New SHRIMP U-Pb zircon ages from the Hartswater group, South Africa: Implications for correlations of the Neoarchean Ventersdorp Supergroup on the Kaapvaal craton and with the Fortescue Group on the Pilbara craton

The Neoarchean Hartswater Group of the western Kaapvaal craton is a bimodal volcanic and sedimentary cratonic cover succession traditionally correlated with the Platberg Group of the ~2.71. Ga Ventersdorp Supergroup, South Africa. Correlation between exposures of the Platberg Group equivalents across the Kaapvaal craton is complicated, because they were deposited within isolated grabens, they display lateral facies changes over short distances, and they are extensively covered by calcrete and sand. Such correlation is important, since these units constitute one of the oldest unconformity-bounded sequences originally compared with sequences from the Pilbara craton (northwestern Australia) for reconstructing the ancient continent " Vaalbara" . Present age constraints, however, imply a ~50 million year discrepancy in the shared geological histories of the cratons. Here we report SHRIMP U-Pb zircon ages from a prominent pyroclastic surge and ash fall deposit in the lower Hartswater Group (2733.4. ±. 3.4. Ma) and from variable quartz-feldspar porphyry in the upper Hartswater Group (2724.3. ±. 5.8. Ma). The new constraints significantly improve correlations of the Platberg Group equivalents on the western Kaapvaal craton, and present a clear solution to the apparent enigma in cross-craton correlation. The data cast doubt on the 2714. Ma age for the Klipriviersberg Group of the east central Kaapvaal craton, and strengthen lithostratigraphic correlations with units from the Pilbara craton (i.e., the Hardey Sandstone, the Bamboo Creek and Spinaway porphyries, the Kylena Basalt, and in part the Tumbiana Formation). When our ages are placed within paleogeographic context a systematic picture of a shared long-lived extensional event emerges

Nature and origin of the protolith succession to the Paleoproterozoic Serra do Navio manganese deposit, Amapa Province, Brazil

Until its closure in 1997, the Serra do Navio deposit, located in Amapá Province, Brazil, was one of the most important sources of high-grade manganese ore to the North American market. The high-grade manganese oxide ores were derived by lateritic weathering from metasedimentary manganese protoliths of the Serra do Navio Formation. The local geological context and nature of this protolith succession are not well understood, due to poor surface outcrop conditions, and intense deformation. However, based on similar age, regional tectonic setting and lithology the Paleoproterozoic volcanosedimentary succession that includes the Serra do Navio Formation is widely believed to be similar in origin and laterally equivalent to the Birimian Supergroup in West Africa. For the present investigation several diamond drill cores intersecting the protolith succession were studied. Detailed petrographic and whole rock geochemical studies permit distinction of two fundamental lithological groups comprising of a total of five lithotypes. Biotite schist and graphitic schist lithotypes are interpreted as former metapelites. A greywacke or pyroclastic protolith cannot be excluded for the biotite schist, whereas the graphitic schist certainly originated as a sulfide-rich carbonaceous mudstone. Rhodochrosite marble, Mn-calcite marble and Mn-silicate rock are grouped together as manganiferous carbonate rocks. Manganese lutite constitutes the most probable protolith for rhodochrosite marble, whereas Mn-calcite marble was derived from Mn-rich marl and Mn-silicate rock from variable mixtures of Mn-rich marl and chert.\ud \ud The sedimentary succession at the Serra do Navio deposit is similar to that encountered at many other black shale and chert-hosted Mn carbonate deposits. A metallogenetic model is proposed, predicting deposition of manganese and closely associated chert in intra-arc basins, in environments that were bypassed by distal siliciclastic (carbonaceous mud) and proximal pyroclastic/siliciclastic detritus. Positive Ce anomalies and δ13CVPDB values of −4.3 to 9.4 per mill suggest that manganiferous carbonates derived during suboxic diagenesis from sedimentary Mn4+ oxyhydroxide precipitates. Metamorphic alteration of manganese carbonate–chert assemblages resulted in the formation of Mn-silicates, most importantly rhodonite and tephroite; porphyroblastic spessartine formed where Mn-carbonate reacted with aluminous clay minerals. Microthermometric studies of fluid inclusions in spessartine porphyroblasts suggests that peak metamorphic conditions reached the upper greenschist facies (1–2 kbars and 400–500 °C). Retrograde metamorphism is marked by partial re-carbonation, expressed by the formation of small volumes of rhodochrosite, and Mn-calcite that are closely associated with quartz, chlorite and minor amounts of sulfides related to post-metamorphic veinlets. It is this metamorphosed succession that sourced the high-grade manganese oxide ores during prolonged lateritic weathering

