关键词: 锆石U-Pb定年, Sr-Nd-Hf同位素, 岩石成因, 花岗岩源区, 阳储岭花岗斑岩, 赣北

Abstract: Granodiorite, monzogranite porphyry, and granite porphyry are exposed in the Yangchuling tungsten ore district, northern Jiangxi. The granodiorite and monzogranite porphyry were formed in Late Jurassic and derived from the same source and the latter is more evolved than the former. Tungsten mineralization dominantly occurs as veinlet-disseminated within the monzogranite porphyry which is cut by the granite porphyry dykes. In this contribution, zircon U-Pb chronological, petrochemical, and Sr-Nd-Hf isotope geochemical studies are carried out on the Yangchuling granite porphyry, aiming to reveal the petrogenetic differences between the granite porphyry and the monzogranite porphyry and granodiorite in combination with other published data and provide new constraints for tungsten ore genesis. LA-ICP-MS zircon U-Pb dating manifests that the granite porphyry was formed at 144.6±1.8 Ma which is consistent with those of the granodiorite and monzogranite porphyry. The granite porphyry is high-Si, K-enriched, and weakly peraluminous, shows distinctly Ba-, Nb-, Sr-, P-, and Ti-depleted trace element patterns and rightward-sloping REE patterns with negative Eu anomalies, indicating fractional crystallization of feldspar, biotite, apatite, and Ti-Fe oxide minerals, etc. The granite porphyry has whole-rock (87Sr/86Sr)i , εNd(t), εHf(t), and zircon εHf(t) values of 0.711329-0.711726, -5.3 to -4.9, -4.6 to -4.2, and mainly -6.0 to -3.0, respectively, suggesting that its source is dominated by ancient crustal materials. Compared with the granodiorite and monzogranite porphyry, the granite porphyry exhibits higher HFSE, ΣREE contents, AMF values, Sr/V ratios and lower Mg# values, Ti/Zr ratios, whole-rock εHf(t) values, implying that it was derived from a more felsic source and is the product of partial melting of ancient metasediments. Compared with the monzogranite porphyry, the granite porphyry displays higher SiO2 contents, (Na2O+K2O)/CaO, Na2O/CaO, Ba/Sr, Rb/Sr ratios and lower CaO, MgO, TiO2, P2O5 contents, δEu values, manifesting that it has experienced stronger magmatic fractionation. The barren granite porphyry is reflective of a W-poor source, while the source of the granodiorite and monzogranite porphyry is relatively W-rich. Both the W-rich source and magmatic fractionation facilitate the formation of t he Yangchuling tungsten deposit.

Key words: Zircon U-Pb dating, Sr-Nd-Hf isotopes, petrogenesis, granite source, Yangchuling granite porphyry, northern Jiangxi