Geochemistry and zircon trace elements composition of the Miocene ore‐bearing biotite monzogranite porphyry in the Demingding porphyry Cu‐Mo deposit, Tibet: Petrogenesis and implication for magma fertility

Abstract

MS zircon U-Pb dating, whole-rock geochemistry, and zircon trace elemental data for the mineralization related biotite monzogranite porphyry in Demingding. Zircon U-Pb dating shows that the weighted mean 206 Pb/ 238 U ages of the Miocene biotite monzogranite porphyry is 20.36 ± 0.46 Ma (MSWD = 2.6, n = 21). The Miocene biotite monzogranite porphyry is characterized by high SiO 2 , K 2 O, and Al 2 O 3 contents and shows adakite-like signatures. These rocks have high Sr/Y ratios, fractionated REE patterns with low HREE abundances, enrichment in LILE compared with HFSE, and have ( 87 Sr/ 86 Sr) i values of 0.7059 to 0.7062, ε Nd (t) values of −2.35 to −1.67 and (-206 Pb/ 204 Pb) i ratios of 18.50-18.55. These features are similar to other Miocene adakite-like intrusions in the Gangdese belt. We propose that the biotite monzogranite porphyry shares the same petrogenesis with other Miocene ore-bearing adakite-like intrusions in the Eastern Gangdese belt and was derived from remelting of the subduction-modified, eclogitized Tibetan lower crust and mixing with hydrous mafic magmas from metasomatized Tibetan mantle. The zircons from biotite monzogranite porphyry have only minimal negative Eu anomalies (Eu N /Eu N * > 0.3), and exhibit large ratios of Ce 4+ /Ce 3+ (average value of 113), 10,000*(Eu N /Eu N *)/Y (3.94-8.14, >1), Ce/Nd (9-58, Average value of 30), (Ce/Nd)/Y (0.008-0.127, >0.003), and low value of Dy/Yb (0.15-0.24, <0.3), indicating that the biotite monzogranite porphyry is relatively hydrous and oxidized. The biotite monzogranite porphyry, therefore, is believed to be a relatively fertile intrusion with certain exploration potential.

Origin and Geodynamic Mechanism of the Tibetan Demingding Porphyry Mo (Cu) Deposit from Oceanic Subduction to Continental Collision

“…Here, we present a detailed isotopic study of the recently discovered Demingding porphyry Mo (Cu) deposit, which is the eastern extension of the Gangdese metallogenic belt [24,25]. Consequently, the discovery of the Demingding porphyry Mo (Cu) deposit enriches the ore deposit association in the eastern part of the Gangdese PCDs metallogenic belt.…”

“…5000∼5822 m) and harsh climatic conditions (snow cover almost year-round), which hampers the geological field mapping. In addition, the Demingding deposit is so unique, most of the Gangdese deposits are Cu-dominated whereas the Demingding deposit is Mo-dominated [25,26], which means this study will play a vital role in our understanding of the diverse nature and styles of the Gangdese metallogenic belt. In this study, we use Lu-Hf isotopes, together with whole-rock geochemistry and zircon U-Pb dating, which is newly designed to achieve the following goals: (1) to explore the origin and geodynamic mechanisms of the Demingding porphyry Mo (Cu) deposit in Tibet; and (2) to assess their significance in the understanding of the regional geodynamic setting and the mineralization styles of the Gangdese metallogenic belt.…”