New 40Ar/39Ar alunite ages from the Colquijirca district, Peru: evidence of a long period of magmatic SO2 degassing during formation of epithermal Au-Ag and Cordilleran polymetallic ores

We present 40Ar/39Ar data acquired by infra-red (CO2) laser step-heating of alunite crystals from the large Miocene Colquijirca district in central Peru. Combined with previously published data, our results show that a long (at least 1.3 My) and complex period of magmatic-hydrothermal activity associated with epithermal Au-(Ag) mineralization and base metal, Cordilleran ores took place at Colquijirca. The new data indicate that incursion of magmatic SO2-bearing vapor into the Colquijirca epithermal system began at least as early as ∼11.9Ma and lasted until ∼10.6Ma. Four alunite samples associated with high-sulfidation epithermal Au-(Ag) ore gave 40Ar/39Ar plateau ages between ∼11.9 and ∼11.1Ma (compared to the previously documented ∼11.6 to ∼11.3Ma). By combining individually these new ages with crosscutting relationships, the duration of the Au-(Ag) deposition period can be estimated to at least 0.4My. Three new 40Ar/39Ar plateau ages on alunite associated with the base-metal Cordilleran ores are consistent with previously obtained ages, all of them between 10.83 ± 0.06 and 10.56 ± 0.06Ma, suggesting that most of the sulfide-rich polymetallic deposits of Smelter and Colquijirca formed during this short period. The recognition of consecutive alunite-bearing and alunite-free mineral assemblages within both the Au-(Ag) and the base-metal Cordilleran ores may suggest that SO2-bearing magmatic vapor entered the epithermal environment as multiple discontinuous pulses, a number of which was not necessarily associated in time with ore fluids. It is likely that a period of SO2-bearing vapor degassing longer than 11.9 to 10.6Ma may be recognized with further more detailed wor

Space and time distribution of Neogene-Quaternary volcanism in the Carpatho-Pannonian Region

Much geochronological (K-Ar, F. T.), biostratigraphical and paleomagetic data has been accumululated during the last decade enabling us for the first time to obtain a reasonably complete picture of the space and time distribution of the Neogene-Quaternary volcanics in the Carpathian-Pannonian region (CPR). Neogene volcanic activity started with high-volume acid calc-alkaline explosive eruptions. The oldest K-Ar ages (20 Ma) for these rocks are found partly m the Pannonian Basin and partly in the West Carpathians. During the Middle Miocene to Quaternary (17-0.2 Ma) calc-alkaline mainly intermediate stratovolcamc complexes were formed first in the West Carpath1ans and later in the East Carpathians. Within the alkaline (shoshonitic, alkali-basaltic, K-trachytic and ultrapotassjc) volcanism, two age groups can be distinguished: an older group (17-7 Ma) and a younger one (6-0.5 Ma). Sporadic Quaternary volcanic activity is confined to the West Carpattans, East Carpathians, Persani Mts. and Apuseni Mts. A very complex picture of events is presented by the radiometnc data and only in some restricted areas can progressive migrat1on of the activity during the course of the Neogene-Quaternary be recognized

Composite volcanoes in the south-eastern part of Izmir-Balikesir Transfer Zone, Western Anatolia, Turkey

During the Early-Middle Miocene (Western Anatolia) several volcanic fields occur along a NE-SW-trending shear zone, known as Izmir-Balikesir Transfer Zone. This is a deformed crustal-scale sinistral strike-slip fault zone crossing the Bornova flysch and extending along the NW-boundary of the Menderes Massif by accommodating the differential deformation between the Cycladic and Menderes core complexes within the Aegean extensional system. Here we discuss the volcanic activity in Yamanlar and Yuntdagi fields that is closely related to the extensional tectonics of the Izmir-Balikesir Transfer Zone and in the same time with the episodic core complex denudation of the Menderes Massif

Mineralogy of the pliocene trachyte and its carbonatitic minette inclusions in Ostrvica, FYR of Macedonia

The trachyte at Ostrvica hill (age 3.21±0.10 Ма) in Vardar zone is the most evolved volcan- ics of the ultrapotassic Pliocene-Quaternary series in F.Y.R. of Macedonia. It is aphyric, with clinopy- roxene and phlogopite microphenocrysts within a sanidine-anorthoclase groundmass. It contains inclu- sions of carbonatitic minette ranging in size from several mm to 6–7 cm. They are light coloured por- phyric rocks, rich in vacuoles, composed of phlogopite and completely altered olivine(?) phenocrysts amongst acicular clinopyroxenes within a feldspar–calcite groundmass with abundant Fe-oxides and acicular apatite microlites. The inclusions are rimmed by a mm thick mixing zone composed of the same minerals but with intermediate composition between that of minette and trachyte. The clinopyroxenes are mainly diopside-augite with low Ti and Al content (with 6Al only in the minette). Positive correla- tions are observed between Na and Fe3+, Al and Ti, and negative one – between Al and Si. In the inclu- sions phlogopites the negative correlation between Mg# and 4Al is found. The feldspars in the trachyte and minette inclusions are Ca-sanidine to Ca-anorthoclase, in the mixing zone – sanidine only. In the in- clusions two plagioclase generations (An41 and An25) exist. The estimated crystallization temperature of the minette clinopyroxenes is 1280–1180С, of plagioclase (An41) – 1130С and in the hosting trachyte – 1080С, at the pressures 6.9 and 7.7 kbar, respectively. The temperature of the feldspars crystalliza- tion (K-Na-feldspars and Pl24) in the minette groundmass is 809–878C. By analogy with other ultrapo- tassic volcanics from F.Y.R Macedonia it is suggested, that the discussed volcanics originated from phlogopite-bearing metasomatised mantle

