Timing of granite pegmatite-type high-purity quartz deposit in the Eastern Qinling,China:constraints from in-situ LA-ICP-MS trace analyses of quartz and monazite U–Pb dating

Eastern Qinling,China is one of the important rare metal metallogenic provinces with extensively distributed granite pegmatite dikes.The No.5 granite pegmatite intruded into the granitic gneiss of the Qinling Group,and the major minerals are quartz(39.8%),K-feldspar(18.8%),albite(36.3%),muscovite(3.4%),and garnet(1.1%).Monazite U–Pb isotopic dating indicates that the No.5 pegmatite from the Eastern Qinling was emplaced at ca.420.2±2.2 Ma,which confirms that highpurity quartz mineralization probably formed during the Early Devonian.In-situ laser ablation inductively coupled plasma mass spectrometry analysis of quartz show that quartz samples from Eastern Qinling have total trace element concentrations(Al,Ti,Sc,Li,B,Cr,Mn,and Fe)ranging from 23.2 to 52.8 ppm,slightly higher than the quartz(impurity element content from 13.4 to 25.9 ppm)of the Spruce Pine high-purity quartz deposit in western North Carolina.The No.5 pegmatite of Eastern Qinling could be defined as one high-purity quartz deposit of China.

Fluid Characteristics and Evolution of the Zhawulong Granitic Pegmatite Lithium Deposit in the Ganzi-Songpan Region, Southwestern China

The Zhawulong granitic pegmatite lithium deposit is located in the Ganzi-Songpan orogenic belt.Fluid inclusions in spodumene and coexisting quartz were studied to understand the cooling path and evolution of fluid within albite–spodumene pegmatite.There are three distinguishable types of fluid inclusions:crystal-rich,CO2–NaCl–H2 O,and NaCl–H2 O.At more than 500°C and 350~480 MPa,crystal-rich fluid inclusions were captured during the pegmatitic magma-hydrothermal transition stage,characterized by a dense hydrous alkali borosilicate fluid with a carbonate component.Between 412°C and 278°C,CO2–Na Cl–H2 Ofluid inclusions developed in spodumene(I)and quartz(II)with a low salinity(3.3–11.9 wt%NaCl equivalent)and a high volatile content,which represent the boundary between the transition stage and the hydrothermal stage.The subsequentNaCl–H2 Ofluid inclusions from the hydrothermal stage,between 189°C and 302°C,have a low salinity(1.1–13.9 wt%NaCl equivalent).The various types of fluid inclusions reveal the P–T conditions of pegmatite formation,which marks the transition process from magmatic to hydrothermal.The oreforming fluids from the Zhawulong deposit have many of the same characteristics as those from the Jiajika lithium deposit.The ore-forming fluid provided not only materials for crystallization of rare metal minerals,such as spodumene and beryl,but also the ideal conditions forthe growth of ore minerals.Therefore,this area has favorable conditions for lithium enrichment and excellent prospecting potential.

Petrogenetic and Metallogenetic Characteristics of the Xikeng Granitic Pegmatites, Fujian Province

The Xikeng pegmatite field lies on the eastern margin of the south China fold system in Fujian Province,and it is located at the junction of three major tectonic units. The distribution of pegmatites is obviously controlled by the fold system.There exists apparent in jectionrelationship between the pegmatites and the surrounding Sinian schist and granulitite.The granitoidsextensively distributed in the field belong either to the Variscan or to the Yenshanian cycle,and it is evidentthat the pegmatites are genetically related to Variscan migmatitic granites. The pegmatites can be grouped into four types:muscovite-orthoclase-albite pegmatite（I）.muscovitedlbite-orthoclase pegmatite（Ⅱ）,muscovite-orthoclase-albite pegmatite（Ⅲ）,and muscovite-albitespodumene pegmatite（IV）.Owing to strong metasomatism and multi-stage emplacement of pegmatitic meltsolution,the sequence of interior assemblage zones in the pegmatites does not always represent the sequenceof original crystallization. The mineral composition of the pegmatites is extremely complicated.81 kinds of minerals have so farbeen found、From type I to type IV,the mineral assemblage tend to get increasingly complex.together withthe synchronous intensification of rare-metal and Sn mineralizations.Most of the type-IV pegmatites are ofeconomic value The features of fluid inclusions in the minerals are significantly different not only in different typos ofpegmatite,but also in different parts of a single pegmatite vein.Theδ18O values of migmatitic granite andpegmatites are comparatively low（9.3-10.4‰）,and those of rock-forming fluids are higher than 9.5‰ Isotopic ages of the pegmatites brangs from 235 to 328 Ma with initial 87Sr/86Sr ratios being ”.715-0.746. According to the temporal and spatial relationships between the pegmatites and the migmatitic granitecombined with the features of the pegmatites themselves,it can be concluded that the Xikeng pegmatites arethe product of differentiation closely related to the migmatitic granite.

