Paleozoic Complex Research Articles

The eastern flank of the Caspian Basin: Sedimentary complexes and sedimentation conditions in the Early-Middle Carboniferous

Carboniferous and Lower Permian Carbonate and terrigenous rocks with the total thickness of >4000 m serve as the productive units in the Paleozoic subsalt complex at the eastern flank of the basin surrounding the northern area of the present-day Caspian Sea (hereafter, Caspian Basin in the broad sense). In recent years, several large oil and gas-condensate fields were discovered in these rocks. The complexity of geological evolution of this region, which is situated at the junction between the East European Platform and the Ural orogen, as well as multiple changes of sedimentation conditions during the Middle and Late Paleozoic, are reflected in the diversity of types of terrigenous and carbonate sediments and their facies alterations. Reconstruction of these environments makes it possible to elucidate specific features of the location of reservoir rocks in vertical and horizontal sections, as well as regularities of variations in their filtration-capacitive properties.

Principal thrust-nappe structures of the Dinarides

The Internal Dinarides include ten larger allochthonous pre-Alpine complexes, similar in many respects to those in the Eastern Alps, Carpathians and Rhodopes. The Dinaride Paleozoic complexes consist mainly of Devonian to Permian formations and are commonly associated with abundant Triassic sediments. In addition, the largest Paleozoic complexes contain subordinate Cambrian-Ordovician formations. The best developed Early Paleozoic complex, which occurs in western Macedonia, is composed of fossiliferous Cambrian metasediments with ophiolites and fossiliferous Ordovician metasediments, interlayered with subordinate metavolcanics and intruded by coeval Ordovician granitoids (461-465 Ma) that were overprinted during the Variscan and Alpine tectonogeneses. It is underthrust by Variscan formations and overthrust by Neoproterozoic Pelagonide formations. Parts of the Paleozoic Drina-Ivanjica complex are composed of fossiliferous Cambrian-Ordovician metasediments containing metamafics and metatuff that were overprinted by Early Cretaceous metamorphism. In the Mid-Bosnian Schist Mts, formations of presumed Cambrian- Ordovician age characteristically consist of gneiss and amphibolite, which can be compared to the Oetztal complexes of the Eastern Alps. Dinaridic Cambrian-Ordovician formations from all three areas were metamorphosed during the late Ordovician deformation under P-T conditions of greenschist and, to a lesser extent, epidote-amphibolite facies (400-500 °C and 4-5 Kbar). Based on geochemical data, Ordovician bimodal volcanics and granitoids indicate a geotectonic setting comparable to recent back-arc basins.

Early Paleozoic formations within pre-Alpine fragments incorporated into the Internal Dinarides

The Internal Dinarides include ten larger allochthonous pre-Alpine complexes, similar in many respects to those in the Eastern Alps, Carpathians and Rhodopes. The Dinaride Paleozoic complexes consist mainly of Devonian to Permian formations and are commonly associated with abundant Triassic sediments. In addition, the largest Paleozoic complexes contain subordinate Cambrian-Ordovician formations. The best developed Early Paleozoic complex, which occurs in western Macedonia, is composed of fossiliferous Cambrian metasediments with ophiolites and fossiliferous Ordovician metasediments, interlayered with subordinate metavolcanics and intruded by coeval Ordovician granitoids (461-465 Ma) that were overprinted during the Variscan and Alpine tectonogeneses. It is underthrust by Variscan formations and overthrust by Neoproterozoic Pelagonide formations. Parts of the Paleozoic Drina-Ivanjica complex are composed of fossiliferous Cambrian-Ordovician metasediments containing metamafics and metatuff that were overprinted by Early Cretaceous metamorphism. In the Mid-Bosnian Schist Mts, formations of presumed Cambrian- Ordovician age characteristically consist of gneiss and amphibolite, which can be compared to the Oetztal complexes of the Eastern Alps. Dinaridic Cambrian-Ordovician formations from all three areas were metamorphosed during the late Ordovician deformation under P-T conditions of greenschist and, to a lesser extent, epidote-amphibolite facies (400-500 °C and 4-5 Kbar). Based on geochemical data, Ordovician bimodal volcanics and granitoids indicate a geotectonic setting comparable to recent back-arc basins.

