U-Pb age and metamorphism of rocks of Voshnevogorsky sequence (South Ural)

In the article present results of U-Pb — dating of zircons and petrologic-geochemical study of garnet-biotite plagiogneises and quartz-plagioclase-amphibole granofels host rocks samples from Vishnevogorsky sequence of the oldest rocks of the southern Urals Eastern domain are presented. U-Pb-dating of zircons were obtained by ion microprobe (SHRIMP II). The maximum age of the substrate plagiogneises Vishnevogorsky sequence not younger than 2700 Ma, and granulitic metamorphism plagiogneises falls on the Proterozoic age range 1740–2220 Ma. The dates obtained for plagiogneises and granofels Vishnevogorsky sequence reflect all major (PR1–P1) age stages of the Urals development. Many of the dated events are manifested only in the zircons generation and are not reflected in the mineral paragenesises of the studied rocks.

Plundering Carlow Castle: First Look at a Unique Mesoarchean-Hosted Cu-Co-Au Deposit

Economically significant and geologically complex veined Cu-Co-Au mineralization was recently discovered at Carlow Castle in the Pilbara region of northwestern Western Australia. The inferred resource estimate for Carlow Castle as of March 2019 is 7.7 million tonnes (Mt) at 1.06 g/t Au, 0.51% Cu, and 0.08% Co, making it one of Australia’s most significant known Cu-Co-Au deposits. Here we provide the first account and scientific analysis of Carlow Castle. This analysis suggests that it is a hydrothermal Cu-Co-Au deposit, with mineralization hosted in sulfide-rich quartz-carbonate veins. The ore is hosted in veins that occur within a pervasively chloritized shear zone through the regionally significant Regal thrust. At Carlow Castle the shear zone associated with this thrust occurs within the Ruth Well Formation, an Archean mafic volcano-sedimentary sequence. Within the mineralized veins the dominant ore minerals are pyrite (FeS2), chalcopyrite (CuFeS2), chalcocite (Cu2S), cobaltite (CoAsS), and electrum (Au,Ag). The genesis of the Carlow Castle deposit is still under investigation; however, the origin of the Cu-Co-Au mineralization is most likely related to the migration of metalliferous fluids along the Regal thrust. Based on Carlow Castle’s stratigraphic position within the Pilbara craton and the craton’s relative stability since the Archean, an Archean age of mineralization is most likely. The distinct Cu-Co-Au enrichment at Carlow Castle makes it unique among Archean ore deposits generally, as the majority of Cu-Co deposits are of maximum Proterozoic age. Therefore, understanding the genesis of the Carlow Castle deposit has important implications for understanding the unique processes through which Cu-Co-Au mineralization outside of basin-hosted ore deposits may be formed, particularly in Archean terranes.

Alkaline rocks of the Ukrainian Shield: Some mineralogical, petrological and geochemical features

The Ukrainian Shield (USh) is a typical province of Proterozoic alkaline magmatism where about 50 massifs and occurrences of alkaline rocks and carbonatites have been found. In spite of the wide distribution of Devonian basaltic- and alkaline magmatic rocks in the Dnieper-Donetsk depression adjacent to the USh, and in a marginal zone of the USh adjacent to folded Donbass, only alkaline rocks of Proterozoic age (1.8-2.1 Ga) that have been identified in the central interior of the USh. Some discrete bodies of 2.8 Ga subalkaline rocks also occur in Bogdanivka massif (Azov area). Occurrences of both Proterozoic (prevailing) and Phanerozoic (Devonian) alkaline rocks and kimberlites are only found in the eastern part of the USh (Azov area). Kimberlites in the central part of the Ukrainian Shield (Kirovograd region) are also of Proterozoic age (ca 1.8 Ga). It is this predominance of Precambrian rocks that makes the USh so different from other alkaline provinces where Phanerozoic alkaline rocks and kimberlites commonly prevail over Precambrian rocks. The lack of Phanerozoic alkaline magmatism on USh is poorly understood. Two main complexes of alkaline rocks - alkaline-ultrabasic (carbonatitic) and gabbro- syenitic - are distinguished in the USh. There are also rare occurrences of rock types such as alkaline- and alkaline-feldspar granites that may represent one separate alkaline-granite complex. Alkaline rocks present in the Eastern (Azov) province and in the Western province display essentially different geochemical character. Those of the Eastern province show characteristics typical of alkaline-ultrabasic rocks (e.g. high contents of incompatible rare elementssuch as Nb, REE, Zr, Y, Sr, whereas those in the Western province are characterized by low contents of Nb and Zr, and REE in some cases. This fact is interpreted as reflecting different geodynamic conditions of their origin. The Eastern rocks were formed in rift settings, the Western rocks in crustal compressional settings (collision, subduction). Various mineral deposits of phosphorus (apatite), niobium, REE, yttrium and zirconium, including unusually rich ores of REE, Y and Zr (Azov and Yastrybetsky) are associated with the alkaline rocks and carbonatites of the USh.

