Copper Mineralization Potential of Late Triassic Granitoids in Northern Yidun Arc, SW China

Xing-Yuan Li,Hao Song,Chun-Kit Lai,Jing-Ru Zhang

doi:10.3390/min9060337

Abstract

Yidun arc is an important constituent of the Sanjiang Tethyan Domain in SW China. The Changdagou pluton, located in the northern part of the Yidun Arc, mainly consists of granodiorite. In this study, we conducted in-situ LA-ICP-MS zircon U-Pb dating, and trace element and Hf isotope analyses on the Changdagou granites. Age dating results yielded a weighted mean U-Pb age of 214.97 ± 0.98 Ma (MSWD = 1.2, 2σ), broadly coeval with extensive late Triassic magmatism across the Yidun Arc. All zircon grains analyzed showed high concentrations of Th, U, and HREE, with positive Ce and negative Eu anomalies. Logfo2 and CeN/CeN* values vary from FMQ −3.14 to FMQ +7.44 (average FMQ +3.98), and 14 to 172 (avg. 98), respectively. The zircon EuN/EuN* (avg. 0.22) ratios have no clear correlation with the CeN/CeN* ratios, suggesting that the former were mainly affected by the magma water content. In addition, zircon εHf(t) values vary in a narrow range (–2.9 to −4.9, avg. −3.4) that clusters around zero, indicating a greater component of mantle-derived magma. Hence, we propose that the Changdagou granodiorite was derived from a highly oxidized, “wet”, Cu-rich source, of the type likely to generate porphyry Cu mineralization. However, these parameters (logfO2, EuN/EuN*, (Ce/Nd)/Y, and εHf(t)) are all lower than those of intrusions associated with Cu ores at Pulang and Lannitang, which may explain why the Cu deposit discovered at Changdagou is small by comparison. Furthermore, on the basis of the decreasing trends of εHf, logfO2, and H2O content from south to north along the Yiduan arc, we infer that the northern segment of the Yidun arc (including Changdagou) was located further away from the subduction front.

Highlights

The Sanjiang Tethyan Domain in the southeastern Tibet Plateau comprises various-continental blocks, volcanic arcs, and ophiolitic belts that were formed during the opening and closure of the Paleo-Tethys (Figure 1) [1]
We propose that the Changdagou granodiorite was derived from a highly oxidized, “wet”, Cu-rich source, of the type likely to generate porphyry Cu mineralization. These parameters (logfO2, EuN /EuN *, (Ce/Nd)/Y, and εHf(t)) are all lower than those of intrusions associated with Cu ores at Pulang and Lannitang, which may explain why the Cu deposit discovered at Changdagou is small by comparison
The NNW-trending Yidun structure is the largest island arc preserved in the domain [2,3,4], and a number of important porphyry copper deposits (PCDs) were found in its southern section, such as the Pulang, Lannitang and Xuejiping

Summary

Introduction

The Sanjiang Tethyan Domain in the southeastern Tibet Plateau comprises various (micro)-continental blocks, volcanic arcs, and ophiolitic belts that were formed during the opening and closure of the Paleo-Tethys (Figure 1) [1]. The NNW-trending Yidun structure is the largest island arc preserved in the domain [2,3,4], and a number of important porphyry copper deposits (PCDs) were found in its southern section, such as the Pulang, Lannitang and Xuejiping. These PCDs were mainly formed in the Late Triassic (208–235 Ma) during the Indosinian Orogeny [5,6,7]. Only a few PCDs have been discovered in the northern section of the arc, with the Changdagou PCD being the largest one [8]. This raises questions on whether the paucity of PCD discovery is an issue of exploration work, deposit preservation, or a combination of these factors.

Methods

Results

Discussion

Conclusion