Geochemical Characteristics and Geological Significance of the Tawangshan gold deposit in Dongfang City, Hainan Province

TheTawangshan gold deposit is located in the southwest of the Gezhen ductile shear zone in southwestern Hainan Island. Major, trace and rare earth element characteristics of the least altered granites and altered granite ores, as well as the oxygen and hydrogen isotopic features of the quartz, the sulfur and lead isotopic features of the pyrites, galena from this deposit were systematically studied. The altered granite ores content of Fe2O3/(Fe2O3+FeO) ranges from 0.409 to 0.410,showing strong magma reducibility. REE characteristics of the granite ores are similar to those of the least altered granites, indicating a close relationship between the mineralization and granite. Hydrogen and oxygen analysis results show that the content of 18OSMOW ranges from 7.7 to 16.3 , δ OH2O ranges from1.0 to 6.8 , suggesting that the ore-forming fluid was the dual nature of the metamorphic and magmatic hydrothermal. The compositions of sulfur isotope and lead isotope imply that the metallogenic materials of the deposit derived from the deep magma mixing with the shell source material contamination. Ore deposit geological features reflect the obvious characteristics of magmatic hydrothermal and porphyritic granite is mineralized rocks, implying the deposit was formed in the post-collisional extensional tectonic setting. Corresponding authors Xiong ying E-mail:32973457@qq.com 1 Introdution The Tawangshan gold deposit is located in the southeast of the Gezhen ductile shear zone, a small gold deposit newly discovered. After exploration, the deposit has submitted 1600kg gold resources. However, due to lack of theoretical research on mining gold mineralization characteristics, mineralization and other systems, further prospecting mining has been caused a lot of constraints. Based on the field of exploration and geochemical analysis, the metallogenic regularity and the genesis of mine have been studied, in order to provide theoretical guidance to further mining prospecting work, as well as enriching the theoretical knowledge Gezhen gold mineralization belt. 2 Regional geological setting Tawangshan gold deposit is located in the western South China fold belt Wuzhishan fold system, Baisha depression belt and hold the plate crown area of the contact portion waterfront-Jinbo rift belt, south-eastern of Gezhen fault. The rock of the area is characterized by Kongliecun group, Tuolie group of Silurian System; Nanhao group, Qingxia group of Carboniferous System; E cha group of Permian System; Lu muwan group of Cretaceous System and Quaternary. Regional faults are DOI: 10.1051/ 04026 (2016) , matecconf/2016 MATEC Web of Conferences 63 630


Introdution
The Tawangshan gold deposit is located in the southeast of the Gezhen ductile shear zone, a small gold deposit newly discovered.After exploration, the deposit has submitted 1600kg gold resources.However, due to lack of theoretical research on mining gold mineralization characteristics, mineralization and other systems, further prospecting mining has been caused a lot of constraints.
Based on the field of exploration and geochemical analysis, the metallogenic regularity and the genesis of mine have been studied, in order to provide theoretical guidance to further mining prospecting work, as well as enriching the theoretical knowledge Gezhen gold mineralization belt.

Regional geological setting
Tawangshan gold deposit is located in the western South China fold belt Wuzhishan fold system, Baisha depression belt and hold the plate crown area of the contact portion waterfront-Jinbo rift belt, south-eastern of Gezhen fault.The rock of the area is characterized by Kongliecun

Sample collection and analysis
The study samples were collected from the deep drill core.Major elements, trace elements and REE samples are mainly collected from unaltered and altered granite (ore) sample, and H-O isotope analysis samples are for the selection of the main mineralized quartz vein type ore of pure quartz minerals, but S-Pb isotopes analysis samples are for s the altered granite ore, the selection of pure mineral pyrite, galena minerals as a single sample.
Major elements, trace elements and REE elements are anglicised in ALS Laboratory (analysis results in Table  that the magma has strong reduction.

Ore-forming elements
The altered granite is rich in Au, Ag, Pb, Zn.The content of Pb, Zn and Au content was a significant positive correlation, suggesting that the gold mineralization is closely with lead-zinc mineralization.
The Cu mineralization is not obvious.Either unaltered granites or altered granites ,the content of W, Mo, presently high-temperature ore-forming elements ,is very low, indicating that the mineralization temperature should be in medium-low temperature.