STRATIGRAPHY AND TECTONIC AND METAMORPHIC EVOLUTION OF THE PORTO AZZURRO UNIT IN THE MONTE CALAMITA PROMONTORY (SOUTHEASTERN ELBA ISLAND, TUSCANY)

The Elba Island has a key role in the reconstructions of the stratigraphic, tectonic, metamorphic and magmatic evolution of the Northern Tyrrhenian Sea and of the inner part of the Northern Apennines chain. The Porto Azzurro Unit, cropping out in the SE part of the Island, is the deepest tectonic unit of the central-eastern Elba structural pile of Tuscan, Ligurian and Ligurian-Piedmontese Nappes, which were intruded by Late Tortonian-Lower Pliocene granitoids and mainly acidic dikes. Moreover, in this part of the Island, the relationships between the uplift of the plutonic bodies and the final deformations of the tectonic stack are well exposed. To improve the geological knowledge of SE Elba, the authors carried out a 1:10.000 geological survey of the Calamita Promontory (mostly made up of the Porto Azzurro Unit) and performed petrographic and meso-/micro-structural studies on its rocks. The Porto Azzurro Unit consists of a Paleozoic, likely pre-Carboniferous basement (Mt. Calamita Fm.), which is unconformably overlain by the ?Triassic Verrucano metasiliciclastics (Barabarca Quartzites) and ?Upper Triassic-?Hettangian metacarbonates. In the Mt.Calamita Fm., five main lithofacies were recognized and mapped. In particular, garnet-bearing, albite micaschist (lithofacies a) geometrically underlie a phyllitic-quartzitic unit (lithofacies b); Porphyroids-like rocks (lithofacies e), metabasite bodies (lithofacies d) and graphite-rich siliciclastics (lithofacies c) are also present. The rocks of the lithofacies a are similar to those of the ?pre-Paleozoic-?Paleozoic Micaschist Complex of the Larderello Geothermal Field, whereas the other lithofacies can be probably correletable with the ?Ordovician formations of the Tuscan Metamorphic Units. The complex deformation-metamorphic evolution of the Porto Azzurro Unit consists of the following events: a) a Variscan tectono-metamorphic event (Dx), recognized in the Mt.Calamita Fm., which is defined by pre- Alpine schistosity and mineralogic relics (garnet); b) two Alpine tectono-metamorphic folding events (D1 and D2) in the Greenschists facies, which deformed also the Mesozoic covers; c) a following folding event (D3) which probably occurred during or immediately after the strong thermometamorphic imprint (including the magnetite-rich skarn bodies), due to the Neogene magmatic intrusions; d) Subsequently, the uplift of the magmatic bodies caused low-angle detachments within the Porto Azzurro Unit (between the Mt.Calamita Fm. and the Mesozoic cover) and between the latter and the overlying tectonic Units (e.g. Zuccale Fault between the Porto Azzurro Unit and the Cretaceous Flysch). A final weak antiformal folding (D4) of the whole promontory took place before the development of NW-SE and N-S trending high –angle normal fault systems, locally sealed by hydrothermal, sometimes Fe-rich mineralizations. The lithostratigraphic, tectonic, metamorphic and magmatic evolution of the Porto Azzurro Unit is similar to that defined for the Larderello geothermal region. Thus, the Mt.Calamita area can be considered as a little older, but similar geological model for all the future interpretations of the deep structure of southern Tuscany crossed by the Crop 18 profile.

Varying depositional environments of gypsum successions in the Upper Miocene Eskisehir-Sivrihisar lacustrine basin, NW Turkiye

The basement rocks of Eskisehir-Sivrihisar basin are made of Upper Paleozoic metamorphic rocks and Upper Cretaceous ophiolite complex. These rocks are overlain by Middle Miocene sedimentary rocks the base. Upper Miocene-Pliocene stratigraphic succession consists of basal conglomerates, sandstones, claystones, limestones, dolomites and tuffs are thinly interbedded with cyclic evaporites. The main clay mineral assemblage consists of smectite, illite and sepiolite that are enriched in different percentage in different horizons. The Upper Miocene-Pliocene stratigraphic succession consists of alterations of gypsum, clayey carbonates and unconsolidated very soft dolomite beds, which are conformably underlain by sepiolite-bearing clayey carbonates and disconformably overlain by alluvium and conglomerate series of Pleistocene age. The Upper Miocene unit includes three different facies, based on sedimentary properties of gypsum from the base to the top; (I) laminated gypsum beds are thinly interbedded with dolomites and green clays; (2) gypsum rosettes within thin reddish and greenish clays and carbonates; and (3) scattered gypsum mainly within carbonates. Gypsums had been deposited in somewhat different depositional conditions in the same basin where multi-periodic evaporative episodes, ranging from saline to schizohaline environments, had been involved. During these episodes, under high Eh-pH intervals and high salinity conditions, three different types of gypsum formations had been developed in a meromictic-type lake under the influence of varying paleoclimatologic conditions and pore water chemistry of brines. All these gypsum morphologies respectively reflect the different conditions of environments of deposition in a Miocene playa lake basin: (1) subaqueous environments in playa lakes with short evaporation episodes; (2) marginal swamps with cyclic fluctuation of lake level; and (3) extended closed-lake with evaporatic lake water. These different gypsum morphologies are associated with distinctive sedimentary subfacies, which are also primarily related to cyclic climatic changes, alternating semi-arid and evaporite conditions, fluctuation of lake water level and sulphate input in the chemistry of lake water from runoff and hydrothermal source adjacent to basin.

