Geotectonic signature and hydrothermal alteration of metabasalts under- and overlying the giant Serra Norte iron deposits, Carajás mineral Province

Silva, Rosaline Cristina Figueiredo e; Lobato, Lydia Maria; Zucchetti, Marcia; Hagemann, Steffen; Vennemann, Torsten

doi:10.1016/j.oregeorev.2020.103407

Cited by 10 publications

(2 citation statements)

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“…Goethite in pore spaces likely formed due to the Fe release during the alteration of vermiculite to kaolinite (Aspandiar & Eggleton, 2002). We indicate two major hydrothermal alteration types of chloritization (chlorite‐montmorillonite‐zeolite ± corrensite alteration of iron and magnesium bearing minerals such as pyroxene and olivine at higher temperature) and sericitization (kaolinite, K‐Fe‐Mg mica, sericite, and goethite alteration of feldspars and mafic minerals under high temperature and low pH condition) (e.g., Aspandiar & Eggleton, 2002; Büchl & Gier, 2003; Figueiredo e Silva et al., 2020; García‐Romero et al., 2005; Mathieu, 2018; Schenato et al., 2003).…”

Section: Discussionmentioning

confidence: 95%

“…However, volcanic rocks are commonly chemically and physically altered by weathering processes and hydrothermal fluids, affecting reservoir potential. Alteration records of volcanic units preserve complex geologic histories of dynamic hydrothermal systems along with emplacement and periods of exposure (e.g., Figueiredo e Silva et al., 2020; Navelot et al., 2018; Schlegel & Heinrich, 2015). Since feldspar and mafic minerals weather in part to clay minerals (e.g., smectite group), clay mineral assemblages are commonly analyzed to evaluate the alteration intensity of volcanic rocks (Alt et al., 1986, 1996; 2010; Bain et al., 1980; Broglia & Moos, 1988; Büchl & Gier, 2003; Çelik et al., 1999; Houston & Smith, 1997).…”

Section: Introductionmentioning

confidence: 99%

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Petrophysical Property Modifications by Alteration in a Volcanic Sequence at IODP Site U1513, Naturaliste Plateau

et al. 2021

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Petrophysical properties of volcanic rocks are controlled by lithology and subsequent modification by alteration processes. Investigating the linkages, using a range of different techniques, are important to establish how petrophysical properties can inform about the alteration state of volcanic rocks. Here, we compile petrophysical data and correlate these with geochemical and mineralogical analyses acquired from a volcanic sequence on the Naturaliste Plateau, offshore southwest Australia (International Ocean Discovery Program Site U1513). The sequence consists of alternating basalt lava flows and volcaniclastic deposits, intruded by multiple dolerite dikes. Variable alteration intensities from fresh-slight to strong are quantified using Chemical Index of Alteration. Intervals of slightly altered dikes exhibit low porosity and high values of bulk density, P-wave velocity, and thermal conductivity. The increase of alteration intensity corresponds to decreases in bulk density to ∼2 g/cm 3 , P-wave velocity to ∼2,000 m/s, thermal conductivity to ∼1.2 W/(m•K) and an increase in porosity up to 50%. Natural Gamma Ray and magnetic susceptibility vary downhole with rock composition and at lithologic boundaries. The distinct variations exhibit a good correlation with primary lithologic characteristics and secondary mineralogical and textural changes attributed to alteration processes. We provide synthesis models of petrophysical variation with alteration intensity. Although differences in primary lithology and alteration type introduce limitations and uncertainties, there is a reasonable applicability of our results to rapidly characterize the alteration intensity and volcanic stratigraphy in volcanic sequences and to calibrate wireline log-based determinations. This will help others to develop strategies for exploration, drilling, and geophysical research of volcanic rocks. Plain Language SummaryWe present the physical properties of rocks comprising a volcanic sequence recovered from the eastern Naturaliste Plateau, offshore southwest Australia. The sequence consists of basalt lava flows and volcaniclastic deposits, which are intruded by multiple dikes. Petrophysical properties of the volcanic rocks are variable with lithology and alteration state. To investigate the linkages, we applied a range of different techniques to correlate petrophysical data with geochemical and mineralogical analyses. The alteration intensity was quantified based on chemical composition into four ranges; fresh-slight, weak, moderate, and strong. Relatively fresh basalt intervals exhibit low porosity and high values of bulk density, P-wave velocity, and thermal conductivity. Increases of alteration intensity correspond to decreases in bulk density to ∼2 g/cm 3 , P-wave velocity to ∼2,000 m/s, thermal conductivity to ∼1.2 W/(m•K), and an increase in porosity up to 50%. Natural Gamma Ray and magnetic susceptibility vary with rock composition and at lithologic boundaries. The petrophysical variations were associated with primary lithologic charact...

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