Sm-Nd Dating and In-Situ LA-ICP-MS Trace Element Analyses of Scheelite from the Longshan Sb-Au Deposit, Xiangzhong Metallogenic Province, South China

Abstract

Longshan is an important Sb-Au ore deposit (3.7 Mt @4.5 wt. % Sb and 4.6 g/t Au) in the Xiangzhong metallogenic province (XZMP), South China. In the present work, trace element composition, Sm-Nd isotope dating, and Sr isotope of scheelite from the Longshan Sb-Au deposit are used to constrain the genesis of the deposit. Based on mineral assemblages and geological characteristics, two types of scheelites can be distinguished (Sch1 and Sch2). Sch1 is granular and cemented by stibnite, while Sch2 is commonly present in stibnite, pyrite, calcite, and quartz veins, indicating that Sch2 is later than Sch1. The Sm-Nd isochron age defined by Sch1 is 210 ± 2 Ma (MSWD = 1.0, n = 4). This age is interpreted as the age of Sb-Au mineralization and overlaps with the 201–228 Ma granitic rocks in the XZMP. Sch1 exhibits high ΣREE + Y contents (43.5 to 104 ppm), low Sr values (2687 to 6318 ppm, average of 4018 ppm), and a narrow range of 87Sr/86Sr values (0.7209 to 0.7210, average of 0.7209). In contrast, the elevated Sr abundance (4525 to 11,040 ppm, average of 6874 ppm) and wide 87Sr/86Sr ratios (0.7209 to 0.7228, average of 0.7214) in Sch2 were possibly caused by fluid-rock interaction mixing with Sr-enriched basement rocks. Sulfides have a narrow range of δ34S values of −1.8‰ to 3.2‰, with an average value of 1.1‰ (n = 7). Geochronological, geochemical and isotopic data suggest that the Longshan Sb-Au deposit is possible genetically related to the Late Triassic granitic intrusion in the XZMP.