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MULTIPULSED MAGMATISM AND DURATION OF THE HYDROTHERMAL SYSTEM OF THE GIANT JIAMA PORPHYRY Cu SYSTEM, TIBET, CHINA
Economic Geology ( IF 5.8 ) Pub Date : 2024-01-01 , DOI: 10.5382/econgeo.5054 Bin Lin 1, 2, 3 , Juxing Tang 1, 2 , Pan Tang 4 , Georges Beaudoin 3 , Crystal Laflamme 3 , Faqiao Li 1 , Wenbao Zheng 1 , Yang Song 1, 2 , Jing Qi 5 , Miao Sun 6 , Huawen Cao 7 , Qiufeng Leng 6 , Aorigele Zhou 1, 2 , Bing Zou 3 , Corey J. Wall 8 , Chao Yang 7
Economic Geology ( IF 5.8 ) Pub Date : 2024-01-01 , DOI: 10.5382/econgeo.5054 Bin Lin 1, 2, 3 , Juxing Tang 1, 2 , Pan Tang 4 , Georges Beaudoin 3 , Crystal Laflamme 3 , Faqiao Li 1 , Wenbao Zheng 1 , Yang Song 1, 2 , Jing Qi 5 , Miao Sun 6 , Huawen Cao 7 , Qiufeng Leng 6 , Aorigele Zhou 1, 2 , Bing Zou 3 , Corey J. Wall 8 , Chao Yang 7
Affiliation
Jiama is the largest porphyry-skarn ore system in the Gangdese metallogenic belt, Tibet. It is composed of porphyry Cu-Mo, Cu-polymetallic skarn, Cu-Pb-Zn manto, and distal vein Au orebodies with associated Ag, W, and Bi. However, the precise timing of the magmatism and hydrothermal events at Jiama remains obscure. Here, using high-precision chemical abrasion-isotope dilution-thermal ionization mass spectrometry (CA-ID-TIMS) U-Pb zircon dating of ore-bearing and post-ore intrusions, we accurately constrain the lifespan of magmatism and hydrothermal mineralization. Monzogranite porphyry dikes are cut by Cu-Mo vein mineralization in the deeper part of the system, indicating that they were emplaced pre-ore, and yield a crystallization age of 15.534 ± 0.007 Ma (mean square of weighted deviates [MSWD] = 0.99, n = 6). A granodiorite porphyry that cuts the monzogranite porphyry and hosts vein and disseminated chalcopyrite and molybdenite is considered synchronous with ore and yields a crystallization age of 15.368 ± 0.007 Ma (MSWD = 1.01, n = 5). These two phases of intrusions are cut by quartz-diorite porphyry bodies, which yield a crystallization age of 15.076 ± 0.006 Ma (MSWD = 0.13, n = 6) and contain weak, subeconomic Cu and almost no molybdenum mineralization. A post-ore barren quartz monzonite porphyry yields a crystallization age of 14.925 ± 0.006 Ma (MSWD = 1.12, n = 6). The lifespan of magmatism at Jiama is thus about 0.61 m.y. The difference with previous molybdenite Re-Os isochron ages from the porphyry (14.7 ± 0.3 Ma), hornfel (14.7 ± 0.4 Ma), and skarn (15.4 ± 0.2 Ma) suggests that high-precision chronology is required to decipher accurate timing of mineralization in porphyry systems such as Jiama. The 40Ar/39Ar ages of hydrothermal biotite coexisting with molybdenite in monzogranite porphyry and hornfels are 15.25 ± 0.17 Ma (MSWD = 1.6) and 15.25 ± 0.24 Ma (MSWD = 0.14), respectively, slightly younger than the granodiorite porphyry and older than weakly mineralized quartz diorite porphyry, which represents the time of the ore-forming hydrothermal event. Thus, Jiama is the product of pulsed magmatism during which a short-lived hydrothermal event formed the giant Cu polymetallic system.
更新日期：2024-01-01
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