Petrographic, geochemical and SHRIMP U-Pb titanite age characterization of the Thabazimbi mafic sills: Extended time frame and a unifying petrogenetic model for the Bushveld Large Igneous Province

Mafic sills occur within and in the vicinity of the Thabazimbi iron ore deposit, near the northern edge of the western limb of the Bushveld Complex. The sills are hosted in the 2.46. Ga Penge Iron Formation of the Transvaal Supergroup. The gabbroic sill

Precise SHRIMP U-Pb zircon age constraints on the lower Waterberg and Soutpansberg Groups, South Africa

Erosional remnants of Paleoproterozoic red bed successions such as the Olifantshoek, Soutpansberg, Waterberg and Palapye Groups cover an extensive area of the Kaapvaal Craton. Depositional ages of these successions have been ill-defined and their latera

Stratigraphy, depositional setting, and shrimp u-pb geochronology of the banded iron formation–bearing bailadila group in the bacheli iron ore mining district, bastar craton, india

The Bailadila Group of the Bastar Craton, India, is host to a 200-m-thick banded iron formation (BIF). We document the lithostratigraphic context for the BIF, informally referred to as the Bose iron formation, and provide radiometric constraints for its depositional age. Field evidence illustrates that the BIF was deposited on an inner-shelf succession with a quartz arenite that grades upward into the BIF through storm-dominated offshore shelf deposits. The quartz arenite to BIF transition records a relative sea level rise from transgressive to highstand systems tract when the BIFs were deposited in a starved outer continental shelf. U-Pb SHRIMP analyses of zircons from the basement of the Bailadila Group yielded mostly highly discordant U-Pb SHRIMP ages. However, the ages fall on well-defined discordia lines from which concordia intercept ages could be determined. These ages, in combination with the ages of a few zircons that are less than 6% discordant, indicate that the granitoid basement crystallized at 3500–3550 Ma. The maximum depositional age of the Bailadila Group is constrained from the weighted mean Pb/ Pb SHRIMP age of 2725 5 57 Ma from detrital zircons from the basal arenites. A well-constrained weighted mean Pb/ Pb SHRIMP age of 2733 5 53 Ma for zircons from a unit that unconformably overlies the Bailadila Group is within error of that age. Stratigraphic relationships suggest that the Bailadila succession is unconformably overlain by the ~2.5 Ga Kotri and Dongargarh Supergroups. The depositional age of the Bailadila Group is well constrained between ~2.7 and 2.5 Ga. In contrast to most other Archean Algoma-type iron formations of peninsular India, which are closely related to volcanic rocks in greenstone belts, the Bose iron formation is associated with siliciclastic shelf succession. It thus is considered a Superior-type iron formation that represents the oldest known one of its kind in India.This work is an outcome of a collaborative researchproject funded by the Department of Science andTechnology (DST) in India and the Department ofScience and Innovation (DSI), as well as the Na-tional Research Foundation (NRF) in South Africa

Dating the Oldest Greenstone in India: A 3.51-Ga precise U-Pb SHRIMP zircon age for Dacitic lava of the Southern Iron Ore Group, Singhbhum Craton

This article reports a precise 3506.8 ± 2.3-Ma U-Pb SHRIMP zircon age for dacitic lava in a well-preserved low-grade metamorphic and low-strained greenstone belt succession of the southern Iron Ore Group, Singhbhum craton, India. This age makes the succ