Lithogeochemical, Re-Os and U-Pb Geochronological, Hf-Lu and S-Pb Isotope Data of the Ga'erqiong-Galale Cu-Au Ore-Concentrated Area: Evidence for the Late Cretaceous Magmatism and Metallogenic Event in the Bangong-Nujiang Suture Zone, Northwestern Tibet, China

摘要

The Ga'erqiong-Galale skarn-porphyry copper-gold ore-concentrated area is located in the western part of the Bangong-Nujiang suture zone north of the Lhasa Terrane. This paper conducted a systematic study on the magmatism and metallogenic effect in the ore-concentrated area using techniques of isotopic geochronology, isotopic geochemistry and lithogeochemistry. According to the results, the crystallization age of quartz diorite (ore-forming mother rock) in the Ga'erqiong deposit is 87.1 +/- 0.4Ma, which is later than the age of granodiorite (ore-forming mother rock) in the Galale deposit (88.1 +/- 1.0Ma). The crystallization age of granite porphyry (GE granite porphyry) in the Ga'erqiong deposit is 83.2 +/- 0.7Ma, which is later than the age of granite porphyry (GL granite porphyry) in the Galale deposit (84.7 +/- 0.8Ma).The quartz diorite, granodiorite, GE granite porphyry and GL granite porphyry both main shows positive epsilon(Hf)(t) values, suggesting that the magmatic source of the main intrusions in the ore-concentrated area has the characteristics of mantle source region. The Re-Os isochron age of molybdenite in the Ga'erqiong district is 86.9 +/- 0.5Ma, which is later than the mineralization age of the Galale district (88.6 +/- 0.6Ma). The main intrusive rocks in the ore-concentrated area have similar lithogeochemical characteristics, for they both show the relative enrichment in large-ion lithophile elements(LILE: Rb, Ba, K, etc.), more mobile highly incompatible lithophile elements(HILE: U, Th) and relatively depleted in high field strength elements (HFSE: Nb, Ta, Zr, Hf, etc.), and show the characteristics of magmatic arc. The studies on the metal sulfides' S and Pb isotopes and Re content of molybdenite indicate that the metallogenic materials of the deposits in the ore-concentrated area mainly come from the mantle source with minor crustal source contamination. Based on the regional tectonic evolution process, this paper points out that the Ga'erqiong-Galale copper-gold ore-concentrated area is the typical product of the Late Cretaceous magmatism and metallogenic event in the collision stage of the Bangong-Nujiang suture zone.