Interface Sampling and Indicator Minerals for Detecting the Footprint of the Lancefield North Gold Deposit under the Permian Glacial Cover in Western Australia

Areas under a thick Permian glacial cover in Western Australia formed as glaciers gouged fresh bedrock and deposited diamictites in disconnected valleys and basins. These areas now present the greatest challenge for mineral exploration in the northeast Yilgarn Craton. At the Lancefield North gold prospect, in the southern part of the Duketon Greenstone Belt, Permian diamictites on average 40 m thick cover unweathered basalt hosting gold mineralization. The basal Permian diamictites consist of fresh, very poorly sorted, angular to rounded, pebble- to boulder-sized, polymictic clasts supported by a matrix of coarse-grained sand and mud. The framework and matrix are cemented by calcite, dolomite, chlorite, and pyrite. These diamictites are stable under alkaline and reducing conditions below the water table. Detrital; fresh sulfides; gold; and opaque oxides, such as pyrite, pyrrhotite, chalcopyrite, sphalerite, arsenopyrite, gersdorffite, cobaltite, pentlandite, scheelite and galena, chromite, ilmenite, and magnetite, are identified in the framework and matrix of the fresh diamictites, and these are identical to those in the primary gold mineralization. Weathering of diamictites and oxidation of detrital and diagenetic sulfides above the water table produced several Fe- and Mn-rich redox fronts and secondary chalcocite and bornite. Interface sampling across the Archean–Permian unconformity shows Au, As, Zn, Ni, Co, and Cd anomalism over the mineralization compared to the background. However, these elements are low in concentration in the redox fronts, where Fe is correlated with As, Cu, Mo, and Sb and Mn is correlated with Co, Ni, and Ba. Gold shows elevated levels in the fresh basal diamictites and decreases in the weathered diamictites over the mineralization. A sampling at or near the Archean–Permian unconformity (interface sampling) only delineates gold mineralization, with no hydromorphic dispersion halo beyond the peripheries. At the Lancefield North prospect, the detrital indicator sulfides are mechanically dispersed up to 500 m to the east of the mineralization in the direction of ice flow. This dispersal distance is controlled by the rough topography of the Archean–Permian unconformity, and it may be greater, but the estimation of the actual distance of transport is limited by the distribution of drill hole locations.

The Effects of Glacial Cover on Riverine Silicon Isotope Compositions in Chilean Patagonia

Proglacial rivers have been shown to have distinctive silicon (Si) isotope compositions, providing new insights into the mechanisms controlling Si cycling in the subglacial environment and suggesting terrestrial Si isotope exports may have varied between glacial and interglacial periods. However, Si isotope data are currently limited to a small number of glacial systems in the northern hemisphere, and it is unclear how compositions might vary across a spectrum of glacial influence. Using Chilean Patagonia as a unique natural laboratory, we present Si isotope compositions of 0.45 μm filtered (fSi), 0.02 μm filtered (DSi), and reactive amorphous (ASi) fractions from 40 river catchments with variable glacial cover and explore the key controls on Si cycling. The 0.45 μm filtered glacier-fed river samples displayed isotopically light compositions and a positive linear correlation with upstream glacial cover. This relationship was controlled by the inclusion of an isotopically light colloidal-nanoparticulate (0.02–0.45 μm) silicate phase that was only present in glacier-fed rivers and dominated Si budgets in these catchments. This phase was predominately composed of feldspars and its lability in seawater is uncertain, representing a significant unknown in resolving glacial Si isotope exports from this region. When the colloidal-nanoparticulates were removed from solution by ultra-filtration, the resultant DSi isotope compositions of glacier-fed catchments were not isotopically distinct from some non-glacial rivers and exhibited no clear relationship with glacial cover. The colloidal-nanoparticulate concentration of other weathering-sensitive elements (Li, Mg, Ba, Sr) also showed a linear relationship with glacial cover, suggesting that their isotopic compositions could be affected in a similar manner. These findings highlight the benefit of size-fractionated sampling and the need for more research to understand the lability of colloidal-nanoparticulate species, especially in glacier-fed rivers. Finally, we explore the controls on river ASi isotope compositions and show how including these reactive particulate phases is critical to quantifying terrestrial Si isotope budgets, both in Patagonia and other global regions.

