Initial discussions regarding the publication of an Ore Mineral Atlas began in 1999. Jason Dunning, then the president of the Mineral Deposits Division and a keen student of ore deposits, thought that there was a need for a simple atlas of ore minerals that would serve as a field reference guide for working geologists and students. Our subsequent years spent in the classroom have reinforced the need for this book. A great debt of thanks is owed to the students who suffered through optical mineralogy labs without this atlas. Our students were fundamental in drawing attention to required contents, in finding mineral specimens, textures or optical properties worthy of photographing, and in some cases researching information on the optical properties or the environment of formation of some minerals.

There has been gold production in Kazakhstan since the ancient times, the earliest primary gold workings having been dated to the Bronze Age (2000-4000 BC). Ancient workings, otherwise called "Chudskie" pits that often contain implements dating to the Stone or Bronze Age, still survive to the present at many gold deposits in the north and east of the country.

Gold production in Kazakhstan resumed only at the beginning of the 18th century, with the first gold produced in 1725 at the Kolyvano-Voskresensky plant in Russia having been recovered from Kazakhstan's pyrite-polymetallic gold-silver deposits at Rudnoi Altai. More than 191 of by-product gold were mined here between 1745 and 1800. Gold production at these properties had increased steadily in the 19th and 20th centuries, and has accounted for 30-40% of the country's total output in recent years.

Геохимическая разведка золота в глубоких выветренных латеритизированных отложениях в регионе Амазонки, Бразилия: на примере месторождения Игарапе Баия

The Igarape Bahia gold mine is located in the Carajds region, Para State, northern Brazil. The area is a typical example ofsupergene gold mineralization related to gossans, where superimposed lateritization processes obliterated their upper horizon and gave rise to new and wider dispersion of gold and of other metals, with meaningful consequences for geological exploration in this environment. An exploration program in this area was carried out by Docegeo, a subsidiary of "Companhia Vale do Rio Doce - CVRD", which is the sponsor of the Carajds mining district and, currently, is also minigfor gold at Igarape Bahia.

The Genesis and Blue Star sedimentary rock-hosted gold deposits occur within the 40-mile-long Carlin trend and are located in Eureka County, Nevada. The deposits are hosted within the Devonian calcareous Popovich Formation, the siliciclastic Rodeo Creek unit and the siliciclastic Vinini Formation. The host rocks have undergone contact metamorphism, decalcification, silicification, argillization, and supergene oxidation.

On the basis of textural features and spatial distributions, both supergene and hypogene origins have been proposed for alunite in sediment-hosted micron gold deposits. If alunite is indeed primary, its presence provides important constraints on the chemistry of the ore fluid. Thus, determination of the genesis of alunite is critical to the understanding of the geologic history of these ore deposits.

At the Post deposit in Nevada K/Ar ages of alunite are much younger than the age of mineralization. Sulfur isotope compositions of alunite from several sediment-hosted micron gold deposits are virtually identical to those of sulfides, suggesting that alunite sulfur came from quantitative (closed-system) oxidation of primary sulfide minerals during weathering. Sulfur and oxygen isotope compositions of barite are markedly different from those of alunite. The oxygen and hydrogen isotope compositions of alunite fall in the supergene alunite fields; data for cogenetic kaolinite fall on the kaolinite line, whereas those for hypogene kaolinite do not. From all available petrographic and geochemical data, it would appear that alunite in the micron gold deposits of Nevada is entirely of secondary supergene origin.

Discriminating productive jasperoids associated with economic gold mineralization from barren jasperoids, those with no known gold association, has long been an objective of Great Basin explorationists. Holland et al. (1988) use factor analysis of a multielement geochemical data set to compare jasperoids associated with Carlin-type gold mineralization with jasperoids in barren systems. They go on to propose a genetic model for Carlin-type deposits based on their interpretation of the factor analysis results. There are problems with their approach, several of which the authors acknowledge. The geologic control for their samples is inadequate, the analytical technique used is inaccurate for several critical elements, and their statistical analysis of the data could be much simpler, easier to interpret, and useful.

Brian K. Jones and Richard A. Leveille raise a number of points regarding the way in which our comparative study of jasperoid geochemistry (Holland et al., 1988) was framed and the implications that might be drawn from our results. Their primary concerns are with (a) the lack of geologic control for samples, (b) the accuracy of analyses for several critical elements, (c) the specific interpretation of factor 3 and its subsequent use in a discussion of genetic implications, and (d) the evaluation of analytical data by means of Q-mode factor analysis. We will address each of these concerns in turn.