Paleozoic tectonostratigraphic units of the northwest and central Dinarides and the adjoining South Tisia

In the Central Dinarides and South Tisia different Paleozoic complexes occur in four geotectonic zones: (1) comparatively autochthonous units located in the cores of disrupted anticlines of the External Dinarides; (2) allochthonous disrupted units accompanied by more predominant Triassic formations in the Sava Nappe, which is thrust onto the northeastern margin of the External Dinarides; (3) allochthonous disrupted units, also together with Triassic formations, in the Pannonian and Durmitor nappes of the Internal Dinarides; and (4) polymetamorphic sequences in basement of the Pannonian Basin and South Tisia, respectively. This paper presents basic geological features for the main Paleozoic areas included in these four zones. The tectonostratigraphic units of the first two zones were related to the Gondwana passive continental margin, those of the third zone to the Paleotethyan oceanic realm, and those of Tisia to the active Laurussia margin. Geodynamic evolution of all these Paleozoic complexes was related to opening and closure of the Rheic and Paleotethys Oceans. Rifting processes along North Gondwana started in the Silurian, locally in the Cambrian–Ordovician, and were followed by the Late Silurian/Devonian opening of the Paleotethys. Subduction processes were active by the end of the Devonian and at the beginning of the Carboniferous along the Laurussia margin. They were followed during the Westphalian by main Variscan deformation during collision of Gondwana and Laurussia. Associated metamorphism was very low-grade in the Paleozoic units of the Sava Nappe, low-grade to epidote–amphibolite grade within the Paleozoic complexes of the Pannonian and Durmitor nappes in the Internal Dinarides, and poly-metamorphic with migmatites and granitoids in South Tisia. These processes gave rise to a Pangea stage with the Variscan basement disconformably overlain by Late Carboniferous and Permian sediments.

Geology and structural controls of the Twin Peaks epithermal gold deposit, East Junggar, Xinjiang, China

The Twin Peaks epithermal gold deposit, located in East Junggar, China, is hosted by the late Paleozoic Kulankazigan island-arc complex. The deposit is structurally controlled by the extensional radial fractures associated with development of the Early Carboniferous Twin Peaks volcanic dome. It is stratigraphically restricted to the upper Batamayineishan Formation, which is subdivided into two units: the lower andesite unit that contains the ore bodies, and the upper rhyolite unit. Four hydrothermal alteration zones have been identified in both East and West Zones of the deposit. Each zone is characterized by a highly silicified core, and then there is an outward progression through adularia–sericite, argillic, and propylitic zones. The presence of adularia and sericite, in addition to the sulfide mineral association, suggests that the gold deposit is of the "adularia-sericite" or "low sulfidation" type. The East Zone ore body is offset by post-mineralization, high-angle reverse faults that strike parallel to the zone and small-scale, strike-slip faults that strike perpendicular to the zone.

