Development,urban planning and political decisions. A triad that built territories at risk     

Lara  Alejandro  Bucci  Felipe  Palma  Cristobal  Munizaga  Juan  Montre-Águila  Victor 《Natural Hazards》2021,109(2):1935-1957

Natural Hazards - Chilean geography exposes the country to high-level risks such as earthquakes and tsunamis. The disasters of 1930, 1960, 2010, and 2014 testify to the continuous link between...  相似文献   

Variation of Mo isotopes from molybdenite in high-temperature hydrothermal ore deposits   总被引：1，自引：0，他引：1  

Ryan Mathur  S. Brantley  A. Anbar  F. Munizaga  V. Maksaev  R. Newberry  J. Vervoort  G. Hart 《Mineralium Deposita》2010,45(1):43-50

Measurable molybdenum isotope fractionation in molybdenites from different ore deposits through time provides insights into ore genesis and a new technique to identify open-system behavior of Re–Os in molybdenites. Molybdenite samples from six porphyry copper deposits, one epithermal polymetallic vein deposit, four skarns, and three Fe-oxide Cu–Au deposits were analyzed. The δ⁹⁷Mo‰ (where ) for all samples varied from 1.34 ± 0.09‰ to −0.26 ± 0.04‰. This is the largest molybdenum isotopic variation in molybdenite from high-temperature ore deposits recorded to date. δ⁹⁷Mo‰ of molybdenite varies as a function of the deposit type and the rhenium and osmium concentrations of the samples. Isotope values for Mo also vary within the individual deposits. In general, molybdenites from porphyry copper deposits have the lightest values averaging 0.07 ± 0.23‰ (1σ). Molybdenites from the other deposit types average 0.49 ± 0.26‰ (1σ). The variations could be related to the fractionation of Mo into different mineral phases during the ore-forming processes. A comparison of the Mo isotope ratios and the Re–Os ages obtained from the same aliquot may possess a geochronological evaluation tool. Samples that yielded robust ages have different Mo isotopic compositions in comparison to samples that yielded geologically unreasonable ages. Another observed relationship between the Re–Os and Mo isotope data reveals a weak correspondence between Re concentration and Mo isotope composition. Molybdenites with higher concentrations of Re correspond to lighter Mo isotope values.  相似文献   

Rb/Sr ages of rocks from the Chilean metamorphic basement     

Fernando Munizaga  Luis Aguirre  Francisco Herve 《Earth and Planetary Science Letters》1973,18(1):87-92

Eleven whole rock Rb/Sr age determinations from the Chilean metamorphic basement — formerly considered as Precambrian — define two limiting reference isochrons of 342 and 273 my. Analized rocks are phyllites and schists of sedimentary origin with mineralogical assemblages mainly corresponding to the greenschist facies.Two metamorphic series characterize the Chilean metamorphic basement: an eastern low P/T series, and a western high P/T series. Four of the analyzed samples belong to the former and seven to the latter.The obtained age is interpreted as the age of a main metamorphic episode of the basement. This episode would have taken place in the Upper Paleozoic.  相似文献   

Lead sources in Mesozoic and Cenozoic Andean ore deposits,north-central Chile (30–34°S)     

