MULTIPULSED MAGMATISM AND DURATION OF THE HYDROTHERMAL SYSTEM OF THE GIANT JIAMA PORPHYRY Cu SYSTEM, TIBET, CHINA,Economic Geology

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MULTIPULSED MAGMATISM AND DURATION OF THE HYDROTHERMAL SYSTEM OF THE GIANT JIAMA PORPHYRY Cu SYSTEM, TIBET, CHINA
Economic Geology ( IF 5.5 ) 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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