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

Abstract

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 °C) through stage II (salinity = 2.7–10.9 wt%, and Th = 236–313 °C) to stage III (salinity = 1.7–8.5 wt%, and Th = 192–262 °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 δDwater values in the range of –66.7 to –60.5‰ and –52.8 to –39.6‰, and δ18O (‰) values in the range of 6.7 to 7.3‰ and 5.8 to 6.9‰, 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‰ to 0.4‰ (average, –1.7‰), 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‰). Fluid boiling and mixing with meteoric water were considered likely to be the possible mechanism for the ore precipitation in Tashan deposit.