Normative minerals and alteration indices developed for mineral exploration

Piché, Mathieu; Jébrak, Michel

doi:10.1016/j.gexplo.2003.10.001

Cited by 30 publications

(33 citation statements)

References 11 publications

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“…Mineralogical changes across the Koudiat Aïcha deposit may also be detected in the calculation of normative mineral abundances using whole-rock chemical compositions (Piché and Jebrak, 2004). The hydrothermal alterations around volcanogenic deposits are largely formed under temperatures of 200-400 °C and moderate (sub-seafloor) pressures, producing a mineralogical alteration assemblage consisting mainly of quartz, chlorite, sericite, albite and calcite (Franklin et al, 2005).…”

Section: Petrographic and Normative Signaturesmentioning

confidence: 99%

Lithogeochemical, mineralogical analyses and oxygen–hydrogen isotopes of the Hercynian Koudiat Aïcha massive sulphide deposit, Morocco

Lotfi

Belkabir

Brunet

et al. 2010

Journal of African Earth Sciences

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Koudiat Aïcha is a Visean stratiform, volcanogenic massive sulphide (VMS) zinc-copperlead deposit, situated northwest of Marrakech, within the Central Domain of the Jebilet massif of the Western Moroccan Meseta. The Central Domain is formed mainly of sedimentary (argillite, siltstone, sandstone, carbonate) and magmatic (gabbro and rhyodacite) rocks that host numerous massive sulphide deposits (e.g., Koudiat Aïcha, Kettara and Draa Sfar) in a thick grayish argillite sequence (rhythmic metapelite). The deposit is stratabound and consists of highly deformed, sheet-like lenses of massive sulphide located structurally on the eastern flank of a large anticline. Prior to metamorphism, the country rocks were subjected to hydrothermal alteration which is particularly pronounced in the immediate vicinity of the sulphide deposits where chloritization and sericitization are prevalent. Hydrothermal alteration extends into both the stratigraphic footwall and the stratigraphic hanging wall. The footwall lacks an obvious pipe zone (sulphide stringers or vent complex) beneath the sulphide mineralization, but is characterized by an increase in the modal proportion of Mg-chlorite and by the breakdown of feldspar and sericite. Chloritization, the most extensive and readily recognizable alteration useful in mineral exploration, is evident for more than 60 m above the subcropping sulphide deposits. The hanging wall rocks show a pervasive sericitization (over 30 m wide) and a weak chlorite alteration accompanied by disseminated nodules of pyrrhotite stretched parallel to the S 1 foliation. Because chlorite and sericite are metamorphic minerals that also occur in unaltered rocks surrounding the sulphide deposits, abundant Mg-rich chlorite and the absence of feldspar in the footwall are used to distinguish hydrothermal alteration facies from metamorphic facies. The chlorite geothermometer reveals temperatures between 250 and 330 °C. Higher temperatures (up to 300 °C) are associated with chlorite located in and adjacent to sulphide mineralization, whereas lower temperatures correlate with distal chlorite in both the footwall and hanging wall rocks.Chemical trends in altered footwall rocks are shown by absolute mass gains for Fe 2 O 3total , MnO and MgO, by absolute mass losses for CaO, K 2 O and Na 2 O, and by a moderate loss in SiO 2 . Oxygen and hydrogen isotope compositions of Koudiat Aïcha lithofacies (6.2-12.4‰ for oxygen and −51‰ to −36‰ for hydrogen) have also been used to determine the temperature and origin of metalliferous fluids. The couple plagioclase-amphibole of gabbros provides equilibrium temperatures between 310 and 380 °C and suggests that the heat source for the ore-forming fluid system may have been igneous. On the other hand, oxygen and hydrogen isotope ratios cluster between normal values for sedimentary and magmatic rocks, suggesting a magmatic-metamorphic origin for the ore fluid.

