Estudo comparativo da distribuição dos minerais pesados nos sedimentos da praia de Zalala e Madal – Quelimane, Zambezia

Abstract

The Zalala and Madal beaches are sandy beaches consisting mainly by very fine sediments distributed along the beaches; the sediments are characterized by dark coloration distributed in the whole beach environment, mostly in the high tide line. These characteristics reveal environments of accumulation of heavy minerals (HM), which are minerals that are distinguished from the common ones like quartz and feldspar by their density and coloration. This study has as main objective to know the heavy minerals distributed in the sediments of Madal and Zalala Beaches . In order to answer the question, work was took place in three fundamental phases: first phase of the field that took place in the low tide during syzygy tide on 6th and 7th December, 2017, second phase laboratory work and third processing of data. The laboratory work was developed in the sedimentology laboratory of the UEM in the geology department, where the samples were prepared to analyze, the sediments were immersed during 24 hours by immersion in HCl and H2O2 for the elimination of carbonate influences and organic matter in the grains, and then washed in distilled water and dried in an oven. After washing and drying, the sediment separation was carried out in millimeter screens, to analyze the nature of the sediments that constitute the beaches, and to select the ideal granulometric size for HM analysis. The fraction selected for HM analysis was 0.125 mm from each sample, where the light or heavy minerals were separated in the fraction using the dense liquid CH2I2 and Xylene for neutralization of the liquid. And finally the separate fraction was taken to the petrology laboratory of the same department for the identification and quantification of HM by binocular loupe. The following minerals were identified along the studied beaches: Chlorite, Muscovite, Tremolite, Hornblende, Augite, TiCl2, Apatite, Andaluzite, Silimanite, Epidote, Topaz, Chalcomenite, Kyanite, Azurite, Xenotime, Titanomagnetite, Hematite, Curite and Kelyanite. Being that greater varieties of minerals were observed in Madal beach than Zalala beach which shows the massive contribution of Bons Sinais estuary during the river discharge. However, in both beaches, the higher HM concentration occurs in the high tide line, caused by the flow and reflux movement of the waves.