Determination of the geochemical weathering indices and trace elements content of new volcanic ash deposits from Mt. Talang (West Sumatra) Indonesia

Abstract

Since the Indonesian archipelago is part of the very active and dynamic Pacific Ring of Fires, the volcanic eruptions occur from time to time. Immediately after the eruption of Mount Talang in West Sumatra (April 12, 2005), volcanic ashes, both unleached and leached were collected. The deposits from Mt. Talang were andesitic to basaltic in composition. The volcanic ash consisted of volcanic glass, plagioclase feldspar in various proportions, orthopyroxene, clinopyroxene, olivine, amphibole, titanomagnetite. We conducted the total elemental analysis of the bulk samples of the volcanic ash. The contents of major, trace and rare elements as well as heavy metals were determined by wet chemical methods and xray fluorescence (XRF) analyses. Although the volcanic ash of Mt. Talang are still very new, an evaluation of the geochemical weathering indi ces was performed with the objective of showing the volcanic ash condition at the early stage of weathering. Eight weathering indices were evaluated. The results showed that the unleached volcanic ash has higher Rux ton Ratio (R), Weathering Index of Parker (WIP), Product of Weathering Index (PWI) and Silica Titanium Index (STI) values compared to the leached ash, while the leached ash exhibited higher Chemical Index of Alteration (CIA), Chemical Index of Weathering (CIW), Vogt's Residual Index (VO), and Plagioclase Index of Alteration (PIA). These weathering indices can be used to quantify the condition of the volcanic ashes at the initial stage of weathering, to evaluate their fertility, to provide a better understanding of element mobility during weathering, and predict the source of soil nutrients as well as determine the products of primary min erals alteration.

Geochemistry of Selected Kaolins from Cameroon and Nigeria

“…The chemical index of alteration (CIA), the chemical index of weathering (CIW) and the index of compositional variability (ICV) for each sample were calculated and compared to the CIA and CIW of well-known kaolins so as to identify any variations between chemical indices of the known kaolins to those of Cameroon and Nigeria. The CIA is interpreted as a measure of the extent of the conversion of feldspar to clays and it is a good measure of the degree of weathering [46] (Equation 2); whereas, CIW is a measure of the extent of conversion of feldspar to clays, but does not take into account the K 2 O, as expressed in Equation 3 [47]. The CIA versus CIW was plotted to determine the intensity of silicate weathering.…”

Trace Metal Concentrations in an Agricultural Watershed: Case Study in the Sumani Watershed, West Sumatera Indonesia

“…However, the EF values for Pb, V, in the vegetable soil and river sediment show moderate enrichment (EF, 2-5). For Pb this could indicate contribution from both human activities (agrochemicals and leaded petrol from vehicles) and natural sources (volcanic ash) as noted by [15,29]. The low EF values for Zn, Cu, Ni, Cr, and Sr are classed as depletion to minimal enrichment, suggesting that no environmental problem exists.…”

“…The high CFs for Pb, Zn and Cu in the vegetable soil may be due to the influence of external discrete sources like scavenging and agricultural runoff, erosion, residue of pesticide, fertilizer and manure applied by farmers. [29] report that volcanic ash from Mount Talang contains trace elements that include Pb (16.5-27.50 mg/kg), Zn (64.88-90.60 mg/kg) and Cu (21.2-38.5 mg/kg), and this material may also constitute a source of these elements. With one exception, CF values for the non-metallic elements Sr and Rb are <1, indicating normal levels in the soils.…”

“…Oxic Hapuldant, Andic Humitropept, Typic Kandiudult, Aeric Tropaquept, Typic Distropept and Typic Eutropept . The geology of the Sumani watershed area consists of the andesitic volcanic and intrusive rocks that form Mount Talang, undifferented volcanic products (basalt to andesite), slates and shales of the Tuhur Formation, limestones (Kuantan Formation) and surficial deposits consisting of river alluvium and alluvial fans [28,29]. A block diagram showing geology feature and sampling location in watershed was generated by kriging topographic geology map using Surfer from Golden Software [30].…”

Laboratory Tools to Quantify Biogenic Dissolution of Rocks and Minerals: A Model Rock Biofilm Growing in Percolation Columns

“…To minimize the danger of HF and complex formation of barely soluble fluorides, 10 mL cold saturated boric acid was added. Weathering indices WIP and CIA were calculated according to Fiantis et al (2010) using the data obtained by ICP-OES or ICP-MS analysis of solid mineral phases. Before and after pH measurements of the liquid phase were taken with a pH meter.…”