The Gramadal Formation shows older U-Pb zircon ages, which reflect a major contribution from Precambrian sources either from the Amazon craton or the EC thus implying a change in provenance. Another change in provenance is documented for the Hualhuani Formation with sources located both in the CC and EC. Finally, the Santonian Chilcane Formation is characterized by a large contribution of Cretaceous to Famatinian zircons indicating that it was mainly sourced from the CC. Our provenance dataset associated with the depositional setting of the Middle Jurassic to Early Cretaceous formations and the cumulative curves of zircon age distribution, indicate that the Arequipa Basin was not a back-arc setting but rather a rift-like setting. Contrary to the older formations, the Chilcane Formation is dominated by contributions from the CC in a retroarc foreland basin setting. This statement further implies that the Andean basin located eastward of the volcanic arc had evolved directly from a rift to a retroarc foreland basin and implies that the control of Andean subduction on these basins might be much younger than previously thought.

Adakitic signal linked to Gondwanan porphyry type deposits from the Andean Frontal Cordillera of Argentina

Article

Apr 2020
CHEM ERDE-GEOCHEM

The Yalguaraz Cu - (Mo) porphyry deposit, genetically linked to the early Permian magmatism (279.9 ± 3.2 Ma), is located at the eastern margin of the Andean Frontal Cordillera of Argentina, 15 km north of the Permian San Jorge Cu porphyry deposit. The geochemistry of this Gondwanan metal-bearing magmatism reveals an arc affinity and an adakite-like signature. The petrogenetic analysis of these rocks also suggests assimilation of the continental crust in the source magmas and a change in the residual mineralogy from amphibole ± plagioclase in San Jorge magmas, to garnet in Yalguaraz magmas. This change to a higher-pressure residual mineralogy suggests increasing crustal thickness, which is consistent with regional geodynamic changes including progressive shallowing probably due to the subduction of an aseismic ridge south of 31 °S in the Andes of Argentina during the lower Permian.

Long-lived crustal damage zones associated with fault intersections in the high Andes of Central Chile

Article

Full-text available

May 2019

Long-lived, high-angle fault systems constitute high-permeability zones that can localize the upward flow of hydrothermal fluids and magma throughout the upper crust. Intersections of these types of structures can develop complex interference patterns, which constitute volumes of damaged rock (networks of small-scale faults and fractures) where permeability may be significantly enhanced. This is relevant for understanding regional-scale structural controls on the emplacement of hydrothermal mineral deposits and volcanic centers, and also on the distribution of areas of active upper-crustal seismicity. In the high Andes of central Chile, regional-scale geophysical (magnetic, gravimetric, seismic) and structural datasets demonstrate that the architecture of this Andean segment is defined by NW-and NE-striking fault systems, oblique to the N-S trend of the magmatic arc. Fault systems with the same orientations are well developed in the basement of the Andes. The intersections of conjugate arc-oblique faults constitute the site of emplacement of Neogene intrusive complexes and giant porphyry Cu-Mo deposits, and define the location of major clusters of upper-crustal earthquakes and active volcanic centers, suggesting that these fault systems are still being reactivated under the current stress regime. A proper identification of one-dimensional, lithospheric-scale high-permeability zones located at the intersections of high-angle, arc-transverse fault systems could be the key to understanding problems such as the structural controls on magmatic and hydrothermal activity and the patterns of upper-crustal seismicity in the high Andes and similar orogenic belts. Keywords: Basement fault intersections, Magma and hydrothermal fluid flow, Central Chile.

Atlas of Siliceous Hot Spring Deposits (Sinter) and other Silicified Surface Manifestations in Epithermal Environments (A.R. Hamilton, K.A. Campbell, and D.M. Guido)

Article

May 2019

Jeffrey Hedenquist

Geology of the Josemaría Porphyry Copper-Gold Deposit, Argentina: Formation, Exhumation, and Burial in Two Million Years

Article

Full-text available

May 2019

Porphyry-Cu Deposits of Turkey

Chapter

Full-text available

Jan 2019

Turkey, located within the western Tethyan-Eurasian Belt contains numerous porphyry copper deposits formed by the subduction, collision and post-collisional events during the closure of NeoTethys Ocean between the latest Cretaceous and late Miocene. These porphyry systems and associated epithermal and skarn deposits are associated with the subduction and post-subduction magmatic rocks emplaced along arc-parallel belts as in eastern Pontides and arc transverse extensional terranes as in the western Anatolian province (WAP) and Southeastern Anatolian Orogenic Belt (SEAOB).

Epithermal Deposits of Turkey

Chapter

Jan 2019

Tolga Oyman

In Europe and Middle East, Turkey is currently positioned as the largest producer of gold with a 2015 production of 27.5 t from predominantly porphyry and epithermal deposits. Although exploration for gold by advanced geochemical methods started in 1980s, Turkey entered into hard-rock mining based on cyanide process for extracting gold from low-grade ore in 2001. Before that, apart from placer mining, gold was sold in concentrate ore as by product in some deposits chiefly mined for base metals. Epithermal deposits are high-grade deposits dominated by open-space textures generally formed at depths of ~2 km with temperatures of < 400 °C. Due to their shallow-depth location, it is regarded that they represent easily mineable source of gold. This chapter is designed to focus attention on the geology of important epithermal gold mineralisation in Turkey with the aim to understand the basic regional and local geological setting and mineralogical and geochemical properties setting for the mineralisation. In the chapter the brief summary of selected epithermal deposits is emphasized the principal characteristics of important epithermal mineralisation all over Turkey including low, intermediate and high sulphidation types without taken into account their major economic element content on the base of reports from government and private companies and published or unpublished studies. Up to date, although literature on epithermal mineralisation in Turkey has been increasing with significant exploration and published data, still numerous questions remain unanswered and provide a source for future research.

Cotabambas: Late Eocene Porphyry Copper-Gold Mineralization Southwest of Cuzco, Peru

Chapter

Jan 2005

Opposite rotations in the Central Andes Bend: Tectonic scenario compared to other cases of opposite rotations and implications for long-term subduction at continental arcs

Article

Nov 2023
J S AM EARTH SCI

Keith Martin

Opposite paleomagnetic block rotations (counter clockwise to the northwest, and clockwise to the south) lie on either side of the axis of the Central Andes Bend. The associated subduction zone is convex in the direction of subduction. In contrast, 20 other cases of opposite rotations mostly relate to rollback of a subduction zone concave in the direction of subduction. Do you have evidence of opposite rotations which may comprise additional cases?

Geology and geochronology of the Pinaya mineral district: Magmatism and porphyry-style mineralization in the southern extension of the Andahuaylas-Yauri belt, Southern Peru

Article

Sep 2023
J S AM EARTH SCI

The Mesozoic magmatic, metamorphic, and tectonic evolution of the eastern Gangdese magmatic arc, southern Tibet

Article

Oct 2021

Magmatic arcs are natural laboratories for studying the growth of continental crusts. The Gangdese arc, southern Tibet, is an archetypal continental magmatic arc that formed due to Mesozoic subduction of the Neo-Tethyan oceanic lithosphere; however, its formation and evolution remain controversial. In this contribution, we combine newly reported and previously published geochemical and geochronological data for Mesozoic magmatic rocks in the eastern Gangdese arc to reveal its magmatic and metamorphic histories and review its growth, thickening, and fractionation and mineralization processes. Our results show that: (1) the Gangdese arc consists of multiple Mesozoic arc-type magmatic rocks and records voluminous juvenile crustal growth. (2) The Mesozoic magmatic rocks experienced Late Cretaceous granulite-facies metamorphism and partial melting, thus producing hydrous and metallogenic element-rich migmatites that form a major component of the lower arc crust and are a potential source for the Miocene ore-hosting porphyries. (3) The Gangdese arc witnessed crustal thickening and reworking during the Middle to Late Jurassic and Late Cretaceous. (4) Crystallization-fractionation of mantle-derived magmas and partial melting of thickened juvenile lower crust induced intracrustal chemical differentiation during subduction. We suggest that the Gangdese arc underwent the following main tectonic, magmatic, and metamorphic evolution processes: normal subduction and associated mantle-derived magmatism during the Late Triassic to Jurassic; shallow subduction during the Early Cretaceous and an associated magmatic lull; and mid-oceanic ridge subduction, high-temperature metamorphism and an associated magmatic flare-up during the early Late Cretaceous, and flat subduction, high-temperature and high-pressure metamorphism, partial melting, and associated crust-derived magmatism during the late Late Cretaceous. Key issues for further research include the temporal and spatial distributions of Mesozoic magmatic rocks, the evolution of the components and compositions of arc crust over time, and the metallogenic processes that occur in such environments during subduction.

