PRECISE AGES FOR LODE GOLD MINERALIZATION IN THE XIAOQINLING GOLD FIELD, SOUTHERN MARGIN OF THE NORTH CHINA CRATON: NEW CONSTRAINTS FROM IN SITU U-Pb DATING OF HYDROTHERMAL MONAZITE AND RUTILE

Abstract

The Xiaoqinling gold field, located along the southern margin of the North China craton, is the second largest gold producer in China, which comprises more than 1,200 auriferous quartz veins with a proven gold reserve of at least 800 tons. Previously, the absolute age of the gold metallogenesis in this area has not been well defined due to the lack of suitable dating minerals. This study presents new in situ laser ablation-inductively coupled plasma-mass spectrometry U-Pb ages of coexisting hydrothermal monazite and rutile for the Fancha gold deposit in this area, which yielded 206Pb/238U ages of 127.5 ± 0.7 Ma (n = 65, mean square of weighted deviates [MSWD] = 1.8) and 129.7 ± 4.3 Ma (n = 37, MSWD = 1.4), respectively. Both ages overlap within analytical uncertainty at the 2σ level of significance, suggesting that both gold-bearing veins were emplaced at ca. 128 Ma. Mineralogical observations indicate that the monazite and rutile precipitated simultaneously with gold from the hydrothermal fluid. Our new data, combined with recently published monazite age, define a more precise gold episode, demonstrating that the gold endowment of the Xiaoqinling area was formed during a relatively brief period at ca. 130 to 127 Ma. We suggest that auriferous fluids were generated as a result of interactions between the enriched mantle and the lower crust, which was driven by westward flat slab subduction of the Paleo-Pacific plate during the late Mesozoic. The peak of lithospheric thinning during the postsubduction may have led to the rapid release of gold from the fertilized mantle. Consequently, the large number of gold-bearing veins in the Xiaoqinling area may ultimately be related to the tectonic evolution and mantle fluid processes that occurred during Early Cretaceous lithospheric extension.

Insights from Dikes for Multistage Granitic Magmatism in the Huayangchuan Uranium Polymetallic Deposit, Qinling Orogen

“…The magmatic evolutionary series shows that the Qinling Orogenic Belt has experienced several global orogenic events from the Neoarchean to the Cenozoic. The Xiaoqinling area has also recorded several tectonic-thermal events [3][4][5][6][7][8][9][10][11][12][25][26][27][28][29][30][31], which could be roughly categorized into three phases: (1) crystalline basement formation of the Neoarchean-Paleoproterozoic-Mesoproterozoic; (2) orogeny of the Neoproterozoic-Middle Triassic caused by plate tectonics and crustal accretion; and (3) post-orogenic continental interior tectonic evolution during the Mesozoic-Cenozoic [3][4][5][6][7][8][9][25][26][27][28][29][30][31][32]. A large number of pegmatite, granite, granite porphyry, and carbonatite rocks of different ages and petrogeneses have formed in the Xiaoqinling area.…”

“…A large number of pegmatite, granite, granite porphyry, and carbonatite rocks of different ages and petrogeneses have formed in the Xiaoqinling area. With magmatism, large scales of different types of mineralization have formed in this area, relating to magmatic-hydrothermal fluids, including molybdenum, gold, rare earth, uranium, niobium, silver, and lead [6][7][8][9][10][11][12][25][26][27][28][29][30][31][32][33].…”

“…The main fault structures in the Xiaoqinling area include the Taiyao, Xiaohe, Huayangchuan, Luonan-Luanchuan, Machaoying, Qinggangping-Jinduicheng, and Zhangjiaping-Bayuan faults. Widely developed faults provide favorable spaces for subsequent magmatism and mineralization [6][7][8][9][10][11][12][25][26][27][28][29][30][31][32][33].…”

“…The Mesozoic U, Mo, Au, Ag-Pb-Zn, Cu, W, and rare earth element (REE) mineralization in the Qinling Orogenic Belt can be clearly distinguished into two mineralization stages, corresponding to early and late tectono-magmatic events, respectively [6][7][8][9][10][11][12][25][26][27][29][30][31][32][33][34][35][36].…”

“…The late mineralization stage occurred from the Late Jurassic to Early Cretaceous (ca. 148-114 Ma) and was mainly related to intracontinental extension and lithospheric thinning-destruction of the NCC [6][7][8][9][10][11][12][25][26][27][29][30][31][32][33][34][35][36].…”