Abstract
Many gold and gold-bearing complex deposits related to the Late Jurassic and Early Cretaceous magmatism are known in Eastern Transbaikalia. The largest deposits are the Lugokan, the Kultuma and the Bystrinsky. These deposits are in a paragenetic relationship with the Late Jurassic magmatic rocks of the Shakhtama complex. According to the available data, the total resources of gold in these three deposits are estimated to be approximately 443 tons: the Lugokan, Au~53 tons, Cu~302 thousand tons; the Kultuma, Au~121 tons, Cu~587 thousand tons, Fe~33 mln t; the Bystrinsky, Au~269 tons, Cu~2070 thousand tons, Fe~67 mln t. One of the main aims of this work was to reveal the criteria of fertility for the classical porphyry type, based on the specific geochemical features of rock-forming and accessory minerals. A comparison of the obtained results with other data on the large porphyry and skarn deposits of the world showed that the magmatic rocks of the Bystrinsky massif, specifically porphyry species dated 159.6–158.6 Ma, are potentially ore-bearing for the porphyry type mineralization. The magmatic rocks that widely occur at the Lugokan and Kultuma deposits are most close to the Fe-skarn deposits. The best indicators of the magma fertility for the porphyry rocks are Ce/Ce*, Eu/Eu*, Yb/Dy, (Ce/Nd)/Y in zircons. Thus, magmatic rocks characterized by Ce/Ce* > 100, Eu/Eu* > 0.4, Yb/Dy > 5.0 and (Ce/Nd)/Y > 0.01 may be classified as high fertile for the classical porphyry mineralization in Eastern Transbaikalia. The plagioclase and biotite chemistry data also showed that the magmatic rocks that occurred at the Bystrinsky deposit are the most fertile for the porphyry type mineralization. The magmatic rocks classified as ore-bearing porphyry type have Al* > 1 in plagioclase, high values of IV(F) and IV(F/Cl) and low ratios of X(F)/X(OH) in biotites. The assessment of the metal fertility of magmatic rocks is most effective in combination with data on both the composition of rock-forming and accessory minerals. The obtained data may be used to develop the methods of prediction and search for gold, copper and iron mineralization.
Highlights
Eastern Transbaikalia is the oldest gold region of Siberia and has remained the largest and most important gold source in Russia for more than 300 years
The plagioclase and biotite chemistry data showed that the magmatic rocks that occurred at the Bystrinsky deposit are the most fertile for the porphyry type mineralization
Geochemistry of the rock-forming and accessory minerals displayed a high efficiency in determining magmatic rock fertility by the example of Au-Cu-Fe-skarn deposits in Eastern Transbaikalia
Summary
Eastern Transbaikalia is the oldest gold region of Siberia and has remained the largest and most important gold source in Russia for more than 300 years. Complex gold, antimony, mercury and other deposits are known to be present within the boundaries of this region. Other genetics of gold deposits (gold-mercury in carbonate rocks, gold-sulfide in black shale, gold-sulfideskarn, gold-copper-molybdenum-porphyry, etc.) have not received due appreciation yet and remain insufficiently studied with respect to geology and geochemistry, though some authors classify them as definite types [1]. A significant increase in gold resources has been achieved due to the exploration and re-evaluation of gold-copperiron-skarn deposits. The largest deposits are the Bystrinsky, Kultuma and Lugokan. According to the available data, the total amount of gold in these three deposits is estimated at about 443 t: the Lugokan, Au~53 t, Cu~302 thousand t, the Kultuma, Au~121 t, Cu~587 thousand t, Fe~33 mln t; the Bystrinsky, Au~269 t, Cu~2070 thousand t, Fe~67 mln t [2]. The deposits had been studied for a long time by many researchers, the formation types of these deposits are discussible: some researchers consider these deposits as typical representatives of the skarn formation, while others relate them to the gold-copper-molybdenum-porphyry type or to the combined skarn-porphyry type
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