1,721,046 research outputs found
Indialite in xenolithic rocks from Somma-Vesuvius volcano (Southern Italy): Crystal chemistry and petrogenetic features
No full textNi-bearing smectites in the Wingellina laterite deposit (Western Australia) at nanoscale: TEM-HRTEM evidences of the formation mechanisms
No full textNi-bearing clays represent the main ore minerals in many laterite districts. Although the world-class Wingellina deposit (Western Australia) is an oxide-dominated ore, about 30% of the total Ni resources are hosted in the saprolitic section of the tenure, making the Ni-bearing clays a strategic target to increase the future ore reserves. In this study we present a detailed micro- to nanotextural TEM-HRTEM investigation of Ni-bearing smectites, which at Wingellina represent the main mineralogical species in the phyllosilicates assemblage. Ni-bearing smectites belong mainly to the dioctahedral (i.e. montmorillonite and nontronite) and to the trioctahedral (saponite and ferrosaponite) groups. The nanoscale TEM-HRTEM imaging indicates that Ni-bearing clays occur either as a replacement of the former clay suite (i.e. polygonal serpentine and chlorite) or as porous clay aggregates (i.e. PCA). Most of PCA was found closely associated with nanometric Co-bearing Mn-oxy-hydroxides. This finding not only provides a better understanding of the early stage formation of Mn-oxy-hydroxides in laterite systems, but is also important to better constrain the Co distribution and targeting within unconventional laterite ore facies. The nanoscale HRTEM imaging coupled with SAED allowed detecting minor Ni-bearing chlorite amounts, which were not found through previous XRPD-based techniques. Moreover, the paragenetic association of chlorite with primary serpentine suggests a pre-lateritic formation for chlorite. The detection of Ni-bearing trioctahedral smectite as alteration product of primary chlorite is of relevant importance, as it fills a gap in the knowledge of ore-formation processes occurring in smectite-endowed laterites
The “calamine” of SW Sardinia (Italy): geology, mineralogy and stable isotope geochemistry of a supergene Zn-mineralisation.
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Deep seated fault‐related volcanogenic H2S as the key agent of high sinkhole concentration areas
No full textKarst collapse sinkholes (KCS) are a peculiar karst morphology resulting from the collapse of the topographic surface caused by subsurface karstification. In Southern Apennine these phenomena are not randomly distributed but concentrate in several zones, named High Sinkhole Concentration Areas (HSCA), showing peculiar geological, structural and hydrogeological conditions. Gas vents and mineral springs are spread out in these HSCA, and are often stricty related to the KCS. Starting from four representative areas, the aim of this study is to ascertain if there is a genetic link between peculiar mineralogical vs. geochemical features of densely fractured/altered rocky masses in KCS, gas vents/springs occurrences and diffuse hypogenic karstification. By means of a multidisciplinar approach (geological/geomorphological, mineralogical and geochemical) we selected and analysed four different kind of samples related to KCS, gas vent and spring occurrences: i) altered to deeply altered limestones sampled in the sinkholes, ii) unaltered limestones sampled in close proximity to sinkhole areas, iii) gypsum‐rich crusts/patinae, precipitated near to gas vents, iv) gypsum‐ and calcite‐rich precipitates occurring at springs or inside caves. Among neoformed non‐carbonate minerals, gypsum is virtually ubiquitous, halides (fluorite, halite, sylvite) also occur in small to trace amounts. The mineralogical assemblages of the different samples show similarities and may be also compatible with hypogenic speleogenesis and with a process of alteration of the carbonate bedrock by means of uprising mineralizing fluids along structural discontinuities. Stable isotopic compositions (S, O) display a strong variability in δ34S and δ18O for sulfate in the different areas, but a deep‐seated sulfur source can be hypothesized for many of the studied KCS‐related samples. This study has important implications for the relationships between areas of high concentration of sinkholes, regional fault systems, mechanical characteristics of rocks and the high seismicity typical of these areas of the Southern Apennines
Vanadium and other critical elements in North Gondwana Silurian black shales: The SE Sardinia (Italy) case
Full text linkVanadium currently represents a critical metal for the global economy, due to its increasing application in low CO2-emission technologies such as vanadium redox flow batteries. Black shale-hosted deposits cover about 80 % of the potential global V resources, although only <2 % of them is economic. During Silurian, significant black shale successions were deposited under strong anoxic conditions in the North Gondwana. This study aims at investigating the deportment of V in association with other trace elements in Silurian black shales of SE Sardinia (Italy), for understanding the nature of the depositional environment and the metallogenetic potential of these rocks at regional scale. Sardinian black shales have variable V amounts, ranging from hundreds to thousands ppm and organic carbon contents from 0.7 to 10.1 wt%. These values, together with observed Th/U, Ni/Co, V/Cr ratios indicate that the initial sedimentary environment was clearly anoxic. The positive correlation between V and total organic carbon indicates that organic matter retains most of V. Local V concentrations in rutile and illite may derive from metal remobilization during diagenesis and low-grade metamorphism. Compared to other coeval Silurian successions of North Gondwana, Sardinian black shales have anomalous values of Sb, Ba, Se, Mo, As, V, and Ag, this suggesting that, in the frame of a peculiar sedimentary process occurred in a similar way at the global scale, distinct controls existed in the various basins
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