Climate controlled catchment erosion in the Himalaya during the late Quaternary

<p>The alluvial sediments deposited in the Indo-Gangetic Plains originated as a result of tectonic and climatic factors controlling the exhumation and erosion of the Hinterland Himalaya. However, erosion distribution over the Himalaya and sediment delivery to the plains, on a shorter millennial time scale, are primarily controlled by the climatic factors such as glacial cover over the Himalaya and intensity of Indian summer monsoon (ISM) precipitation. Therefore, these alluvial sediment archives record important information about the past climatic changes. Here, we report the geochemical record of <sup>87</sup>Sr/<sup>86</sup>Sr, <sup>143</sup>Nd/<sup>144</sup>Nd (ε<sub>Nd</sub>), and δ<sup>13</sup>C of sediment organic matter (δ<sup>13</sup>C<sub>SOM</sub>) in a ~45 m long drill-sediment core collected from a buried channel of the paleo-Yamuna River in the northwest Indo-Gangetic Plains, Haryana to infer variations in provenance, paleoclimate, and paleovegetation during the late Quaternary. The Sr–Nd isotopic compositions (<sup>87</sup>Sr/<sup>86</sup>Sr: 0.75144–0.79241, ε<sub>Nd</sub>: –15.9 to –19.7) of the core sediments suggest their derivation from isotopically distinct Higher Himalaya and Lesser Himalaya end-member sources in the catchment. Down-core variability in the isotopic compositions show increased contribution from the Higher Himalaya during marine isotope stage (MIS) 1 and late MIS 3 interglacial periods due to receding glacial cover and intense ISM. The δ<sup>13</sup>C<sub>SOM </sub>values (−21.6‰ to −27.0‰, average: −25.6‰) in the core samples imply a C<sub>3</sub> dominant paleovegetation in the catchment. Down-core variability in the δ<sup>13</sup>C<sub>SOM</sub> exhibits significant correlation with the ISM precipitation intensity, implying an increased abundance of C<sub>4</sub> plant in response to the ISM intensification during MIS 1, and early and late MIS 3.</p>

Vulnerability of C stocks in Polylepis forests of the Peruvian Andes under climate change – evidence from laboratory incubations, microbial nutrient constraints and enzyme activities

<p>Soils are the largest stock of terrestrial carbon, the dynamics of soil organic C (SOC) are controlled by microbial physiology, but how it promotes stable SOC and how it would change with warming, remains unknown. The Huascarán National Park (HNP), the largest mass of tropical glaciers in the world, has lost 20-30% of its glacial cover and the temperatures in this biosphere have risen 0.1°C per decade since 1970. However, no information on the HNP soil carbon stocks is available. As managing SOC is important for global warming mitigation, we study the soil C stocks in Polylepis forests of three valleys in the HNP along a temperature gradient relative to elevation (3300 to 4500 m asl), and their vulnerability to decomposition with increasing temperatures and combined labile C and nutrient (N+P) additions.</p><p>We found that higher altitude soils have higher C:N:P ratios which indicates that, as expected, soils at high altitudes are nutrient limited. Also, the activities of the N acquiring enzymes: NAGase and leucine-aminopeptidase, C acquiring enzymes: beta-glucosidase, cellobiosidase, beta-xylosidase and phosphatase were positively correlated with altitude, which indicate that N and P availability decreased with altitude across our gradient. This could make high altitude soils vulnerable to C losses, not just due to increased temperatures, but also due to increased rhizosphere priming effects. Climate warming might increase plant growth and belowground C allocation, which in turn could lead to priming due to nutrient mining.</p><p>We found no differences across altitudes in microbial biomass (Cmic) measured with the chloroform fumigation extraction method. We are currently analysing microbial community composition (by PLFA’s and DNA based methods). We will present data on microbial CUE of glucose decomposition, and how it is related to soil C/N ratios, nutrient availability and nutrient requirements, and community composition of the microbes. We also aim to test whether higher CUE is related to higher C stabilisation potential in the form of microbial necromass residues (amino sugars), or higher C loss when microbes efficiently growing on labile substrates will also increase the decomposition of more stable SOC (priming).</p>

The Montellina Spring as an Example of Water Circulation in an Alpine DSGSD Context (NW Italy)

