Origin of metallogenic fluids and materials of the Tashan porphyry host tin deposit, eastern Guangdong, Southeast China: Constraints from fluid inclusions, H-O, S, Pb, and He-Ar isotopes

The Tashan deposit is hosted and genetically associated with the highly fractionated A-type granite porphyry formed at ca. 138 Ma. Its Sn metallogenic processes can be subdivided into three stages: biotite-K-feldspar-cassiterite (stage I, main Sn mineralization), quartz-cassiterite (stage II), and chlorite-sulphides (stage III). Fluid inclusion study indicates that the hydrothermal fluids from stage I (salinity = 5.2-12.8 wt%, and Th = 303-376 degrees C) through stage II (salinity = 2.7-10.9 wt%, and Th = 236-313 degrees C) to stage III (salinity = 1.7-8.5 wt %, and Th = 192-262 degrees C) are of H2O-CO2-salt composition and its temperature and salinity from early to late stages tend to decrease. The H and O isotopes of quartz from stage II and stage III show & delta;Dwater values in the range of -66.7 to -60.5%o and -52.8 to -39.6%o, and & delta;18O (%o) values in the range of 6.7 to 7.3%o and 5.8 to 6.9%o, respectively, suggesting contributions of both magmatic fluids and meteoric water. Inclusion-trapped fluids in stage II pyrite show 3He/4He, Hemantle (%), and 40Ar/36Ar values of 0.07-0.35 Ra, 0.76%-4.28%, and 302.6-309.0, respectively, indicating that the metallogenic fluids were derived mainly from crustal sources, with minor proportions of mantle source input (<4.28%), consistent with the magma sources of the granite porphyry. Lead isotopes indicate that there is no difference for 206Pb/204Pb, 207Pb/204Pb, and 208Pb/204Pb ratios between the sulfide minerals from the orebodies and the fertile granites parental to Sn mineralization in Eastern Guangdong, indicating a magmatic Pb origin. Sulfur isotopic values obtained from sulfides are in the range of -4.5%o to 0.4%o (average, -1.7%o), implying an initially of magmatic origin with some contamination of sedimentary sulfur through the interaction with sedimentary rocks of Jinji Formation (-6.67 to -2.41%o). Fluid boiling and mixing with meteoric water were considered likely to be the possible mechanism for the ore precipitation in Tashan deposit.