Metallogenesis of the Siding Pb-Zn deposit in Guangxi, South China: Rb-Sr dating and C-O-S-Pb isotopic constraints

Abstract

The Siding Pb-Zn deposit is located in the transition zone between the Yangtze Craton and the Cathaysian Block on the southwestern margin of the Jiangnan Orogenic Belt and is a representative example of the Pb-Zn deposits found in northern Guangxi, South China. In this study, sphalerite Rb-Sr dating and C-O-S-Pb isotope analyses were used to investigate the mineralization age and source of the ore-forming minerals in the Siding Pb-Zn deposit. The δ13CPDB and δ18OSMOW values of the gangue mineral calcites were determined to be between −5.0 and −1.1 (average = −2.6) and between 13.2 and 18.4 (average = 16.4), respectively. These values are roughly consistent with those of the carbonate minerals in the ore-hosting strata, namely, −1.63 to 0.83 (average = −0.34) and 19.0–22.0 (average = 20.9), respectively, indicating a mainly sedimentary origin of the ore-forming fluids. The δ34S values of the ore minerals were determined to be −17.1 to 5.1 (average = −2.6), while they were −8.6 to 5.1 (average = −0.8) for sphalerite, −7.8 to 2.7 (average = −1.6) for galena, and −17.1 to 2.3 (average = −7.3) for pyrite. The 206Pb/204Pb, 207Pb/204Pb, and 208Pb/204Pb ratios of the sulfides (pyrite, galena, and sphalerite) were determined to be 18.12–18.76 (average = 18.50), 15.66–15.97 (average = 15.80), and 38.36–39.71 (average = 38.96), respectively, which are consistent with those of limestone in the region (206Pb/204Pb = 17.65–18.77, 207Pb/204Pb = 15.60–15.91, and 208Pb/204Pb = 37.82–39.59). Pb and S isotope analyses showed that the ore-forming materials originated from the crust, as also substantiated by the (87Sr/86Sr)i ratios (0.710806–0.713740) of the sphalerite. The isochron age determined by Rb-Sr dating was 360 ± 5.0 Ma, indicating the formation of the Siding deposit in the Late Devonian (Hercynian Period). This mineralization age substantially differs from those determined for the Dachang, Tongshanling, Huangshaping, and Shuikoushan Pb-Zn deposits on the southern margins of the Jiangnan Orogenic Belt, but is comparable with those of the adjacent Daliangzi, Bokouchang, and Dadongla Pb-Zn deposits in northeastern Guizhou. We therefore propose that the formation of the Siding Pb-Zn deposit is related to a basin-scale fluid flow induced by Late Devonian extensional rifting in South China, in response to the tectonic evolution of the southwestern Yangtze Craton.