Alpine areas, with normally fissured bedrock outcrops, do not typically contain important hydrologic reservoirs, except for small aquifers located in Quaternary sediments. By contrast, mountainous areas affected by deep-seated gravitational slope deformations (DSGSD), especially if covered by glacial sediments, contain large aquifers and are consequently promising for water exploitation. This last geological setting is observed, for example, in the lower Dora Baltea Valley (near the confluence with the Renanchio Basin) in which the Montellina Spring is located and exhibits a very high discharge. A multidisciplinary approach (detailed geological survey of the bedrock and Quaternary cover, as well as hydrogeological research based on tracer tests, hydrochemical analyses, and water balance studies) was used, allowing for a reconstruction of the geological and hydrogeological setting of the investigated area, also considering its environmental implications. The consequent hydrogeological model derives from the coexistence of some factors. In detail, the thick glacial cover, widespread in the intermediate sector of the slope, represents an important aquifer with a slow groundwater flow to the spring. The buried glacial valley floor, hosting this cover, can convey the groundwater from the high Renanchio Basin zone towards the low sector. The loosened bedrock of the low sector, consequent to DSGSD phenomena, favors the concentration of groundwater along the contact with the underlying normal fissured bedrock outcropping at the base of the slope. Finally, the flow until the spring essentially takes place through N100° trend open fractures and trenches. Part of the Montellina Spring discharge is also fed by the low Renanchio Stream, as highlighted by fluorescein tests, essentially using NE-SW oriented open fractures on the bedrock. The results of the investigation on the Montellina Spring can provide some insight regarding the hydrological potential of other alpine areas with a similar geological setting.

Строение и морфология ледникового рельефа в бассейне р. Кица (Умбозерская)

In the article the issues of composition and morphology of accumulative relief in the central part of the Kola region are considered. The main role in composition of the glacial forms is determined to belong to squamous, diapir and folded laciodislocations. Regularities of spatial arrangement and morphological characteristics of the relief forms, which correspond to glaciodislocations of different types, have been defined. It is concluded that three rows of marginal formations corresponding to individual retreat stages of the last glacial cover in the Late Pleistocene were developed on the studied area. Obtained data are important to determination of dynamic features of the north sector of the White Sea Ice Stream. Moreover, they may be used as criteria to prediction of mineral-building materials. В статье рассмотрены вопросы строения и морфологии аккумулятивного рельефа в центральной части Кольского региона. Установлена ведущая роль чешуйчатых, диапировых и складчатых гляциодислокаций в строении форм ледникового генезиса. Определены закономерности пространственного расположения и морфологические характеристики форм рельефа, соответствующие гляциодислокациям разного типа. Сделан вывод о развитии в районе работ трех цепочек краевых образований, соответствующих отдельным фазам деградации последнего ледникового покрова в позднем плейстоцене. Полученные данные имеют большое значение для установления особенностей динамики северного сектора беломорского ледникового потока, а также могут быть использованы в виде критериев прогнозирования минерально-строительного сырья.

Two additions to the moss flora of the South Shetland Islands in the maritime Antarctic

<em>Tortella fragilis</em> (Drumm.) Limpr. (Pottiaceae) and <em>Bryum nivale</em> Müll. Hal. (Bryaceae) are recorded for the first time from the South Shetland Islands in the northern maritime Antarctic. They were discovered in the Admiralty Bay area on King George Island, the largest island of this archipelago. The two species are briefly characterized morphologically, their habitats are described, and their distribution in the Antarctic is mapped. Discovery of these species has increased the documented moss flora of King George Island to 67 species, strengthening it in the leading position among individual areas with the richest diversity of moss flora in Antarctica. Likewise, <em>T. fragilis</em> and <em>B. nivale</em> represent remarkable additions to the moss flora of the South Shetland Islands, which currently consists of 92 species and one variety, making this archipelago by far the richest bryofloristically amongst large geographic regions of the Antarctic. Comparison of recent (2018) and old (1985) photographs revealed a significant retreat of glacial cover and suggests that the collection site was likely opened for colonization only within the last several decades. The record of <em>T. fragilis</em> is biogeographically relevant, and constitutes an intermediate site between the species’ occurrences in the Antarctic Peninsula and southern South America. The present record of <em>B. nivale</em> is the fourth discovery of the species worldwide, which may be helpful for the future designation of the distribution of this extremely rare species.