Geology and mineralization of the Songpan-Ganze-West Kunlun pegmatite-type rare-metal metallogenic belt in China:An overview and synthesis

The Songpan-Ganze orogenic belt on the northeastern margin of the Tibetan Plateau extends westward from the Songpan-Ganze terrain in western Sichuan to the Tianshuihai region in West Kunlun,Xinjiang.It hosts numerous giant spodumene pegmatite deposits and ore fields,including Jiajika and Ke’eryin in western Sichuan Province,Zhawulong on the border between the Sichuan and Qinghai Provinces,and Dahongliutan in Xinjiang Region.These form the Songpan-Ganze-West Kunlun(SP-GZ-WK) pegmatite-type rare-metal metallogenic belt.The pegmatite type rare-metal deposits in this belt are hosted in the metamorphic thermal domes in the metamorphosed flysh of the Triassic Xikang and Bayankalashan Groups.The mineralized pegmatites are intimately related to the Li-and volatile-rich two-mica granites that are peraluminous and have high(Li+Na+K)/(Mn+Fe+Mg+Ca+Ti) ratios.Pegmatites and granites in individual ore field throughout the belt typically form a cogenetic granite-pegmatite system,in which pegmatite dikes commonly surround granites.Spodumene is the predominant ore mineral in most pegmatites with limited hydrothermal alteration.In the granite-pegmatite systems,granitic magmas were emplaced under P-T conditions of 800–850°C and ~550 MPa,while spodumene crystallized in an alkaline environment.The granite-pegmatite systems share similar Sr-Nd-Hf-Li isotopic compositions to the metasediments of the Xikang and Bayankalashan Groups.The δ7Li values tend to increase from the granites to the Li-poor pegmatites,whereas the reverse is observed between the Li-poor and Li-rich pegmatites.These geochronological data suggest that the granite-pegmatite systems formed in the Late Triassic and tend to be progressively younger from the outer to the inner zones of the metallogenic belt.These characteristics show that the granitic-pegmatitic melts were derived from the anatexis of the Xikang and Bayankalashan Groups during the Paleo-Tethyan orogeny in the Late Triassic.The separation of pegmatitic melts from granitic magmas can be best explained using the Jiajika-style “melt-melt immiscibility” or the Ke’eryin-style “fractional crystallization+melt-melt immiscibility” model.High-maturity terrestrial sediments are of key importance for the anatexis that results in the granitepegmatite melts.The bidirectional tectonic stresses in the Songpan-Ganze orogenic belt may have caused the mineralization difference between the Jiajika deposit and the Ke’eryin ore field.These features indicate the controls of the combination of orogenic deformation,metapelites anatexis,and magmatic differentiation on the rare-metal mineralization of pegmatites.We suggest that pegmatites,pegmatite–parental granite,and their protoliths are important indicators for rare-metal mineralization in the SP-GZ-WK pegmatite type rare-metal metallogenic belt.Based on the widespread presence of fertile metasediments and well development of metamorphic thermal dome,highly differentiated granites,and regional zonation of pegmatites,the Zhawulong ore field is the most prospective area for rare metals and thus should be the priority for future exploration.