H-O isotope
The hydrogen and oxygen isotopic date of the Tawangshan gold deposit are listed in Table 2. Theδ D of all samples range from -59.0 -99.0 ,showing significant isotopic fractionation occurrence.The δ 18 O SMOW of all samples range from 7.7 ~16.3 .The δ 18 O H2O of all samples range from 1.0 ~6.8 , with an average of 4.1

S isotope
The sulfur isotope of pyrite, galena values are listed in Table 3.The δ 34 S of all sample range from 6.3‰ to 9.1‰, with an average of 7.8‰ and range of 2.8 .Sulfur isotope variation range is narrow, relatively homogeneous composition and exhibiting a relatively enriched in 34 S isotope characteristics.The Tawangshan gold deposit is a magmatic hydrothermal deposits, formed after the collision extensional environment.

Fig. 1
Fig.1 Chondrite normalized REE patterns of the granites Projecting the isotope date (Table2) onto hydrogen and oxygen isotopic composition diagram (Fig.2), showing that the almost sample of isotope date are fallen on the area near the magmatic water, and some sample is fallen metamorphic water area.This phenomenon indicates that ore-forming fluids have reaction with metamorphic rocks as it flowing from deep.As well as, the rain hydrothermal may be fallen in mineralization process, and may be very favourable.Therefore, the ore-forming fluid of the Tawangshan gold deposit has a characteristic with metamorphic and magmatic hydrothermal as a mixed fluid characteristic.

Fig. 2
Fig.2 Plot of hydrogen and oxygen isotopes for gold ores of the Tawangshan gold deposit

Fig. 3
Fig.3 Sulfur isotope histograms for gold ores of the Tawangshan gold deposit

Fig. 4 5 . 3
Fig.4 Diagram showing evolutionary tectonic setting of Pb isotope from the Tawangshan gold deposit A-mantle; B-orogenic belt C-upper crust D-lower crust

Fig. 5 Fig. 6 6 Conclusions
Fig.5 Δβ-Δγ diagram of genetic classification of ore lead isotopes from Tawangshan gold deposit 1-mantle-derived lead;2-upper crust -derived lead;3-mixed upper crust and mantle-derived lead 3a.magmatism 3b.sedimentation 4-lead from chemical deposition 5-lead from submarine hydrothermalism 6-lead from medium-deep matamorphism 7-lower crust-derived lead from matamorphism 8-lead from orogenic belt 9-lead from upper crust of ancient shale 10-lead from retrogrande metamorphism group, Tuolie group of Silurian System; Nanhao group, Qingxia group of Carboniferous System; E cha group of Permian System; Lu muwan group of Cretaceous System and Quaternary.Regional faults are

3 Mining geology and mineralization characteristics 3.1 Geological characteristics
The strata exposed area is mainly Quaternary stratigraphy, Late Palaeozoic Permian strata.Quaternary strata are mainly distributed in the wash, by the alluvial and alluvial gravel, clay, and loam composition.Permian strata exposed in the south and southeast of the area, with wide 100-800m, length of 4km, tending to the north-west, dipping 50-65°.The rock of Permian strata is characterized by crystalline limestone, microcrystalline biolistic limestone and metamorphic siliceous sandstone.The structural fault is dominated by NNE -NEE trend.The NNE-trending faults which strike 10 °, tend to the north-west, dip 70-80 °.This group faults cut through the Yanshanian biotite granite and Permian strata, with filling with broken quartz veins, lamprophyre vein and diorite vein.The NEE-trending group faults tend to northwest, dip 35 ° -55 °, followed by east-west fault was compressive echelon distribution, the local formation of gold-polymetallic ore body.gold belt: as the smallest alteration zones ,this belt were circled a gold orebody ,with length of 50m, width of 3m, Au average grade of 1.2g/t .
The content of SiO 2 in unaltered granite ranges from 69.05 to 76.96wt.%.The total alkali content ranges from 7.75 to 9.40wt.%.The Al 2 O 3 content ranges from 12.15 to 14.19wt.%.The K 2 O content is higher than the Na 2 O content.The rate of K 2 O / Na 2 O ranges from 1.24 to 3.35, ). H-O isotope analysis was finished in Wuhan Institute of Geology and Mineral Resources isotope geochemistry laboratory, with MAT261 Mass Spectrometer.Sulfur and lead isotopes are analysis in State Key Laboratory of Geological Processes and Mineral Resources measured at China University of Geosciences (Wuhan).

Table 1
Major, rare earth element and ore metal contents of the rocks and ores from the Tawangshan gold deposit

Table 2
Oxygen and hydrogen isotopic date of the Tawangshan

Table 3
Sulfur isotope results from the Tawangshan gold deposit

Table 4
Lead isotope results from the Tawangshan gold deposit