The Evolution Of Yanshanian Granite And Tungsten Mineralization In Southern Jiangxi Province And Adjacent Region

Shilei quartz diorite is one of the most special diorites in Chongyi-Shangyou-Dayu area, southern Jiangxi. Zircon U-Pb dating for one quartz diorite yields an emplacement age of 433.5±3.4 Ma. Four samples are with middle contents of silica, high contents of Al2O3 and low contents of P2O5. They contain high contents of large ion lithophile elements such as K, Rb, Cs and light rare elements and low contents of high field strong elements such as Nb, Ta, Ti, P. Apatites are enriched in rare elements, their light rare elements contents are much higher than heavy rare elements contents. They have a low 8Eu (δEu=0.37-0.45. The Sr-Nd isotope compositions are characterized by the follows:distinctively midlle initial Sr isotopic ratios (/sr= 0.7073-0.7132); low initial Nd isotopic ratios (εNd(t)=-4.97～-8.41), two-stage model age ranging from 1.58 to 1.86 Ga; zircon Hf isotopic analysis yields main εNd(t) values of -8 to-2, with two-stage model age 1.77 ±0.09Ga. These characters indicate that Shilei quartz-diorite is the product of an intensive interaction between crust and mantle. The lithosphere of this area perhaps once thinned in late-caledonian. There is no direct link between Shilei quartz-diorite and Piaotang tungsten deposit, but the quartz-diorite might provide some source to tungsten-related mesozoic granite.Yingqian pluton is the only xenoliths-bearing rock reported in southern Jiangxi. There is a skarn-type W-polymetallic ore field surrounding it. Its metallogenic feature is obviously different from other tungsten mines in southern Jiangxi but similar with many tungsten deposits in southern Hunan. The host rock is granodiorite, two tested samples are with high contents of Alk, K2O and Al2O3; middle contents of CaO, MgO and TFeO. Two xenoliths samples are with high contents of Al2O3, CaO, MgO and TFeO. Ree patterns, spider diagrams, Sr-Nd isotopes and trace elements’ratios all show similar characteristics between host rocks and xenoliths. εHf (t) of the host rocks vary from-6.9 to 5.4, most of them are close to 0, two-stage model ages vary from 0.90 to 2.05 Ga, the chaotic Hf isotope composition show that host rock have suffered a large degree of contamination by xenoliths.Granite related to quartz vein type tungsten ore has a complete evolution chain (biotite graniteâ†' the two-mica graniteâ†' muscovite granite). Garnet and a small amount of plagioclase with low An can be found in these rocks, but no amphibole there. Generally, these rocks are S-type granites and have characteristics such as super acid, ACNK> 1.1 and low total REE; δEu and LR/HR of which are both very low, HREE enriched; K/Rb ratios and Nb/Ta ratios are significantly lower than normal granites K/Rb:150-350, Nb/Ta:12); Y/Ho ratio is generally higher than 28, Rb, Cs, Y enriched, Ba, Sr, Ti lose. With the increase of evolution intensity:the tungsten content, DI, SiO2 content, ACNK, Rb/Sr ratios, Y/Ho ratios, fluid inclusions in quartz and water-bearing minerals tended to increase; K/Rb ratios, Nb/Ta ratios, ΣREE,8Eu and dark minerals gradually decreased; the amount of Zircon and other accessory minerals became smaller and fewer.Re-Os isotope study of molybdenites indicate fine-grained granite-type mineralization age of ZhangDongkeng is 155.4 ± 2.1 Ma and quartz vein-type mineralization age of whitch is 154.6 ± 1.7Ma; Xiatongling tungsten ore’s formation age is 152.0 ±3.3 Ma; Tieshanlong tungsten ore’s formation age is 146.4 ± 6.1 Ma; Maoping’s quartz vein type tungsten ore’s formation age is 157.4 ± 2.2 Ma. All of these tungsten ore’s molybdenites have low Re contents, suggest ore-forming materials are mainly from the crust. Molybdenites from Xiatongling and Hukeng have higher Re content, which may be a result of being close to Pingxiang-Guangfeng deep fault. Rb-Sr micro-isochron method is first applied to determine the ore-forming age by single grain of muscovite growing at the edge of wolframite-bearing quartz vein, result shows that the mineralization age is 147.1±3.4Ma.The homogenization temperatures of fluid inclusions from both Maoping and Tieshanlong tungsten deposit have two peaks. Crystallizations of wolframites were at higher temperatures but during narrow temperature ranges. None of these kinds of fluid inclusions’salinity is high. Gas composition of fluid incluisions contains a certain amount of carbon dioxide, methane and nitrogen. Woframite always grow with triplite, fluorite, beryl, lithium iron mica, topaz, pyrite, molybdenite and other minerals in quartz vein tungsten deposit. We can conclude that there were a variety of volatile (e.g. CO2, CH4, H2S, P, Li, Be, F) in ore-forming fluid during its involution, these volatile can escape during immiscibility and be absorbed by related-minerals (e.g. triplite, fluorite, beryl, lithium iron mica, topaz) which may eventually induce the crystallizations of wolframites.17 Sulfide samples from Laoanli and Baoshan were selected for sulfur isotope study, the results show that 834S range is very short and very close to zero, whitch is consistent with previous studies, suggest that the sulfur in this area has a single source whitch may be mainly inherited from the granite formed by melting of the crust. Five quartz samples from Pangushan tungsten ore formed in the main mineralization stage were used for hydrogen and oxygen isotope study. Results indicate that ore-forming fluid in the main mineralization stage is mainly composed by magmatic water, which is consistent with the formers’conclusion that ore-forming fluid of quartz vein type tungsten deposit in the main mineralization stage mainly consist of magmatic water, and meteoric water mixed in the late stage. Muscovites from Xushan, Tieshanlong and Maoping tungsten deposit have high/sr, which may suggest that related granites have shallow sorces and have evolved highly and there was no mantle material involved during the formation of those deposits.He-Ar isotope indicate the ore-forming fluids at Tieshanlong are dominated by crustal fluids with some atmospheric water also being present. Mantle fluid participation was very low. Comparing these results with the work of previous studies using H-O isotopes, it is concluded that only a very small amount of mantle fluid was involved during the process of magma formation. The involvement of waters with a meteoric signature may have a long history. The earliest event can be traced back to the deposition of terrigenous clastic sediments carrying the "old" atmospheric water; and then incorporated into a granitic magma. Following intrusion and differentiation and the final stages of fluid evolution, this "magmatic water" mixed with a "fresh" meteoric water and completed the ore precipitation process.