In this volume John Carranza not only offers a comprehensive review of the current state-of-the-art of processing geochemical data, their integration with complementary geodata sets and multivariate data analysis using spatial statistics to create maps enhanced for mineral exploration, but also brings the Handbook series to something of a milestone. This marks the first volume in which the topic of an earlier volume (Vol. 2) is in effect revisited and updated; though the approach and format are – appropriately – entirely fresh.

Data presented in this report pertain to the igneous intrusions of north-central and northeast Nevada and were compiled as part of the Metallogeny of the Great Basin project conducted by the U.S. Geological Survey between 2001 and 2007. The geographic area addressed in this compilation is approximately bounded by lats 38.5° and 42°N., long 118.5° W., and the Nevada-Utah border (fig. 1). The area contains numerous large plutons and smaller stocks but also contains many small, shallowly emplaced intrusive bodies, including dikes, sills, and intrusive lava dome complexes. The age, composition, and geographic distribution of intrusions in north-central and northeast Nevada (hereafter, the study area) are summarized by du Bray and Crafford (2007). Intrusive igneous rocks, of multiple ages, are known to be major constituents of the geologic framework in the study area (Stewart and Carlson, 1978). Abundant middle to late Mesozoic and early to middle Cenozoic intrusions in the study area are probably byproducts of subduction-related processes, including back-arc magmatism, that prevailed along the west edge of the North American plate during this interval.

Geochemical orientation surveys were completed over covered Carlin-type gold deposits in the Cortez mine area with the expressed aim of identifying and evaluating exploration methods to discover Au ore under transported alluvial cover in Nevada. Orientation tests were designed to assess the utility of geochemical applications at various scales of exploration, both drill targets at the deposit scale and “footprints” associated with deposits at the district scale.

Detailed surveys were completed over the covered Gap deposit, located adjacent to the giant Pipeline deposit. Both Carlin-type gold mineralization and earlier, spatially associated, base metal skarn mineralization at Gap were located by soils, soil gas, and vegetation. Loam soils at 6- to 12-cm depth provided a consistent and uniformly available sample medium. Gold ore under 10 m of cover in the northern portion of the Gap deposit was readily detected by analysis of Au by fire assay and ultra trace aqua regia methods in the -80 mesh fraction of these loam soils. Arsenic anomalies occur over the northern end and over the main ore zone at Gap, where there is 25 to 50 m of alluvial cover. Zinc concentrations in soil show the most coherent spatial relationship with underlying Au ore. Tests of MMI-B and Enzyme Leach selective leaches did not result in significant enhancement of the anomalies relative to aqua regia. CO2 and O2 in soil gas indicate faults and underlying mineralized carbonates at Gap, where weathering reactions likely generated CO2 from acid reaction with carbonate. Elevated Au and As in mixed sagebrush and shadscale occur over most ore zones, with the highest Au concentrations over the main ore zone rather than the shallowly buried northern zone. Like soils, elevated Zn in vegetation shows the most coherent spatial relationship with underlying ore.

The geochemical analysis of fades is a special part of geochemistry and geology. The development of this research was initiated by BISCHOF (1847-1851), who was the first to attempt to recognize sediments of different origin by geochemical means. In his now famous book he listed some chemical elements belonging to typical environments, such as boron in marine sediments and metallic sulphides in zones rich in sulphuretted hydrogens. Moreover he was the first author to suppose that all "soluble rocks" of the continents must be present in the oceans. This early concept of facies was supplemented by ROTH (1879-1890) who discovered new elements in the ocean waters and in the ashes of marine organisms. However, the data used by both of these workers were quantitatively unsatisfactory and can only be considered as the qualitative results of inadequate chemical analyses <...>