Rayleigh Wave Group Velocity Tomography of Siberia, China and the Vicinity

—Rayleigh waves are used in a tomographic inversion to obtain group velocity maps of East Asia (40° E–160° E and 20° N–70° N). The period range studied is 30 to 70 seconds. Seismograms used for this study were recorded at CDSN stations, at a temporary broadband seismic array in Tibet, at several SRO stations, and Kirnos-equipped stations established in Asia by the former Soviet Union, in Siberia, in the Sakhalin and in Mongolia. Altogether more than 1200 paths were available in the tomographic inversion. The study area includes the Angara craton, the geologically ancient core of Asia, and the subsequently accreted units, the Altaids (a Paleozoic collision complex), the Sino-Korean platform (a chain of Archaen terranes separated by belts of active structures), the south China platform (a collage of Precambrian, Paleozoic and Mesozoic metamorphic and igneous terranes), as well as the Tibetan plateau (an active tectonic feature created in late Cenozoic through collision of the Indian subcontinent and the Asian continent). Many of these main units are recognizable in the tomographic images as distinctive units; Tibet appears as a prominent low velocity (about −15% from the average) structure, with western and central Tibet often appearing as the areas with the lowest velocities, the Central Asian fold-belt, and the Angara craton are consistently high group velocity areas. Some lesser tectonic features are also recognizable. For example, Lake Baikal is seen as a high velocity feature at periods greater than 40 seconds. However, the high group velocity feature does not stop near the southern end of Lake Baikal; it extends south-southwestward across Mongolia. The North China Plain, a part of the platform where extensional tectonics dominate, is an area of high velocities as a result of relatively thin crust. The south China block, the least tectonically active region of China, is generally an area of high velocity. For periods longer than 40 seconds, a NNE trending high group velocity gradient clearly exists in eastern China; the velocities are noticeably higher in the east. From the group velocity maps, average dispersion curves at twelve locations were determined and inverted to obtain velocity structures. Main results of group velocity inversion include: (1) a Tibetan crust of around 60 km thick, with low crustal and upper mantle shear velocities, at 3.3 km/s and 4.2 km/s, respectively; (2) with the Moho constrained at 40–43 km, the Angara craton and the Central Asian foldbelt have a VS in excess of 4.6 km/s; (3) relatively low shear velocities are obtained for tectonically active areas. In many parts of the study area, where Precambrian basement is exposed, the process in the crust and upper mantle due to recent tectonic activities have modified the crust and upper mantle velocity structures under the Precambrian terranes, they are no longer underlain by high velocity crust and mantle.

Diagenesis of Deeply Buried Eagle Mills Sandstones: Implications for Paleo-Fluid Migration and Porosity Development: ABSTRACT

ABSTRACT Eagle Mills strata (Triassic-Jurassic) unconformably overlie the Paleozoic basement complex and thus, form the basal sedimentary unit within the Gulf of Mexico Basin. Jurassic-aged basaltic dikes and sills have intruded Eagle Mills strata. Werner-Louann evaporates disconformably overlie the Eagle Mills Formation. These sedimentary and igneous rocks preserve the earliest record of Gulf of Mexico rifting. Deeply buried (15,000 to 18,000 ft/4,573 to 5,488 m) Eagle Mills sandstones have subarkosic and sublithic modal compositions. These sandstones exhibit evidence of a complex and prolonged diagenetic history, including: early chlorite cementation; mechanical compaction; quartz and feldspar overgrowths; nonferroan calcite and dolomite cementation; dissolution of framework grains; kaolinite precipitation; ferroan calcite cementation; albitization; saddle dolomite and anhydrite cementation; and pyritization. Pyrobitumens coat early cements indicating that most diagenesis post-dated hydrocarbon migration. Marked shifts in paleo-water chemistry are recorded by diagenetic phases in Eagle Mills sandstones. The Eagle Mills paragenetic sequence is indicative of progressive burial into a high-temperature (>150° C) regime where thermochemical sulfate reduction was the dominant diagenetic process. Pervasive late burial dissolution of detrital feldspars in some Eagle Mills sandstones provides direct evidence for deep-seated sourcing of metal cations which promoted diagenesis of overlying Mesozoic strata. These petrographic data support interpretations of the Mesozoic Gulf Coast Basin which imply vertical mass-transfer of diagenetic fluids along faults.

Tectonism, magmatism and sedimentary basin development, Paleozoic to Paleogene, New Caledonia

