The Genetic Difference Between Two Metallogenic Granites And The Ore-forming Material Source Of The Huangshaping Deposit In Southern Hunan

The Huangshaping polymetallic deposit is the largest lead-zinc mine in southern Hunan Province. There are various kinds of magmatic rocks distributing in this mining area, associated with W-Sn-Cu-Pb-Zn-Ag polymetallic mineralization. It’s also a reprensitative deposit in southern Hunan with porphyry-skarn-vein Cu-Pb-Zn-Ag and W-Sn polymetallic superimposed mineralization. The metallogenic difference of the two kinds of rock mass(quartz porphyry and granite porphyry) is the foundation of polymetallic mineralization in the mining area. Meanwhile, the reason that the small-size igneous rock led to large-scale metal deposit attracts extensive attention, especially that the sulfur source issue is still controversial. To answer the questions above, this paper studied the different genetic characteristics and sulfur isotopic composition of two kinds of granites from the isotope chronology, isotope geochemistry, element geochemistry and mineral micro-zone analysis, respectively.Here, three types of granite including dacite porphyry, granite porphyry and quartz porphyry in Huangshaping were collected for zircon U-Pb dating and Hf isotope analysis. The results show that the zircon U-Pb ages of the dacite-porphyry, granite porphyry and quartz porphyry are 158.5 ± 0.9 Ma, 155.2 ± 0.4 Ma and 160.8 ± 1.0 Ma, respectively. Igneous zircons of Middle-Late Jurassic have low and similar εHf(t) values of-3.2 ~-7.6 and Mesoproterozoic(1.4 ~ 1.7 Ga) depleted-mantle model ages, which is interpreted to reflect derivation from old crust source. These data also provide important evidence for temporal-spatial connections of emplacement of the granitiods and W-Sn-Cu-Pb-Zn-Ag polymetallic mineralization in the Huangshaping mining area.In addition, we found that granite porphyry and quartz porphyry have differnces in emplacement height, factors of formation(temperature and oxygen fugacity) and the degree of magmatic differentiation from the geological survey and indoor experiment which includes petrogeochemistry and mineral micro-zone analysis. The results suggest that the magma relatively high oxygen fugacity and low-temperature, the high emplacement of quartz porphyry may be the key to Cu polymetallic deposit, and the high temperature and high differentiation degree of granite porphyry reduing magma perhaps was important to W-Sn minerallization.Based on the previous studies, we systematically studied the sulfur isotope composition of quartz porphyry and granite porphyry samples collected from the different locations of mining area to clarify the source of sulfur in the Huangshaping deposit. The results show that the δ34S values of quartz porphyry and granite porphyry range from + 4.1‰ to + 7.5‰, and from 4.9‰ to + 11.4‰, respectively. Considering the influence of the alteration by the fluid with high δ34S value, the δ34S values of the granitoid rocks(+4.1‰ to + 11.4‰) are probably slightly higher than these of corresponding granitic magma, but they are also well consistent with the δ34S value of typical S-type granites. Based on the above, it is indicated that the sulfur of sulfides with high δ34S values was partly originated from the carbonate strata besides the magmatic sulfur, which is probably one of the most important reasons that the largest lead-zinc deposit in southern Hunan Province occurred in the Huangshaping mining area.