Zircon U-Pb dating and geochemical study of the Xianggou granite in the Ma’anqiao gold deposit and its relationship with gold mineralization

Abstract

Single zircon LA-ICP-MS U-Pb dating and lithogeochemical studies have been performed on the Xianggou monzonitic granitic porphyry outcropped in the Ma'anqiao gold deposit. A weighted average U-Pb age of 242.0±0.8 Ma for Xianggou monzonitic porphyry has been obtained. This corresponds with the conclusions of previous studies indicating a syn-orogenic age (242±21 Ma) of the Qinling Orogenic Belt, suggesting that the formation of the Xianggou granite should be associated with the collisional event of the North China Plate and the Yangtze Plate in the Indosinian period. The Xianggou granite is characterized by the high silicon and alkali of high K calc-alkaline series granites. It is rich in Al (Al 2 O 3 =14.49%-15.61%) and Sr (457.10-630.82 ppm), poor in Y (<16 ppm) and HREE (Yb<0.45 ppm), and exhibits high ratios of Sr/Y (76.24-97.34) and (La/Yb) N (29.65-46.10), as well as strongly fractionated REE patterns. These geochemical characteristics suggest the Xianggou granite can be classified as C-type adakitic rock. The initial Sr isotope ratios for the Xianggou granite vary from 0.70642 to 0.70668, ε Nd (t) values from −4.54 to −3.98, and T DM values from 1152 Ma to 1220 Ma. The low ε Nd (t) and I Sr and high T DM values, as well as Na 2 O/K 2 O ratios of the Xianggou granite are close to 1 (Na 2 O/K 2 O=0.95-1.10), indicating that it is not an I-type adakite formed by partial melting of the subducting oceanic crust, nor adakitic rock formed by melting of the underplated basaltic lower crust, but the product of partial melting of the nonunderplated basaltic thickened lower crust. Zircons from the Xianggou pluton have a homogeneous Hf isotopic composition with negative ε Hf (t) values (between −9.7 and −5.9, with an average of −6.9), indicating that the rock-forming materials were mostly extracted from the ancient crust, not from the depleted mantle. The Xianggou monzonitic granitic porphyry is rich in LILE and LREE and depleted in HSFE, HREE and Y; the composition of trace element and REE are similar to those of the syn-collisional granites. The geological and geochemical characteristics of the Xianggou granite reveal that it was a product of partial melting of the basaltic rocks from the thickened lower crust, triggered by continental collision, which occurred in the geodynamic background of continental-continental collision and shearing within the crust. The Xianggou granite was intruded in the compressive orogenic environment 242 Ma ago, but the gold mineralization occurred in the transitional environment of compression to extension around 170 Ma ago, lagging behind the intrusive age of the Xianggou granite by about 70 Ma. Meanwhile, the distribution of trace elements and REEs of the Xianggou monzonitic granitic porphyry is distinct from that of ores, suggesting the absence of direct genetic relationship between the Xianggou granite and gold mineralization. In contrast, the relatively high ore-forming elemental content of the Xianggou monzonitic granitic porphyry is due to the rock having experienced Au-bearing hy...

Episodic Triassic magmatism in the western South Qinling Orogen, central China, and its implications

“…Most granites to the other side of CHF Fault, in the ESQL have U–Pb zircon ages between 220 and 205 Ma, except for some small bodies such as the 241 ± 1 Ma Xianggou Granite (Fig. ; Zhu et al ., ). The 220–205 Ma granites form the T 3 ‐ESQL suite, and the ~240 Ma granites form the T 2 ‐ESQL suite.…”

Geochemistry of the Yangla volcanic rocks and its relationship to Cu mineralization in the Yangla copper deposit, western Yunnan, China

“…Fresh samples of the volcanic rocks, without late-stage veins, were analyzed for major elements, trace elements, and rare earth elements (REEs) at the Institute of Physical Geography and Geochemistry Exploration, Chinese Academy Geoscience, Langfang, China. For details of the analytical procedure, see Zhu et al (2009b). The major elements were determined by Panatica Axios PW4400 X-ray fluorescence spectrometer (XRF), the GAU11aGSD4a standards were used for monitoring in this procedure, and the analytical accuracies were better than 2%.…”

Geochronology and geochemistry of the Dashui adakitic granitoids in the western Qinling Orogen, central China: implications for Triassic tectonic setting

“…Sun et al ., ; Jin et al ., ; Wang et al ., ; C.L. Zhang et al ., ; Zhu et al ., ; Chen, ; Wang et al ., ).…”

“…Zhang et al ., ), with most granitoids intruding at ~220 Ma. For a long time, the Triassic intrusions were generally considered to be syn‐collisional granitoids (Sun et al ., ; Zhu et al ., ), while Lu et al . () and Wang et al .…”