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Generation of Cu-Au skarn mineralization by mafic magma recharge; insights from the Bozymchak Deposit in the Chatkal-Kurama region, Kyrgyzstan, West Tianshan

Zu Bo, Zhang Hao, Guoxiang Chi, Wang Rui, Reimar Seltmann, A. E. Williams-Jones, Nikolay Pak and Xue Chunji
Generation of Cu-Au skarn mineralization by mafic magma recharge; insights from the Bozymchak Deposit in the Chatkal-Kurama region, Kyrgyzstan, West Tianshan
Geological Society of America Bulletin (November 2024) 137 (5-6): 1964-1984

Abstract

Large numbers of igneous intrusions are emplaced in the magmatic arcs above subduction zones, but only a small fraction of them are mineralized with Cu+ or -Au+ or -Mo. Despite significant advances in recognizing the importance of magma source, volatile content, and redox condition in controlling mineralization, the magmatic processes required to form a mineral deposit are still poorly understood. Here, we demonstrate that mafic recharge to the magma chamber is critical for Cu-Au mineralization, as exemplified by the Bozymchak Cu-Au skarn deposit in the Chatkal-Kurama arc of Kyrgyzstan, West Tianshan. The Bozymchak intrusion associated with the mineralization comprises monzonite porphyry and granodiorite porphyry. A sensitive high-resolution ion microprobe zircon U-Pb age of 305+ or -2 Ma was obtained for the monzonite porphyry, which is consistent with the U-Pb age of zircon from the granodiorite porphyry (304 Ma) and an Re-Os age for the molybdenite (305 Ma). These ages indicate that both the monzonite porphyry and granodiorite porphyry were coeval with mineralization. The monzonite porphyry exhibits high-K calc-alkaline (K (sub 2) O=3.36-3.50 wt%), metaluminous and magnesian-rich characteristics, enrichment in large ion lithophile elements (LILEs; e.g., Cs, Th, Ba, K, and Pb), and negative anomalies in high field strength elements (HFSEs; e.g., Nb, Ta, and Ti). These geochemical signatures, combined with the Sr-Nd-Hf isotopic signatures [ISr(avg)=0.7059, epsilon Nd(t)=-3.5 to -2.8, epsilon Hf(t)=-3.8 to +1.4], suggest that the magma was the product of partial melting of a metasomatized mantle wedge and was subjected to subsequent assimilation and fractional crystallization (AFC). The development of disequilibrium textures in both the monzonite porphyry and the granodiorite porphyry, such as acicular apatite, reverse zoning of plagioclase, and coexisting high-Al and low-Al amphiboles, indicates that the magma evolved in an open crustal magma chamber with mafic magma recharge. The magmas were moderately oxidized ( approximately Delta FMQ +1.0; FMQ is the fayalite-magnetite-quartz oxygen buffer) and water-rich, with 5.9 wt% and 6.5 wt% H (sub 2) O in the granodiorite porphyry and monzonite porphyry, respectively. The repeated influx of hot mafic magma batches prolonged the existence of the magma chamber and promoted the maturation of the arc magma. In addition to introducing more Cu and Au, the replenishment of mafic magma in the chamber also introduced additional H (sub 2) O and Cl, as shown by the presence of high-Al amphiboles and the elevated oxygen fugacity, which further promoted Cu-Au mineralization.


ISSN: 0016-7606
EISSN: 1943-2674
Coden: BUGMAF
Serial Title: Geological Society of America Bulletin
Serial Volume: 137
Serial Issue: 5-6
Title: Generation of Cu-Au skarn mineralization by mafic magma recharge; insights from the Bozymchak Deposit in the Chatkal-Kurama region, Kyrgyzstan, West Tianshan
Affiliation: China University of Geosciences, School of Earth Resources, Wuhan, China
Pages: 1964-1984
Published: 20241126
Text Language: English
Publisher: Geological Society of America (GSA), Boulder, CO, United States
References: 115
Accession Number: 2024-092991
Categories: Igneous and metamorphic petrology
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. sect., 4 tables, geol. sketch map
N41°00'00" - N42°00'00", E70°00'00" - E72°00'00"
Secondary Affiliation: University of Regina, CAN, CanadaChina University of Geosciences, CHN, ChinaNatural History Museum, GBR, United KingdomMcGill University, CAN, CanadaState Agency of Geology and Mineral Resources, KGZ, Kyrgyzstan
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2025, American Geosciences Institute. Reference includes data from GeoScienceWorld, Alexandria, VA, United States. Reference includes data supplied by the Geological Society of America, Boulder, CO, United States
Update Code: 202452

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