Miocene volcanism of the Cserhat Mts (N Hungary): Integrated volcano-tectonic, geochronologic and petrochemical study

New K/Ar ages and paleomagnetic data connected with volcano-tectonic observations detected three intermediate (andesitic) and three acidic (dacitic-rhyolitic) magmatic phases. Cserhát magmatic activity occurred between 21-12 Ma. The timing of the initial and final acidic and intermediate phases may be connected with the Mátra volcano situated to the east. During the Badenian (15-14 Ma) the volcano-tectonic evolution was relatively independent in the Cserhát Mts. The third acidic and intermediate volcanic phases, which developed in the Lower Sarmatian, show similar features as the final phases of the Mátra volcano. Based on the major and trace element geochemistry the acidic rocks result from partial melting of the lower crust. Most of the intermediate volcanic rocks were generated from a rather homogeneous fluid-modified source (lithospheric), as triggered by an important heat transfer event. Initial melts sometimes experienced mixing or contamination in the lower or upper crust. This was a period of strong extensive tectonics. The rock of the second and third intermediate phases suggests minor fractional crystallization in the intermediary magma chamber(s)

Late Miocene to Pleistocene potassic volcanism in the Republic of Macedonia

The potassic (K) to ultrapotassic (UK) volcanic rocks cropping out in the Vardar Zone of Macedonia and southern Serbia span in age from Late Miocene (6.57 Ма) to Pleistocene (1.47 Ма). The main identified outcrops are in the Kumanovo, Sveti Nikole, Shtip and Demir Kapia areas; the southernmost occurrences of these volcanic rocks are located in the large Kozuf Massif (Voras Massif in Greece) at the Macedonia–Greek border. Three distinct groups may be distinguished. The first group has a shoshonitic affinity and occurs in the Kozuf Massif (LMg-K group); it includes shoshonites to rare rhyolites, with latites and trachytes being the most widespread products. The second group consists of potassic rocks (HMg-K group, K2O/Na2O between 1.0 and 1.8) occurring in both southern Serbia (Cer and Slavujevci) and Macedonia (Djuristhe, near Sveti Nikole). The third group, present only in Macedonia, consists of ultrapotassic rocks (UK group, K2O/Na2O >1.8, Mg# >71) classified as UK shoshonites, UK latites and UK phonotephrites; overall, they show a “Roman Province type” affinity (Group III of Foley, Venturelli, Green, Toscani, Earth Sci Rev 24:81–134, 1987). Geochemically, the studied rocks exhibit strong enrichment in LILE, Th and Pb, as well as relative depletion in Ta–Nb and Hf; such signatures are typical of magmas generated in convergent geotectonic settings. In the HMg-K and UK rocks, Sr and Nd isotopic ratios vary from 0.70768 to 0.71040, and 0.51243 to 0.512149, respectively. The rocks of the LMg-K group show relatively limited Sr and Nd isotope variations (0.7087–0.7093 and 0.51233–0.51229), which correlate with a decrease in MgO and increase in SiO2 contents. The geochemical features of the LMg-K volcanic rocks indicate that their evolution was mainly driven by fractional crystallization coupled with contamination by feldspar-rich crustal materials. In contrast, the HMg-K and UK rocks have not been significantly modified by crustal contamination, and their geochemical features are considered to reflect lithospheric mantle heterogeneity acquired during the subduction of the Western Vardar Ocean and the Apulian plate. The metasomatizing agent was apparently more enriched in Zr, Th, Ta and Ce than in fluid-mobile elements, such as Pb and Cs, suggesting that it was characterized by a high melt/fluid ratio. The potassic and ultrapotassic magmatic activity developed in response to the Pliocene–Pleistocene extension in the Vardar Zone, in turn related to the opposite propagation of extension in the Aegean and Pannonian basins (respectively SW and NE)

Late Alpine Ultra- to High Potassic Volcanic Rocks in Republic of Macedonia: Mineralogy, Geochemistry, and Age

