Heavy mineral as a tool to refine the stratigraphy of kaolin deposits in the Rio Capim Area, Northern Brazil

Ana M Góes,Dilce F Rossetti,Anderson C Mendes

doi:10.1590/s0001-37652007000300009

Abstract

Studies of heavy minerals in kaolin deposits from the Ipixuna Formation in the Rio Capim area (Northern Brazil) showed a mature to super mature assemblage dominated by zircon and tourmaline, and subordinately rutile, kyanite and staurolite. These minerals do not change much throughout the whole section; however, each kaolin unit displays a particular signature, defined by differences in the proportions of the whole assemblage of heavy minerals, as well as of their textural characteristics. This work revealed that the lower and upper kaolin units can be definitely considered as distinct depositional sequences. A higher proportion of opaque minerals and higher zircon values characterize the lower unit. The higher volumes of anhedric, rounded to sub-rounded grains of zircon and tourmaline in the upper unit suggests that this includes grains that were undergone to a higher degree of reworking. The increased volume of unaltered staurolite and kyanite in the upper unit leads to conclude that, even considering sediment reworking, a distinct source must be invoked. The results also show that the characteristics of the heavy mineral assemblage from the intermediate unit are comparable with those from the upper unit, which suggests they might record a same stratigraphic sequence.

Highlights

The Ipixuna Formation corresponds to a thin, typically kaolinitized stratigraphic unit of the Itapecuru Group, preserved between Albian and Neogene deposits along the Rio Capim area in the northeast of the State of Pará (Fig. 1)
This paper aims to characterize the assemblage of heavy minerals of the kaolin units of the Ipixuna Formation in a quarry of the Rio Capim area in order to provide new elements to better evaluate if they can, be part of different stratigraphic units
The results presented show that the characteristics of the heavy mineral assemblage from the intermediate unit are comparable with those from the upper kaolin unit

Summary

Introduction

The Ipixuna Formation corresponds to a thin (usually 40 m thick), typically kaolinitized stratigraphic unit of the Itapecuru Group, preserved between Albian and Neogene deposits along the Rio Capim area in the northeast of the State of Pará (Fig. 1). Because of its valuable kaolin reserve that has fed the international market of paper production in these last decades, this unit has been increasingly studied on several aspects. Given the sedimentary nature of the kaolin deposits, many sedimentological studies have been carried out lately in order to. An important aspect that has been reinforced in recent publications is that these units, rather than been gradational in nature and closely related to differentiation during progressive weathering, as previously proposed

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