Richard M. Tosdal  Francisco Munizaga 《Mineralium Deposita》2003,38(2):234-250

Mesozoic and Cenozoic ore deposits in the Chilean Andes between La Serena (~30°S) and Santiago (~34°S) include polymetallic vein, low- and high-sulfidation epithermal vein, skarn, porphyry copper-molybdenum and porphyry copper-gold. These deposits are associated with volcanic and plutonic complexes emplaced in eastward-migrating longitudinal arcs which formed during subduction along the continental margin of South America since the Middle Jurassic. Stratabound, but epigenetic, volcanic rock- and sedimentary rock-hosted manto deposits contain additional copper resources. Lead isotopic compositions in ore minerals from 29 deposits vary with age and geographic location, and hence with basement and host rocks. Lead in most ore deposits is derived from temporally related igneous rocks, except for the manto deposits whose lead is derived from host volcanic and sedimentary rock sequences. Lead in the ore deposits is dominated by two crustal sources. Low ²⁰⁷Pb/²⁰⁴Pb characterizes one source whereas high ²⁰⁷Pb/²⁰⁴Pb characterizes the second source. Lead isotopic compositions of Jurassic and Miocene ore minerals (²⁰⁶Pb/²⁰⁴Pb>18.50; ²⁰⁷Pb/²⁰⁴Pb>15.61) lie along the average crustal growth curve. By contrast, most Cretaceous deposits have ore minerals with lower ²⁰⁶Pb/²⁰⁴Pb (<18.39) and ²⁰⁷Pb/²⁰⁴Pb (<15.58) than Jurassic ore minerals. The shift in lead isotopic composition to lower lead isotopic values precludes derivation of lead from a source of similar composition to those in the Jurassic or Tertiary deposits. For Cretaceous deposits, polymetallic and low-sulfidation epithermal veins and a skarn have lower ²⁰⁶Pb/²⁰⁴Pb than a porphyry copper-gold system and peripheral gold veins at Andacollo (18.43-18.50). Late Cretaceous veins from the Bellavista deposit have the lowest ²⁰⁶Pb/²⁰⁴Pb (18.33) of all deposits. Ore minerals in Miocene and Pliocene porphyry copper-molybdenum deposits have higher ²⁰⁶Pb/²⁰⁴Pb (18.58-18.67) than Cretaceous deposits, consistent with their age being younger. The Miocene and Pliocene ore minerals also have higher ²⁰⁷Pb/²⁰⁴Pb (15.58-15.66) than Cretaceous ore minerals, thereby requiring an additional input from the high-²⁰⁷Pb/²⁰⁴Pb source into the younger deposits. Miocene auriferous deposits in the north have similar ²⁰⁶Pb/²⁰⁴Pb values as the Miocene and Pliocene porphyry copper-molybdenum deposits in the south, but they are distinguished by higher and variable ²⁰⁷Pb/²⁰⁴Pb (15.61-15.66) and ²⁰⁸Pb/²⁰⁴Pb (38.54-39.01), which are arrayed along steep mixing trends. These ore minerals have the largest input of high-²⁰⁷Pb/²⁰⁴Pb material in the deposits studied. By contrast, lead in the epigenetic manto deposits appears to be derived from the host volcanic or sedimentary rock-dominated sequences, and locally exhibits large-scale isotopic heterogeneity within a deposit. Overall, the lead isotopic compositions of ore minerals mimic the values and variations established in age-equivalent rock sequences. The low-²⁰⁷Pb/²⁰⁴Pb material in the deposits is derived from Cretaceous igneous rocks or their sources as they evolved with time; low ²⁰⁷Pb/²⁰⁴Pb characterizes these rocks. By contrast, high-²⁰⁷Pb/²⁰⁴Pb material is likely derived from Carboniferous to Triassic igneous rocks or their sources, as this lead isotopic characteristic dominates these rocks.  相似文献   

Timing and formation of porphyry Cu–Mo mineralization in the Chuquicamata district, northern Chile: new constraints from the Toki cluster     

Fernando Barra  Hugo Alcota  Sergio Rivera  Victor Valencia  Francisco Munizaga  Victor Maksaev 《Mineralium Deposita》2013,48(5):629-651

The recently discovered Toki cluster, which includes the Toki, Quetena, Genoveva, Miranda, and Opache porphyry Cu–Mo prospects, is located 15 km south–southwest of the Chuquicamata–Radomiro Tomic mines in northern Chile. These prospects occur in an area of 5?×?6 km and are completely covered with Neogene alluvial deposits. Inferred resources for the cluster are estimated at about 20 Mt of fine copper, with Toki and Quetena contributing ～88 % of these resources. Mineralization in these deposits is associated with tonalite porphyries that intruded andesites and dacites of the Collahuasi Group and intrusions of the Fortuna–Los Picos Granodioritic Complex. Hypogene mineralization in the Toki cluster consists mainly of chalcopyrite–bornite with minor molybdenite with mineralization grading outward to a chalcopyrite–pyrite zone and ultimately to a pyrite halo. Alteration is dominantly of the potassic type with K-feldspar and hydrothermal biotite. Sericitic alteration is relatively restricted to late quartz–pyrite veins (D-type veins). Previous K–Ar geochronology for the cluster yielded ages within a range of 34 to 40 Ma. Four new Re–Os ages for Toki indicate that molybdenite mineralization occurred in a single pulse at ～38 Ma. Re–Os ages for three different molybdenite samples from Quetena are within error of the Toki mineralization ages. These ages are concordant with a new zircon U–Pb age of 38.6?±?0.7 Ma from the tonalite porphyry in Quetena. Two Re–Os ages for Genoveva (38.1?±?0.2 and 38.0?±?0.2 Ma) are also within error of the Toki and Quetena molybdenite ages. Four Re–Os molybdenite ages for Opache range between 36.4 and 37.6 Ma. The Miranda prospect is the youngest with an age of ～36 Ma. Four new Re–Os ages for the Chuquicamata deposit range between 33 and 32 Ma, whereas nine new ⁴⁰Ar/³⁹Ar ages of biotite, muscovite, and K-feldspar range between 32 and 31 Ma. Analyzed molybdenites have Re and Os concentrations that vary between 21–3,099 ppm and 8–1,231 ppb, respectively. The highest Re and Os concentrations are found in the Toki prospect. Three new ⁴⁰Ar/³⁹Ar ages for the Toki cluster are younger than the Re–Os mineralization ages. The age spectra for these three samples show evidence of excess argon and have similar inverse isochron ages of 35 Ma that probably reflect a late hydrothermal phyllic event. The new geochronological data presented here for the Toki cluster indicate that molybdenite mineralization occurred within a very short period, probably within 2 Ma, and synchronously (at ～38 Ma) in three mineralization centers (Toki, Quetena, and Genoveva). Furthermore, mineralization at the Toki cluster preceded the emplacement of the Chuquicamata deposit (35–31 Ma) and indicates that porphyry Cu–Mo mineralization occurred episodically over a period of several million years in the Chuquicamata district.  相似文献   