The studies volcanics outcrop in Vardar zone and span in the age form the Pliocene (2.04-3.24Ma) to the Pliocene (1.47-1.81Ma)according to the TAS diagram and K/Na ratio they are ultrapotassic (phonotephrites to ultrapotassic shoshonites and latites ) and high potassic rocks (hoshonites and latites to trachytes)

New 40Ar/39Ar alunite ages from the Colquijirca district, Peru: evidence of a long period of magmatic SO2 degassing during formation of epithermal Au–Ag and Cordilleran polymetallic ores

We present 40Ar/39Ar data acquired by infra-red (CO2) laser step-heating of alunite crystals from the large Miocene Colquijirca district in central Peru. Combined with previously published data, our results show that a long (at least 1.3 My) and complex period of magmatic-hydrothermal activity associated with epithermal Au–(Ag) mineralization and base metal, Cordilleran ores took place at Colquijirca. The new data indicate that incursion of magmatic SO2-bearing vapor into the Colquijirca epithermal system began at least as early as ∼11.9 Ma and lasted until ∼10.6 Ma. Four alunite samples associated with high-sulfidation epithermal Au–(Ag) ore gave 40Ar/39Ar plateau ages between ∼11.9 and ∼11.1 Ma (compared to the previously documented ∼11.6 to ∼11.3 Ma). By combining individually these new ages with crosscutting relationships, the duration of the Au–(Ag) deposition period can be estimated to at least 0.4 My. Three new 40Ar/39Ar plateau ages on alunite associated with the base-metal Cordilleran ores are consistent with previously obtained ages, all of them between 10.83 ± 0.06 and 10.56 ± 0.06 Ma, suggesting that most of the sulfide-rich polymetallic deposits of Smelter and Colquijirca formed during this short period. The recognition of consecutive alunite-bearing and alunite-free mineral assemblages within both the Au–(Ag) and the base-metal Cordilleran ores may suggest that SO2-bearing magmatic vapor entered the epithermal environment as multiple discontinuous pulses, a number of which was not necessarily associated in time with ore fluids. It is likely that a period of SO2-bearing vapor degassing longer than 11.9 to 10.6 Ma may be recognized with further more detailed work

Triassic fluid mobilization and epigenetic lead-zinc sulphide mineralization in the Transdanubian Shear Zone (Pannonian Basin, Hungary)

International audienceA combined fluid inclusion, fluid inclusion plane, lead isotope and K/Ar radiometric age dating work has been carried out on two lead-zinc mineralizations situated along the Periadriatic-Balaton Lineament in the central part of the Pannonian Basin, in order to reveal their age and genetics as well as temporal-spatial relationships to other lead-zinc-fluorite mineralization in the Alp-Carpathian region. According to fluid inclusion studies, the formation of the quartz-fluorite-galena-sphalerite veins in the Velence Mts is the result of mixing of low (0-12 NaCl equiv. wt. %) and high salinity (10-26 CaCl2 equiv. wt. %) brines. Well-crystallized (R3-type) illite associated with the mineralized hydrothermal veins indicates that the maximum temperature of the hydrothermal fluids could have been around 250 degrees C. K/Ar radiometric ages of illite, separated from the hydrothermal veins provided ages of 209-232 Ma, supporting the Mid- to Late-Triassic age of the hydrothermal fluid flow. Fluid inclusion plane studies have revealed that hydrothermal circulation was regional in the granite, but more intensive around the mineralized zones. Lead isotope signatures of hydrothermal veins in the Velence Mts (Pb-206/Pb-204 = 18.278-18.363, Pb-207/Pb-204 = 15.622-15.690 and Pb-208/Pb-204 = 38.439-38.587) and in Szabadbattyan (Pb-206/Pb-204 = 18.286-18.348, Pb-207/Pb-204 = 15.667-15.736 and Pb-208/Pb-204 = 38.552-38.781) form a tight cluster indicating similar, upper crustal source of the lead in the two mineralizations. The nature of mineralizing fluids, age of the fluid flow, as well as lead isotopic signatures of ore minerals point towards a genetic link between epigenetic carbonate-hosted stratiform-stratabound Alpine-type lead-zinc-fluorite deposits in the Southern and Eastern Alps and the studied deposits in the Velence Mts and at Szabadbatty n. In spite of the differences in host rocks and the depth of the ore precipitation, it is suggested that the studied deposits along the Periadriatic-Balaton Lineament in the Pannonian Basin and in the Alps belong to the same regional scale fluid flow system, which developed during the advanced stage of the opening of the Neo-Tethys Ocean. The common origin and ore formation process is more evident considering results of large-scale palinspastic reconstructions. These suggest, that the studied deposits in the central part of the Pannonian Basin were located in a zone between the Eastern and Southern Alps until the Early Paleogene and were emplaced to their current location due to northeastward escape of large crustal blocks from the Alpine collision zone