Características metalogenéticas de los sistemas de mineralización tipo pórfidos-epitermales y yacimientos relacionados, ubicados en la Cordillera Occidental del Perú

Book

Full-text available

Apr 2022

During 2017, the Geological Mining and Metallurgical Institute of Peru (INGEMMET) carried out the project called GE33B-4 “Metallogenetic Characteristics of the porphyry and epithermal deposits of the Western Mountain Range”. This research had as main objective the contribution to the knowledge of the Metallogeny of the porphyry and epithermal type deposits in the area of study. Furthermore, this Andean tectonic domain comprises the regions of (1) Cajamarca-La Libertad, (2) Ancash, Junin- Cerro de Pasco, (3) Apurimac-Cusco-Arequipa-Puno. In this regard, specific mines and projects were evaluated, including Tantahuatay, Cerro Corona, Los Pircos, La Zanja, Yanacocha, El Galeno, La Carpa, Lincuna, Michiquillay, Orcopampa, Zafranal, Mina Aguila, Trapiche, Antilla, among others. For carrying out this study, a total of 764 rock and ore samples were used to hold lithogeochemical, petromineragraphic, fluid inclusions, Terraspec spectrometry and isotopic (stable and radiogenic) studies. In addition to the results of these studies, the historical data from the INGEMMET geoscientific database, as well as the information obtained through relevant geoscientific articles and theses from the study area, have been used, processed and in some cases they have been reinterpreted. In this sense, it allows us to conclude that this mountain range originated as a consequence of the convergence of the Farallón / Nazca plates below the South American plate. Therefore, it was the one event that marked the beginning of the calco-alkaline and hydrothermal magmatic activity that led to the location of mineral deposits of the porphyry and epithermal type along it, from the Lower Jurassic to the present. Likewise, it highlighted at least two periods of mineralization, one between 40 to 30 Ma. associated with the Eocene-Miocene Arc Plutonism tectonostratigraphic Unit (PeoNm-pA). Thus, in the southern sector there are deposits such as Cotabambas, Las Bambas Tintaya Los Chancas, Trapiche, Porvenir Atacocha and Quicay and another between 20 to 8 Ma.; (Michiquillay, Yanacocha, Lagunas Norte, Antamina, Morococha, Toromocho, Cerro de Pasco, Orcopampa, Shila Paula Selene, among others), related to the Eocene-Miocene Arc Volcanism Stratigraphic Tectono Unit (PeoNm-vA). In addition, it has also been related to the use of Tectono-Stratigraphic units, a criterion that has facilitated the integration and better understanding of geoscientific information. Furthermore, it allowed the understanding of the main metallogenetic characteristics of these deposits as well as the geological processes that are precursors and generators of mineralization. Thus, with this tool, lithogeochemical parameters that indicate the presence of fertile magmas have been evidenced, which differ from each other in the north, center and south sectors. In that regard, it has allowed the preparation of metallogenetic maps for the three sectors in which the area in question was divided.

درآمدی بر سیستمهای پورفیری (پراکندگی، مشخصات ناحیه ای و محلی، جایگاه تکتونیکی، روابط ولکانیکی، اثر سنگ دیواره ، روابط رگه رگچه ای و دگرسانی).

Conference Paper

Full-text available

Feb 2022

Origin and evolution of the Masjed Daghi Cu-Au-Mo porphyry and gold epithermal vein system, NW Iran: constraints from fluid inclusions and sulfur isotope studies

Article

Full-text available

Aug 2021
MINER PETROL

The Masjed Daghi porphyry-epithermal Cu-Au-Mo deposit in the northern Arabian-Eurasian collision zone of the Alborz Magmatic Assemblage, NW Iran, is hosted by an early Miocene quartz monzodiorite to diorite intrusion that intruded Eocene volcanic rocks. Potassic, phyllic, argillic, and propylitic alterations associated with four stages of porphyry mineralization (I to IV) are distinguished. Late high-sulfidation epithermal veins of mainly quartz or quartz-barite are enclosed in concentric zones of advanced argillic, argillic, silicic, and propylitic alterations. Poly-phase brine inclusions from the stage ΙΙ porphyry mineralization have homogenization temperatures (Th) between 305 and 600 ºC, with salinity from 30.2 to 73.9 wt% NaCl equivalent. Brines inclusions of stages ΙΙΙ and ΙV have Th from 192 to 466 ºC and salinity from 20.6 to 59.2 wt% NaCl equivalent. These brine inclusions were trapped with vapor-rich inclusions, which have Th from 122 to 318 ºC and low-moderate salinity of 0.3 to 22.3 wt% NaCl equivalent. Fluid inclusions from quartz and sphalerite in epithermal veins yielded Th ranges of 123–298 °C and 121–218 °C, and salinity ranges of 1.9–12.8 and 1.9–11.2 wt% NaCl equivalent, respectively. The δ³⁴S values of sulfide minerals from stages ΙΙ and ΙΙΙ porphyry mineralization vary from + 0.9 to + 2.3‰, whereas the δ³⁴S values of sulfides from the late epithermal veins range from + 1.2 to -1.1‰. These characteristics are consistent with a similar magmatic source for both the fluids of porphyry mineralization and subsequent high-sulfidation epithermal veins. The Masjed Daghi deposit that represents a telescoped porphyry-epithermal system of copper–gold mineralization in the center and peripherals of the early Miocene intrusive stocks shows both similarities and differences to other Tethyan deposits in the Alpine-Himalayan orogenic belt.

Petroleum Basins and Hydrocarbon Potential of the Andes of Peru and Bolivia

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Jan 2018

Early Jurassic arc related magmatism associated with porphyry copper mineralization at 1 Zafranal, Southern Peru unraveled by zircon U-Pb ages 2

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Jul 2019

Early Jurassic arc-related igneous rocks host porphyry copper prospects and gold-bearing quartz vein deposits in southern Peru. Ten new zircon U-Pb ages for wall rocks of gold-bearing quartz veins, Jurassic rocks and copper-mineralized porphyry bodies in Zafranal porphyry copper, together with published ages for Jurassic rocks, reveal a continuous magmatic evolution of the early Jurassic arc. The Jurassic rocks and gold-bearing quartz vein systems in the western flank of the Western Cordillera are hosted by Paleo- and Meso-proterozoic orthogneisses of the Arequipa Massif (1.75-1.44 Ga) that underwent Grenville-age metamorphism ~1 Ga. The early mafic magmatism is recorded between 199.6-193.2 Ma, and was followed by dominantly felsic magmatism from 184.1-174.9 Ma. Both magmatic events have formed the thinnest intrusive belt (

Tectonic Evolution of the Central Andes: From Terrane Accretion to Crustal Delamination.

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Nov 2018

Victor A. Ramos

The analysis of the pre-Andean history of the Central Andes shows a complex tectonic evolution. The basement of the Andean continental margin was formed by the accretion of Precambrian blocks during the formation of Rodinia in late Mesoproterozoic times. There are two magmatic arcs of Grenvillian age, one developed on the margin of the craton, known as the Sunsas belt, and another on the accreted terranes. The suture between these blocks with the Amazonian craton has been continuously reactivated by tectonic and magmatic processes. The terranes of Paracas and Arequipa, both of Grenvillian age, have a contrasting Paleozoic evolution. The Arequipa terrane amalgamated to the craton by the end of the Mesoproterozoic, and during the Paleozoic its suture acted as a crustal weakness zone. This zone concentrated the extension and the formation of a large platform in the retro-arc basin, where the Eopaleozoic sediments accumulated. The Famatinian magmatic arc of Ordovician age (475-460 Ma) is preserved in this segment along the continental margin. The Eopaleozoic extension that affected the Paracas terrane reopened the old suture and formed oceanic crust between Amazonia and Paracas. The subduction of this oceanic crust developed a magmatic arc over the cratonic margin, which is preserved in the Eastern Cordillera of Peru as orthogneisses associated with metamorphic rocks of Famatinian age. There are ophiolitic assemblages, paired metamorphic belts, and intense deformation associated with the Paracas collision (460 Ma) against the Amazonian craton. In northern Eastern Cordillera of Peru the late Paleozoic orogen has within-plate granitic belts and was far away from the active margin. The orogen was deformed and uplifted in two phases (336–285 Ma and 280–235 Ma) known as the early and late Gondwanide orogenies. They are preserved as medium grade metamorphic belts developed along the Paracas segment. Further south along the Arequipa segment in southern Peru and Bolivia, the late Paleozoic–Triassic rocks are represented by granites and acidic volcanic rocks, which are not metamorphosed and are associated with sedimentary rocks. Relics of a magmatic arc are exposed as tonalites and metamorphic rocks 1 260 Ma2 along the northern continental margin of Peru and in the near offshore platform. The extensional regime that dominated most of the Mesozoic developed rift basins in the hanging-wall of the terrane sutures, which controlled the structural highs and basin margins. The Peruvian Late Cretaceous orogeny produced the emplacement of the Coastal batholith, the beginning of deformation along the coast, and the first foreland basins. The giant Ayabacas submarine syn-tectonic collapse is also controlled by previous sutures. The Cenozoic Andean evolution was dominated by a wave of shallowing of the subducted slab, the migration of the magmatism to the foreland, the steepening of the oceanic plate, and the consequent “inner arc” magmatism. The “inner arc” plutonic and volcanic rocks are the expression of deep crustal melts, associated with crustal delamination and lithospheric mantle removal. The flattening of the oceanic slab is related to ablative subduction and shortening in the Altiplano and Eastern Cordillera. The steepening is associated with rapid removal of mantle lithosphere and crustal delamination, expressed at surface by the “inner arc” magmatism. The suture crustal weakness zones between different terranes partially controlled the location of the delaminated blocks and the “inner arc” magmatism. Both processes triggered the lower crust ductile shortening and subsequent upper crustal brittle development of the sub-Andean fold-and-thrust belt.