Three pre-Cretaceous basement terranes are recognised in New Caledonia: 1. Karagreu­ Boghen Terrane - an old accretionary complex, metamorphosed to greenschist facies, of uncertain age but probably Early Permian or older and tentatively correlated with Mid-Late Paleozoic complexes of New England Fold Belt. 2. Mt. Canala-Teremba Terrane - arc type volcanics and volcaniclastics of Upper Permian to Early Jurassic age and correlated with the Brook Street Terrane of New Zealand. 3. Ponerihouen-Baie St. Vincent Terrane - volcaniclastic and terrigenous sandstones and argillites of Mid Triassic to Jurassic age and correlated with the Murihiku and Waipapa Terranes of New Zealand. The Karagreu-Boghen and Mt. Canala-Teremba Terranes were probably juxtaposed by the Late Triassic. The three basement terranes were stitched together by late Mesozoic intrusives and Rangitata (Early Cretaceous) metamorphism and deformation. Late Cretaceous-Paleocene extensional sedimentary basins with bimodal volcanism were developed to the N (Diahot Basin) and S (Noumea Basin). The Cretaceous basalts of the Diahot basin are ocean floor type while those of the Noumea Basin are arc type and represent the final extensional stage of Mesozoic subduction. The allochthonous Cretaceous-Eocene West Coast basalts, believed to be New Caledonia Basin ocean floor, are normal MORB-type tholeiites with some arc affinities. The West Caledonian Fault post dates Early Oligocene obduction of the New Caledonian ultramafic sheet and has 55 km of right lateral transcurrent movement. Vertical movement on this fault has also played a major role in Miocene uplift particularly in the north of the island.

Types of epithermal silver deposits, northeastern Russia

Three main epithermal silver provinces occur in northeastern Russia: (1) the Cretaceous Okhotsk-Chukotka volcanic plutonic belt (Russia's part of the Circum-Pacific belt), (2) adjacent Mesozoic orogenic belts, and (3) Paleozoic complexes formed of intermediate massifs. Within the most studied Okhotsk-Chukotka province, three types of deposits are distinguished by structural position and geologic environments: (1) those in volcanic intrusive domes, (2) those in siliceous subvolcanic bodies, and (3) those in contact halos around granodioritic intrusions. Gold-silver, silver-lead-zinc, and tin-silver ore deposits are distinguished, according to the ore composition. The silver deposits of the Ducat ore district are examples of these three types.Genetically, ore mineralization of the three types differs. Gold-silver mineralization was formed in near-surface, open hydrothermal systems during mixing of metalliferous solutions with meteoric waters, as indicated by low salinities (2.5-3.5% NaCl equiv) of the fluid inclusions. Subvolcanic and intrusive bodies were the local heat sources, which caused a field with high thermal gradients (avg 200 degrees -370 degrees C). Boiling of the fluids was the most effective mechanism of ore deposition with which ore shoot formation was connected as evidenced by texture and fluid inclusion data. In contrast, silver-lead-zinc and tin-silver mineralizations formed in closed hydrothermal systems in which boiling did not occur. Their relatively low uniform temperatures (avg 240 degrees -320 degrees C) and low thermal gradients were associated with a more steady regime of Ag-Pb-Zn-Sn ore deposition compared to the gold-silver deposits. The relatively high salinity of fluids (up to 7.5% NaCl equiv) resulted from the absence of mixing of metalliferous solutions and meteoric waters.

Diagenetic And Sedimentologic Aspects Of Eagle Mills-Werner Conglomerate Sandstones (Triassic-Jurassic), Northeast Texas

ABSTRACT The Eagle Mills-Werner sequence occurs in deep wells (12,000 to 18,000 ft.) in northeast Texas and southwest Arkansas. Eagle Mills sandstones unconformably overlie the Paleozoic complex and disconformably underlie the Werner Conglomerate. Werner-Louann evaporites overlie Eagle Mills-Werner siliciclastics. Basaltic sills and dikes transect these sandstones and conglomerates. Eagle Mills-Werner strata consist of greenish-gray conglomerates and green, red, and pink, coarse-grained, lithic-feldspathic arenites which are interbedded with red, gray, and green shales and siltstones. Lithic arenites and conglomerates contain volcanic and sedimentary rock fragments. These strata represent nonmarine paleoenvironments developed within grabens and are the earliest record of Gulf of Mexico rifting. Eagle Mills-Werner sandstones have undergone a complex diagenetic history, including: chlorite cementation, compaction, quartz and feldspar overgrowths, early carbonate cementation, dissolution of framework grains, chloritization and albitization of feldspars, late cementation by ferroan calcite and ferroan dolomite and late replacement by anhydrite and pyrite. Pyrobitumens coat early chlorite cements indicating that most diagenesis post-dated hydrocarbon migration. This suite of authigenic phases records progressive burial of Eagle Mills-Werner strata into a high-temperature diagenetic regime where thermochemical sulfate reduction was the dominant process.

