Mineralogy and geochemistry of an ore-forming intrusion in the Nurkazgan Cu-Au deposit in Kazakhstanm and thier metallogenic significance
The Nurkazgan porphyry Cu-Au deposit,which hosts Cu and Au reserves of 3.93 Mt and 229 t,respectively,is located in northeast Kazakhstan.The intrusion associated with the Cu-Au mineralization was composed of diorite and granodiorite.Electron microprobe analysis showed that plagioclase in the diorite is mainly andesine,while hornblende is mainly magnesian hornblende.The intrusions are of high-K calc-alkaline series,showing enrichment of large-ion lithophile elements and light rare earth elements and depletion of high field strength elements.The Sr/Y and La/Yb ratios were similar to those of normal island arc rocks.The Re-Os isotopic model age of the molybdenite sample is 433±4 Ma,which is close to the age of the host rock(440 Ma to 437 Ma).Combining with previous research,it is inferred that the Nurkazgan deposit was the product of magmatic-hydrothermal mineralization during northwestward subduction of the Balkhash-Junggar oceanic crust.The oxygen fugacity,water content,and pressure of the ore-related magma estimated on the basis of the composition of hornblende in the diorite are-13.5 to-12.1(ΔFMQ=3.1 to 3.6),0.1%to 1.9%,and 20 MPa to 250 MPa,respectively.The high oxygen fugacity and water content of the magmatic system associated with mineralization in Nurkazgan are very conducive to the formation of porphyry deposits.
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