Source and Tectonic Setting of Porphyry Mo Deposits in Shulan, Jilin Province, China

The Shulan area in Jilin Province is a part of the Lesser Xing’an–Zhangguangcai Range polymetallic ore belt, which is an important Cu–Mo ore region of northeast China. The discovery of three large Mo ore deposits (Fu’anbu, Chang’anbu, and Jidetun) highlights its potential for porphyry Mo ore deposits. Here we investigated the tectonic setting and mineralization of Mo ore deposits in the Shulan area, based on comparative study of the Fu’anbu, Chang’anbu, and Jidetun deposits. The ore-controlling structures are NE–SW- and NW–SE-trending faults. The main ore mineral in all three deposits is molybdenite. The ore bodies are all hosted in granites, have a stratiform or lenticular shape, and have strongly altered wall rocks. These observations indicate the Mo deposits in the Shulan area are typical porphyry Mo deposits. All were formed during the early Yanshanian (199.6–133.9 Ma). Biotite adamellites from the Chang’anbu deposit yield a U–Pb age of 182.10 ± 1.20 Ma. Molybdenites from the Fu’anbu and Jidetun deposits have Re–Os isochron ages of 166.9 ± 6.7 and 169.1 ± 1.8 Ma, respectively. Quartz and ore minerals were analysed for H–O and S–Pb isotopes, respectively. The results suggest the ore-forming materials were predominantly of upper-mantle origin, with secondary contributions from the lower crust. The ore-hosting granites have high concentrations of SiO2 (66.67–75.43 wt.%) and Al2O3 (12.91–16.44 wt.%), low concentrations of MgO (0.09–1.54 wt.%), and Ritman index (σ = K2O + Na2O)2/(SiO2 − 43)) ratios of 2.09–2.57. The granites are enriched in large-ion lithophile elements and depleted in high-field-strength elements, and have negative Eu anomalies. The ore-hosting rocks are geochemically similar to granites in northeastern China that were generated in a collisional orogeny. We conclude that early Yanshanian (199.6–133.9 Ma) mantle–crust-derived magmatism caused by the subduction of the Palaeo-Pacific Plate was the main source of Mo deposits in the Shulan area.

The Mineralization Age of the Gupao Gold Deposit, Guangxi

The Dayaoshan, which has nearly 200 gold deposits (or mineralization points), is one of the most important gold deposits distribution areas in Guangxi, and the Gupao gold deposit is an important representative one. Previous researches have carried out numerous works there to guide the gold prospecting work. Due to multiple episodes of gold mineralization and multiple sources materials in ore-forming, there are heated debates on the era of the mine, and the main mineralization age of the Gupao gold deposit is focused on the Caledonian or Early Yanshanian. According to the distribution characteristics of the gold ore body showing in the Zhilong, Gulinao, and Dawangding gold deposit, the discussion of macro-tectonic setting of the area, as well as the comparative study of surrounding gold deposits, we conclude that the main mineralization age of the Dawangding gold deposit is Early Yanshanian, and the main mineralization may be controlled by the nearly east-west trending fold which was caused by the north-south extrusion.