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Section: Petrographic and Normative Signaturesmentioning

confidence: 99%

Lithogeochemical, mineralogical analyses and oxygen–hydrogen isotopes of the Hercynian Koudiat Aïcha massive sulphide deposit, Morocco

Lotfi

Belkabir

Brunet

et al. 2010

Journal of African Earth Sciences

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“…To quantify chloritisation, for example, it is tempting to calculate chlorite proportions using a method designed for greenschist facies rocks, such as NORMAT (Piché and Jébrak 2004) or CONSONORM_LG (Trépanier et al 2015). However, highgrade metamorphism likely modified the volatile (LOI) content of rocks and calculating low-grade normative assemblages with an erroneous LOI may result in under-estimation of the amount of pre-metamorphic carbonate and sulphide, and over-estimation of chlorite.…”

Section: Page 16 Of 59mentioning

confidence: 99%

“…Trépanier et al 2015) and will not be discussed further in this contribution. Alternatively, alteration indices can be calculated using the proportions of minerals observed in thin sections or, as is more often feasible in exploration contexts, that have been calculated using normative solutions such as early calculations (Barth 1959;Riverin and Hodgson 1980), NORMAT (Piché and Jébrak 2004), CONSONORM_LG (Trépanier et al 2015) or CONSONORM_HG ).…”

Section: Introductionmentioning

confidence: 99%

The Coulon deposit: quantifying alteration in volcanogenic massive sulphide systems modified by amphibolite-facies metamorphism

Mathieu

Bouchard

Pearson³

2016

Can. J. Earth Sci.

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Abstract:The Coulon deposit is a volcanogenic massive sulphide (VMS) system in the James Bay area, Superior Craton, Québec, that was metamorphosed to amphibolite-facies conditions. The chemistry and mineralogy of the VMS-related alteration halo proximal to the mineralised sulphide lenses are investigated, using samples collected in the field and 5583 chemical analyses provided by Osisko Ltd. Alteration is quantified using mass balance and normative calculations, and the application and performance of these methods in an exploration context are investigated. In VMS systems, altered rocks proximal to the ore zones are characterised by multi-element metasomatism, which is best quantified by mass balance methods that have been successfully applied in the study area. However, mass balance calculations necessitate the documentation of a precursor, which is not always possible in an exploration context; therefore an alternative method (i.e. alteration indices) was also evaluated. In most VMS systems, proximal alteration is characterised by chlorite (chloritisation), muscovite (sericitisation), and quartz (silicification) while, at the Coulon deposit, altered rocks contain mostly cordierite, biotite, sillimanite, and quartz. Alteration indices were calculated using observed and normative minerals, and provide satisfactory results similar to those obtained with mass balance calculations. Using these results, recommendations are made to estimate the intensity of alteration in the core shack using the proportions of observed minerals.Alteration indices are sensitive to the composition of precursors and, due to high grade metamorphism, chloritisation and sericitisation are not precisely quantified. Recognising these limitations is essential to successful quantification of alteration in areas metamorphosed to high-grade conditions.

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“…The density measurements on 72 outcrop samples are then compared to calculated densities using the normative calculation program NORMAT® (Piché and Jebrak, 2004) based on the chemical composition of the rocks (Table 2.). The comparison between calculated and measured densities (Fig.…”

Section: Chemical Composition Of Rocks and Density Calculationmentioning

confidence: 99%

A 3D gravity data interpretation of the Matagami mining camp, Abitibi Subprovince, Superior Province, Québec, Canada

Boszczuk

Cheng

Hammouche

et al. 2011

Journal of Applied Geophysics

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Normative minerals and alteration indices developed for mineral exploration

Cited by 30 publications

References 11 publications

Lithogeochemical, mineralogical analyses and oxygen–hydrogen isotopes of the Hercynian Koudiat Aïcha massive sulphide deposit, Morocco

Lithogeochemical, mineralogical analyses and oxygen–hydrogen isotopes of the Hercynian Koudiat Aïcha massive sulphide deposit, Morocco

The Coulon deposit: quantifying alteration in volcanogenic massive sulphide systems modified by amphibolite-facies metamorphism

A 3D gravity data interpretation of the Matagami mining camp, Abitibi Subprovince, Superior Province, Québec, Canada

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