CARACTERIZAÇÃO DOS ESTROMATÓLITOS DA FORMAÇÃO CAPIRU (PROTEROZÓICO) NAS REGIÕES DE MORRO AZUL E MORRO GRANDE: LESTE DO PARANÁ

As regiões de Morro Azul e de Morro Grande no leste do Paraná abrigam exposições de estromatólitos, compostos por formas colunares e esteiras microbianas na Formação Capiru do Grupo Açungui de idade Proterozóica. Estes estromatólitos estão associados a metadolomitos e indicam provável controle microbiano na geração de dois diferentes grupos: a) esteiras microbianas na região de Morro Azul e b) estromatólitos colunares na região de Morro Grande. Os estromatólitos colunares possuem até 35 cm de altura por 15 cm de diâmetro, ocorrem em colunas simples ou ramificadas, geralmente associadas a estruturas sedimentares plano-paralelas e a marcas de onda. Em planta, os estromatólitos são elipsoidais a circulares, onde a laminação interna se apresenta de ondulada a moderadamente convexa. As esteiras microbianas são compostas de uma sucessão de lâminas finas associadas a estruturas características de exposição subaérea como tepees e gretas de contração. As características morfológicas das estruturas estromatolíticas, associadas às estruturas sedimentares observadas nas diferentes litofácies, permitem caracterizar distintos ambientes de plataforma para as duas regiões: para a de Morro Azul, um ambiente de supramaré; enquanto para a de Morro Grande, um ambiente variando de entremarés a inframaré. CHARACTERIZATION OF STROMATOLITES IN THE CAPIRU FORMATION (PROTEROZOIC) IN THE MORRO AZUL AND MORRO GRANDE REGIONS: EASTERN PARANÁ Abstract The Morro Azul (região de Morro Azul) and the Morro Grande (região de Morro Grande) regions in eastern Paraná contain columnar stromatolites and microbial mats in the Capiru Formation of the Açungui Group of Proterozoic age. These structures are associated with metadolomites, indicating probable microbial control in the formation of two different groups of stromatolites: a) columnar stromatolites in região de Morro Grande and b) microbial mats in the região de Morro Azul. Columnar stromatolites reach up to 35 cm in height and 15 cm in diameter as columns or branched generally associated with plane-parallel sedimentary structures and wave marks. In cross-section, the stromatolites are elliptical to circular, and the lamination is wavey to moderately convex. The microbial mats are composed of a succession of fine laminal associated with structures characteristic of subaerial exposure, such as tepees and mud cracks. The morphlogic features of the stromatolites and the observed sedimentary structures in the different lithofacies suggest distinct shelf environments for the two regions: for região de Morro Azul, a supratidal facies, while in the região de Morro Grande, an environment varying from intertidal to infratidal.

Chronology of Avalonian events on Presqu'île du Cap Miquelon (Le Cap), Saint-Pierre et Miquelon (France)

U/Pb geochronology and field studies on Presqu'île du Cap Miquelon demonstrate that amphibolite-grade metamorphism, ductile deformation, and subsequent plutonism in this part of the Appalachian Avalon Zone are of Proterozoic age. Clear, crosscutting relationships between a dated granite dyke (part of the Cap Blanc granite) and foliated, amphibolite-grade metasedimentary and metaigneous rocks provide a younger age limit of [Formula: see text] Ma for tectonism. Proterozoic titanite and hornblende ages indicate that no significant younger thermal overprint occurred such as those recorded in nearby southern Newfoundland. Deformation and metamorphism of the country rocks and intrusion of the Cap Blanc granite are at least 30 Ma older than the onset of deposition of the youngest Proterozoic volcano-sedimentary successions in adjacent insular Newfoundland. Possible equivalents of these younger sequences occur near Cap Blanc, and contain what may be interpreted as clasts of granite, dated at 620 ± 3 Ma. The Miquelon metamorphic sequence is unique with respect to the southern Newfoundland Appalachians in representing a significant area of Proterozoic migmatite, not observably affected by tectonothermal events after 580 Ma.