MINERAIS PESADOS NA FRAÇÃO AREIA DO COLÚVIO-CASCALHO DIAMANTÍFERO DO GARIMPO DE PAININ (ITAITUBA, PARÁ, BRASIL)

The present work describes the heavy minerals identified in the sand fraction of the diamond-rich alluvium of the Painin garimpo, located on the right bank of the Tapajós River, in Itaituba, Pará. In general, secondary diamond deposits, such as those found in several regions of Brazil (Minas Gerais, Bahia, Goiás, etc.) have a very characteristic assemblage of heavy minerals, in which their minerals are known as diamond satellites. In Painin these minerals were extracted from the concentration of gravel obtained with the aid of a pan, after the extraction of pebbles, silt and clay fractions. The sand fraction was sieved in several fractions and from the fractions 0.25-0125 and 0.125-0.062 mm, the non-opaque heavy minerals were separated using bromoform as a heavy liquid. Minerals were identified by optical microscopy and x-ray diffraction. They stand out in descending order and according to the fraction sand, staurolite, tourmaline, corundum, rutile, diaspore, gold, topaz, zircon, anatase and kyanite. Of these, only corundum and diaspore are not classic heavy minerals from sedimentary rocks of the great Amazon region. These two minerals are together with the phosphates of the alunite supergroup, often found in the satellites of the secondary Painin diamond deposits, but not mentioned in those mentioned above, and likely to have an affinity with the primary nature of the diamond. Rutile, anatase and iron oxides are most frequently cited in these satellites. Probably corundum, diaspore and the alunite supergroup phosphates are characteristic for Painin.

Comparison between modified LST Fastfloat and conventional HF methods for pollen preparation in highly minerogenic sediments

Pollen analysis is a commonly used method to interpret vegetation and environmental change. The standard pollen preparation technique in minerogenic sediments involves the use of hydrofluoric acid (HF) which is highly toxic. Currently the European legislation requires that hazardous chemicals should be substituted with less hazardous or non-toxic chemicals if possible. In the present paper the authors introduce a safer pollen preparation method, based on the use of low-toxic heavy liquid lithium heteropoly-tungstate (LST Fastfloat) and provide instructions for pollen preparation with the LSTFastflow method. Furthermore, five paired samples were processed from clayey and silty sediments with LST Fastfloat and conventional HF methods and the pollen and spore counting results obtained from these two methods were compared to test if there is statistically significant differences between the taxa. Calculation of the 95% confidence interval revealed statistical agreement in all studied taxa except one taxon in one sample pair. However, the study revealed systematic differences within two taxa, Betula and Pinus. Thus caution is needed when comparing results obtained by HF and heavy liquid (LST Fastfloat) methods.