Multistage magmatic-hydrothermal activity and W-Cu mineralization at Jiepai, Guangxi Zhuang Autonomous Region, South China: Constraints from geochronology and Nd-Sr-Hf-O isotopes

Abstract

The Jiepai W-Cu deposit, located in the northeastern Guangxi Zhuang Autonomous Region in South China, occurs along the contact zone between the Yuechengling granite batholith and the Cambrian dolomitic limestones and slates. The main body of the batholith is made of a Silurian monzogranite in the south and a Triassic monzogranite in the north. A number of Jurassic to Cretaceous fine-grained granite intrusions are present as stocks and dikes intersecting the batholith. The deposit includes five types of W-Cu ores, including (1) contact-zone scheelite skarn occurring at the lithological contact between monzogranite and dolomitic limestone, (2) strata-bound scheelite skarn hosted by dolomitic limestone, (3) disseminated or banded scheelite within gneissic granite, (4) titanite-bearing scheelite quartz veins cross-cutting the skarns and limestone, and (5) disseminated Cu sulfides within granodiorite, respectively. In this paper, we report new geochronological data obtained from zircon U-Pb, molybdenite Re-Os, and biotite and muscovite Ar-Ar analyses with the aim of constraining the timing of magmatic and mineralization events. Zircon SHRIMP U-Pb analyses of all the granitoids exposed in the deposit and its vicinity reveal six stages of magmatic emplacement dated at 448.4 ± 4.6 Ma, 434.6 ± 3.5 Ma, 429.4 ± 7.6 Ma, 219.2 ± 1.5 Ma, 156.0 ± 3.0 Ma, and 149.7 ± 2.2 Ma (weighted 206Pb/238U mean ages). Molybdenite Re-Os and muscovite and biotite Ar-Ar analyses reveal four W mineralization events that were associated with the magmatic emplacement at 448.4 ± 4.6 Ma, 429.4 ± 7.6 Ma, 219.2 ± 1.5 Ma, and 151.4 ± 1.9 Ma, and three Cu mineralization events at 434.3 ± 5.1 Ma, 152.2 ± 1.1 Ma, and 141.0 ± 2.5 Ma, respectively. The granites at the deposit and its vicinity document weak fractionation of light and heavy REEs, contain low concentrations of Ba, Nb, Sr, P, and Ti, but high concentration of Ta. Neodymium isotopic data of the W-mineralized Late Ordovician granites (εNd(t) = −4.87, T2DM = 1.6 Ga) imply magma mixing of mafic mantle material with Paleoproterozoic and/or Mesoproterozoic continental crust. By contrast, the Silurian granites (εNd(t) = −10.15 to −13.49) were formed by anatexis of the Paleoproterozoic continental crust. High-precision Hf-O isotope data obtained in this study indicate partial melting of the lower crust as the main source of the younger granites, and further reveal a complex evolution process that involved two or more sources of magmas.