38 research outputs found

    Macro-scale ore-controlling faults revealed by micro-geochemical anomalies

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    Whereas the mechanism of fluid flow, and thus structural control, linked with mineral deposit formation is quite understood, the specific structures that likely provided controls on mineralization at certain geographic scales are not readily known for a given region unless it is well-explored. This contributes uncertainty in mineral prospectivity analysis in poorly-explored regions (or greenfields). Here, because the spatial distribution of mineral deposits has been postulated to be fractals (i.e., the patterns of these features are self-similar across a range of spatial scales), we show for the first time that micro-geochemical anomalies (as proxies of micro-scale patterns of ore minerals), from few discrete parts of the Sossego iron-oxide copper-gold (IOCG) deposit in the Carajas Mineral Province (CMP) of Brazil, exhibit trends of macro-scale faults that are known to have controlled IOCG mineralization in the CMP. The methodology described here, which led to this novel finding, would help towards detecting mineral exploration targets as well as help towards understanding structural controls on mineralization in greenfields9CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO - CNPQFUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULO - FAPESP2014-9/401316; 2017-3/3097122015/11186-3FAPESP (Sao Paulo Research Foundation)Fundacao de Amparo a Pesquisa do Estado de Sao Paulo (FAPESP) [2015/11186-3]; CNPq (Brazilian National Council for Scientific and Technological Development)National Council for Scientific and Technological Development (CNPq) [2014-9/401316, 2017-3/309712]; Vale Compan

    Decadal–centennial-scale solar-linked climate variations and millennial-scale internal oscillations during the Early Cretaceous

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    Understanding climate variability and stability under extremely warm ‘greenhouse’ conditions in the past is essential for future climate predictions. However, information on millennial-scale (and shorter) climate variability during such periods is scarce, owing to a lack of suitable high-resolution, deep-time archives. Here we present a continuous record of decadal- to orbital-scale continental climate variability from annually laminated lacustrine deposits formed during the late Early Cretaceous (123–120 Ma: late Barremian–early Aptian) in southeastern Mongolia. Inter-annual changes in lake algal productivity for a 1091-year interval reveal a pronounced solar influence on decadal- to centennial-scale climatic variations (including the ~ 11-year Schwabe cycle). Decadally-resolved Ca/Ti ratios (proxy for evaporation/precipitation changes) for a ~ 355-kyr long interval further indicate millennial-scale (~ 1000–2000-yr) extreme drought events in inner-continental areas of mid-latitude palaeo-Asia during the Cretaceous. Millennial-scale oscillations in Ca/Ti ratio show distinct amplitude modulation (AM) induced by the precession, obliquity and short eccentricity cycles. Similar millennial-scale AM by Milankovitch cycle band was also previously observed in the abrupt climatic oscillations (known as Dansgaard–Oeschger events) in the ‘intermediate glacial’ state of the late Pleistocene, and in their potential analogues in the Jurassic ‘greenhouse’. Our findings indicate that external solar activity forcing was effective on decadal–centennial timescales, whilst the millennial-scale variations were likely amplified by internal process such as changes in deep-water formation strength, even during the Cretaceous ‘greenhouse’ period

    Radiocarbon dates on buried tree from debris-avalanche deposit in northern Yatsugatake volcanoes

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    Here we present radiocarbon dates of tree-ring collected from debris-avalanche deposit along the Ohtsuki River in northern Yatsugatake volcanoes, central Japan. The tree sample was collected in the eastern part of Lake Matsubara (N36.052837, E138.456496), central Japan. -- The tree trunk used in this study was deeply excavated from the debris deposit during land reclamation works which were conducted from 1980s to 1990s. The analytical tree samples for radiocarbon analyses were collected from the tree trunk in 1999

    Fe-oxide bands of Navajo concretion and Kimberley zebra rock

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    Here we present analytical results of Fe-bands of layered concretions from Jurassic eolian Navajo Sandstone in Utah (United States) and zebra rocks from Neoproterozoic Johnny Cake Shale Member in the Kimberley region (Western Australia), using micro-XRF mapping techniques. The Navajo concretions were collected from the outcrop of Spencer Flat of Grand Staircase–Escalante National Monument and the zebra rocks were obtained at the Zebra Gallery that the stone owner collected from the zebra rock quarry around Lake Argyle, south of Kununurra, Western Australia

    Paleoenvironment records from Lake Baikal VER99G12 sediment core

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    Here we present the paleoenvironment records of biogenic silica content, total organic carbon content, and C/N molar ratio in sediment cores collected from Lake Baikal in 1999, in order to reconstruct the paleoenvironment changes during the periods from last glacial period to Holocene. The biogenic silica content was quantified by ICP-AES analysis and the total organic and nitrogen was determined using CHNS coder

    Generalized conditions of spherical carbonate concretion formation around decaying organic matter in early diagenesis

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    Abstract Isolated spherical carbonate concretions observed in marine sediments are fascinating natural objet trouve because of their rounded shapes and distinct sharp boundaries. They occur in varied matrices and often contain well preserved fossils. The formation process of such concretions has been explained by diffusion and rapid syn-depositional reactions with organic solutes and other pore water constituents. However, the rates, conditions and formation process of syngenetic spherical concretions are still not fully clear. Based on the examination of different kinds of spherical concretions from several locations in Japan, a diffusion based growth diagram was applied to define the generalized growth conditions of spherical concretions formed around decaying organic matter. All analytical data imply that the spherical concretions formed very rapidly, at least three to four orders of magnitude faster than previously estimated timescales. The values indicate that spherical concretions are preferentially grown within clay- to silt-grade marine sediments deposited in relatively deep (a few tens of metres) environments dominated by diffusive solute transport, very early in diagenesis