Abstract: Disseminated Mississippi Valley-type (MVT) mineralization occurs throughout northeastern Wisconsin, USA, and is recognized as the source of regionally extensive natural groundwater contamination in the form of dissolved arsenic, nickel, and other related metals. Although considerable attention has been given to arsenic contamination of groundwater in the region, limited attention has been focused on characterizing the bedrock sources of these and other metals. A better understanding of the potential sources of groundwater contamination is needed, especially in areas where groundwater is the dominant source of drinking water. This article describes the regional, stratigraphic, and petrographic distribution of MVT mineralization in Paleozoic rocks of northeastern Wisconsin, with a focus on sulfide minerals. Whole-rock geochemical analysis performed on 310 samples of dolomite, sandstone, and shale show detectable levels of arsenic, nickel, cobalt, copper, lead, zinc, and other metals related to various sulfide mineral phases identified using scanning electron microscopy. MVT minerals include pyrite, marcasite, sphalerite, galena, chalcopyrite, fluorite, celestine, barite, and others. We describe the first nickel- and cobalt-bearing sulfide mineral phases known from Paleozoic strata in the region. Arsenic, nickel, and cobalt are sometimes present as isomorphous substitutions in pyrite and marcasite, but discrete mineral phases containing nickel and cobalt elements are also observed, including bravoite and vaesite. Locally abundant stratigraphic zones of sulfide minerals occur across the region, especially in the highly enriched Sulfide Cement Horizon at the top of the Ordovician St. Peter Sandstone. Abundant quantities of sulfides also appear near the contact between the Silurian Mayville Formation and the underlying Maquoketa and Neda formations in certain areas along and east of the Niagara escarpment. This article illustrates how a detailed geochemical and mineralogical investigation can yield a better understanding of groundwater quality problems.
Abstract: Optical image analysis (OIA) supporting microscopic observation can be applied to improve ore mineral characterization of ore deposits, providing accurate and representative numerical support to petrographic studies, on the polished section scale. In this paper, we present an experimental application of an automated mineral quantification process on polished sections from Zaruma-Portovelo intermediate sulfidation epithermal deposit (Ecuador) using multispectral and color images. Minerals under study were gold, sphalerite, chalcopyrite, galena, pyrite, pyrrhotite, bornite, hematite, chalcocite, pentlandite, covellite, tetrahedrite and native bismuth. The aim of the study was to quantify the ore minerals visible in polished section through OIA and, mainly, to show a detailed description of the methodology implemented. Automated ore identification and determination of geometric parameters predictive of geometallurgical behavior, such as grade, grain size or liberation, have been successfully performed. The results show that automated identification and quantification of ore mineral images are possible through multispectral and color image analysis. Therefore, the optical image analysis method could be a consistent automated mineralogical alternative to carry on detailed ore petrography.
Abstract: Climate change has led to an increase in extreme weather events and desertification of vast areas of southern Argentina. Water shortages are a major concern, and this problem is expected to be exacerbated in the future. An exploration program was undertaken to investigate the groundwater occurrence in areas of the Chubut River basin in order to provide new supply options for pastoral farming. The investigation involved the drilling of exploration holes and construction of bores for long-term monitoring. Water quality and hydraulic test data were also collected. Findings from the study indicate that alluvial sediments extend to a maximum of 45 m below the surface, and are underlain by a sequence of clays and subordinated sands that exceed 100 m in thickness. The bulk of groundwater lies within the shallow sediments, which act as an unconfined aquifer. Hydraulic conductivities up to 10 m/day were estimated from pumping tests, although granulometric analyses indicate that higher values may occur. Chemical characterization indicates that waters are typically fresh, low in sodium, and largely suitable for stock-grazing or horticulture. Anomalous salinities at one of the sites are likely due to the effects of a nearby waste dump. Even though further work is required, the study contributes to a better understanding of the dynamics of the hydrogeological system in the basin under a warming climate, and provides useful information for the expansion of economic activities in remote communities of Argentina.
Abstract: A history of modern (1973–2015) surface area variability for Lake Basotu in north-central Tanzania has been reconstructed using archived Landsat images from the dry season between June and October. This record was compared to local weather data as well as larger scale weather patterns. The lake has been in a state of decline interrupted by major flood events since the beginning of the satellite record. From 1973 to 1997, the lake area was between 0.97 km2 and 4.28 km2. Lake extent abruptly increased to 13.86 km2 in 1998, when a co-occurrence of El Niño and a positive Indian Ocean Dipole led to extensive flooding. It is hypothesized that local agricultural practices leading to soil erosion and subsequent basin sedimentation have most likely increased the sensitivity of Lake Basotu to climatic fluctuations.
Abstract: Lacustrine sediment accumulation provides meaningful and diverse long-term records of environmental change. This overview highlights the usefulness of the paleolimnological approach in evaluating the magnitude and direction of human-induced environmental change in lakes and their catchments. Because of the services they provide, freshwater ecosystems have always been significantly affected by human activities. However, the rate and extent of human-induced change in continental freshwaters and their catchments has considerably increased since the beginning of industrialization (mid-18th century), and are even more pronounced since the advent of the “Great Acceleration” (since the mid-20th century). Global change, including climate and landscape changes, loss of biodiversity, species introductions and the spread of pollutants, leave traces in lake sediment archives that provide valuable long-term information with which to evaluate and quantify past environmental changes. This paper outlines how the knowledge gleaned from an interdisciplinary paleolimnological approach can benefit the development of mitigation and adaptation measures to current global change at various latitudes.
Abstract: Fossil forests have world-wide distribution, commonly preserving mineralized wood that displays vivid hues and complex color patterns. However, the origin of petrified color has received little scientific attention. Color of silicified wood may be influenced by the presence of relict organic matter, but the most significant contribution comes from trace metals. This study reports quantitative analysis of trace metals in 35 silicified wood samples, determined using LA-ICP-MS spectrometry. The most important of these metals is Fe, which can produce a rainbow of hues depending on its abundance and oxidation state. Cr is the dominant colorant for bright green fossil wood from Arizona, USA and Zimbabwe, Africa. Complex color patterns result from the progressive nature of the fossilization process, which causes wood to have varying degrees of permeability during successive episodes of permineralization. These processes include simple diffusion, chromatographic separation, infiltration of groundwater along fractures and void spaces, and oxidation/reduction.