CONSONORM_LG: a new method of norm and alteration indexes calculation for low grade metamorphic rocks altered by VMS related hydrothermal systems

French Title: CONSONORM_LG: une nouvelle méthode de calcul de norme et d'indices d'altération pour les roches métamorphiques de bas grade associées à des systèmes hydrothermaux de type VMS

Lucie Mathieu, CONSOREM (Consortium de Recherche en Exploration Minérale - mineral exploration research consortium), Département des sciences appliquées, UQAC, Chicoutimi, QC, Canada, Sylvain Trépanier, Mines Virginia, 300 Saint-Paul, suite 200, Québec, QC, Canada and Réal Daigneault, Centre d'études sur les Ressources minérales (CERM), Département des sciences appliquées, UQAC, Chicoutimi, QC, Canada

Contact First Author: Lucie Mathieu; mathiel@tcd.ie

Abstract ID#: 34247

 

English Abstract:
The CONSONORM_LG provides a standardised solution to approximate metamorphic parageneses as well as indexes for estimating chemical and/or mineralogical changes induced by hydrothermal alteration. These indexes are particularly performant for identifying and quantifying the Fe-Mg, K and CO2 alterations common in VMS systems (Volcanogenic Massif Sulphides).

The CONSONORM_LG is designed for silicate, Fe-Ti oxides and/or carbonate-dominated rocks that may contain sulphides, and it approximates the main parageneses of metamorphic rocks for three temperature-pressure conditions of the green schist and lower amphibolite facies (cf. 2SV350, 2SV450 and 2AMP575 facies of the norm). For each of the facies modelled, the norm calculates silicate assemblages using an Al-Ca-FeMg-NaK tetrahedron that is a convenient way to represent a large amount of silicate assemblages. In addition to silicates, the CONSONORM_LG calculates several accessory minerals from minor elements, Fe-Ti oxides, sulphides from analysed sulphur and/or from analysed metals and carbonates from analysed CO2 or from normative CO2 estimated from the LOI using the NORMAT method. The CONSONORM_LG also calculates several alteration indexes to estimate Fe-Mg (cf. chloritization), Ca (cf. propylitic alteration), Na and K alterations (cf. sericitization, phyllic alterations) and Al relative gains (cf. argilization for example). Carbonatation indexes are also calculated using the amount of normative minerals formed by this type of alteration, i.e. carbonates, chlorite and muscovite.

During this presentation, the calculation sequence of the CONSONORM_LG will be presented and validated using published whole rock analyses and petrographic descriptions. Then, the alteration indexes provided by this normative method will be tested using several natural samples of alteration halos associated with VMS-type deposits.

Back to: VMS Deposits and Their Geological Environment I