Late Paleozoic K/Ar ages of blueschists from Pichilemu,Central Chile     

Francisco Herve  Francisco Munizaga  Estanislao Godoy  Luis Aguirre 《Earth and Planetary Science Letters》1974,23(2):261-264

Two crossite concentrates and one blueschist whole rock were analyzed by the K/Ar method. These samples belong to the high/intermediate pressure Western Series of the Chilean metamorphic basement and, in this area, are intruded by a small monzonite body.Ages obtained were 211 m.y. and 329 m.y. for the mineral concentrates and 211 m.y. for the whole rock. Discussion based on crystal size as a factor for retention of⁴⁰Ar during localized re-heating of the metamorphic rocks due to the monzonitic intrusion leads to the acceptance of 329 m.y. as the minimum age of crossite crystallization. This age agrees with the whole rock Rb/Sr limiting reference isochrons (273–342 m.y.) previously obtained for the metamorphic basement of Central Chile which did not include samples of the present area.This age provides the first evidence of a Paleozoic blueschist assemblage in the eastern Pacific border and would suggest the existence of a Late Paleozoic subduction zone along the western margin of South America.  相似文献   

Age of Cu(-Fe)-Au mineralization and thermal evolution of the Punta del Cobre district, Chile   总被引：1，自引：0，他引：1  

R. Marschik  B. S. Singer  F. Munizaga  C. Tassinari  R. Moritz  L. Fontboté 《Mineralium Deposita》1997,32(6):531-546

The Punta del Cobre belt is located 15?km south of Copiapó, northern Chile. It comprises several Cu(-Fe)-Au deposits in the Punta del Cobre and Ladrillos districts, east of the Copiapó river, and the Ojancos Nuevo district, with the new Candelaria mine, and Las Pintadas district, west of the river. The mineralization in the Punta del Cobre belt is characterized by a simple hypogene mineral assemblage of chalcopyrite, pyrite, magnetite, and hematite. Average ore grades are 1.1 to 2% Cu, 0.2 to 0.6?g/t Au, and 2 to 8?g/t Ag. Massive magnetite occurs as veins and irregularly shaped bodies. The ore is spatially associated with alkali metasomatism and in particular with potassic alteration. The Cu(-Fe)-Au deposits are hosted mainly in volcanic rocks of the Punta del Cobre Formation (pre-upper Valanginian) that underlie Neocomian limestones of the Chañarcillo Group. This region experienced backarc basin formation in the Neocomian, uplift and granitoid intrusions in the middle Cretaceous, and eastward migration of the magmatic front of about 30?km between middle Cretaceous and Paleocene. To determine the timing of ore deposition and to reconstruct parts of the thermal history of the Punta del Cobre district, in the eastern part of the belt, we have obtained ⁴⁰Ar/³⁹Ar incremental-heating and Rb-Sr analyses of mineral and whole-rock samples. An ⁴⁰Ar/³⁹Ar incremental-heating experiment on hydrothermal biotite, formed synchronous with the Cu(-Fe)-Au mineralization, yielded an inverse isochron age of 114.9?±?1.0 Ma (all errors reported at ±2σ), consistent with a Rb-Sr isochron of 116.8?±?2.7 Ma calculated from 7 whole-rock samples. These data are interpreted to represent the age of potassic alteration that accompanies mineralization. Ore formation temperatures of 400?°C to 500?°C were previously estimated based on paragenetic relationships. Shearing at the Candelaria deposit occurred after ore deposition and before the main stage of batholith emplacement. Published K-Ar ages for the middle Cretaceous batholith near the Punta del Cobre belt range from 119 to 97?Ma. Our data suggest that the mineralization is related to the earlier stages of batholith emplacement. The biotite age spectrum indicates that the Punta del Cobre district was not affected by temperatures above ～300?°C–350?°C, the closure temperature for argon in biotite, during the contact metamorphic overprint produced by later emplaced batholithic intrusions. Whole-rock ⁴⁰Ar/³⁹Ar ages are considerably younger; incremental-heating experiments yielded an inverse isochron age of 90.7?±?1.2?Ma and weighted mean plateau ages of 89.8?±?0.6?Ma and 89.5?±?0.6?Ma. These samples are dominantly K-feldspar, for which we assume an argon closure temperature of ～150?°C, thus they give the age of cooling below ～150?°C–200?°C.  相似文献   

