Abstract. The Baolun quartz vein type Au deposit, is located at the southwestern Hainan Island. It occurs next to a Triassic ilmenite‐series/S‐type syenogranite complex. A 40 Ar/ 39 Ar plateau age for muscovite from the master orebody is dated to be 219.4±0.6 Ma, suggesting that the gold deposit genetically related to the granite pluton. In the Baolun mining area, orebodies of auriferous quartz vein and wall rock alteration occur in NNW‐striking fracture zones hosted by weakly metamorphosed turbidite of the Lower Silurian age. Eight fracture zones, 400∼1300 m long and 10∼30 m wide, have been identified. The five fracture zones of them form orebodies. The ores are mainly of quartz vein type. More than 20 orebodies in shapes of vein and lens of 195∼751 m in length and 0.20∼7.49 m in thickness are known, and 14 of them occur in the No. 1 vein belt. Silicification, sericitization and pyritization are closely related to the Au mineralization. The ores exhibit commonly 1.54∼29.48 g/t in Au grade, partially >98 g/t. The master orebody is 720 m long and 2.62 m thick in average, with 9.53∼29.27 g/t Au. Gold reserves of more than 70 t have been proven by geological exploration. More than 20 metallic minerals including native gold and sulfides such as pyrite, pyrrhotite, chalcopyrite, and others are identified to be formed in four ore‐forming stages: (1) Au‐coarse grain quartz stage, (2) Au‐fine grained quartz stage, (3) Au‐bismuthide‐bismuth sulfosalt‐sulfide‐quartz stage, and (4) calcite‐sulfide‐quartz stage. The Au mineralization in this deposit occurred mainly in the first three stages. A variety of Bi‐ and Te‐bearing minerals is closely associated with native gold suggesting that the mineralization may take place in a relatively high temperature.
Abstract: Sulfur isotope data (δ 34 S) of sulfides of more than 6700 samples from 157 ore deposits associated with Early and Late Yanshanian granitic and volcanic activities in South China are reviewed and summarized. Averaged δ 34 S values of individual deposits vary from ‐9. 3 to +20. 6%, and show a normal distribution pattern with the average of +2%. About 88 % of the ore deposits have values within the range, −2.5 ˜ +13.6‰, of associated Yanshanian granitoids. There is a temporal‐spatial variation of δ 34 S values of the ore deposits. However, no clear zonal distribution parallel to geotectonic NNE lineaments was observed. Spatial distribution of ore sulfide δ 34 S values in most of the NE part of the whole studied area coincides with that of Yanshanian granitoids and volcanic rocks. A downward tendency of the average values in time is: +3. 0% (n=7, J 1 ) → +1. 6% (n=29, J 2 ) → +1. 7% (n=68, J 3 ) → +1. 8% (n=37, K 1 ) → −1. 5% (n=16, K 2 ). There is an “island” of high and variable δ 34 S values (0˜ +16.5‰) occurring within a generally low trough zone (−8 ˜ 0%) of N‐S about 800 km and E‐W 100 to 300 km, bounded by 110°E ˜ 116°E longitudes and 22°N ˜ 31°N latitudes. The island occurs at the junction of three tectonic units and a NE‐trending crustal matching line implying a variety of magmatism occurred at the junction. The low trough zone coincides with a low ferric/ferrous ratio zone of Early Yanshanian granitoids, indicating their genetic relationship. Different genetic types of ore deposits show different histogram patterns suggesting different relationships to magmatic rocks and host strata. Granite/greisen/pegmatite type deposits are most closely associated with granitoids, with average ore sul‐fide δ 34 S values for individual ore deposits ranging between ‐2. 0 and +4. 1%, and an average of +0. 5% (n = 15) close to type meteoric value of 0%. Porphyry‐type deposits have also narrow range of −2.2 ˜ + 4.9‰, with an average value of +1. 1% (n = 18). Skarn‐type dominated ore deposits have a nearly normal distribution pattern with an average of +1. 6% (n = 62), ranging from ‐5. 3 to +11. 5%. Volcano‐subvolcanic ore deposits range between ‐3. 1 and +5. 9% with an average of +2. 3% (n = 19). Other types of hydrothermal ore deposits have averaged δ 34 S values of individual ones from ‐9. 3 to +20. 6%, with average value of +1. 3% (n=43). Vertical and horizontal zonations of δ 34 S values of ore deposits around their associated granitoid plutons are observed in several localities. Such zonations may be caused by interaction between magma and/or magmatic fluids and host sedimentary rocks, as well as the evolution of physico‐chemical conditions of ore‐forming fluids. Spatial distribution of ore sulfur isotope compositions is also clearly controlled by tectonics and deep faults. Ore sulfur isotope composition is sometimes strongly affected by host sedimentary rocks, especially by evaporite sulfur with much higher δ 34 S value and partly by biogenic sulfur with low δ 34 S value. The δ 34 S values of Yanshanian granitoids are from ‐2. 5 to +13. 6% for both rock samples and pyrite/pyrrhotite separates from granitic rocks, with similar spatial distribution pattern to those of associated ore deposits. The ore deposits associated with ilmenite‐series granitoids have δ 34 S values ranging between ‐7. 5 and +10. 4% with an average of +1. 0%, while the ore deposits associated with magnetite‐series granitoids ranging between −8.0 ˜ +11.5‰ with an average of +1. 1%. δ 34 S values of ore deposits tend to converge to +3% as the Fe 2 O 3 /FeO ratio of associated granitoids increases from 0. 45 to 8. 7.
The Qianlishan complex, located in Hunan Province of South China, is closely associated with intense W-dominated polymetallic mineralization. The Qianlishan complex is composed of three phases: the main-phase porphyritic and equigranular granites, granite porphyry, and mafic dykes. Geochronologically, the zircon U-Pb dating results show that the porphyritic and equigranular granites have ages of approximately 159 and 158 Ma, respectively, similar to those of mafic dykes (approximately 158 Ma), while the granite porphyry was formed later at approximately 145 Ma. Geochemically, the mafic dykes are characterized by calc-alkaline high-Mg andesite (HMA) with high MgO, TiO2, Mg#, and CA/TH index. They exhibit significantly depleted εNd(t) and εHf(t) with high Ba/La, La/Nb, and (La/Yb)N, indicating that they formed from mixing melts of depleted asthenospheric mantle and metasomatized subcontinental lithospheric mantle (SCLM). The main-phase granites are peraluminous and are characterized by high SiO2, low (La/Yb)N ratios, and relative depletion in Ba, Sr, Ti, and Eu. They also display negative correlations between La, Ce, Y, and Rb contents, suggesting that they are highly fractionated S-type granites. Furthermore, they show high εNd(t) and εHf(t), CaO/Na2O ratios, HREE, and Y contents, indicating that they were produced by parental melting of ancient basement mixed with mantle-derived components. In contrast, the granite porphyry shows A-type signature granites, with higher εNd(t) and εHf(t) and CaO/Na2O ratios than the main-phase granites but similar Zr/Nb and Zr/Hf ratios to the mafic dykes, suggesting that they are the products of partial melting of a hybrid source with ancient basement and the mafic dykes. We thus infer that the slab roll-back led to generation of Qianlishan back-arc basalt and HMA and further triggered the formation of the Qianlishan granite.
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