New Geochronological and Lead Isotopic Data for Porphyry-Skarn Cu-Mo-Au Deposits in the Andahuaylas-Yauri Batholith, Southeastern Part of Peru

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Mar 2019

Geology and Mineralization in the Colca area of Peru

Article

Mar 2011

Chulho Heo

Assessing copper fertility of intrusive rocks using field portable X-Ray fluorescence (pXRF) data

Article

Apr 2019

Based on a global compilation of whole-rock geochemical data, Sr/Y and Sr/MnO are identified as effective discriminators between ore-forming and unprospective intrusions in the porphyry Cu setting. Intrusive rocks are classified into three fertility groups – prospective, unprospective and mixed-signal – designed to assist explorers as a discrimination tool, narrowing the exploration search space in porphyry Cu districts. Portable X-ray fluorescence (pXRF) data of Sr, Y and MnO were collected on pulp powders and rock slabs from six porphyry Cu (±Mo ± Au) districts. Pre- and post-mineralization intrusions from porphyry Cu districts have lower Sr/Y and Sr/MnO values than syn-mineralization intrusions from the same districts, although absolute values are variable between districts. pXRF data were compared to conventional whole-rock data to determine if pXRF data were appropriate substitutes for conventional whole-rock methods of evaluating the ore-forming potential of intrusive rocks. pXRF data collected on pulp material were found to be more accurate (within 16% of conventional methods) and more precise (<5% relative standard deviation (RSD)) than those collected on intact rock slabs (within 37% of conventional methods and <24% RSD). These differences are attributed to the grain size and mineral homogeneity of samples. Despite the low precision of pXRF analyses on individual rock slabs (mean RSD of 24% Sr/Y and 32% Sr/MnO), the mean values for each sample plot in the expected fertility field on the Sr/Y and Sr/MnO diagram. Our results demonstrate that in situ pXRF data collection provides an effective discriminator of Cu fertility, and represents a powerful field exploration tool. Supplementary material: Tabulated pXRF data for all samples including standards are available at https://doi.org/10.6084/m9.figshare.c.4447769

Marco metalogénico regional de los megadepósitos de tipo pórfido cuprífero del norte grande de Chile

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Jan 1988

Estratigraf??a del Terciario en el Noroeste Argentino

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Jan 1999

Magmatism, tectonism, and mineral deposits of the central Andes (22°-33 °S)

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Kimmeridgian to Paleocene tectonic and geodynamic evolution of the Peruvian (and Ecuadorian) margin

Article

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Jan 1994

Etienne Jaillard

Three main tectonic periods are recognized between Kimmeridgian and Paleocene times in the Peruvian-Ecuadorian margin. The "Viru" period comprises a Kimmeridgian event probably equivalent to the Araucan phase of Argentina and Chile, a Tithonian phase related to terrane accretions and collision tectonics along the Ecuadorian margin and to a sudden extension along the north Peruvian margin, and a Berriasian event most probably originated by the incipient South Atlantic rifting. The "Mochica" period begins with tensional and volcanic precursor events (Late Aptian-earliest Albian). It continues with extensional effusions of coastal, back-arc or arc volcanic centres, which alternate with compressive crises (Early and Middle Albian). It ends with the accretion and deformation (thrusting ?) of the Albian volcanic arc or back-arc volcanic system (Late Albian-Early Middle Cenomanian). The "Peruvian" phase starts with a paleogeographic change probably triggered by the incipient coastal uplift (Turonian-Coniacian boundary), and continues in the Late Coniacian-Early Santonian with the initiation of northeastward overthrusts located in the southwestern boundary of the western Trough. It culminates in the latest Campanian, with the creation of intermontane basis which express the onset of the southwestern thrusts, and of foreland basins related to the onset of new overthrusts located in the northeastern boundary of the western Trough. An extensional regime was prbably dominant during the latest Jurassic and Early Cretaceous times, leading to formation of the main sedimentary basins, with an apparent quiescence of the subduction-related volcanic systems... (D'après résumé d'auteur)

Geochronology of Miocene plutons and exhumation history of the El Teniente region, Central Chile (34-35°8)

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Full-text available

Jan 1997

4°Arf3 9 Ar mineral dating and whole rock chemical analyses of Miocene to Pliocene Andean granitoids near the El Teniente copper deposit (34°S) provide new evidence for rapid Neogene exhumation. This exhumation is attributed to crustal thickening that culminated in the Late Miocene-Early Pliocene coincident with the emplacement of the ore deposit. Three groups of Neogene plutons in the forearc of the active Southern Volcanic Zone (SVZ) are considered . The oldest and westernmost is represented by the La Obra pluton (19.6 ± 0.5 Ma, biotite) which has chemical affinit es with the host Late Oligocene-Early Miocene Coya-Machalí Formation volcanic rocks. Slow cooling of this pluton is required by a 3.4 my difference between biotite and K-feldspar 4°Arf3 9 Ar ages. Modeling shows that this cooling is consistent with an exhumation rate of -0.55 mm/yr between 19.6 Ma and 16.2 Ma. The second group, termed the El Teniente Plutonic Complex, consists of plutons with biotite ages clustering at -11 to 12 Ma and -8 to 9 Ma. These plutons have chemical affinities with the Middle to Late Miocene Teniente Complex (Fare/lones Formation) volcanic rocks whose chemical characteristics suggest that they erupted through a thicker crustthan the Coya-Machalí units. A 0.7 my diffBrence bEtween biotite (8.4±0.3 Ma) and K-feldspar ages in the Nacimiento Río Cortaderal pluton requires an exhumatiol rate of -3 mm/ yr between 8.4 and 7.7 Ma. Although modeled exhumation rates depend on estimates of mineral closure temperatures, paleo-geothermal gradients, and errors in age determinations, a higher exhumation rate forthe NacimientJ Rio Cortaderal pluton than the La Obra pluton is a robust result of modeling . A third group of plutons (Young Plutonic Complex) farther west, is characterized by biotite ages of 6.6 to 5.6 Ma. Their steeper rare earth element patterns and more Enriched isotopic signatures, are consistent with emplacement in a crust even more thickened by Late Miocene compressiolal deformation. An elevated paleo-geothermal gradient, consistentwith the Miocene magmatic-arc environment, best explains the cooling histories of these plutons. Their mineral ages are interpreted as being contro/led by exhumation associated with Grustal thickening due to compressional deformation related to crustal shortening . The data are consistent with a moderate regional deformation associated with eastward shift of the magmatic front between 20 to 16 Ma, and a stronger regional deformation associated with frontal are migration between 8 and 5 Ma.

Senonian-Paleocene charophyte succession of the Peruvian Andes

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Full-text available

Aug 1994
CRETACEOUS RES

A synthesis of the available sedimentological and stratigraphic data on the Late Cretaceous and Paleocene deposits of the peruvian Andes permits determination of the age-range of the succession and stratigraphic range of the main charophyte species. Feistiella ovalis may appear in the late Santonian(?). It persists up to the middle(?) Campanian, where it is associated with Platychara perlata, which still occurs in the late Campanian. Feistiella gildemeisteri and Platychara grambastii are commonly found in association with Amblyochara peruviana. In other parts of Peru, these species occur together with Amblyochara rolli, A. begudiana, Feistiella costata and Saportanella aff. maslovi, strongly supporting a pre-Tertiary, mainly Maastrichtian age. Early Paleocene species are only local and poorly known. The Nitellopsis supraplana-Maedlerı́ella association seems to characterize a late time-span of the Paleocene, though a possible extension into the Eocene cannot be ruled out.

Magma source variations for mid-late Tertiary magmatic rocks associated with a shallowing subduction zone and a thickening crust in the central Andes (28 to 33°S)

Chapter

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Jan 1991

The distribution, petrology, and geochemistry of mid-late Tertiary magmatic rocks in the Main Andean Cordillera over the modem zone of shallow subduction ("flatslab"-28 to 33°S) correlate with the shallowing of the subducted plate and the thickening of the crust in central Chile and Argentina. The evolving characteristics of these "flat-slab" magmatic rocks suggest that crustal thickening occurred earlier in the central (near 30.5°) and northern (near 28°S) regions than in the southern region (near 33°S). Crustal thicknesses approximated by comparing the chemical characteristics (particularly the La/Yb ratios) of the "flat-slab" magmatic rocks with those of similar rocks in the modem Southern Volcanic Zone indicate that the crust thickened from =35 to 40 km in the late Oligocene to ~55 to 65 km in the late Miocene in the northern and central "flat-slab." As the region was under compression, ductile deformation in the lower crust accompanying magmatism was probably responsible for these relatively rapid crustal thickness increases. The mineralogy of crustal residues calculated from basaltic composition parents for the "flat-slab" volcanic rocks changes from a hydrous amphibole garnet-plagioclase assemblage to an almost anhydrous plagioclase-poor garnet granulite assemblage as the crust thickens. Geochemically, these changes are reflected in the melts by increasing La/Yb ratios and Sr contents associated with decreasing Eu anomalies. A limit to crustal thickening may be the attainment of mantle density by lower crustal rocks as garnet and AI-rich pyroxene replace plagioclase. Early Miocene (=20 Ma) back-arc alkaline basalts at 31°S have relatively low 87Sr/86Sr ratios (~0.7036) and high Nd (+4.5) compared to "flat-slab" calc-alkaline magmatic rocks. This fact combined with evidence for increasing crustal thickness suggests that progressively higher 87Sr/86Sr ratios and lower nd (87Sr/86Sr = 0.7046 to 0.7064; Nd = + 1.2 to -3.5) in the "flat-slab" volcanic rocks correlate with an increase in crustal contamination through time. The crustal contaminant could contain an important component of underplated basalts and residue from crustal melting associated with the formation of the extensive late Paleozoic-early Mesozoic Choiyoi granite-rhyolite complex that outcrops in this region. An additional component derived from subducted sediment or by sub-continental erosion associated with progressive shallowing of the subduction zone cannot be precluded.

