Gold Deposits of the CIS

Geoscience Canada, March, 2009 by Richard J. Goldfarb

Gold Deposits of the CIS

Gregory Levitan

Xlibris (2008)

ISBN: 978-1-4363-5354-0

ISBN: 978-1-4363-5353-3

Price $29.99 (Hardback), $19.99 (Paperback)

Gold Deposits of the CIS (i.e. Commonwealth of Independent States) provides a series of brief descriptions of the major gold deposits and resources of the former Soviet Union (FSU). This region of Eurasia, extending from latitude 30[degrees]E (Ukraine) to 175[degrees]E (Kamchatka), and as far south as latitude 39[degrees]N (Tajikistan), is defined as containing the world's largest cumulative gold reserve. Although a few major deposits such as Muruntau, Kumtor, and Sukhoi Log have recently received attention in the Western economic geology literature, many of the large gold systems in this region lack any English-language geological description beyond a few vague sentences on company websites. Thus, this book attempts to fill a need in the basic ore geology literature.

The author of the volume, Gregory Levitan, is among the few individuals qualified to fill such a need in the economic geology field. He worked on mineral deposits for the Soviet Ministry of Geology for 35 years within the FSU, before moving to the West and spending the most recent fifteen years as a consultant specializing on gold ores within the same vast region. His most recent experience is reflected in the inclusion of available mining and mineral economics data on described deposits, material commonly lacking in other published descriptions of gold deposits within the FSU.

The book begins with two brief introductory chapters, one on the history of exploration and mining, and the second describing the complex classification system of gold deposits in the CIS. The classification system is based on gold ore host rocks and is used to subdivide the remainder of the book. Deposits are grouped into those associated with Archean and Paleoproterozoic host rocks (Chapter 3), and Neoproterozoic through Phanerozoic sedimentary, intrusive, and volcanic host rocks (Chapter 4). Most western readers will recognize orogenic, intrusion-related, skarn, and Carlin-type deposits as being described within the first three groups of host rocks, and the epithermal deposit types as being discussed within the volcanic rock-related section of the book. These four groups of gold deposits are further subdivided into sections within chapters 3 and 4; these sections are based on both, mineralization style and major mineralogical signatures of the ores. The deposits discussed in this book are strictly those in which gold, or rarely silver, is the dominant ore component. Hence, large auriferous porphyry copper deposits, such as the giant Almalyk system in Uzbekistan, are not described.

Chapters 3 and 4 are three- to five-page-long descriptions of 51 major gold deposits that occur in the FSU. Each description typically includes location coordinates, regional and local geological descriptions, maps and cross-sections of variable quality, ore and alteration mineralogy, available grade and tonnage data, any published geochronology, summary of interesting geochemical features, and the dominant genetic interpretation(s) on ore formation. Chapter 3 summarizes the older FSU gold deposits; these Precambrian ores are basically the orogenic gold deposits of the Ukrainian Shield in the southwestern corner of the East European Platform.

Chapter 4 discusses the remaning gold deposits and thus constitutes the bulk of the book. The sedimentary rock-hosted deposits are divided into those hosted by a) metamorphic sequences, b) black shales and carbonates, and c) sedimentary and carbonate rocks. The first of these groups is characterized by limited arsenic concentrations in pyrite, relatively high formation pressures and temperatures, 'greenstone' (probably meaning greenschist) facies metamorphism, and thick flysch over mature continental crust, which would suggest a back-arc tectonic setting. These ores in metamorphic sequences are further broken down into 'deposit types' that include gold-feldspar-carbonatequartz (Kumtor), gold-quartz (Sovetskoye), gold--feldspar--carbonate-sulfide (Muruntau), and gold-quartz [ or -] carbonate (Sukhoi Log). At times, the numerous levels of classifications seem to become too complex and can be contradictory and confusing. For example, in the section describing the gold-feldspar-carbonate-quartz type deposits, a discussion of Muruntau follows that of Kumtor and begins by stating Muruntau is another example of gold--feldspar--carbonate-sulfide type mineralization. What happened to the 'quartz'? Furthermore, the Muruntau mineralization is said to reflect two stages of hydrothermal activity, and to contain five assemblages that are not related to these stages, although the fifth assemblage is actually called a 'stage'. The second sedimentary rock-hosted group (black shales and carbonates) includes deposits such as Olimpiada, Bakirchok, and Daugyztau. Many features of this group are not obviously different than the features of the first group; for example, host rocks are affected by greenschist metamorphism, gold-beating arsenopyrite is present, and formation temperatures above 400[degrees]C are reported for some of the largest deposits. Yet some deposits in this group are lower temperature and seem to resemble epizonal Sb-rich orogenic gold deposits, such as the Alaskan Donlin Creek deposit. Also, gold--mercury--quartz deposits in this group have similarities with Carlin ores; these include Kyuchus in eastern Russia and perhaps Vorontsovka in the Urals. If I had to generalize, my opinion would be that this second group includes some of the same mesozonal orogenic gold deposits that are grouped within metamorphic sequence host rocks, as well as epizonal orogenic and Carlin-type gold deposits. The third group (sedimentary and carbonate rocks) is suggested to consist of epithermal gold deposits in lower greenschist facies rocks and distal to any known igneous rocks. The silver-rich nature of these deposits (e.g. Okzhetpes) and reported low-temperature phases such as kaolinite and dickite, are used to support such an interpretation.