Hydrothermal rutile chemistry and U-Pb age fingerprinting of the formation of the giant Nurkazgan porphyry Cu-Au deposit, Central Kazakhstan
Feng H. Seltmann R. Shen P. Chu X. Suo Q. Seitmuratova E. Shatov V.
November 2024Elsevier B.V.
Ore Geology Reviews
2024#174
The porphyry Cu-related intrusions commonly comprise multiple phases such as the large Nurkazgan porphyry Cu-Au deposit in Central Kazakhstan, hosted in the Karagandinsky dioritic to granitic intrusive complex. Here, SHRIMP and LA-ICP-MS zircon U-Pb dating on the multiple ore-bearing intrusions from this complex confirms a punctuated magmatic history distributed over 35 m.y., and marked by three episodic porphyry events rather than a single event, with the oldest event being the early granodiorite and quartz diorite porphyries at ca. 437–440 Ma, the second being the quartz diorite porphyry at 429.7 ± 2.1 Ma, and the last being the late granodiorite and quartz diorite porphyries at 402.8 ± 3.7 Ma and 402.0 ± 3.9 Ma, respectively. The mineralization is related to the two younger episodic intrusions of quartz diorite porphyry at ∼ 430 Ma and ∼ 402 Ma, respectively. SIMS U-Pb dating of hydrothermal, Cu-rich (up to 20.9 ppm) rutile from the breccia-type ores directly constrains the timing of porphyry mineralization at 428.9 ± 6.9 Ma, which is coincident with the emplacement age of the ∼ 430 Ma quartz diorite porphyry, and thus demonstrates this porphyry as a causative intrusion generating main-stage mineralization. This close genetic link is also supported by the chondrite-normalized REE patterns of rutile, which show remarkably similar light REE-enrichments and moderate negative Eu anomalies to those of the ∼ 430 Ma quartz diorite porphyry. A molybdenite sample obtained from the main-ore stage vein, however, has a Re-Os age of 418.6 ± 1.8 Ma, which is slightly younger than the U-Pb age determinations of rutile. This indicates that the Re-Os isotope system was disturbed by the second (post-ore) thermal event related to ∼ 402 Ma quartz diorite porphyry. In line with published data, this study suggests that the rutile U-Pb age in combination with its REE patterns can be a powerful tool to trace the causative porphyry. Moreover, the typical LREE-enriched REE patterns coupled with the high Cu anomalies, inherited from the causative porphyry and related exsolving fluids, can be as diagnostic proxies for distinguishing the porphyry Cu-related hydrothermal rutile from those formed in orogenic gold deposits. Based on these two geochemical discriminators and U-Pb ages, rutile can serve as unique fingerprints to help improve porphyry copper exploration in green field or covered terranes to complement detrital zircon fertility indicators.
Geochemical fingerprints , Nurkazgan , Porphyry copper deposit , Rutile and zircon , U-Pb age and chemistry
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Key Laboratory of Mineral Resources, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing, 100029, China
Centre for Russian and Central EurAsian Mineral Studies, Natural History Museum London, Cromwell Road, London, SW7 5BD, United Kingdom
University of Chinese Academy of Sciences, Beijing, 100049, China
Faculty of Land and Resource Engineering, Kunming University of Science and Technology, Kunming, 650093, China
Satpaev Institute of Geological Sciences, Almaty, 050010, Kazakhstan
Karpinsky Russian Geological Research Institute, St. Petersburg, 199106, Russian Federation
Key Laboratory of Mineral Resources
Centre for Russian and Central EurAsian Mineral Studies
University of Chinese Academy of Sciences
Faculty of Land and Resource Engineering
Satpaev Institute of Geological Sciences
Karpinsky Russian Geological Research Institute
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