SHRIMP U–Pb dating of the Antucoya porphyry copper deposit: new evidence for an Early Cretaceous porphyry-related metallogenic epoch in the Coastal Cordillera of northern Chile     

Victor Maksaev  Francisco Munizaga  Mark Fanning  Carlos Palacios  José Tapia 《Mineralium Deposita》2006,41(7):637-644

The Antucoya porphyry copper deposit (300 Mt at 0.45% total Cu) is one of the largest deposits of a poorly known Early Cretaceous porphyry belt in the Coastal Cordillera of northern Chile. It is related to a succession of granodioritic and tonalitic porphyritic stocks and dikes that were emplaced within Jurassic andesitic rocks of the La Negra Formation immediately west of the N–S trending sinistral strike-slip Atacama Fault Zone. New zircon SHRIMP U–Pb data indicate that the porphyries of Antucoya crystallized within the time span from 142.7 ± 1.6 to 140.6 ± 1.5 Ma (±2 σ), and late, unmineralized, NW–SE trending dacite dikes with potassic alteration and internal deformation crystallized at 141.9 ± 1.4 Ma. The Antucoya porphyry copper system appears to be formed after a change of stress conditions along the magmatic arc from extensional in the Late Jurassic to transpressive during the Early Cretaceous and provides support for an Early Cretaceous metallogenic episode of porphyry-type mineralization along the Coastal Cordillera of northern Chile.  相似文献   

Late Paleozoic–Early Triassic magmatism on the western margin of Gondwana: Collahuasi area, Northern Chile     

Francisco Munizaga  Victor Maksaev  C.M. Fanning  S. Giglio  G. Yaxley  C.C.G. Tassinari   《Gondwana Research》2008,13(3):407-427

The basement in the ‘Altiplano’ high plateau of the Andes of northern Chile mostly consists of late Paleozoic to Early Triassic felsic igneous rocks (Collahuasi Group) that were emplaced and extruded along the western margin of the Gondwana supercontinent. This igneous suite crops out in the Collahuasi area and forms the backbone of most of the high Andes from latitude 20° to 22°S. Rocks of the Collahuasi Group and correlative formations form an extensive belt of volcanic and subvolcanic rocks throughout the main Andes of Chile, the Frontal Cordillera of Argentina (Choiyoi Group or Choiyoi Granite-Rhyolite Province), and the Eastern Cordillera of Peru.Thirteen new SHRIMP U–Pb zircon ages from the Collahuasi area document a bimodal timing for magmatism, with a dominant peak at about 300 Ma and a less significant one at 244 Ma. Copper–Mo porphyry mineralization is related to the younger igneous event.Initial Hf isotopic ratios for the ~ 300 Ma zircons range from about − 2 to + 6 indicating that the magmas incorporated components with a significant crustal residence time. The 244 Ma magmas were derived from a less enriched source, with the initial Hf values ranging from + 2 to + 6, suggestive of a mixture with a more depleted component. Limited whole rock ¹⁴⁴Nd/¹⁴³Nd and ⁸⁷Sr/⁸⁶Sr isotopic ratios further support the likelihood that the Collahuasi Group magmatism incorporated significant older crustal components, or at least a mixture of crustal sources with more and less evolved isotopic signatures.  相似文献   

Exploration potential of Cu isotope fractionation in porphyry copper deposits   总被引：6，自引：0，他引：6  

Ryan Mathur  Spencer TitleyFernando Barra  Susan BrantleyMarc Wilson  Allison PhillipsFrancisco Munizaga  Victor MaksaevJeff Vervoort  Garret Hart 《Journal of Geochemical Exploration》2009

We examined the copper isotope ratio of primary high temperature Cu-sulfides, secondary low temperature Cu-sulfides (and Cu-oxides) as well as Fe-oxides in the leach cap, which represent the weathered remains of a spectrum of Cu mineralization, from nine porphyry copper deposits. Copper isotope ratios are reported as δ⁶⁵Cu‰ = ((⁶⁵Cu/⁶³Cu_sample/⁶⁵Cu/⁶³Cu_{NIST 976 standard}) − 1) ? 10³. Errors for all the analyses are ± 0.14‰ (determined by multiple analyses of the samples) and mass bias was corrected through standard-sample-standard bracketing. The overall isotopic variability measured in these samples range from − 16.96‰ to 9.98‰.  相似文献