Characteristics and controls of the largest porphyry copper-gold and epithermal gold deposits in the circum-Pacific region

Article

Full-text available

Jun 1997

Richard H Sillitoe

Eleven gold‐rich porphyry copper and 14 epithermal gold deposits around the Pacific rim contain > 200 t (‐7 million oz) of gold. These large porphyry‐type deposits conform to a single overall model, whereas the large epithermal gold deposits are varied in both genetic type and mineralisation style. Most regional and local characteristics of the largest porphyry and epithermal deposits fail to explain convincingly their extremely high gold contents. Nevertheless, a number of hypothetical processes operative alone, or in combination, in the mantle, in upper crustal magma chambers and at the sites of gold accumulation are believed to maximise the likelihood of exceptional gold concentrations. Partial melting of the upper parts of stalled lithospheric slabs in the mantle, immediately following collision or arc migration, promotes oxidation of mantle sulfides and the release of gold. These tectonic scenarios may also result in rapid cooling and uplift‐induced depressurisation of upper crustal magma chambers, thereby accelerating the release of gold‐bearing magmatic fluids. Upper crustal magma mixing and passive degassing of the resultant SO2 are also considered to favour gold availability. Rheological and permeability contrasts at sites of gold deposition are important controls on the size and tenor of gold deposits. The summation of these mechanisms tends to result in short‐lived, areally restricted gold‐forming events, commonly as an end‐stage of arc development. These hypothetical processes translate into several practical criteria of potential use to explorationists. Both large gold‐rich porphyry and epithermal deposits seem to be more common in atypical arc settings and in association with unusual, especially highly potassic, igneous rocks. During the search for gold‐rich porphyry deposits, high hydrothermal magnetite contents, very young arcs in the tropical environment and impermeable host rocks, especially limestones, deserve emphasis. In contrast, large epithermal gold deposits are commonly controlled by marked lithologic differences and associated with flow‐dome and/or maar‐diatreme systems.

Andean tectonics related to geometry of subducted Nazca plate

Article

Full-text available

Jan 1983

Seismological and geological data show that tectonic segmentation of the Andes coincides with segmentation of the subducted Nazca plate, which has nearly horizontal segments and 30o E-dipping segments. Characterisitcs of Andean tectonics. Early Cenozoic tectonics of W N. America were quite similar to the Neogene Andes. However, duration of segmentation was longer and the width of deformation was greater in the W US. Patterns of crustal seismicity are systematically related to Plio-Quaternary structural provinces, implying that current deformational processes have persisted since at least the Pliocene. Strain patterns in the forearc region are complex and perhaps extensional and a broad region of the Altiplano-Puna and Eastern Cordillera appears to be aseismic.

Early Tertiary “Incaic” tectonism, uplift, and volcanic activity, Andes of central Peru

Article

Full-text available

Jan 1979

Potassium-argon age determinations on volcanic strata that overlie an extensive postorogenic erosion surface in the Western Cordillera show that the "Incaic pulse" of compressive deformation as well as subsequent uplift and erosion of the Andes of central Peru had taken place before 40 to 41 m.y. ago. Intense volcanic activity, which began before the end of uplift and erosion, continued for about 6 m.y. into early Oligocene time. The timing of these events suggests that uplift and volcanic activity, and perhaps also the preceding tectonic pulse, may have been initiated by the same global disturbance that produced the abrupt change in direction of movement of the Pacific lithospheric plate reflected by the bend in the Hawaiian-Emperor volcanic chain.

Stratigraphy and chronology of Late Cretaceousearly Paleogene strata in Bolivia and northwest Argentina

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Jun 1997

Integration of sequence stratigraphy, magnetostratigraphy, Ar/Ar dating, and paleontology considerably advances knowledge of the Late Cretaceous-early Paleogene chronostratigraphy and tectonic evolution of Bolivia and adjacent areas. The partly restricted marine El Molino Formation spans the Maastrichtian and Danian ( 73-60.0 Ma). Deposition of the alluvial to lacustrine Santa Lucia Formation occurred between 60.0 and 58.2 Ma. The wedespread erosional unconformity at the base of the Cayara Formation is 58.2 Ma. This unconformity separates the Upper Puca and Corocoro supersequences in Bolivia, and is thus coeval with the Zuni-Tejas sequence boundary of North America. The thick overlying Potoco and Camargo formation represent a late Paleocene-Oligocene foreland fill. (Résumé d'auteur)

El Salvador, Chile Porphyry Copper Deposit Revisited: Geologic and Geochronologic Framework

Article

Full-text available

Jan 1997

The Eocene (42 to 41 Ma) El Salvador porphyry copper deposit in the Indio Muerto district, northern Chile (26° 15′ S Lat.), formerly thought to have formed at the culmination of a 9-m.y. period of episodic magmatism, is shown by new mapping, U-Pb and K-Ar geochronology, and petrologic data to have formed during the younger of two distinct but superposed magmatic events-a Paleocene (∼63 to 58 Ma) and an Eocene (44 to 41 Ma) event. In the district, high-K Paleocene volcano-plutonic activity was characterized by a variety of eruptive styles and magmatic compositions, including a collapse caldera associated with explosive rhyolitic magmatism (El Salvador trapdoor caldera), a post-collapse rhyolite dome field (Cerro Indio Muerto), and andesitic-trachyandesitic stratovolcanos (Kilometro Catorce-Los Amarillos sequence). Pre-caldera basement faults were reactivated during Paleocene volcanism as part of the collapse margin of the caldera. Beneath Cerro Indio Muerto, where the porphyry Cu deposit subsequently formed, the intersection of two major basement faults and the NNE-striking rotational axis of tilted ignimbrites of the Paleocene El Salvador caldera localized emplacement of post-collapse rhyolite domes and peripheral dikes and sills. Subsequent Eocene rhyolitic and granodioritic-dacitic porphyries intruded ~14 m.y. after cessation of Paleocene magmatism along the same NNE-striking structural belt through Cerro Indio Muerto as did the post-collapse Paleocene rhyolite domes. Eocene plutonism over a 3-m.y. period was contemporaneous with NW-SE-directed shortening associated with regional sinistral transpression along the Sierra Castillo fault, lying ∼10 km to the east. Older Eocene rhyolitic porphyries in the Indio Muerto district were emplaced between 44 and 43 Ma, and have a small uneconomic Cu center associated with a porphyry at Old Camp. The oldest granodioritic-dacitic porphyries also were emplaced at ∼44 to 43 Ma, but their petrogenetic relation to the rhyolitic porphyries and younger granodioritic-dacitic porphyries in the district is unclear. The main porphyry Cu-Mo-related granodioritic-dacitic stocks in Quebrada Turquesa on Cerro Indio Muerto intruded, cooled, and were mineralized within ∼1 m.y. between 42 and 41 Ma. Volumetrically minor late- to post-mineral porphyries are slightly more mafic than earlier granodioritic-dacitic porphyries, a compositional trend possibly repeated on several scales and more than once over the 3-million-year Eocene magmatic history of the Indio Muerto district. This compositional trend requires either addition of basaltic material into an open-system silicic magma chamber or tapping of progressively deeper levels of a vertically zoned magma chamber. Eocene porphyry magmas were more hydrous and their residual source mineralogy richer in garnet than the relatively anhydrous Paleocene rocks, whose source was rich in pyroxene. The presence of inherited zircons in Paleocene and Eocene rocks requires interaction with crustal rocks of Paleozoic and/or Proterozoic age.Paleocene and Eocene igneous rocks in the Indio Muerto district were emplaced during distinct magmatic-tectonic events that are unrelated, although spatially associated. The districtscale Paleocene and Eocene eruptive styles and geochemical and mineralogic characteristics mimic characteristics of similar-aged igneous rocks throughout northern Chile (20°30′ S Lat. to 27° S Lat.), attesting to the regional nature of the Paleocene and Eocene events. Porphyry Cu mineralization in the district furthermore is associated not only with an Eocene granodioriticdacitic (42 to 41 Ma) complex, but also with one of an older Eocene (44 to 43 Ma) rhyolitic porphyry, implying that a long period of precursor magmatism is not required for generation of the El Salvador porphyry Cu-Mo deposit. Rather, the episodic magmatism preceding porphyry Cu mineralization reflects repeated structural localization through time of superimposed highlevel volcano-plutonic complexes in an active magmatic arc.

