LAUSR

Abstract Northern Guangdong of South China occurs many large tungsten deposits, including Shirenzhang, Meiziwo and Yaoling quartz-vein type wolframite deposits. In this study, we carried out a detailed study on fluid inclusions and C-H-O-S-Pb isotopic analyses of mineral separates for these three deposits, in order to resolve the origin and evolution of ore-forming fluids and the ore deposition mechanism. The ore veins in these deposits present a similar mineral paragenesis that could be divided into three stages: (I) pre-ore stage, (II) syn-ore stage, and (III) post-ore stage. The pre-ore stage is the magmatic-hydrothermal transition stage, which is marked by fluid exsolution from the highly fractionated granites, accompanied with potassic alteration and greisenization. The syn-ore stage can be further divided into two stages: silicate-oxide stage (stage II-1) that is characterized by significant tin-tungsten mineral deposition, and sulfide stage (stage II-2) that is characterized by abundant sulfide minerals deposition. The post-ore stage is dominated by quartz and fluorite. The three deposits show similar temperature and salinity variations for syn-ore and post-ore stages. In the Shirenzhang deposit, the fluid temperature and salinity range from 239 to 301 ℃ and 1.4 to 8.7 wt% NaCl equiv in stage II-1, from 206 to 256 ℃ and 1.4 to 7.0 wt% NaCl equiv in stage II-2, and from 186-236 ℃ and 1.4 to 8.6 wt% NaCl equiv in stage III. In the Meiziwo deposit, the fluid temperature and salinity range from 242 to 310 ℃ and 1.1 to 8.6 wt% NaCl equiv in stage II-1, from 196 to 252 ℃ and 1.4 to 8.1 wt% NaCl equiv in stage II-2, and from 188-234 ℃ and 1.2 to 7.3 wt% NaCl equiv in stage III. In the Yaoling deposit, the fluid temperature and salinity range from 230 to 304 ℃ and 1.2 to 9.0 wt% NaCl equiv in stage II-1, from 203 to 258 ℃ and 1.4 to 6.5 wt% NaCl equiv in stage II-2, and from 184-231 ℃ and 1.6 to 8.3 wt% NaCl equiv in stage III. The ore-forming fluids in the three deposits belong to a medium temperature, low-salinity H 2 O-NaCl system, with trace amounts of volatile components including CO 2 , CH 4 and N 2 . The C-H-O isotope data (δ 13 C CO2 = -18.9 to -6.7‰; δ 18 Owater = +1.1 to +6.3‰; δD H2O = -78 to -55‰) indicate that the ore-forming fluids were mainly magmatic water, which might be modified by fluid-rock interaction and mixing with meteoric water. Sulfur (δ 34 S = -7.0 to +0.3‰) and Pb isotope data ( 206 Pb/ 204 Pb = 18.531-18.693, 207 Pb/ 204 Pb = 15.728-15.753, 208 Pb/ 204 Pb = 38.902-39.081) suggest that the ore metal and sulfur are of magmatic origin. The involvement of both organic matter in metasedimentary rocks during fluid-rock interaction and oxidized meteoric water may have been responsible for the negative δ 34 S and δ 13 C values. Fluid boiling, fluid-rock interaction and minor input of meteoric water might have been effective factors for the precipitation of wolframite, cassiterite and scheelite. The sulfide precipitation may have resulted from cooling and dilution of magmatic fluids by mixing with meteoric water.