The Carlin disseminated gold deposit occurs in an autochthonous sequence of Paleozoic sedimentary rocks exposed in a structural window in the Roberts Mountains thrust in north-central Nevada. The upper 175 m of the Silurian Roberts Mountains Formation hosts the majority of ore at Carlin and is characterized by laminated, fine-grained, calcareous and/or dolomitic argillaceous siltstone with local coarser grained siltstones and <0.25- to >50-cm-thick lenticular interbeds of sand- and granule-sized calcareous bioclastic debris or fossil hash. Detailed studies of drill core and exposures in the East pit of the Carlin mine show that alteration and mineralization are zoned away from crosscutting fault conduits and these more permeable bioclastic beds, indicating that these two features were major inflow zones for hydrothermal fluid.

In unoxidized rocks, unaltered calcareous siltstone (1) containing quartz, dolomite, calcite, illite, K feldspar, and pyrite is progressively converted to assemblages of (2) quartz + dolomite + calcite + illite + pyrite, (3) quartz + dolomite + illite-K mica + pyrite, (4) quartz + illite-K mica + pyrite, and (5) quartz + kaolinite-dickite + pyrite adjacent to inflow zones where jasperoids are developed. Gold most consistently enriches the zone of calcite and dolomite removal (3 and 4 above), though it occurs in all zones, locally in high concentrations. This zoned alteration was accomplished by a C02-rich acidic fluid. This acidic alteration enhanced the passage of fluids by extensive carbonate removal to form zones of higher permeability.

Oxidation is wholly a supergene effect related to deep weathering, because the oxidation is superimposed on both mineralized and altered rocks with only minor effect on the major element chemistry; it has produced low-temperature goethitic Fe oxides rather than higher temperature hematite and is not spatially related to Au distribution at the mine or on a district scale.

Because of extensive carbonate removal leading to local volume reduction through collapse and/or compaction, geochemical effects are examined using ratios to relatively immobile elements such as Al and Ti. Extensive depletion of Ca, Mg, and C02 and introduction of Si, Au, and S have occurred. Potassium is depleted in the conversion of illite to dickite-kaolin-ite in proximal silicified inflow zones, and Fe enriches some pyritized rock. Carbonate removal and silicification are two separate processes, both of which are spatially associated with mineralization. Mineralized decarbonated rocks and barren footwall rocks commonly are not silicified, and intensely silicified proximal alteration zones are generally low grade.

The term "Carlin-type" deposit has been applied to a number of low-grade, sedimentary rock-hosted gold deposits that have been discovered and brought into production in the western United States since the 1960s. Carlin-type deposits are characterized by replacement of carbonate and silty carbonate rocks by silica, pyrite, barite, various arsenic, mercury, antimony, and thallium minerals and by introduction of micron-size gold (Radtke and Dickson, 1974). These deposits are believed to have formed in the upper few kilometers of the earth's crust under conditions that are similar in some respects to present-day geothermal systems.

The Mercur mining district in west-central Utah contains a number of gold deposits of this type. The district is located approximately 90 km southwest of Salt Lake City in the southwest portion of the Oquirrh Mountains, a typical north-south-trending range of the Basin and Range physiographic province (Fig. 1). Two major orebodies, Mercur-Sacra-mento and Marion Hill, are present in small hills in the center of the steep, east-west-trending Mercur Canyon. Initial production of silver in the Mercur district was from an interval of silicified limestone known as the "Silver ledge" (Spurr, 1895), a term which was later changed to "Silver chert." Fine gold was discovered in 1883 in a stratigraphic interval 30 m above the Silver chert. Production terminated in 1917 after more than 1.2 million ounces of gold had been produced (Butler et al., 1920). The district was reopened in 1983 with the Getty Mining Company as the principal operator.

The first geologic description of the Mercur district was given by Spurr (1895). Butler et al. (1920) gave a concise, accurate review of the geology, stratigraphy, and mineral production at Mercur. Gilluly's (1932) work remains the most comprehensive published study of the southern Oquirrh Mountains. Lenzi (1973) published data on the background geochemistry at Mercur. Tafuri (1976) described the general geology and mineralization at Mercur.

This communication gives a detailed discussion of the hydrothermal alteration of the Mercur deposits. The discussion will provide a framework for continuing studies of the paragenesis and geochemistry at Mercur as well as allowing comparison with alteration assemblages of other Carlin-type deposits.

The book is an English translation of a sketch “ Gcologiya I Polcznye Iskopacmye Primorskogo Kraya”, published by Dalnauka in 1995.

Geology and mineral deposits of Primorsky Krai (Territory) arc discussed using ihe terrane concept as a method of regional tectonic analysis. Description of terranes, classified magmatic complexes, and inctallogenic belts is given. Every economic coal and lode deposit discovered in Primorsky Krai is briefly described.

Color map of terranes. maps of the distribution of coal and lode deposits and inctallogenic belts are enclosed.

The book could be of interest for regional, mapping, and economic geologists

This report summarizes the geology and nonfuel mineral resources of Greenland, Europe, Russia, and Northern Central Asia and is a preliminary part of a major U.S. Geological Survey study called the Global Mineral Resource Assessment Project. This report is one of a series of regional reports covering the world and provides basic data on the identified resources and geologic setting, together with a brief appraisal of the potential for undiscovered mineral resources. The data in the regional report are derived from published information. An important source of data on production statistics, economic factors that affect the mineral industries, and historical information, is available in U.S. Geological Survey (USGS) publications Minerals Yearbook and the annual Mineral Commodity Summaries (available at http://minerals.usgs.gov/minerals).