Magmatic and Metallogenic Evolution of the Central Andes

Chapter

Jan 1999

Ulrich Petersen

Sedimentological analysis of the 'Red Beds' from the Sicuani intermontane basin, southern Peru

Article

Jan 1987

Activity began with the first Andean tectonic compressive movements in Senonian times. The sedimentation is mainly fluvial. Pebbly braided rivers correspond to more proximal parts and floodplains with channels to more distal. The constant infilling indicates a regional northwards palaeoslope. Describes the relatively high rate of sedimentation, the infilling lead by ancient major faults and the existence of compressive synsedimentary deformations. -from English summary

Are outsized porphyry copper deposits either anatomically or environmentally distinctive?

Article

Jan 1993

Alan H. Clark

Antapaccay project - Geology

Conference Paper

Jan 2000

Geology and exploration progress of the Accha zinc deposit, Cusco, Peru

Article

Jan 2000

Orogenic evolution of the Peruvian Andes: The Andean cycle

Article

Jan 1999

Víctor Benavides-Cáceres

The Miocene metallogenic belt of central and northern Peru

Article

Jan 1999

Contrasting metallogenesis and regional settings of circum Pacific Cu-Au porphyry systems

Article

Jan 1990

S.R. Titley

Andean mineralization: A model for the metallogeny of convergent plate margins

Article

Jan 1976

Richard H Sillitoe

Mesozoic and Cenozoic Stratigraphy and Tectonic Events of Puno-Santa Lucia Area, Department of Puno, Peru

Article

Jan 1974
AAPG BULL

Jorge A. Portugal

The Puno-Santa Lucia area is in the higher parts of the Andes in southern Peru. The oldest rocks in the area are quartzite and shale of the lower Paleozoic Cabanillas Group, more than 2,000 m thick. The Jurassic Lagunillas Group is divided into three units with an aggregate thickness of 1,505 m. The Cretaceous rocks are included in the Huancane Group and the Moho Group, the combined thickness of which is 410 m. The Ayavacas Limestone, upper member of the Moho Group, contains fossils of Cenomanian age. Trachytes of Cretaceous age are present near Juliaca and on the Capachica Peninsula. Redbeds, Cotacucho, Vilquechico, and Munani Formations, mapped by Newell within the Tertiary Puno Group, are considered here to be Late Cretaceous on the basis of their stratigraphic positio . Apparently these formations were deposited in a closed basin between the Cordillera Occidental and Cordillera Oriental. The Puno Group of probable Tertiary age consists of two units: the Saracocha Formation below, consisting mainly of conglomerate, is widely distributed in the southwestern part of the area, but is absent in the northeast; and the Tacaza Formation above, a volcanic sequence, also present in the southwestern part, shows the thickest sections along the Cordillera Occidental with thinning toward the east. Olivine basalt flows and tuffs of the Sillapaca Formation unconformably overlie the Puno Group. Three orogenies have been identified.

The Farallón Negro Group, northwest Argentina: Magmatic, hydrothermal and tectonic evolution and implications for Cu-Au metallogeny in the Andean back-arc

Article

Jul 1998

Cenozoic formation of the Central Andes: A geophysical perspective

Article

Jan 1999

Variations in zoning patterns in porphyry ore deposits

Article

Jan 1974

Skarn deposits

Article

Jan 1981

La cuenca de Arequipa (Sur Perú) durante el Jurásico-Cretácico inferior

Article

Jan 1982

Metallogeny, geological evolution, and thermochronology of the Chilean Andes between latitudes 21° and 26° south, and the origin of major porphyry copper deposits

Article

Victor Maksaev

METALLOGENY AND THERMOCHRONOLOGY OF THE CHILEAN ANDES BETWEEN LATITUDES 21 AND 26 SOUTH, AND A CONCEPTUAL MODEL FOR THE ORIGIN OF MAJOR PORPHYRY COPPER DEPOSITS Victor Maksaev ABSTRACT The geologic evolution of the Antofagasta segment of the Chilean Andes (21-26S) has been dominated by persistent subduction-related calc-alkaline magmatism. The position of the magmatic front migrated ensuing tectonic pulses that are recorded in the stratigraphy. Hydrothermal processes associated with over 300 Ma of virtually continuous igneous activity generated most of the metallic ore deposits. These include some of the world's largest porphyry copper deposits and significant concentrations of gold, silver, copper, iron, and sulphur. Field observations and new 40Ar-39Ar, K-Ar, and fission track data indicate that the most important metallic mineral deposits of this Andean segment were formed during three discrete metallogenic epochs: (1) Middle to Late Jurassic copper stratabound and vein copper deposits of the Coastal Cordillera Metallogenic Belt (2) Paleocene epithermal silver and gold vein deposits, and sub-economic porphyry copper type, and breccia pipe deposits in the western section of the Domeyko Cordillera Metallogenic Belt; and (3) Late Eocene-Early Oligocene giant porphyry copper deposits along the Domeyko Cordillera Metallogenic Belt. The metallogenic analysis suggests that geologic, tectonic, and geomorphic factors influenced arc-related magmatic activity, hydrothermal, and supergene processes. This accounts for the extraordinary specialization and recurrence of copper mineralization of the region. The thermochronological data is consistent with formation of major porphyry copper deposits following uplift. Geochemical and isotopic data support the hypothesis that porphyry copper mineralization resulted from a period of deep magma generation ensuing crustal thickening. Characteristic magmas with restricted Sr, Nd, and Pb isotopic compositions and optimum proportion of volatiles extracted metals from their source, transported their loads to near-surface where late-magmatic/hydrothermal processes concentrated metals and sulphur. Limited regional denudation resulting from aridity since the Late Cretaceous contributed to the formation and preservation of rich supergene ores.

Tectonics and magmatism in the Peruvian Andes from late Oligocene time to the Present

Article

Jan 1991

An overview of the tectonic and magmatic evolution of the Peruvian Andes since late Oligocene time is presented. From 30 to 26 Ma, the weak deformation and the nearly total quiescence of magmatic activity correlates with a very low convergence rate between the Farallon and the South American plates. From 26 Ma to the Present, the tectonic regime outside the sub-Andean retroarc foreland has been unstable, characterized by long periods of tectonic quiescence separated by five short-lived generalized compressional events dated approximately at 26, 17,10,7, and 2 Ma, respectively. During the quiescent tectonic periods, Andean shortening was minor and occurred mainly in the sub-Andean foreland, whereas extensional tectonics prevailed within the High Andes and the fore-arc. Conversely, most of the late Cenozoic Andean shortening, even in the sub-Andean foreland, occurred during the generalized compressional events. The following model can be invoked to interpret this unstable tectonic regime: during the tectonically "quiet" periods, most of the westward drift of the South American plate is accommodated by an absolute westward overriding of the continental plate over a retreating Nazca slab. In this steady-state regime, the compressional events may be considered as instabilities of the dynamic equilibrium between lithospheric motion and Andean deformation. During the compressional events, virtually all the westward drift of South America is accommodated by the tectonic shortening of the Andes, i.e., there is no slab retreat. The calc-alkaline arc remained stable from 26 Ma to the Present in southern Peru and from 26 Ma to 4 Ma in central Peru after which the slab shallowed. Calc-alkaline magmatism is the normal product of a subduction beneath an asthenospheric mantle wedge and is quite independent of the Andean state of stress. In central Peru, back-arc alkaline magmatism appeared when the convergence rate was the highest, i.e., during the Miocene, while in southern Peru, Miocene to Present shoshonitic volcanism was controlled by deep-seated faults. Peraluminous felsic magmatism of the Cordillera Oriental of southeastern Peru was controlled by the underthrusting of the Brazilian shield under the Andes.

The "Red Beds Overthrust' of Cuzco, southern Peru: stratigraphic evidence, paleogeographic and tectonic interpretations

Article

Jan 1993

Sedimentological and stratigraphic studies show the Cuzco sedimentary series to include Senonian and Paleocene deposits. The thick overlying, partly Cretaceous "Red Beds' thus constitute a regional-scale subhorizontal nappe. This latter likely proceeded from the south and was emplaced probably by gravity sliding between Paleocene and Oligocene times. There is an abridged English version. -English summary

Geología de los cuadrángulos de Chalhuanca, Antabamba y Santo Tomas

Technical Report

Jan 1981

Víctor Pecho

Steiger, R. H. & Jaeger, E. Subcommission on geochronology: convention of the use of decay constants in geo- and cosmochronology. Earth Planet. Sci. Lett. 36, 359-362

Article

Oct 1977
EARTH PLANET SC LETT

Cenozoic stratigraphy and basin tectonics of the Andes Mountains, 20Â°â»Â²â¸sup 0/ south latitude

Article

Jan 1987

Clastic sedimentary basins have evolved during the past 40 m.y. in the central Andes (lat. 20Â°â»Â²â¸sub 0/S) in response to shifting patterns of magmatism and deformation. The distribution of these basins and their genetic relations to uplifted areas are analogous to the basins and mountain belts of the North American Rocky Mountains during the Late Cretaceous and early Cenozoic. Petroleum exploration has focused on zones underlying the upper Cenozoic strata along the eastern margin of the Andes mountain belt. Between about 40 and 25 Ma, a nonmarine basin extended across the region that is now the Andes Mountains. Between about 25 and 10 Ma, the western part of the former basin became the site of a volcanic arc; sediment accumulation continued in the east, where marine intercalations demonstrate the low elevation of the basin. After 10 Ma, the volcanic arc remained active and locally widened, and crustal shortening caused regionally important thrust and reverse faulted ranges. During the past 10 m.y., up to 4000 m of coarse clastic debris accumulated in a foreland basin on the eastern flank of the mountains; meanwhile in the interior of the mountains, over 4,0000 m of fine-grained strata and evaporites accumulated in local depocenters. 8 figures.

