Thin section micro-photographs showing samples from AS and GS: A-B) Least altered sample with low LOI from AS (AL2088), showing primary features and phases such as plagioclase (Pl) and clinopyroxene (Cpx) with minor chlorite as main secondary phase; C-D) Altered sample from the GS (AL2075) with high LOI (10.5%), showing primary phases such as plagioclase and a big amount of secondary phases including chlorite (Chl) and calcite (Cal), which helps to explain the high LOI; E-F) Altered sample from AS (AL2077B) with high LOI (15.1%), showing primary phases such as plagioclase and secondary phases including chlorite (Chl) and calcite (Cal).