Structure of Pre-Caspian Depression and Major Oil and Gas Fields of the Region

As a single unified depression, the pre-Caspian basin has been formed from Paleozoic to Cenozoic time. The basin is superimposed on two large pre-Permian depressions. On the Astrakhan-Aktyubinsk zone of uplifts between them is found sharply reduced Carboniferous and Devonian sections. Modern structural plan clearly displays two major structural stages: Subsalt (Paleozoic) and post (post-Kungurian). The post-salt stage is characterized by wide development of salt dome tectonics. It corresponds with its own petroliferous stage containing numerous, mostly small oil accumulations in terrigenous Mesozoic reservoirs. Large recent discoveries-Astrakhan condensate, Karachaganak and Kanazhol-Sinelnikov oil/condensate, Tengiz oil, and other fields-are associated with the Subsalt Paleozoic complex ranging from Lower Permian to the top of Upper Devonian. The Subsalt stage has its own regularities in hydrocarbon phase differentiation; large reserves concentration; dominantly productive carbonates with various reservoirs; and presence of structural, depositional, and erosional factors controlling formation of oil and gas traps. The paper describes major distributional features of the various arc-and-type Permian and Carboniferous formations, which in conjunction with Subsalt paleotemperature data and geochemistry of organic matter represents a basis for the forecast of new discoveries.

Dynamic Growth of Selected Paleozoic Reef Complexes: ABSTRACT

Dynamic Growth of Selected Paleozoic Reef Complexes: ABSTRACT

Buried structural traps in upper Paleozoic strata of the Orenburg region and their petroleum prospects

Analysis of drilling data within the Orenburg sector of the northern marginal zone of the Caspian Basin and the Sol'-Ilets rise has shown that horizons of the Moscovian Stage of Late Carboniferous and Early Permian age rest on an eroded surface of Bashkirian deposits in a transgressive succession.Changes in thicknesses in the upper Paleozoic stratigraphic complexes indicate a significant discordance between the structural plans of the Artinskian and Bashkirian deposits and the possibility of discovering buried traps here, promising in the search for oil and gas.

Paleozoic Oil and Gas Complexes of the Baltic Syneclise

Principal directions for exploration of new commercial accumulations of oil and gas in the main Paleozoic prospective complexes in the Baltic syneclise, including its sea portion, have been based on an analysis of the lithologic-facies composition, structural features, attitude of the rocks, and the distribution of the reservoir horizons and possible different types of traps. The promise of the deep parts of the southeastern Baltic Sea region, where a large number of local uplifts have been identified, and traps of nonanticlinal and combined types have been recorded, is emphasized where the principal focus for the generation of oil hydrocarbons inthe Baltic syneclise is located. As compared with the land area, it is suggested that there is an increase in the supply stock and the capacity parameters of the traps and an improvement in the conditions of preservation of petroleum accumulations here.

Paleozoic dike complexes of the Kola peninsula and Northern Karelia

(1978). Paleozoic dike complexes of the Kola peninsula and Northern Karelia. International Geology Review: Vol. 20, No. 3, pp. 273-280.

Mi Vida prospect; a porphyry copper-type deposit in northwestern Argentina

Mi Vida is a porphyry copper-type deposit located in northwestern Argentina in the province of Catamarca. It was investigated by Cities Service Minerals during a two-year exploration program which included geological, geochemical, and hydrothermal alteration studies, as well as 7,927 meters of diamond drilling.A Precambrian or lower Paleozoic complex composed of schists, migmatites, and granites was intruded by a syenodiorite stock with differentiated marginal facies and associated bodies of andesite porphyry and andesite flow breccias. Related to this intrusive event is a biotitic and biotitic-sericitic alteration phase accompanied by pyrite-chalcopyrite-bornite-molybdenite-magnetite mineralization. A volcanic event followed, during which rhyolites were emplaced. After this a huge breccia pipe body was formed. A sericitic-siliceous alteration, with the unusual alteration minerals alunite and zunyite, is related to this last event. Also related to the breccia is a mineralizing pulse with a very unusual assemblage: pyrite-covellite-bornite-enargite-molybdenite-sphalerite-galena-marcasite-rhodochrosite-native sulfur.It is concluded that Mi Vida is, perhaps, an example of a deposit midway between the porphyry copper deposits and the volcanic-exhalative copper-lead-zinc deposits found in several parts of the world.

Early Paleozoic ophiolite complexes of Newfoundland: Isotopic ages of zircons: Comment and reply

Early Paleozoic ophiolite complexes of Newfoundland: Isotopic ages of zircons: Comment and reply

Early Paleozoic ophiolite complexes of Newfoundland: Isotopic ages of zircons: Comment and reply

Early Paleozoic ophiolite complexes of Newfoundland: Isotopic ages of zircons: Comment and reply