Sediment-hosted gold deposits: Distal products of magmatic-hydrothermal systems

Article

Jan 1990
GEOLOGY

Sediment-hosted or Carlin-type gold deposits are currently thought to have been generated at shallow levels in geothermal systems, the gold having been scavenged from host sedimentary sequences by meteoric hydrothermal fluids. In contrast, we propose that gold was contributed by magmatic hydrothermal fluids and was deposited on the peripheries of base and precious-metal districts, up to several kilometres from progenitor intrusions. Support for our model is provided by relations at Bau in eastern Malaysia, Bingham in Utah, and elsewhere, combined with geologic, chronologic, and metallogenic observations from the three principal alignments of gold-bearing deposits in Nevada. The proposed model has important exploration implications, and can be tested.

Multiple pulses of Neogene compressive deformation in the Ayacucho Intermontane Basin, Andes of Central Peru

Article

Jan 1984

Strata of the Neogene Ayacucho intermontane basin can be divided into 3 tectonostratigraphic units 1) Larampuquio volcanics - largely intermediate lavas and coarse conglomerates (18.3+ or -0.6, 17.3+ or -0.2Ma), 2) Huanta Formation-lower lacustrine and volcaniclastic sedimentary rocks (11.4+ or -0.5Ma) and upper intermediate lavas, tuffs and conglomerates (9.3+ or -0.3Ma) 3) Ayacucho Formation 7.7-6.0Ma, interfingering volcaniclastic sediments, silicic tuffs and intermediate to acid lavas. These are all described and interpreted. Including the 1st phase of Quechuan deformation (early-mid Miocene) there were at least 4 pulses of crustal compression during the Cenozoic separated by periods during which the compressional stresses were relaxed, if not replaced by extension at times.-M.J.Bennell-Baker

Tectonic trigger for the formation of late Miocene Cu-rich breccia pipes in the Andes of central Chile

Article

Jan 1994
GEOLOGY

During the late Miocene, the decreasing angle of subduction below the Andes of central Chile caused a reduction in the influx of new magma and heat into the base of magmatic systems that had been active throughout the Miocene. This led to their cooling and solidification, triggering the release of large volumes of metal-rich magmatic fluids from middle- and upper-crustal magma chambers and generating a group of economically significant Cu-rich breccia pipes. The Sr- and Nd-isotopic compositions of the magmatic fluids that formed these brecccas, determined from breccia-matrix minerals, were variable, implying that these fluids were not exsolved from a specific Cu-porphyry magma, as is often invoked to explain Andean Cu deposits. Instead, the formation of the late Miocene deposits in central Chile was tectonically triggered by cooling of a variety of magma types during the last stages of existence of long-lived Andean magmatic systems as both subduction angle and, as a result, subarc magma supply decreased.

Zongo-San Gaban zone: Eocene foreland boundary of the Central Andean orogen, northwest Bolivia and southeast Peru

Article

Jan 1988
GEOLOGY

Discordant muscovite and biotite K-Ar dates of samples taken in six transects through the Cordillera Oriental of southeast Peru and northwest Bolivia, combined with â´Â°Ar/Â³â¹Ar age spectra, reveal a northwest-trending, structurally cryptic, tectonothermal zone of late Eocene age (ca. 38 Ma) that overprints Triassic and older igneous and metamorphic rocks. The zone is at least 450 km long but is less than 25 km wide; temperatures along its northeast boundary are estimated to have reached 350Â°C. No Paleogene magmatism has been recognized that could account for the thermal resetting of the K-Ar isotopic system. Uplift, erosion, and southwest-verging thrusting accompanied the development of this domain, which defined the foreland boundary of the orogen prior to inception of northeast-verging Andean thrusting in Miocene time. It is proposed that this tectonothermal zone, the Zongo-San Gaban zone (ZSGZ), which involves thrusting and basement shortening, is the southerly manifestation of the Incaic compressional deformation, which produced the thin-skinned Maranon thrust and fold belt (MTFB) north of the Abancay deflection of central Peru.

Andean Crustal and Upper Mantle Structure

Article

May 1971

David E. James

Phase and group velocities of Rayleigh and Love waves have been used to derive models of the structure of the crust and upper mantle beneath southern Peru, Bolivia, and northern Chile. A three-dimensional model of crustal structure has been obtained that shows crustal thickness varying from about 11 km (including water layer) in the ocean basin to 30 km along the coast to more than 70 km beneath the western cordillera and western part of the altiplano. The crust thins eastward and beneath the eastern cordillera is only 50–55 km thick. The crust beneath the crest of the Andes appears to thin to the north and south of the altiplano region, and the maximum crustal thickness in those parts of the Andes not associated with the altiplano may be on the order of 55–60 km. Mean crustal velocities within this region of the Andes are characteristically low; typical values of mean P- and S-wave velocities are ∼6.2 km/sec and 3.45 km/sec, respectively. No significant low-velocity zone for shear waves has been found in the upper 150 km of the mantle beneath the continental area studied, although subcrustal velocities for the entire region are somewhat low. The lowest uppermost mantle velocities measured are for the region between La Paz, Bolivia, and Huancayo, Peru. Here the upper mantle shear velocity corresponds to the axis of the high electrical conductivity anomaly that has been found in the Andean region. Beneath the oceanic areas, a major shear-wave low-velocity zone is required to satisfy phase- and group-velocity observational data. The top of this zone is at a depth of 50–60 km, and the low velocities extend to a depth probably in excess of 200 km. There is a slight suggestion that the upper boundary of the low-velocity zone may be dipping toward the continent.

To each plutonic rock its proper name

Article

Mar 1976
EARTH-SCI REV

A. L. Streckeisen

The paper comments on the recommendations on which the IUGS Subcommission on the Systematics of Igneous Rocks agreed at Montreal, August 1972. Plutonic rocks are classified and named according to mineral contents. For nomenclature are considered: Q = quartz, A = alkali feldspar (incl. albite), P = plagioclase, F = feldspathoids, M = mafic and related minerals. Rocks with M less than 90 are named according to their positions in the QAPF diagram, the light-colored constituents being calculated to the sum 100. The following are treated: granitoids and related rocks, ultramafic and gabbroic rocks, charnockitic rocks, feldspathoidal rocks. A color index is used to distinguish the leuco- and mela-types of each rock group in comparison with normal types.

New K_Ar age determinations of intrusive rocks from the Cordillera Occidental and Altiplano of central Peru: Identification of magmatic pulses and episodes of mineralization

Article

Dec 1988
J S AM EARTH SCI

The post-Albian evolution of the Andes of central Peru is characterized by igneous activity, both effusive and intrusive, and by at least six distinct episodes of compressional tectonics. New KAr age determinations have been made of intrusive rocks from the Cajatambo-Oyón-Cerro de Pasco area. In conjunction with already published information, these new data permit a better estimate of the ages and the lateral extent of successive Cenozoic magmatic arcs. Metallogenetic implications of the 26.3–29.3 Ma age of mineralized Milpo-Atacocha intrusions are also discussed.ResumenLa evolución post-Albiana de los Andes del Perú central está caracterizada por actividad ígnea, tanto efusiva como intrusiva, y por lo menos seis episodios de tectónica compresional. Se efectuaron nuevas determinaciones de edades KAr de rocas intrusivas del area de Cajatambo-Oyón-Cerro de Pasco. Estos nuevos datos, en conjunción con información anteriormente publicada, permiten una mejor estimación de la edades y extensión lateral de los sucesivos arcos magmáticos cenozoicos. Iqualmente se discuten las implicancias metalogenéticas de la edad de 26.3–29.3 Ma de las mineralizaciones de las intrusiones Milpo-Atacocha.

A note on the calculation of errors in conventional KAr dating

Article

Feb 1982
CHEM GEOL

Ajoy K. Baksi

An evaluation is made of the various formulae available in the literature for calculation of errors in KAr dating. Guidelines are laid down for the use of the most suitable formulae.

Implication of 40Ar/39Ar dating of Early Tertiary volcanic rocks from the north-Chilean Precordillera

Article

Feb 1992
TECTONOPHYSICS

Since the Early Jurassic, subduction-induced volcanic activity in the north-Chilean Andes (21–23,5°S) has migrated 200–300 km eastward from the present coast (Jurassic magmatic arc) to the Western Cordillera (Miocene-Recent volcanic rocks). Due to the paucity of chronological data, however, the exact age and extent of various magmatic sub-belts within this area are not well constrained. In the Precordillera, a sequence of 1500–5000-m-thick red bed sediments is partly intercalated with and mostly covered by predominantly intermediate calc-alkaline tuffs and lavas. Presently, the age of this sequence is considered to be Upper Jurassic and/or Cretaceous. From this sequence eleven biotites and seven hornblendes were analyzed and yielded plateau ages of between 48 and 38 Ma, indicating Upper Eocene volcanic activity in the eastern part of the Precordillera. In contrast, volcanic activity in the western part of the Precordillera has been dated at 92 ± 2.5 Ma, indicating an earlier onset of volcanism and, therefore, sedimentation of the red beds. In the Late Eocene, the intense volcanism ceased in this area contemporaneous with decreasing relative convergence rate of the Nazca Plate and the South American continent. This final phase of Eocene volcanism coincided with a period of important deformation, the “Incaic phase”. Biotites from two ash-fall tuffs, separated by a distinct angular unconformity, yield identical ages of 38.50 ± 0.90 Ma and 38.45 ± 0.60 Ma. These dates provide the best age estimate of the “Incaic phase” in the North Chilean Precordillera.

