Известия Томского политехнического университета: Инжиниринг георесурсов (Jan 2019)
MAGMATIZM AND EPITHERMAL Ag-Au ORE MINERALIZATION OF KRASNOYARSK GOLD ORE FIELD OF GORNY ALTAI
Abstract
The relevance of the study is caused by the need of researching petrology, geochemistry subvolcanic rocks and epithermal Ag-Au ore mineralization of Krasnoyarsk ore field of Gorny Altai. Different types of ore mineralization: copper, cobalt, arsenic, tungstain and gold, are associated in space and paragenetic with subvolcanic stocks of granitoids. High sulfidation type of Ag-Au ore mineralization was researched first in Gorny Altai. The main aim of the research is to study petrology, geochemical features of rocks and ore mineralization of Krasnoyarsk deposit using the experimental diagrams, which allow solving the genetic problems and revealing the physic-chemical features of petro- and oregenesis. Methods. Elements were determined in rocks by inductively coupled plasma method on the mass spectrometer «ОРTIMA-4300» in the Laboratory of Institute of mineralogy, geochemistry and crystallochemistry of rare elements (Moscow). Isotopes of sulfur and oxygen were determined on the mass-spectrometer МI 1201В in the same laboratory. Results. Subvolcanic stocks of granitoids of the Middle Devonian of Korgonskiy complex are the main ore generating objects in Krasnoyarsk ore field. These granitoids are of the peraluminous type with varying contents of Mg and Fe. The tetrad effect of REE fractionation (W-type) is revealed in rocks. The contents of Au and Ag in rocks increase with decreasing value of tetrad effect of REE fractionation (W-type). The deep magma chamber evolved toward increasing its level with the formation of sharply acid-sulfur characteristics and with the formation of near ore argillizites. Mineralization of the Krasnoyarsk deposit is represented by a series of nested quartz lodes with the formation of a kind of linear stockwork. Ores are formed in three stages: sulfidic, telluridic and postmineral. The main ore minerals are pyrite, galenite, sphalerite, tetrahedrite, tennantite, electrum, tetradymite, seldom – altaite, hessite, enargite, luzonite. The main minerals of lodes are quartz, calcite, chlorite, siderite, kaolinite, montmorillonite, illite. Gold content in ores changes from 0,5 to 29,6 ppm, silver – from 15 to 5000 ppm. Ratio of Ag/Au in ores is from 135 to 150. This indicates that the Krasnoyarsk deposit belongs to the Ag-Au type. The temperatures of homogenization of gas-liquid inclusions in quartz of different generations from stage to stage decreased from 265 to 175 °C. The sulfur fugacity decreased from the first stage (–10–11) to the second one (–15–16), fTe2 increased from (–15) to (–10) and fO2 increased from (–39,5) to (–37). Isotopes of sulfur and oxygen indicate a magmatic source for sulfur and meteoric for oxygen.
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