Gravity measurements in Kenya

summary . A new catalogue of gravity data from Kenya has been prepared and is briefly described here. New Bouguer anomaly maps have also been compiled and a copy is included.     

An Analysis of the Published Mineral Resource Estimates of the Haji-Gak Iron Deposit,Afghanistan

The Haji-Gak iron deposit of eastern Bamyan Province, eastern Afghanistan, was studied extensively and resource calculations were made in the 1960s by Afghan and Russian geologists. Recalculation of the resource estimates verifies the original estimates for categories A (in-place resources known in detail), B (in-place resources known in moderate detail), and C₁ (in-place resources estimated on sparse data), totaling 110.8 Mt, or about 6% of the resources as being supportable for the methods used in the 1960s. C₂ (based on a loose exploration grid with little data) resources are based on one ore grade from one drill hole, and P₂ (prognosis) resources are based on field observations, field measurements, and an ore grade derived from averaging grades from three better sampled ore bodies. C₂ and P₂ resources are 1,659.1 Mt or about 94% of the total resources in the deposit. The vast P₂ resources have not been drilled or sampled to confirm their extent or quality. The purpose of this article is to independently evaluate the resources of the Haji-Gak iron deposit by using the available geologic and mineral resource information including geologic maps and cross sections, sampling data, and the analog-estimating techniques of the 1960s to determine the size and tenor of the deposit.     

Susceptibility assessment of earthquake-triggered landslides in El Salvador using logistic regression

This work has evaluated the probability of earthquake-triggered landslide occurrence in the whole of El Salvador, with a Geographic Information System (GIS) and a logistic regression model. Slope gradient, elevation, aspect, mean annual precipitation, lithology, land use, and terrain roughness are the predictor variables used to determine the dependent variable of occurrence or non-occurrence of landslides within an individual grid cell. The results illustrate the importance of terrain roughness and soil type as key factors within the model — using only these two variables the analysis returned a significance level of 89.4%. The results obtained from the model within the GIS were then used to produce a map of relative landslide susceptibility.     

Late Quaternary paleoenvironments of an ephemeral wetland in North Dakota,USA: relative interactions of ground-water hydrology and climate change

This study of fossils (pollen, plant macrofossils, stomata and fish) and sediments (lithostratigraphy and geochemistry) from the Wendel site in North Dakota, USA, emphasizes the importance of considering ground-water hydrology when deciphering paleoclimate signals from lakes in postglacial landscapes. The Wendel site was a paleolake from about 11,500 ¹⁴C yr BP to 11,100 ¹⁴C yr BP. Afterwards, the lake-level lowered until it became a prairie marsh by 9,300 ¹⁴C yr BP and finally, at 8,500 ¹⁴C yr BP, an ephemeral wetland as it is today. Meanwhile, the vegetation changed from a white spruce parkland (11,500 to 10,500 ¹⁴C yr BP) to deciduous parkland, followed by grassland at 9,300 ¹⁴C yr BP. The pattern and timing of these aquatic and terrestrial changes are similar to coeval kettle lake records from adjacent uplands, providing a regional aridity signal. However, two local sources of ground water were identified from the fossil and geochemical data, which mediated atmospheric inputs to the Wendel basin. First, the paleolake received water from the melting of stagnant ice buried under local till for about 900 years after glacier recession. Later, Holocene droughts probably caused the lower-elevation Wendel site to capture the ground water of up-gradient lakes.     

Flameless Atomic Absorption Determination of Gold and Palladium in Geological Reference Samples

Gold and palladium have been determined in 42 geological reference samples with graphite furnace AAS after aqua regia digestion and SnCl₂-Hg extraction. A brief discussion on the quality of these analyses also is presented.