Porphyry Gold Deposits of the Refugio District, Maricunga Belt, Northern Chile

Article

Nov 2000

John L. Muntean

The porphyry gold deposits of the Refugio district and similar deposits in the Maricunga belt contain the lowest known copper to gold ratios (% Cu/ppm Au = ∼0.03) of any porphyry-type deposit. The gold deposits are associated with subvolcanic andesitic to dacitic intrusions emplaced into coeval volcanic rocks. Both the Verde and Pancho deposits are zoned in space from a deeper zone of banded quartz veinlets associated with chlorite-magnetite- albite and/or pyrite-albite-clay alteration to a shallow zone of pyrite- albite-clay and local quartz-alunite ledges. Pancho contains an additional, deepest, porphyry copperlike zone, with quartz veinlets (A-veinlets) and potassic alteration. Relative to Verde, Pancho is telescoped, with all three zones present within a 400-m-vertical interval. The porphyry copperlike zone at Pancho is characterized by A-veinlets and pervasive potassic alteration, both restricted to intrusive rocks. A-veinlets range from hairline streaks of magnetite ± biotite with minor quartz and chalcopyrite, and K feldspar alteration envelopes to sugary quartz veinlets <1 cm in width with magnetite and chalcopyrite and no alteration envelopes. Hypersaline liquid inclusions coexisting with vapor-rich inclusions indicate temperatures above 600°C and salinities as high as 84 wt percent NaCl equiv. A pressure estimate of 250 bars indicates a depth of 1,000 m, assuming lithostatic pressure. Potassic alteration consists of a central zone of magnetite-K feldspar-oligoclase that changes outward to a biotite-rich zone. Total sulfide content, predominately as chalcopyrite, is generally <1 vol percent, whereas magnetite content is 2 to 5 percent. Where A-veinlets and potassic alteration predominate, grades are typically 0.1 wt percent hypogene copper and 0.5 to 1 ppm gold. Banded quartz veinlets are present at both Verde and Pancho, where they occur mostly above A-veinlets and cut A-veinlets where they overlap. They are less than 2 cm in thickness and lack alteration envelopes. Dark gray bands, whose color is due to abundant vapor-rich fluid inclusions and micrometer-sized grains of magnetite, commonly occur as symmetric pairs near the vein walls. The bands are commonly botryoidal and are continuous through quartz grains, suggesting that the quartz recrystallized from a silica gel. Rare liquid-rich fluid inclusions in quartz indicate temperatures ≤350°C and salinities <35 wt percent NaCl equiv. Estimated pressures are <200 bars, suggesting depths of 190 to 1,500 m under hydrostatic pressure. Gold occurs both in the dark bands with magnetite and outside the dark bands with pyrite, chlorite, illite, and K feldspar. Banded veinlets occupy steeply dipping radial and shallowly dipping concentric fractures. Zones of abundant banded veinlets without early A-veinlets generally contain 0.5 to 2 ppm gold and <0.05 wt percent hypogene copper. Most of the differences between porphyry gold deposits at Refugio and porphyry copper deposits can be attributed to shallower depths of formation-less than 1 km compared to 1.5 to 4 km that is typical for porphyry copper deposits. Shallower depths resulted in lower sulfide concentrations, local garnet veinlets, widespread albite-bearing alteration, and most importantly banded quartz veinlets, which are unique to porphyry gold deposits. Banded quartz veinlets are a direct result of episodic intrusion of magma to within 1 km of the surface and exposure of high- temperature magmatic fluids to hydrostatic pressures. Episodic rupturing of a brittle-ductile boundary surrounding the intrusive centers at Verde and Pancho led to flashing of magmatic fluids, loss of sulfur to vapor, and low sulfide/gold ratios in ore.

Laser probe 40 Ar/ 39 Ar ages of early- and late-stage alteration assemblages, Rosario porphyry copper-molybdenum deposit, Collahuasi District, I Region, Chile

Article

May 1998

Sensibly identical laser probe 40 Ar/ 39 Ar dates of 32.9 + or - 0.5 (2Sigma ) and 32.9 + or - 0.6 Ma are determined for, respectively, early-stage hydrothermal biotite and late-stage hydrothermal muscovite from the giant Rosario porphyry copper deposit in the Collahuasi district of northern Chile. The age determinations were carried out on ca. 1 cm 2 , 1- to 0.5-mm-thick wafers of altered rock or on smaller chips broken therefrom, obviating the requirement for mineral separation and permitting direct petrographic control of the analytical procedure. The age data, although not unambiguous, imply that this extremely large hydrothermal center was emplaced over a short interval. Hydrothermal activity in this central Andean transect migrated eastward over a period of ca. 3 to 4 m.y., from Copaquire, through Quebrada Blanca to Rosario, the intensity of mineralization increasing with time. Rosario, Chuquicamata, and La Escondida, the largest of the "West Fissure" (Domeyko fault system) array, were apparently emplaced coevally, in the terminal stage of the late Eocene-early Oligocene metallogenic episode.

A revised Late Eocene age for porphyry Cu magmatism in the Escondida area, northern Chile

Article

Dec 1999

New U-Pb zircon and 40Ar/ 39Ar single-crystal incremental-heating biotite dates are reported for porphyritic rocks from three mineralized centers in the Escondida region of northern Chile; all dates are reported with 2σ errors. At the Chimborazo porphyry Cu prospect, a weighted mean 40Ar/ 39Ar plateau age of 38.09 ± 0.30 Ma has been obtained for igneous biotite from a syn- or postmineralization feldspar-biotite-quartz porphyry intrusion. At the Zaldivar porphyry Cu mine, zircon and biotite have been analyzed from a similar synmineralization feldspar-biotite-quartz porphyry (the Llamo porphyry): the zircon U-Pb age is 38.7 ± 1.3 Ma, whereas the weighted mean 40Ar/ 39Ar plateau age of igneous biotite is slightly younger at 37.40 ± 0.18 Ma. U-Pb dating of two other rhyolitic quartz-feldspar porphyry bodies that host much of the ore at Zaldivar shows that these rocks are Paleozoic in age (Antigua porphyry: 290 ± 4 Ma; Zaldivar porphyry: broadly coeval with Antigua but age poorly defined). At the Escondida deposit, the reportedly synmineralization Escondida porphyry is dated by U-Pb at 37.9 ± 1.1 Ma, whereas the reportedly postmineralization Rhyolitic porphyry returned a U-Pb age of 34.7 ± 1.7 Ma. These results indicate a single pulse of synmineralization magmatism in the Escondida district at ~38 Ma, followed by minor largely nonmineralizing intrusive events. The timing of main-stage porphyry mineralization at Escondida is apparently bracketed by the ages of the Escondida (37.9 ± 1.1 Ma) and Rhyolitic porphyries (34.7 ± 1.7 Ma). Previously published K-Ar dates for intrusive rocks and alteration minerals at Escondida, which range from 39 to 31 Ma, are interpreted to reflect variable degrees of disturbance of the K-Ar system by later intrusive events and/or by supergene weathering processes. An age of ~38 Ma for ore-forming porphyry magmatism in the Escondida region is significantly older than previously accepted best estimates based on K-Ar and U-Pb dating (32-34 Ma) but still falls within the age range of other large porphyry systems within the north-south-trending West Fissure Zone of northern Chile (31-42 Ma). A common feature of the porphyry intrusions at Zaldivar and Escondida, and also at Chuquicamata and El Salvador, is the presence of zircons with inherited upper Paleozoic cores. These cores are interpreted to reflect interaction between arc magmas and crustal rocks during melting, assimilation, storage, and homogenization (MASH) and assimilation and fractional crystallization (AFC) processes at various crustal levels.

Patterns of mineralization and alteration below the porphyry copper orebody at El Salvador, Chile

Article

Feb 1995

L. B. Gustafson

Three diamond drill holes, angled below the lowest haulage level at El Salvador, have doubled the vertical exposure of the deposit and revealed very different features of alteration and mineralization below this major porphyry copper orebody. Sulfide assemblages persist with depth, but the total sulfide content diminishes. Magnetite becomes a part of all sulfide assemblages, except very late pyritic D veins. Residual traces of pyrrhotite-chalcopyrite found locked in quartz and as abundant and widespread inclusions in pyrite apparently represent the remains of an early prograde mineralization obliterated by intense sulfidation of subsequent events. Relicts of specularite veinlets may be a similar phenomenon. Changes in vein type and other patterns of mineralization are described. -from Author

Geologic and geochronologic constraints on the metallogenic evolution of the Andes of southeastern Peru

Article

Nov 1990

The post-Paleozoic metallogenic evolution of southeastern Peru is clarified on the basis of the stratigraphic and lithologic settings of the majority of the known metallic ore deposits and a regional program of K-Ar and 40Ar-39Ar geochronology. This central Andean transect displays a range of mineralization types unparalleled in other regions of the country. Contrasting magmatic, tectonic, and metallogenic relationships are shown by the calc-alkaline shoshonitic Upper Triassic-Holocene Main Arc magmatic domain, underlying the present Cordillera Oc¬cidental and Altiplano, and the more restricted Triassic-Pliocene Inner Arc domain of the Cordillera Oriental, which incorporates a great variety of igneous suites and exhibits a cor¬respondingly diverse metallogeny. Major economic mineralization occurred simultaneously in the two domains only during the late Oligocene to early Miocene interval. The earliest significant Andean W, Cu, Mo, Sn, and Au mineralization is hosted largely by weakly peraluminous granites of the Upper Triassic to Lower Jurassic (190-225 Ma) Carabaya batholith in the Inner Arc; magma genesis resulted from sediment anatexis along the margin of the Permian ensialic Mitu rift. Renewed rifting in the Middle Jurassic (ca. 170-180 Ma) in this area was associated with the emplacement of the volcano-plutonic Allinccapac Peralkaline Complex, syenitic plutons of which host minor Cu, Ag, and Zr (-REE) vein systems. Mesozoic mineralization in the Main Arc, weak in comparison to that in other central Andean transects, comprises Upper Jurassic (145-165 Ma) Cu-Au veins (e.g., Rosa Maria), and mid-Cretaceous (ca. 95-110 Ma) Cu (Santiago, Valparaiso) and Fe (Morritos, Cerro Pelado) veins of the llo-Ite district. Restricted Upper Cretaceous (ca. 80 Ma) Cu-Pb-Zn-Ag veins in the Crucero district of the Inner Arc are interpreted as recording a brief episode of arc broadening or bifurcation. Large-scale porphyry Cu(-Mo, Ag) centers were emplaced in the Main Arc in the interval 52.15 (Cuajone) to 57.1 Ma (Toquepala) as the terminal stage in the evolution of the subaerial volcanic succession of the Upper Cretaceous-Paleogene Toquepala Group, which had previously experienced only minor Cu(-Pb-Ag-Au) vein mineralization at ca. 80 (Challatita) and 62 Ma (Lluta district). The early Eocene event represents the metallogenic culmination of the Peruvian Coastal batholith and its extension in northern Chile. In contrast, only the northern extremity of the upper Eocene-lower Oligocene arc of northern Chile occurs in the study area, and the minor Ataspaca Cu-Mo-Pb-Zn-Ag stockwork and skarn mineralization (39-45 Ma) is a pale reflection of the coeval array of giant porphyry copper deposits farther south. Much of south¬eastern Peru lacked magmatism immediately before and after the ca. 40-Ma Incaic orogeny and hence experienced a metallogenic hiatus. The Main Arc was resuscitated in the Santa Lucia area at 31 to 32 Ma; at 28.5 ± 1 Ma it abruptly broadened to a width of ca. 235 km. However, hydrothermal activity remained restricted in both scale and distribution. The moderate-sized Berenguela (ca. 27 Ma) and Santa Barbara (23.5 Ma) epithermal Ag deposits are associated with calc-alkaline subvolcanic centers, in the latter case emplaced in the initial stages of cordilleran uplift. Post-Oligocene mineralization in the Main Arc was also apparently sparse in comparison to the broadly contemporary epithermal Ag-Au-base metal deposits of central and south-central Peru, but it comprises the Au-rich veins of the Maiiazo camp (19 Ma) and the Ag veins of the Cacachara (6.5-7 Ma) and Compuerta camps (7 Ma). The Inner Arc revived at 28 to 29 Ma, simultaneously with the Main Arc broadening. Anatexis resulting from shoshonitic basalt injection generated strongly peraluminous mon¬zogranite stocks with which are spatially associated major, high-grade, lithophile and base metal lode systems, including San Rafael (23-24 Ma) and Palca 11 (24-25 Ma), now the most productive hard-rock Sn and W deposits of the Western Hemisphere. However, the widespread middle and late Miocene peraluminous magmatism in this region failed to produce Sn poly- metallic mineralization of the scale developed in Bolivia at this time; only the small yesica vein system (17.4 Ma) has been confirmed to contain Sn, and the Sb veins of the area (e.g., Collpa: 12.3 Ma) are also of restricted size. In contrast, the uranium stockworks (6.8-8.0 Ma) associated with the rare element-enriched, rhyolitic Macusani Volcanics are large and appar¬ently of high grade. Although sharing several metallogenic features with contiguous central Andean transects, southeastern Peru differs markedly from other areas of the country in the nature and age of mineralization. Thus, the Inner Arc domain does not persist to the northwest, and the radical and commonly abrupt changes we define in the distribution of magmatism, and hence min¬eralization, during the middle and late Tertiary are apparently unrepresented in central Peru. The individual metallogenic evolution of this region is ascribed to the inferred occurrence of a marked deflection in the western boundary of the South American plate throughout the Andean orogeny.

Age and regional tectonic and metallogenetic implications of igneous activity and mineralization in the Andahuaylas-Yauri belt of southern Peru

Article

Feb 1984

The Andahuaylas-Yauri belt is a 300 km elongate mineral province located W, S and SW of Cuzco, Peru. Mineralization is mainly Cu- and Fe-skarns, at or near quartz monzonite plutons of Oligocene, 33-34 m.y. age, and a few base- and precious-metal vein-districts. The belt is suggested to be a southeast continuation of the late Eocene-early Oligocene volcanic arc of central Peru, for which no mineralization is known. A difference in subduction geometry from central to southern Peru is discussed in explaining contrasts in petrography and in position of the two parts of the belt relative to the present trench. -G.J.N. Dept. Geological Sciences, Mackay School of Mines, Univ. of Nevada-Reno, Reno, NV 89557, USA.

The porphyry copper deposit at El Salvador, Chile

Article

Aug 1975

Epithermal lead-zinc vein-type deposits of the Toyoha mine, Hokkaido, Japan, occur in the Green Tuff region of Miocene age. The veins are divided into two groups, those of E-W and NW-SE systems, which have different structural and mineral features. The Soya vein, representative of the NW-SE system, is characterized by the common occurrence of banding and symmetrical structures in the vein, which are useful to establish the succession of mineralization. Stages of mineralization recognized in the vein are (1) sulfide stage which is composed of sphalerite-pyrite-quartz with minor hematite, sphalerite-galena-pyrite, sphalerite-pyrite, and pyrite-pyrrhotite subbands; (2) carbonate-pyrite-clay stage which is composed of carbonate-pyrite-montmorillonite and carbonate-pyrite-alabandite subbands; and 3) carbonate stage which is composed of manganocalcite-pyrite-quartz and calcite-quartz subbands from outside (earlier) to inner side (later). About 20 primary minerals occur in the deposits. The probable secondary minerals (kaolinite, goethite, caryopilite, native silver, and szmikite) are also widely distributed. Composition of sphalerite coexisting with iron minerals such as hematite, pyrite, and pyrrhotite was analyzed by electron microprobe analyzer. The FeS of the sphalerite increases with successive mineralizations. Compositional zoning in a sphalerite grain was also studied. Compositional zoning of manganese content in a sphalerite grain enclosed by manganese minerals (rhodochrosite or alabandite) shows a parabola-like profile. Although compositional zoning in sphalerite and wide occurrence of secondary minerals suggest that postdepositional processes have modified the original assemblage and chemical composition of minerals in the deposits to some extent, the following features are clarified for Toyoha mineralization on the basis of detailed mineralogical and geochemical studies: (1) wide variation of oxygen fugacity throughout the ore formation and (2) reducing processes in the sulfide stage. Those features are compared and discussed with studies previously reported for other types of deposits.

Seismicity and Shape of the Subducted Nazca Plate

Article

Nov 1992

An updated compilation of earthquake locations and focal mechanism solutions from the International Seismological Centre and Preliminary Determination of Earthquakes is the basis of a comprehensive study of the geometry of the Wadati-Benioff zone beneath western South America. The new data support previous mapping of a sharp flexure rather than a tear in the subducted Nazca plate beneath southern Peru and provide evidence for a similar flexure in the southward transition from nearly horizontal subduction to a slab with about 30 deg dip at latitude 33 deg S. In contrast, the transition from 30 deg slab dip beneath Bolivia to a nearly horizontal dip in the region between 28 deg S-32 deg S is more gradual, occurring over several hundred kilometers of along-strike distance between 20 deg S and 32 deg S. This southward flattening corresponds to a broadening of a horizontal, benchlike part of the subducted plate formed between 100 and 125 km depth. The transition in continental tectonic style near 27 deg S-28 deg S, from a wide, volcanically active plateau to a narrow, nonvolcanic cordillera, appears not to be associated with the main slab flattening, which begins to the north of these latitudes, but with a more abrupt change in curvature of the subducted slab, from convex upward to concave upward, immediately below the plate boundary interface. The concept of Gaussian curvature is applied to slab bending to explain how subduction geometry is affected by the shape of the South American plate.

Porphyry-Style Alteration and Mineralization of the Middle Eocene to Early Oligocene Andahuaylas-Yauri Belt, Cuzco Region, Peru

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